What is Mango?
Great programmers should use great tools! Writing bug-free software is hard, but Mango is a language that has your back:
- Prevent mistakes with a strong, static type system
- Write composable code using immutability by default
- Prevent data races using ownership (affine types)
- Never forget to handle errors or clean up resources with linear types
- Describe state precisely through non-nullability and sum types
- Trust your invariants with easy enforcement
- Catch errors early by doing things compile-time when possible
- Powerful, but not too powerful, macros
(These are planned features and are subject to change.)
The guiding principle is that you should be able to reason about small parts of code, because Mango pushes towards good coding practices, and there are many invariants that you can rely on.
Can I use Mango today?
Mango is still in early development, so unfortunately not. It won't be ready for production use for at least some years.
What languages is Mango similar to?
While Mango is a mix of many influences, perhaps its closest ancestor is Rust. It shares many of the safety features of Rust, but is less low level, and does not compete with C in performance. The syntax does not resemble Rust's though, and is closer to Python's.
Where can I run Mango?
Mango compiles to WebAssembly, the portable, safe and high-performance compile target that is included in browsers.
WebAssembly is also available outside browsers, so you can use Mango for both the frontend and the backend for seamless integration.
Staying up-to-date
You can star or follow on Github, follow Mango news on Twitter or join the group on LinkedIn. Other channels, like live chat, will likely be set up later.
I'd like to get involved
That's great, glad you like the project! Development happens on Github. Bugs, suggestions, code contributions, documentation, community management, testing - all help is welcome!


Copying a Flight Tracker Project
REDCap has a difficult time copying a Flight Tracker project to another server, so the software has its own way of achieving this copy. Many people set up Flight Tracker on a development server, only to move it to production later. To achieve this move, use the following steps:
- Get a “supertoken” on the Flight Tracker server from your local REDCap Administrator. You can coach her/him that it’s available in REDCap’s Control Center under the API Tokens page. This supertoken is 64-characters long, unlike the simple API token, which is 32-characters long. You should keep this supertoken secret.
- Open up Flight Tracker’s General → Configure Application page.
- Copy/paste your supertoken into the supertoken field and save the settings by clicking the button.
- Finally, go to the General menu and open the page Copy Project to Another Server. Then you should be able to initiate the copy from here. It may take some time (minutes to tens of minutes, not hours), so please be patient.


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PERLIPC
Section: Perl Programmers Reference Guide (1)Updated: 2009-08-10
Index Return to Main Contents
NAME
perlipc - Perl interprocess communication (signals, fifos, pipes, safe subprocesses, sockets, and semaphores)DESCRIPTION
The basic IPC facilities of Perl are built out of the good old Unix signals, named pipes, pipe opens, the Berkeley socket routines, and SysV IPC calls. Each is used in slightly different situations.Signals
Perl uses a simple signal handling model: the %SIG hash contains names or references of user-installed signal handlers. These handlers will be called with an argument which is the name of the signal that triggered it. A signal may be generated intentionally from a particular keyboard sequence like control-C or control-Z, sent to you from another process, or triggered automatically by the kernel when special events transpire, like a child process exiting, your process running out of stack space, or hitting file size limit.For example, to trap an interrupt signal, set up a handler like this:
sub catch_zap { my $signame = shift; $shucks++; die "Somebody sent me a SIG$signame"; } $SIG{INT} = 'catch_zap'; # could fail in modules $SIG{INT} = \&catch_zap; # best strategy
Prior to Perl 5.7.3 it was necessary to do as little as you possibly could in your handler; notice how all we do is set a global variable and then raise an exception. That's because on most systems, libraries are not re-entrant; particularly, memory allocation and I/O routines are not. That meant that doing nearly anything in your handler could in theory trigger a memory fault and subsequent core dump - see ``Deferred Signals (Safe Signals)'' below.
The names of the signals are the ones listed out by "kill -l" on your system, or you can retrieve them from the Config module. Set up an @signame list indexed by number to get the name and a %signo table indexed by name to get the number:
use Config; defined $Config{sig_name} || die "No sigs?"; foreach $name (split(' ', $Config{sig_name})) { $signo{$name} = $i; $signame[$i] = $name; $i++; }
So to check whether signal 17 and SIGALRM were the same, do just this:
print "signal #17 = $signame[17]\n"; if ($signo{ALRM}) { print "SIGALRM is $signo{ALRM}\n"; }
You may also choose to assign the strings 'IGNORE' or 'DEFAULT' as the handler, in which case Perl will try to discard the signal or do the default thing.
On most Unix platforms, the "CHLD" (sometimes also known as "CLD") signal has special behavior with respect to a value of 'IGNORE'. Setting $SIG{CHLD} to 'IGNORE' on such a platform has the effect of not creating zombie processes when the parent process fails to "wait()" on its child processes (i.e. child processes are automatically reaped). Calling "wait()" with $SIG{CHLD} set to 'IGNORE' usually returns "-1" on such platforms.
Some signals can be neither trapped nor ignored, such as the KILL and STOP (but not the TSTP) signals. One strategy for temporarily ignoring signals is to use a local() statement, which will be automatically restored once your block is exited. (Remember that local() values are ``inherited'' by functions called from within that block.)
sub precious { local $SIG{INT} = 'IGNORE'; &more_functions; } sub more_functions { # interrupts still ignored, for now... }
Sending a signal to a negative process ID means that you send the signal to the entire Unix process-group. This code sends a hang-up signal to all processes in the current process group (and sets $SIG{HUP} to IGNORE so it doesn't kill itself):
{ local $SIG{HUP} = 'IGNORE'; kill HUP => -$$; # snazzy writing of: kill('HUP', -$$) }
Another interesting signal to send is signal number zero. This doesn't actually affect a child process, but instead checks whether it's alive or has changed its UID.
unless (kill 0 => $kid_pid) { warn "something wicked happened to $kid_pid"; }
When directed at a process whose UID is not identical to that of the sending process, signal number zero may fail because you lack permission to send the signal, even though the process is alive. You may be able to determine the cause of failure using "%!".
unless (kill 0 => $pid or $!{EPERM}) { warn "$pid looks dead"; }
You might also want to employ anonymous functions for simple signal handlers:
$SIG{INT} = sub { die "\nOutta here!\n" };
But that will be problematic for the more complicated handlers that need to reinstall themselves. Because Perl's signal mechanism is currently based on the signal(3) function from the C library, you may sometimes be so unfortunate as to run on systems where that function is ``broken'', that is, it behaves in the old unreliable SysV way rather than the newer, more reasonable BSD and POSIX fashion. So you'll see defensive people writing signal handlers like this:
sub REAPER { $waitedpid = wait; # loathe SysV: it makes us not only reinstate # the handler, but place it after the wait $SIG{CHLD} = \&REAPER; } $SIG{CHLD} = \&REAPER; # now do something that forks...
or better still:
use POSIX ":sys_wait_h"; sub REAPER { my $child; # If a second child dies while in the signal handler caused by the # first death, we won't get another signal. So must loop here else # we will leave the unreaped child as a zombie.  And so on. while (($child = waitpid(-1,WNOHANG)) > 0) { $Kid_Status{$child} = $?; } $SIG{CHLD} = \&REAPER; # still loathe SysV } $SIG{CHLD} = \&REAPER; # do something that forks...
Signal handling is also used for timeouts in Unix, While safely protected within an "eval{}" block, you set a signal handler to trap alarm signals and then schedule to have one delivered to you in some number of seconds. Then try your blocking operation, clearing the alarm when it's done but not before you've exited your "eval{}" block. If it goes off, you'll use die() to jump out of the block, much as you might using longjmp() or throw() in other languages.

For more complex signal handling, you might see the standard POSIX module. Lamentably, this is almost entirely undocumented, but the t/lib/posix.t file from the Perl source distribution has some examples in it.
Handling the SIGHUP Signal in Daemons
A process that usually starts when the system boots and shuts down when the system is shut down is called a daemon (Disk And Execution MONitor). If a daemon process has a configuration file which is modified after the process has been started, there should be a way to tell that process to re-read its configuration file, without stopping the process. Many daemons provide this mechanism using the "SIGHUP" signal handler. When you want to tell the daemon to re-read the file you simply send it the "SIGHUP" signal.Not all platforms automatically reinstall their (native) signal handlers after a signal delivery. This means that the handler works only the first time the signal is sent. The solution to this problem is to use "POSIX" signal handlers if available, their behaviour is well-defined.
The following example implements a simple daemon, which restarts itself every time the "SIGHUP" signal is received. The actual code is located in the subroutine "code()", which simply prints some debug info to show that it works and should be replaced with the real code.
#!/usr/bin/perl -w use POSIX (); use FindBin (); use File::Basename (); use File::Spec::Functions; $|=1; # make the daemon cross-platform, so exec always calls the script # itself with the right path, no matter how the script was invoked. my $script = File::Basename::basename($0); my $SELF = catfile $FindBin::Bin, $script; # POSIX unmasks the sigprocmask properly my $sigset = POSIX::SigSet->new(); my $action = POSIX::SigAction->new('sigHUP_handler', $sigset, &POSIX::SA_NODEFER); POSIX::sigaction(&POSIX::SIGHUP, $action); sub sigHUP_handler { print "got SIGHUP\n"; exec($SELF, @ARGV) or die "Couldn't restart: $!\n"; } code(); sub code { print "PID: $$\n"; print "ARGV: @ARGV\n"; my $c = 0; while (++$c) { sleep 2; print "$c\n"; } } __END__
Named Pipes
A named pipe (often referred to as a FIFO) is an old Unix IPC mechanism for processes communicating on the same machine. It works just like a regular, connected anonymous pipes, except that the processes rendezvous using a filename and don't have to be related.To create a named pipe, use the "POSIX::mkfifo()" function.
use POSIX qw(mkfifo); mkfifo($path, 0700) or die "mkfifo $path failed: $!";
You can also use the Unix command mknod(1) or on some systems, mkfifo(1). These may not be in your normal path.
# system return val is backwards, so && not || # $ENV{PATH} .= ":/etc:/usr/etc"; if ( system('mknod', $path, 'p') && system('mkfifo', $path) ) { die "mk{nod,fifo} $path failed"; }
A fifo is convenient when you want to connect a process to an unrelated one. When you open a fifo, the program will block until there's something on the other end.
For example, let's say you'd like to have your .signature file be a named pipe that has a Perl program on the other end. Now every time any program (like a mailer, news reader, finger program, etc.) tries to read from that file, the reading program will block and your program will supply the new signature. We'll use the pipe-checking file test -p to find out whether anyone (or anything) has accidentally removed our fifo.
chdir; # go home $FIFO = '.signature'; while (1) { unless (-p $FIFO) { unlink $FIFO; require POSIX; POSIX::mkfifo($FIFO, 0700) or die "can't mkfifo $FIFO: $!"; } # next line blocks until there's a reader open (FIFO, "> $FIFO") || die "can't write $FIFO: $!"; print FIFO "John Smith (smith\@host.org)\n", `fortune -s`; close FIFO; sleep 2; # to avoid dup signals }
Deferred Signals (Safe Signals)
In Perls before Perl 5.7.3 by installing Perl code to deal with signals, you were exposing yourself to danger from two things. First, few system library functions are re-entrant. If the signal interrupts while Perl is executing one function (like malloc(3) or printf(3)), and your signal handler then calls the same function again, you could get unpredictable behavior---often, a core dump. Second, Perl isn't itself re-entrant at the lowest levels. If the signal interrupts Perl while Perl is changing its own internal data structures, similarly unpredictable behaviour may result.There were two things you could do, knowing this: be paranoid or be pragmatic. The paranoid approach was to do as little as possible in your signal handler. Set an existing integer variable that already has a value, and return. This doesn't help you if you're in a slow system call, which will just restart. That means you have to "die" to longjmp(3) out of the handler. Even this is a little cavalier for the true paranoiac, who avoids "die" in a handler because the system is out to get you. The pragmatic approach was to say ``I know the risks, but prefer the convenience'', and to do anything you wanted in your signal handler, and be prepared to clean up core dumps now and again.
In Perl 5.7.3 and later to avoid these problems signals are ``deferred''-- that is when the signal is delivered to the process by the system (to the C code that implements Perl) a flag is set, and the handler returns immediately. Then at strategic ``safe'' points in the Perl interpreter (e.g. when it is about to execute a new opcode) the flags are checked and the Perl level handler from %SIG is executed. The ``deferred'' scheme allows much more flexibility in the coding of signal handler as we know Perl interpreter is in a safe state, and that we are not in a system library function when the handler is called. However the implementation does differ from previous Perls in the following ways:
- Long-running opcodes
-
As the Perl interpreter only looks at the signal flags when it is about
to execute a new opcode, a signal that arrives during a long-running
opcode (e.g. a regular expression operation on a very large string) will
not be seen until the current opcode completes.
N.B. If a signal of any given type fires multiple times during an opcode (such as from a fine-grained timer), the handler for that signal will only be called once after the opcode completes, and all the other instances will be discarded. Furthermore, if your system's signal queue gets flooded to the point that there are signals that have been raised but not yet caught (and thus not deferred) at the time an opcode completes, those signals may well be caught and deferred during subsequent opcodes, with sometimes surprising results. For example, you may see alarms delivered even after calling alarm(0) as the latter stops the raising of alarms but does not cancel the delivery of alarms raised but not yet caught. Do not depend on the behaviors described in this paragraph as they are side effects of the current implementation and may change in future versions of Perl.
- Interrupting IO
-
When a signal is delivered (e.g. INT control-C) the operating system
breaks into IO operations like "read" (used to implement Perls
<> operator). On older Perls the handler was called
immediately (and as "read" is not ``unsafe'' this worked well). With
the ``deferred'' scheme the handler is not called immediately, and if
Perl is using system's "stdio" library that library may re-start the
"read" without returning to Perl and giving it a chance to call the
%SIG handler. If this happens on your system the solution is to use
":perlio" layer to do IO - at least on those handles which you want
to be able to break into with signals. (The ":perlio" layer checks
the signal flags and calls %SIG handlers before resuming IO operation.)
Note that the default in Perl 5.7.3 and later is to automatically use the ":perlio" layer.
Note that some networking library functions like gethostbyname() are known to have their own implementations of timeouts which may conflict with your timeouts. If you are having problems with such functions, you can try using the POSIX sigaction() function, which bypasses the Perl safe signals (note that this means subjecting yourself to possible memory corruption, as described above).
- Restartable system calls
-
On systems that supported it, older versions of Perl used the
SA_RESTART flag when installing %SIG handlers. This meant that
restartable system calls would continue rather than returning when
a signal arrived. In order to deliver deferred signals promptly,
Perl 5.7.3 and later do not use SA_RESTART. Consequently,
restartable system calls can fail (with $! set to "EINTR") in places
where they previously would have succeeded.
Note that the default ":perlio" layer will retry "read", "write" and "close" as described above and that interrupted "wait" and "waitpid" calls will always be retried.
- Signals as faults
- Certain signals, e.g. SEGV, ILL, and BUS, are generated as a result of virtual memory or other ``faults''. These are normally fatal and there is little a Perl-level handler can do with them, so Perl now delivers them immediately rather than attempting to defer them.
- Signals triggered by operating system state
- On some operating systems certain signal handlers are supposed to ``do something'' before returning. One example can be CHLD or CLD which indicates a child process has completed. On some operating systems the signal handler is expected to "wait" for the completed child process. On such systems the deferred signal scheme will not work for those signals (it does not do the "wait"). Again the failure will look like a loop as the operating system will re-issue the signal as there are un-waited-for completed child processes.
If you want the old signal behaviour back regardless of possible memory corruption, set the environment variable "PERL_SIGNALS" to "unsafe" (a new feature since Perl 5.8.1).
Using open() for IPC
Perl's basic open() statement can also be used for unidirectional interprocess communication by either appending or prepending a pipe symbol to the second argument to open().
And here's how to start up a child process you intend to read from:
open(STATUS, "netstat -an 2>&1 |") || die "can't fork: $!"; while (<STATUS>) { next if /^(tcp|udp)/; print; } close STATUS || die "bad netstat: $! $?";
If one can be sure that a particular program is a Perl script that is expecting filenames in @ARGV, the clever programmer can write something like this:
% program f1 "cmd1|" - f2 "cmd2|" f3 < tmpfile
and irrespective of which shell it's called from, the Perl program will read from the file f1, the process cmd1, standard input (tmpfile in this case), the f2 file, the cmd2 command, and finally the f3 file. Pretty nifty, eh?
You might notice that you could use backticks for much the same effect as opening a pipe for reading:
print grep { !/^(tcp|udp)/ } `netstat -an 2>&1`; die "bad netstat" if $?;
While this is true on the surface, it's much more efficient to process the file one line or record at a time because then you don't have to read the whole thing into memory at once. It also gives you finer control of the whole process, letting you to kill off the child process early if you'd like.
Be careful to check both the open() and the close() return values. If you're writing to a pipe, you should also trap SIGPIPE. Otherwise, think of what happens when you start up a pipe to a command that doesn't exist: the open() will in all likelihood succeed (it only reflects the fork()'s success), but then your output will fail---spectacularly. Perl can't know whether the command worked because your command is actually running in a separate process whose exec() might have failed. Therefore, while readers of bogus commands return just a quick end of file, writers to bogus command will trigger a signal they'd better be prepared to handle.

Filehandles
Both the main process and any child processes it forks share the same STDIN, STDOUT, and STDERR filehandles. If both processes try to access them at once, strange things can happen. You may also want to close or reopen the filehandles for the child. You can get around this by opening your pipe with open(), but on some systems this means that the child process cannot outlive the parent.Background Processes
You can run a command in the background with:
system("cmd &");
The command's STDOUT and STDERR (and possibly STDIN, depending on your shell) will be the same as the parent's. You won't need to catch SIGCHLD because of the double-fork taking place (see below for more details).
Complete Dissociation of Child from Parent
In some cases (starting server processes, for instance) you'll want to completely dissociate the child process from the parent. This is often called daemonization. A well behaved daemon will also chdir() to the root directory (so it doesn't prevent unmounting the filesystem containing the directory from which it was launched) and redirect its standard file descriptors from and to /dev/null (so that random output doesn't wind up on the user's terminal).
use POSIX 'setsid'; sub daemonize { chdir '/' or die "Can't chdir to /: $!"; open STDIN, '/dev/null' or die "Can't read /dev/null: $!"; open STDOUT, '>/dev/null' or die "Can't write to /dev/null: $!"; defined(my $pid = fork) or die "Can't fork: $!"; exit if $pid; die "Can't start a new session: $!" if setsid == -1; open STDERR, '>&STDOUT' or die "Can't dup stdout: $!"; }
The fork() has to come before the setsid() to ensure that you aren't a process group leader (the setsid() will fail if you are). If your system doesn't have the setsid() function, open /dev/tty and use the "TIOCNOTTY" ioctl() on it instead. See tty(4) for details.
Non-Unix users should check their Your_OS::Process module for other solutions.
Safe Pipe Opens
Another interesting approach to IPC is making your single program go multiprocess and communicate between (or even amongst) yourselves. The open() function will accept a file argument of either "-|" or "|-" to do a very interesting thing: it forks a child connected to the filehandle you've opened. The child is running the same program as the parent. This is useful for safely opening a file when running under an assumed UID or GID, for example. If you open a pipe to minus, you can write to the filehandle you opened and your kid will find it in his STDIN. If you open a pipe from minus, you can read from the filehandle you opened whatever your kid writes to his STDOUT.
use English '-no_match_vars'; my $sleep_count = 0; do { $pid = open(KID_TO_WRITE, "|-"); unless (defined $pid) { warn "cannot fork: $!"; die "bailing out" if $sleep_count++ > 6; sleep 10; } } until defined $pid; if ($pid) { # parent print KID_TO_WRITE @some_data; close(KID_TO_WRITE) || warn "kid exited $?"; } else { # child ($EUID, $EGID) = ($UID, $GID); # suid progs only open (FILE, "> /safe/file") || die "can't open /safe/file: $!"; while (<STDIN>) { print FILE; # child's STDIN is parent's KID_TO_WRITE } exit; # don't forget this }
Another common use for this construct is when you need to execute something without the shell's interference. With system(), it's straightforward, but you can't use a pipe open or backticks safely. That's because there's no way to stop the shell from getting its hands on your arguments. Instead, use lower-level control to call exec() directly.
Here's a safe backtick or pipe open for read:
# add error processing as above $pid = open(KID_TO_READ, "-|"); if ($pid) { # parent while (<KID_TO_READ>) { # do something interesting } close(KID_TO_READ) || warn "kid exited $?"; } else { # child ($EUID, $EGID) = ($UID, $GID); # suid only exec($program, @options, @args) || die "can't exec program: $!"; # NOTREACHED }
And here's a safe pipe open for writing:
# add error processing as above $pid = open(KID_TO_WRITE, "|-"); $SIG{PIPE} = sub { die "whoops, $program pipe broke" }; if ($pid) { # parent for (@data) { print KID_TO_WRITE; } close(KID_TO_WRITE) || warn "kid exited $?"; } else { # child ($EUID, $EGID) = ($UID, $GID); exec($program, @options, @args) || die "can't exec program: $!"; # NOTREACHED }
It is very easy to dead-lock a process using this form of open(), or indeed any use of pipe() and multiple sub-processes. The above example is 'safe' because it is simple and calls exec(). See ``Avoiding Pipe Deadlocks'' for general safety principles, but there are extra gotchas with Safe Pipe Opens.
In particular, if you opened the pipe using "open FH, "|-"", then you cannot simply use close() in the parent process to close an unwanted writer. Consider this code:
$pid = open WRITER, "|-"; defined $pid or die "fork failed; $!"; if ($pid) { if (my $sub_pid = fork()) { close WRITER; # do something else... } else { # write to WRITER... exit; } } else { # do something with STDIN... exit; }
In the above, the true parent does not want to write to the WRITER filehandle, so it closes it. However, because WRITER was opened using "open FH, "|-"", it has a special behaviour: closing it will call waitpid() (see ``waitpid'' in perlfunc), which waits for the sub-process to exit. If the child process ends up waiting for something happening in the section marked ``do something else'', then you have a deadlock.
This can also be a problem with intermediate sub-processes in more complicated code, which will call waitpid() on all open filehandles during global destruction; in no predictable order.
To solve this, you must manually use pipe(), fork(), and the form of open() which sets one file descriptor to another, as below:
pipe(READER, WRITER); $pid = fork(); defined $pid or die "fork failed; $!"; if ($pid) { close READER; if (my $sub_pid = fork()) { close WRITER; } else { # write to WRITER... exit; } # write to WRITER... } else { open STDIN, "<&READER"; close WRITER; # do something... exit; }
Since Perl 5.8.0, you can also use the list form of "open" for pipes : the syntax
open KID_PS, "-|", "ps", "aux" or die $!;
forks the ps(1) command (without spawning a shell, as there are more than three arguments to open()), and reads its standard output via the "KID_PS" filehandle. The corresponding syntax to write to command pipes (with "|-" in place of "-|") is also implemented.
Note that these operations are full Unix forks, which means they may not be correctly implemented on alien systems. Additionally, these are not true multithreading. If you'd like to learn more about threading, see the modules file mentioned below in the SEE ALSO section.
Avoiding Pipe Deadlocks
In general, if you have more than one sub-process, you need to be very careful that any process which does not need the writer half of any pipe you create for inter-process communication does not have it open.The reason for this is that any child process which is reading from the pipe and expecting an EOF will never receive it, and therefore never exit. A single process closing a pipe is not enough to close it; the last process with the pipe open must close it for it to read EOF.
There are some features built-in to unix to help prevent this most of the time. For instance, filehandles have a 'close on exec' flag (set en masse with Perl using the $^F perlvar), so that any filehandles which you didn't explicitly route to the STDIN, STDOUT or STDERR of a child program will automatically be closed for you.
So, always explicitly and immediately call close() on the writable end of any pipe, unless that process is actually writing to it. If you don't explicitly call close() then be warned Perl will still close() all the filehandles during global destruction. As warned above, if those filehandles were opened with Safe Pipe Open, they will also call waitpid() and you might again deadlock.
Bidirectional Communication with Another Process
While this works reasonably well for unidirectional communication, what about bidirectional communication? The obvious thing you'd like to do doesn't actually work:
open(PROG_FOR_READING_AND_WRITING, "| some program |")
and if you forget to use the "use warnings" pragma or the -w flag, then you'll miss out entirely on the diagnostic message:
Can't do bidirectional pipe at -e line 1.
If you really want to, you can use the standard open2() library function to catch both ends. There's also an open3() for tridirectional I/O so you can also catch your child's STDERR, but doing so would then require an awkward select() loop and wouldn't allow you to use normal Perl input operations.
If you look at its source, you'll see that open2() uses low-level primitives like Unix pipe() and exec() calls to create all the connections. While it might have been slightly more efficient by using socketpair(), it would have then been even less portable than it already is. The open2() and open3() functions are unlikely to work anywhere except on a Unix system or some other one purporting to be POSIX compliant.
Here's an example of using open2():
use FileHandle; use IPC::Open2; $pid = open2(*Reader, *Writer, "cat -u -n" ); print Writer "stuff\n"; $got = <Reader>;
The problem with this is that Unix buffering is really going to ruin your day. Even though your "Writer" filehandle is auto-flushed, and the process on the other end will get your data in a timely manner, you can't usually do anything to force it to give it back to you in a similarly quick fashion. In this case, we could, because we gave cat a -u flag to make it unbuffered. But very few Unix commands are designed to operate over pipes, so this seldom works unless you yourself wrote the program on the other end of the double-ended pipe.
A solution to this is the nonstandard Comm.pl library. It uses pseudo-ttys to make your program behave more reasonably:
require 'Comm.pl'; $ph = open_proc('cat -n'); for (1..10) { print $ph "a line\n"; print "got back ", scalar <$ph>; }
This way you don't have to have control over the source code of the program you're using. The Comm library also has expect() and interact() functions. Find the library (and we hope its successor IPC::Chat) at your nearest CPAN archive as detailed in the SEE ALSO section below.
The newer Expect.pm module from CPAN also addresses this kind of thing. This module requires two other modules from CPAN: IO::Pty and IO::Stty. It sets up a pseudo-terminal to interact with programs that insist on using talking to the terminal device driver. If your system is amongst those supported, this may be your best bet.
Bidirectional Communication with Yourself
If you want, you may make low-level pipe() and fork() to stitch this together by hand. This example only talks to itself, but you could reopen the appropriate handles to STDIN and STDOUT and call other processes.
#!/usr/bin/perl -w # pipe1 - bidirectional communication using two pipe pairs # designed for the socketpair-challenged use IO::Handle; # thousands of lines just for autoflush :-( pipe(PARENT_RDR, CHILD_WTR); # XXX: failure? pipe(CHILD_RDR, PARENT_WTR); # XXX: failure? CHILD_WTR->autoflush(1); PARENT_WTR->autoflush(1); if ($pid = fork) { close PARENT_RDR; close PARENT_WTR; print CHILD_WTR "Parent Pid $$ is sending this\n"; chomp($line = <CHILD_RDR>); print "Parent Pid $$ just read this: `$line'\n"; close CHILD_RDR; close CHILD_WTR; waitpid($pid,0); } else { die "cannot fork: $!" unless defined $pid; close CHILD_RDR; close CHILD_WTR; chomp($line = <PARENT_RDR>); print "Child Pid $$ just read this: `$line'\n"; print PARENT_WTR "Child Pid $$ is sending this\n"; close PARENT_RDR; close PARENT_WTR; exit; }
But you don't actually have to make two pipe calls. If you have the socketpair() system call, it will do this all for you.
#!/usr/bin/perl -w # pipe2 - bidirectional communication using socketpair # "the best ones always go both ways" use Socket; use IO::Handle; # thousands of lines just for autoflush :-( # We say AF_UNIX because although *_LOCAL is the # POSIX 1003.1g form of the constant, many machines # still don't have it. socketpair(CHILD, PARENT, AF_UNIX, SOCK_STREAM, PF_UNSPEC) or die "socketpair: $!"; CHILD->autoflush(1); PARENT->autoflush(1); if ($pid = fork) { close PARENT; print CHILD "Parent Pid $$ is sending this\n"; chomp($line = <CHILD>); print "Parent Pid $$ just read this: `$line'\n"; close CHILD; waitpid($pid,0); } else { die "cannot fork: $!" unless defined $pid; close CHILD; chomp($line = <PARENT>); print "Child Pid $$ just read this: `$line'\n"; print PARENT "Child Pid $$ is sending this\n"; close PARENT; exit; }
Sockets: Client/Server Communication
While not limited to Unix-derived operating systems (e.g., WinSock on PCs provides socket support, as do some VMS libraries), you may not have sockets on your system, in which case this section probably isn't going to do you much good. With sockets, you can do both virtual circuits (i.e., TCP streams) and datagrams (i.e., UDP packets). You may be able to do even more depending on your system.The Perl function calls for dealing with sockets have the same names as the corresponding system calls in C, but their arguments tend to differ for two reasons: first, Perl filehandles work differently than C file descriptors. Second, Perl already knows the length of its strings, so you don't need to pass that information.
One of the major problems with old socket code in Perl was that it used hard-coded values for some of the constants, which severely hurt portability. If you ever see code that does anything like explicitly setting "$AF_INET = 2", you know you're in for big trouble: An immeasurably superior approach is to use the "Socket" module, which more reliably grants access to various constants and functions you'll need.
If you're not writing a server/client for an existing protocol like NNTP or SMTP, you should give some thought to how your server will know when the client has finished talking, and vice-versa. Most protocols are based on one-line messages and responses (so one party knows the other has finished when a ``\n'' is received) or multi-line messages and responses that end with a period on an empty line (``\n.\n'' terminates a message/response).
Internet Line Terminators
The Internet line terminator is ``\015\012''. Under ASCII variants of Unix, that could usually be written as ``\r\n'', but under other systems, ``\r\n'' might at times be ``\015\015\012'', ``\012\012\015'', or something completely different. The standards specify writing ``\015\012'' to be conformant (be strict in what you provide), but they also recommend accepting a lone ``\012'' on input (but be lenient in what you require). We haven't always been very good about that in the code in this manpage, but unless you're on a Mac, you'll probably be ok.Internet TCP Clients and Servers
Use Internet-domain sockets when you want to do client-server communication that might extend to machines outside of your own system.Here's a sample TCP client using Internet-domain sockets:
#!/usr/bin/perl -w use strict; use Socket; my ($remote,$port, $iaddr, $paddr, $proto, $line); $remote = shift || 'localhost'; $port = shift || 2345; # random port if ($port =~ /\D/) { $port = getservbyname($port, 'tcp') } die "No port" unless $port; $iaddr = inet_aton($remote) || die "no host: $remote"; $paddr = sockaddr_in($port, $iaddr); $proto = getprotobyname('tcp'); socket(SOCK, PF_INET, SOCK_STREAM, $proto) || die "socket: $!"; connect(SOCK, $paddr) || die "connect: $!"; while (defined($line = <SOCK>)) { print $line; } close (SOCK) || die "close: $!"; exit;
And here's a corresponding server to go along with it. We'll leave the address as INADDR_ANY so that the kernel can choose the appropriate interface on multihomed hosts.   : ''); } $SIG{CHLD} = \&REAPER; # loathe SysV } $SIG{CHLD} = \&REAPER; while(1) { $paddr = accept(Client, Server) || do { # try again if accept() returned because a signal was received next if $!{EINTR}; die "accept: $!"; }; my ($port, $iaddr) = sockaddr_in($paddr); my $name = gethostbyaddr($iaddr, AF_INET); logmsg "connection from $name [", inet_ntoa($iaddr), "] at port $port"; spawn sub { $|=1; print "Hello there, $name, it's now ", scalar localtime, $EOL; exec '/usr/games/fortune' # XXX: `wrong' line terminators or confess "can't exec fortune: $!"; }; close Client; } sub spawn { my $coderef = shift; unless (@_ == 0 && $coderef && ref($coderef) eq 'CODE') { confess "usage: spawn CODEREF"; } my $pid; if (! defined($pid = fork)) { logmsg "cannot fork: $!"; return; } elsif ($pid) { logmsg "begat $pid"; return; # I'm the parent } # else I'm the child -- go spawn open(STDIN, "<&Client") || die "can't dup client to stdin"; open(STDOUT, ">&Client") || die "can't dup client to stdout"; ## open(STDERR, ">&STDOUT") || die "can't dup stdout to stderr"; exit &$coderef(); }
This server takes the trouble to clone off a child version via fork() for each incoming request. That way it can handle many requests at once, which you might not always want. Even if you don't fork(), the listen() will allow that many pending connections. Forking servers have to be particularly careful about cleaning up their dead children (called ``zombies'' in Unix parlance), because otherwise you'll quickly fill up your process table. The REAPER subroutine is used here to call waitpid() for any child processes that have finished, thereby ensuring that they terminate cleanly and don't join the ranks of the living dead.
Within the while loop we call accept() and check to see if it returns a false value. This would normally indicate a system error that needs to be reported. However the introduction of safe signals (see ``Deferred Signals (Safe Signals)'' above) in Perl 5.7.3 means that accept() may also be interrupted when the process receives a signal. This typically happens when one of the forked sub-processes exits and notifies the parent process with a CHLD signal.
If accept() is interrupted by a signal then $! will be set to EINTR. If this happens then we can safely continue to the next iteration of the loop and another call to accept(). It is important that your signal handling code doesn't modify the value of $! or this test will most likely fail. In the REAPER subroutine we create a local version of $! before calling waitpid(). When waitpid() sets $! to ECHILD (as it inevitably does when it has no more children waiting), it will update the local copy leaving the original unchanged.
We suggest that you use the -T flag to use taint checking (see perlsec) even if we aren't running setuid or setgid. This is always a good idea for servers and other programs run on behalf of someone else (like CGI scripts), because it lessens the chances that people from the outside will be able to compromise your system.
Let's look at another TCP client. This one connects to the TCP ``time'' service on a number of different machines and shows how far their clocks differ from the system on which it's being run:
#!/usr/bin/perl -w use strict; use Socket; my $SECS_of_70_YEARS =<PHONE_NUMBER>; sub ctime { scalar localtime(shift) } my $iaddr = gethostbyname('localhost'); my $proto = getprotobyname('tcp'); my $port = getservbyname('time', 'tcp'); my $paddr = sockaddr_in(0, $iaddr); my($host); $| = 1; printf "%-24s %8s %s\n", "localhost", 0, ctime(time()); foreach $host (@ARGV) { printf "%-24s ", $host; my $hisiaddr = inet_aton($host) || die "unknown host"; my $hispaddr = sockaddr_in($port, $hisiaddr); socket(SOCKET, PF_INET, SOCK_STREAM, $proto) || die "socket: $!"; connect(SOCKET, $hispaddr) || die "bind: $!"; my $rtime = ' '; read(SOCKET, $rtime, 4); close(SOCKET); my $histime = unpack("N", $rtime) - $SECS_of_70_YEARS; printf "%8d %s\n", $histime - time, ctime($histime); }
Unix-Domain TCP Clients and Servers
That's fine for Internet-domain clients and servers, but what about local communications? While you can use the same setup, sometimes you don't want to. Unix-domain sockets are local to the current host, and are often used internally to implement pipes. Unlike Internet domain sockets, Unix domain sockets can show up in the file system with an ls(1) listing.
% ls -l /dev/log srw-rw-rw- 1 root 0 Oct 31 07:23 /dev/log
You can test for these with Perl's -S file test:
unless ( -S '/dev/log' ) { die "something's wicked with the log system"; }
Here's a sample Unix-domain client:
#!/usr/bin/perl -w use Socket; use strict; my ($rendezvous, $line); $rendezvous = shift || 'catsock'; socket(SOCK, PF_UNIX, SOCK_STREAM, 0) || die "socket: $!"; connect(SOCK, sockaddr_un($rendezvous)) || die "connect: $!"; while (defined($line = <SOCK>)) { print $line; } exit;
And here's a corresponding server.  : ''); } $SIG{CHLD} = \&REAPER; # loathe SysV } $SIG{CHLD} = \&REAPER; for ( $waitedpid = 0; accept(Client,Server) || $waitedpid; $waitedpid = 0, close Client) { next if $waitedpid; logmsg "connection on $NAME"; spawn sub { print "Hello there, it's now ", scalar localtime, "\n"; exec '/usr/games/fortune' or die "can't exec fortune: $!"; }; } sub spawn { my $coderef = shift; unless (@_ == 0 && $coderef && ref($coderef) eq 'CODE') { confess "usage: spawn CODEREF"; } my $pid; if (!defined($pid = fork)) { logmsg "cannot fork: $!"; return; } elsif ($pid) { logmsg "begat $pid"; return; # I'm the parent } # else I'm the child -- go spawn open(STDIN, "<&Client") || die "can't dup client to stdin"; open(STDOUT, ">&Client") || die "can't dup client to stdout"; ## open(STDERR, ">&STDOUT") || die "can't dup stdout to stderr"; exit &$coderef(); }
As you see, it's remarkably similar to the Internet domain TCP server, so much so, in fact, that we've omitted several duplicate functions---spawn(), logmsg(), ctime(), and REAPER()--which are exactly the same as in the other server.
So why would you ever want to use a Unix domain socket instead of a simpler named pipe? Because a named pipe doesn't give you sessions. You can't tell one process's data from another's. With socket programming, you get a separate session for each client: that's why accept() takes two arguments.
For example, let's say that you have a long running database server daemon that you want folks from the World Wide Web to be able to access, but only if they go through a CGI interface. You'd have a small, simple CGI program that does whatever checks and logging you feel like, and then acts as a Unix-domain client and connects to your private server.
TCP Clients with IO::Socket
For those preferring a higher-level interface to socket programming, the IO::Socket module provides an object-oriented approach. IO::Socket is included as part of the standard Perl distribution as of the 5.004 release. If you're running an earlier version of Perl, just fetch IO::Socket from CPAN, where you'll also find modules providing easy interfaces to the following systems: DNS, FTP, Ident (RFC 931), NIS and NISPlus, NNTP, Ping, POP3, SMTP, SNMP, SSLeay, Telnet, and Time---just to name a few.A Simple Client
Here's a client that creates a TCP connection to the ``daytime'' service at port 13 of the host name ``localhost'' and prints out everything that the server there cares to provide.
#!/usr/bin/perl -w use IO::Socket; $remote = IO::Socket::INET->new( Proto => "tcp", PeerAddr => "localhost", PeerPort => "daytime(13)", ) or die "cannot connect to daytime port at localhost"; while ( <$remote> ) { print }
When you run this program, you should get something back that looks like this:
Wed May 14 08:40:46 MDT 1997
Here are what those parameters to the "new" constructor mean:
- Proto
- This is which protocol to use. In this case, the socket handle returned will be connected to a TCP socket, because we want a stream-oriented connection, that is, one that acts pretty much like a plain old file. Not all sockets are this of this type. For example, the UDP protocol can be used to make a datagram socket, used for message-passing.
- PeerAddr
- This is the name or Internet address of the remote host the server is running on. We could have specified a longer name like "www.perl.com", or an address like "<IP_ADDRESS>". For demonstration purposes, we've used the special hostname "localhost", which should always mean the current machine you're running on. The corresponding Internet address for localhost is "127.1", if you'd rather use that.
- PeerPort
- This is the service name or port number we'd like to connect to. We could have gotten away with using just "daytime" on systems with a well-configured system services file,[FOOTNOTE: The system services file is in /etc/services under Unix] but just in case, we've specified the port number (13) in parentheses. Using just the number would also have worked, but constant numbers make careful programmers nervous.
Notice how the return value from the "new" constructor is used as a filehandle in the "while" loop? That's what's called an indirect filehandle, a scalar variable containing a filehandle. You can use it the same way you would a normal filehandle. For example, you can read one line from it this way:
$line = <$handle>;
all remaining lines from is this way:
@lines = <$handle>;
and send a line of data to it this way:
print $handle "some data\n";
A Webget Client
Here's a simple client that takes a remote host to fetch a document from, and then a list of documents to get from that host. This is a more interesting client than the previous one because it first sends something to the server before fetching the server's response.
#!/usr/bin/perl -w use IO::Socket; unless (@ARGV > 1) { die "usage: $0 host document ..." } $host = shift(@ARGV); $EOL = "\015\012"; $BLANK = $EOL x 2; foreach $document ( @ARGV ) { $remote = IO::Socket::INET->new( Proto => "tcp", PeerAddr => $host, PeerPort => "http(80)", ); unless ($remote) { die "cannot connect to http daemon on $host" } $remote->autoflush(1); print $remote "GET $document HTTP/1.0" . $BLANK; while ( <$remote> ) { print } close $remote; }
The web server handing the ``http'' service, which is assumed to be at its standard port, number 80. If the web server you're trying to connect to is at a different port (like 1080 or 8080), you should specify as the named-parameter pair, "PeerPort => 8080". The "autoflush" method is used on the socket because otherwise the system would buffer up the output we sent it. (If you're on a Mac, you'll also need to change every "\n" in your code that sends data over the network to be a "\015\012" instead.)
Connecting to the server is only the first part of the process: once you have the connection, you have to use the server's language. Each server on the network has its own little command language that it expects as input. The string that we send to the server starting with ``GET'' is in HTTP syntax. In this case, we simply request each specified document. Yes, we really are making a new connection for each document, even though it's the same host. That's the way you always used to have to speak HTTP. Recent versions of web browsers may request that the remote server leave the connection open a little while, but the server doesn't have to honor such a request.
Here's an example of running that program, which we'll call webget:
% webget www.perl.com /guanaco.html HTTP/1.1 404 File Not Found Date: Thu, 08 May 1997 18:02:32 GMT Server: Apache/1.2b6 Connection: close Content-type: text/html <HEAD><TITLE>404 File Not Found</TITLE></HEAD> <BODY><H1>File Not Found</H1> The requested URL /guanaco.html was not found on this server.<P> </BODY>
Ok, so that's not very interesting, because it didn't find that particular document. But a long response wouldn't have fit on this page.
For a more fully-featured version of this program, you should look to the lwp-request program included with the LWP modules from CPAN.
Interactive Client with IO::Socket
Well, that's all fine if you want to send one command and get one answer, but what about setting up something fully interactive, somewhat like the way telnet works? That way you can type a line, get the answer, type a line, get the answer, etc.This client is more complicated than the two we've done so far, but if you're on a system that supports the powerful "fork" call, the solution isn't that rough. Once you've made the connection to whatever service you'd like to chat with, call "fork" to clone your process. Each of these two identical process has a very simple job to do: the parent copies everything from the socket to standard output, while the child simultaneously copies everything from standard input to the socket. To accomplish the same thing using just one process would be much harder, because it's easier to code two processes to do one thing than it is to code one process to do two things. (This keep-it-simple principle a cornerstones of the Unix philosophy, and good software engineering as well, which is probably why it's spread to other systems.)
Here's the code:
#!/usr/bin/perl -w use strict; use IO::Socket; my ($host, $port, $kidpid, $handle, $line); unless (@ARGV == 2) { die "usage: $0 host port" } ($host, $port) = @ARGV; # create a tcp connection to the specified host and port $handle = IO::Socket::INET->new(Proto => "tcp", PeerAddr => $host, PeerPort => $port) or die "can't connect to port $port on $host: $!"; $handle->autoflush(1); # so output gets there right away print STDERR "[Connected to $host:$port]\n"; # split the program into two processes, identical twins die "can't fork: $!" unless defined($kidpid = fork()); # the if{} block runs only in the parent process if ($kidpid) { # copy the socket to standard output while (defined ($line = <$handle>)) { print STDOUT $line; } kill("TERM", $kidpid); # send SIGTERM to child } # the else{} block runs only in the child process else { # copy standard input to the socket while (defined ($line = <STDIN>)) { print $handle $line; } }
The "kill" function in the parent's "if" block is there to send a signal to our child process (current running in the "else" block) as soon as the remote server has closed its end of the connection.
If the remote server sends data a byte at time, and you need that data immediately without waiting for a newline (which might not happen), you may wish to replace the "while" loop in the parent with the following:
my $byte; while (sysread($handle, $byte, 1) == 1) { print STDOUT $byte; }
Making a system call for each byte you want to read is not very efficient (to put it mildly) but is the simplest to explain and works reasonably well.
TCP Servers with IO::Socket
As always, setting up a server is little bit more involved than running a client. The model is that the server creates a special kind of socket that does nothing but listen on a particular port for incoming connections. It does this by calling the "IO::Socket::INET->new()" method with slightly different arguments than the client did.- Proto
- This is which protocol to use. Like our clients, we'll still specify "tcp" here.
- LocalPort
- We specify a local port in the "LocalPort" argument, which we didn't do for the client. This is service name or port number for which you want to be the server. (Under Unix, ports under 1024 are restricted to the superuser.) In our sample, we'll use port 9000, but you can use any port that's not currently in use on your system. If you try to use one already in used, you'll get an ``Address already in use'' message. Under Unix, the "netstat -a" command will show which services current have servers.
- Listen
- The "Listen" parameter is set to the maximum number of pending connections we can accept until we turn away incoming clients. Think of it as a call-waiting queue for your telephone. The low-level Socket module has a special symbol for the system maximum, which is SOMAXCONN.
- Reuse
- The "Reuse" parameter is needed so that we restart our server manually without waiting a few minutes to allow system buffers to clear out.
Once the generic server socket has been created using the parameters listed above, the server then waits for a new client to connect to it. The server blocks in the "accept" method, which eventually accepts a bidirectional connection from the remote client. (Make sure to autoflush this handle to circumvent buffering.)
To add to user-friendliness, our server prompts the user for commands. Most servers don't do this. Because of the prompt without a newline, you'll have to use the "sysread" variant of the interactive client above.
This server accepts one of five different commands, sending output back to the client. Note that unlike most network servers, this one only handles one incoming client at a time. Multithreaded servers are covered in Chapter 6 of the Camel.
Here's the code. We'll
#!/usr/bin/perl -w use IO::Socket; use Net::hostent; # for OO version of gethostbyaddr $PORT = 9000; # pick something not in use $server = IO::Socket::INET->new( Proto => 'tcp', LocalPort => $PORT, Listen => SOMAXCONN, Reuse => 1); die "can't setup server" unless $server; print "[Server $0 accepting clients]\n"; while ($client = $server->accept()) { $client->autoflush(1); print $client "Welcome to $0; type help for command list.\n"; $hostinfo = gethostbyaddr($client->peeraddr); printf "[Connect from %s]\n", $hostinfo ? $hostinfo->name : $client->peerhost; print $client "Command? "; while ( <$client>) { next unless /\S/; # blank line if (/quit|exit/i) { last; } elsif (/date|time/i) { printf $client "%s\n", scalar localtime; } elsif (/who/i ) { print $client `who 2>&1`; } elsif (/cookie/i ) { print $client `/usr/games/fortune 2>&1`; } elsif (/motd/i ) { print $client `cat /etc/motd 2>&1`; } else { print $client "Commands: quit date who cookie motd\n"; } } continue { print $client "Command? "; } close $client; }
UDP: Message Passing
Another kind of client-server setup is one that uses not connections, but messages. UDP communications involve much lower overhead but also provide less reliability, as there are no promises that messages will arrive at all, let alone in order and unmangled. Still, UDP offers some advantages over TCP, including being able to ``broadcast'' or ``multicast'' to a whole bunch of destination hosts at once (usually on your local subnet). If you find yourself overly concerned about reliability and start building checks into your message system, then you probably should use just TCP to start with.Note that UDP datagrams are not a bytestream and should not be treated as such. This makes using I/O mechanisms with internal buffering like stdio (i.e. print() and friends) especially cumbersome. Use syswrite(), or better send(), like in the example below.
Here's a UDP program similar to the sample Internet TCP client given earlier. However, instead of checking one host at a time, the UDP version will check many of them asynchronously by simulating a multicast and then using select() to do a timed-out wait for I/O. To do something similar with TCP, you'd have to use a different socket handle for each host.
#!/usr/bin/perl -w use strict; use Socket; use Sys::Hostname; my ( $count, $hisiaddr, $hispaddr, $histime, $host, $iaddr, $paddr, $port, $proto, $rin, $rout, $rtime, $SECS_of_70_YEARS); $SECS_of_70_YEARS =<PHONE_NUMBER>; $iaddr = gethostbyname(hostname()); $proto = getprotobyname('udp'); $port = getservbyname('time', 'udp'); $paddr = sockaddr_in(0, $iaddr); # 0 means let kernel pick socket(SOCKET, PF_INET, SOCK_DGRAM, $proto) || die "socket: $!"; bind(SOCKET, $paddr) || die "bind: $!"; $| = 1; printf "%-12s %8s %s\n", "localhost", 0, scalar localtime time; $count = 0; for $host (@ARGV) { $count++; $hisiaddr = inet_aton($host) || die "unknown host"; $hispaddr = sockaddr_in($port, $hisiaddr); defined(send(SOCKET, 0, 0, $hispaddr)) || die "send $host: $!"; } $rin = ''; vec($rin, fileno(SOCKET), 1) = 1; # timeout after 10.0 seconds while ($count && select($rout = $rin, undef, undef, 10.0)) { $rtime = ''; ($hispaddr = recv(SOCKET, $rtime, 4, 0)) || die "recv: $!"; ($port, $hisiaddr) = sockaddr_in($hispaddr); $host = gethostbyaddr($hisiaddr, AF_INET); $histime = unpack("N", $rtime) - $SECS_of_70_YEARS; printf "%-12s ", $host; printf "%8d %s\n", $histime - time, scalar localtime($histime); $count--; }
Note that this example does not include any retries and may consequently fail to contact a reachable host. The most prominent reason for this is congestion of the queues on the sending host if the number of list of hosts to contact is sufficiently large.
SysV IPC
While System V IPC isn't so widely used as sockets, it still has some interesting uses. You can't, however, effectively use SysV IPC or Berkeley mmap() to have shared memory so as to share a variable amongst several processes.
Here's an example of a semaphore:
use IPC::SysV qw(IPC_CREAT); $IPC_KEY = 1234; $id = semget($IPC_KEY, 10, 0666 | IPC_CREAT ) || die "$!"; print "shm key $id\n";
Put this code in a separate file to be run in more than one process. Call the file take:
# create a semaphore $IPC_KEY = 1234; $id = semget($IPC_KEY, 0 , 0 ); die if !defined($id); $semnum = 0; $semflag = 0; # 'take' semaphore # wait for semaphore to be zero $semop = 0; $opstring1 = pack("s!s!s!", $semnum, $semop, $semflag); # Increment the semaphore count $semop = 1; $opstring2 = pack("s!s!s!", $semnum, $semop, $semflag); $opstring = $opstring1 . $opstring2; semop($id,$opstring) || die "$!";
Put this code in a separate file to be run in more than one process. Call this file give:
# 'give' the semaphore # run this in the original process and you will see # that the second process continues $IPC_KEY = 1234; $id = semget($IPC_KEY, 0, 0); die if !defined($id); $semnum = 0; $semflag = 0; # Decrement the semaphore count $semop = -1; $opstring = pack("s!s!s!", $semnum, $semop, $semflag); semop($id,$opstring) || die "$!";
The SysV IPC code above was written long ago, and it's definitely clunky looking. For a more modern look, see the IPC::SysV module which is included with Perl starting from Perl 5.005.
 (Actually, some of the new Socket conversion functions croak() on bad arguments.) It is therefore essential to check return values from these functions. Always begin your socket programs this way for optimal success, and don't forget to add -T taint checking flag to the #! line for servers:
#!/usr/bin/perl -Tw use strict; use sigtrap; use Socket;
BUGS
All these routines create system-specific portability problems. As noted elsewhere, Perl is at the mercy of your C libraries for much of its system behaviour. It's probably safest to assume broken SysV semantics for signals and to stick with simple TCP and UDP socket operations; e.g., don't try to pass open file descriptors over a local UDP datagram socket if you want your code to stand a chance of being portable.AUTHOR
Tom Christiansen, with occasional vestiges of Larry Wall's original version and suggestions from the Perl Porters.SEE ALSO
There's a lot more to networking than this, but this should get you started.For intrepid programmers, the indispensable textbook is Unix Network Programming, 2nd Edition, Volume 1 by W. Richard Stevens (published by Prentice-Hall). Note that most books on networking address the subject from the perspective of a C programmer; translation to Perl is left as an exercise for the reader.
The IO::Socket(3) manpage describes the object library, and the Socket(3) manpage describes the low-level interface to sockets. Besides the obvious functions in perlfunc, you should also check out the modules file at your nearest CPAN site. (See perlmodlib or best yet, the Perl FAQ for a description of what CPAN is and where to get it.)
Section 5 of the modules file is devoted to ``Networking, Device Control (modems), and Interprocess Communication'', and contains numerous unbundled modules numerous networking modules, Chat and Expect operations, CGI programming, DCE, FTP, IPC, NNTP, Proxy, Ptty, RPC, SNMP, SMTP, Telnet, Threads, and ToolTalk---just to name a few.
Index
- NAME
- DESCRIPTION
- Signals
- Named Pipes
- Using open() for IPC
- Sockets: Client/Server Communication
- TCP Clients with IO::Socket
- TCP Servers with IO::Socket
- UDP: Message Passing
- SysV IPC
- NOTES
- BUGS
- AUTHOR
- SEE ALSO
This document was created by man2html, using the manual pages.
Time: 05:29:08 GMT, December 24, 2015


BARBARIANS AT THE GATE A film review by James Berardinelli Copyright 1993 James Berardinelli
First Air Date: 3/20/93 Running Length: 1:49 Rated: NR (Language, brief nudity)
Starring: James Garner, Jonathan Pryce, Peter Riegert, Joanna Cassidy, Fred Dalton Thompson, Leilani Ferrer Director: Glenn Jordan Producer: Ray Stark Screenplay: Larry Gelbart based on the book by Bryan Burrough and John Helyar Music: Richard Gibbs Released by HBO Pictures (in association with Columbia Pictures)
BARBARIANS AT THE GATE, a made-for-HBO movie, recounts the events surrounding the biggest leveraged buyout in history, that of RJR Nabisco in 1988. Based on the bestseller of the same name, this film presents in some detail the decisions leading up to and the process by which RJR Nabisco's CEO F. Ross Johnson (James Garner) attempts to buy out his own company. Of greater interest, however, is the power struggle that develops between Johnson and Wall Street investment banker Henry Kravis (Jonathan Pryce), who intends to force Johnson out and take over RJR Nabisco on his own.
In general, the quality of most made-for-TV movies is abysmal. Low production values, shoddy direction, and poor acting abound. There are exceptions, of course, but not many. For that reason, in a year when there have been three too many Amy Fisher movies on the small screen, it's refreshing to come upon something with the intelligence, wit, and general high quality of BARBARIANS AT THE GATE.
BARBARIANS AT THE GATE is a story of high stakes, betrayal, and one- upsmanship that is told with a flair. Despite the nature of the subject, the general tone is lighthearted and at times even playful. From start to finish, there are few powerfully serious dramatic moments in BARBARIANS AT THE GATE. The film offers a different point-of-view on leveraged buyouts and other such mega-buck dealings. Most of us are used to looking in from the outside on these high-profile financial struggles; BARBARIANS AT THE GATE presents an insider's perspective - and not just any insider, but that of the "man at the top".
It's a credit to the production team that they're able to do so much with this movie. There's a lot of humor (most of it dry), a fair amount of tension, and numerous subtle-yet-pointed jabs at a "game" that rewards the losers with $23 million (after taxes). Pacing is excellent, especially during the last half-hour as the story builds to its climax. The furious rushing around of the characters is effectively translated to the audience. Whether you know the outcome or not, BARBARIANS AT THE GATE is captivating.
One would think that it would be difficult, if not impossible, to present a story with someone like F. Ross Johnson as the protagonist. After all, this is a very rich man involved in the kind of financial slight-of-hand that most Americans despise. However, screenwriter Larry Gelbart (taking cues from the Burrough/Helyar book) has managed to make Johnson a sympathetic and often-likable figure. Admittedly, the movie takes a few liberties. Some of Johnson's less-admirable traits have been downplayed, and he's presented as caring more about the work and the people who do it than the money he stands to make.
If this isn't the best performance of James Garner's career, it certainly tops anything he's done recently. It's difficult to gauge how much of the audience's rapport with Johnson comes as a result of the actor playing the role, but the job done by Garner is no small factor. His portrayal perfectly mixes greed, humanity, good-naturedness, and incompetence.
As Johnson's rival, Henry Kravis, Jonathan Pryce is equally as good, albeit with less screen time. Pryce makes the most of his opportunities and, although the Kravis is presented as a two-dimensional villain, Pryce's steely-eyed, tight-lipped performance gives the audience a good sense that this is a man not only to be reckoned with, but feared.
As much as the average person may despise the financial fakery of a leveraged buyout that results in thousands of lost jobs, BARBARIANS AT THE GATE, by looking at the situation from a different perspective, turns into a highly-entertaining film.  His morals, like those of anyone in a situation where a million dollars is small change, are screwed up - and the film takes delight in showing this in several wickedly-funny scenes - but the presentation of how he manages, and sometimes mismanages, the buyout is fascinating. More engaging is the battle between Johnson and Kravis, which has all the tension and drama of a high-stakes chess match.
BARBARIANS AT THE GATE is certainly a worthwhile effort, and, for those who can get past the natural distaste of the subject matter, likely to provide a witty, entertaining two hours. It's the equal of many of the better theatrically-released mainstream movies.
Rating: 8.7 (A-, ***)
- James Berardinelli<EMAIL_ADDRESS>.
The review above was posted to the
rec.arts.movies.reviews newsgroup (de.rec.film.kritiken for German reviews).
The Internet Movie Database accepts no responsibility for the contents of the
review and has no editorial control. Unless stated otherwise, the copyright
belongs to the author.
Please direct comments/criticisms of the review to relevant newsgroups.
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The formatting of the review is likely to differ from the original due
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Related links: index of all rec.arts.movies.reviews reviews


string pg_last_notice ( resource $connection )
pg_last_notice() returns the last notice message from the PostgreSQL server on the specified connection. The PostgreSQL server sends notice messages in several cases, for instance when creating a SERIAL column in a table. With pg_last_notice(), you can avoid issuing useless queries by checking whether or not the notice is related to your transaction. Notice message tracking can be set to optional by setting 1 for pgsql.ignore_notice in php.ini. Notice message logging can be set to optional by setting 0 for pgsql.log_notice in php.ini. Unless pgsql.ignore_notice is set to 0, notice message cannot be logged.
A string containing the last notice on the given connection, or FALSE on error.


{% include 'header.html' %}
Taxonomic Tree View - Mian
{% include 'navigation.html' %} {% include 'loading-bar.html' %}
Taxonomic Tree View
{% include 'project_list.html' %}
{% include 'filtering_options.html' %}
Visualization Parameters
Categorical Variable
Taxonomic Display Level
Kingdom
Phylum
Class
Order
Family
Genus
Species
OTU
Metric
Non-Zero OTU-Sample Counts
Non-Zero Sample Counts
Mean OTU-Sample Abundance
Median OTU-Sample Abundance
Max OTU-Sample Abundance
Exclude Unclassified
Yes
No
{% include 'notifications.html' %} {% include 'download_container.html' %}
{% include 'footer-viz-d3v4.html' %}


Plunkett & MacLeane ***
rated R USA Films starring Robert Carlyle, Jonny Lee Miller, Liv Tyler, Michael Gambon, Alan Cumming based on an original screenplay by Selwyn Roberts written by Robert Wade, Neal Purvis and Charles McKeown directed by Jake Scott
"Plunkett & MacLeane", the new 18th century action-adventure from music video director Jake Scott, defies all the rules of conventional period piece logic. It is hip, vibrant, and a lot of fun. The film reunites "Trainspotting" stars Robert Carlyle and Jonny Lee Miller as Plunkett & MacLeane, two ex-cons paired together against their will to become Britain's most notorious highwaymen. Plunkett provides the skills, and MacLeane provides the social stature. The two collaborate in order to steal from the rich and give to...themselves. When the men hold up the coach of the Lord Chief Justice Gibson (Michael Gambon), MacLeane falls in love at first sight with the Lord's feisty niece, Rebecca (Liv Tyler). While Plunkett tries to rob money for the two to get to America, MacLeane tries to win the affections of Rebecca. When I saw "Plunkett & MacLeane", I wasn't quite sure what to expect. However, after a couple rough opening scenes, Jake Scott (relative of directors Ridley and Tony Scott) presents us with an immensely likable, techno-beat-driven period piece adventure for the MTV generation. Scott's film might be hard-pressed to find an audience, since it's quirky tone seems to appeal neither to the costume drama crowd nor the younger action crowd. Hopefully, moviegoers will look past the facade and "Plunkett & MacLeane" can become an art house hit. Whatever the outcome of its theatrical run, "Plunkett & MacLeane" is quite an enjoyable little film, and an admirable debut for Jake Scott.
a capsule review by Akiva Gottlieb, The Teenage Movie Critic<EMAIL_ADDRESS>http://teenagemoviecritic.8m.com
The review above was posted to the
rec.arts.movies.reviews newsgroup (de.rec.film.kritiken for German reviews).
The Internet Movie Database accepts no responsibility for the contents of the
review and has no editorial control. Unless stated otherwise, the copyright
belongs to the author.
Please direct comments/criticisms of the review to relevant newsgroups.
Broken URLs inthe reviews are the responsibility of the author.
The formatting of the review is likely to differ from the original due
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Related links: index of all rec.arts.movies.reviews reviews


WITNESS LIST
Agriculture & Livestock Committee
October 7, 2014 - 12:00 PM
Agricultural import traffic delays
On:
Bazan, Luis (Pharr International Bridge)
Brouwen, Alfredo (City of Pharr - International Bridge)
Darling, Jim (City of McAllen)
Erickson, Bret (TIPA)
Godinez, Anthony (Lineage Logistics, Godinez International LLC)
Heller, Paul (Paramount Citrus)
Patridge, Keith (McAllen Economic Development Corp.)
Sanchez, Richard (State Rep. Sergio Munoz)
Spamer, Joaquin (AIPA)
Vale, Sam (South Texas Assets Consortium)
1


GOOD WILL HUNTING (Miramax - 1997) Starring Matt Damon, Robin Williams, Ben Affleck, Minnie Driver, Stellan Skarsgard Screenplay by Matt Damon & Ben Affleck Produced by Lawrence Bender Directed by Gus Van Sant Running time: 126 minutes
*** (out of four stars) Alternate Rating: B
Note: Some may consider portions of the following text to be spoilers. Be forewarned.
-------------------------------------------------------------
I think there's one thing that its many enthusiasts and handful of detractors can safely agree on: there isn't anything remotely innovative about Gus Van Sant's latest film, GOOD WILL HUNTING, co-written by stars Matt Damon and Ben Affleck. It is what it is -- a relentlessly feelgood drama following a conventional, utterly predictable storyline focused upon a directionless young man with talent to burn, and the attempts of those around him to help him find the right path. The film's about as unsubtle as a brick through your front window, but damned if it isn't effective.
20-year old Will Hunting (Matt Damon) is a once-in-a-generation-type genius who can instantly recall obscure passages from texts and has the inherent raw ability to casually solve mathematical problems which are considered year-long endeavours by some of the world's greatest minds. However, Will's decidedly working-class, and cheerfully so; the film presents the irony of a high school dropout toiling as a janitor at the prestigious MIT who's more brilliant than any of the university's students *or* teachers. He's also a bit of a handful; orphaned and in and out of foster homes during his childhood, Will's had several run-ins with the law. When award-winning professor Lambeau (Stellan Skarsgard of BREAKING THE WAVES and INSOMNIA, in another fine performance) presents his class with a thorny mathematical challenge, he's taken aback when the correct solution appears on the blackboard outside the lecture hall the very next day. None of the students take credit for the anonymous answer (they must be pretty honourable over at MIT; at my old school, you'd find no shortage of brownnosers who'd falsely lay claim to the honour in a heartbeat), but Lambeau is stunned to find that it's Will who's the resident genius when he catches the janitor scrawling the solutions to a second challenge on the blackboard. Before Lambeau can take the prodigy under his wing, Will finds himself under arrest after zealously striking a police officer intervening in a neighbourhood altercation involving him and his buddies Chuckie (Ben Affleck), Morgan (Casey Affleck), and Billy (Cole Hauser). Lambeau convinces the authorities to give Will parole, hinging on a weekly math session and the promise of counseling.
It's at this point where the film shifts its focus to where its interest lies: the relationship that develops between Will and similarly-wounded therapist Sean McGuire (Robin Williams), and how after initial dislike and mistrust, they slowly bond and eventually help each other overcome past traumas. Cue the maudlin music.
The film's hokey and sentimentalist, but it works, successfully remaining uplifting and heartwarming despite its obvious generic formulism. To a good extent, the film's ability to overcome problems associated with predictability can be credited to the solid performances turned in from its impressive cast. Mr. Williams is fine in his quiet, self-contained role, never lapsing into his typical zany persona; he carries himself with demeanour of a man whose silent sadness weighs upon him like an anchor. Meanwhile, Mr. Damon impresses as the title character, effortlessly alternating through Will's many faces -- street tough, brilliant genius, charming suitor, exasperating smart-ass, fragile soul -- he's convincingly persuasive in all of them.
Credit has to be allocated to helmer Gus Van Sant as well, who fortunately refrains from beating the audience over the head during the film's frequent emotionally poignant moments. His helming is thoroughly competent workmanship, with one scene standing out as particularly visually striking: a sequence with Will and new love Skylar (Minnie Driver) contentedly chatting in bed, which is wonderfully lit and shot in close-up by cinematographer Jean Yves Escoffier as a great tapestry of flesh and shadows filling the frame, gently shifting and rolling like a series of wakes on the sea.
The GOOD WILL HUNTING screenplay is exceedingly neat and tidy, ensuring that everything is brought full circle, and that every major event in the film meticulously ties into a prior anecdote. This may or may not be a good thing -- it's certainly tidy screenwriting, but it comes across as overly calculated, and plays out onscreen with a noticeable loss of spontaneity, particularly in the film's coda where key lines are dropped like dominos.
I admired that the film's screenplay had the temerity to make its protagonist not only impertinent and belligerent (albeit, naturally, in a loveable, audience-winning sort of way), but even occasionally downright cruel to those around him, goading other sympathetic characters and zeroing in on their soft spots. However, the change in the Lambeau character as the film progressed seemed particularly arbitrary, an artificial means with which to bring the plot to a head.
The themes and storyline of GOOD WILL HUNTING are hardly fresh; they are, however, executed effectively. There's a great deal of crowdpleasing material in the film -- one-upmanship of hissable characters, warm fuzzy emotional epiphanies, cute snappy one-liners -- and if one can ignore the sheer predictability of the story and overlook the shameless tugging on the heartstrings, there's much to enjoy.
If anything, the genesis of the GOOD WILL HUNTING project is more interesting than the film itself. Penned by childhood buddies Matt Damon and Ben Affleck while they were struggling actors, their screenplay generated a bidding war among the studios which quickly elevated to a figure of an even million dollars -- if the actors would detach themselves from the project. Resolved to stay on as actors on their project, the duo stuck to their guns and eventually sold the screenplay (with themselves attached as stars) to Castle Rock Entertainment for a lesser fee of $500 000. The project eventually made its way over to Miramax, who have to be delighted with the way things have worked out; during the interim, these two then-unknowns have blossomed into the hottest young actors working today -- Mr. Affleck, fresh from the critically-acclaimed Kevin Smith film CHASING AMY, will appear in the upcoming summer Bruce Willis vehicle ARMAGEDDON, as well as Dimension's sci-fi thriller PHANTOMS and New Line's comedy BALLING THE JACK. Meanwhile, Mr. Damon seems to have been anointed as Hollywood's new It guy (taking over from pal Matthew McConaughey), scoring coveted roles with directors as esteemed as Francis Ford Coppola (JOHN GRISHAM'S THE RAINMAKER) and Steven Spielberg (the upcoming SAVING PRIVATE RYAN). Well done, gents -- but as for GOOD WILL HUNTING: cripes, what's with the ridiculous title?
- Alex Fung email<EMAIL_ADDRESS>web : http://www.ncf.carleton.ca/~aw220/
-- Alex Fung<EMAIL_ADDRESS>| http://www.ncf.carleton.ca/~aw220/ "There was a six-year-old girl sitting near me, and she piped up 'That's Harvey Keitel' within seconds of the film's start. I want to know what that kid's been seeing." - Charles Odell
The review above was posted to the
rec.arts.movies.reviews newsgroup (de.rec.film.kritiken for German reviews).
The Internet Movie Database accepts no responsibility for the contents of the
review and has no editorial control. Unless stated otherwise, the copyright
belongs to the author.
Please direct comments/criticisms of the review to relevant newsgroups.
Broken URLs inthe reviews are the responsibility of the author.
The formatting of the review is likely to differ from the original due
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interface ObjectBuilderInterface
Methods
|
__construct(string $fullyQualifiedName, string $type)
The constructor takes 2 arguments in order to build the base object definition it requires. |
||
| ObjectDefinitionBuilder |
imports(ObjectNameDefinition $objectDefintion)
Adds a definition to import, e.g. |
|
| ObjectDefinitionBuilder |
importsName(string $fullyQualifiedName)
Rather than define and object and pass it to import, you can simply use this function for convenience and give it a fully qualified class name. |
|
| ObjectDefinitionBuilder |
injects(ObjectDefinition $objectDefinition)
Specifies an object that should be imported and then injected into a constructor. |
|
| ObjectDefinitionBuilder |
injectsName($fullyQualifiedName, $alias = null)
Same as injects but accetps a fully qualified class name instead of a pre-built object definition for convenience. |
|
| ObjectDefinitionBuilder |
uses(ObjectDefinition $objectDefinition)
Specifies a trait to be used by the object. |
|
| ObjectDefinitionBuilder |
usesName(string $fullyQualifiedName)
Same as uses() but accepts a fully qualified class name for convenience. |
|
| ObjectDefinitionBuilder |
extend(ObjectDefinition $objectDefinition)
An object should be extended from. |
|
| ObjectDefinitionBuilder |
extendName(string $fullyQualifiedName)
Same as extend() but accepts a fully qualified class name for convenience. |
|
| ObjectDefinitionBuilder |
implement(ObjectDefinition $objectDefinition)
An interface that this object will implement. |
|
| ObjectDefinitionBuilder |
implementName(string $fullyQualifiedName)
Same as implement() but accepts a fully qualified class name for convenience. |
|
| ObjectDefinitionBuilder |
objectVariable($scope, ObjectDefinition $objectDefinition)
Adds a variable into the class to represent the specified object. |
|
| ObjectDefinitionBuilder |
objectVariableName($scope, $fullyQualifiedName)
Same as objectVariable() but accepts a fully qualified name string in place of an object definition for convenience. |
|
| ObjectDefinitionBuilder |
defineVariable(VariableDefinition $variableDefinition)
Very simply defines the specified variable inside the object. |
|
| ObjectDefinitionBuilder |
defineVariableName($scope, $name, $type, $description = null)
Same as defineVariable but takes a series of parameters and constructs the VariableDefinition object rather than requiring the object to be pre-defined. |
|
| ObjectDefinition |
make()
Returns the object definition containing all of the parameters captured by the builder. |
|
| ObjectPresenter |
present()
Returns the presenter that represents the object made by the builder. |
Details
at line 28
public
__construct(string $fullyQualifiedName, string $type)
The constructor takes 2 arguments in order to build the base object definition it requires.
at line 36
public ObjectDefinitionBuilder
imports(ObjectNameDefinition $objectDefintion)
Adds a definition to import, e.g.
- "use" in the top of the file.
at line 47
public ObjectDefinitionBuilder
importsName(string $fullyQualifiedName)
Rather than define and object and pass it to import, you can simply use this function for convenience and give it a fully qualified class name.
The builder will create the object defintion for you and call the imports() function.
at line 57
public ObjectDefinitionBuilder
injects(ObjectDefinition $objectDefinition)
Specifies an object that should be imported and then injected into a constructor.
This will also create the related class variable as necessary.
at line 67
public ObjectDefinitionBuilder
injectsName($fullyQualifiedName, $alias = null)
Same as injects but accetps a fully qualified class name instead of a pre-built object definition for convenience.
You may also pass an alias if you want the import to be alias'd.
at line 76
public ObjectDefinitionBuilder
uses(ObjectDefinition $objectDefinition)
Specifies a trait to be used by the object.
This is a "use" statement inside the class definition.
at line 84
public ObjectDefinitionBuilder
usesName(string $fullyQualifiedName)
Same as uses() but accepts a fully qualified class name for convenience.
at line 93
public ObjectDefinitionBuilder
extend(ObjectDefinition $objectDefinition)
An object should be extended from.
The generated definition will contain methods to easily generate the "object extends other_object" statement.
at line 101
public ObjectDefinitionBuilder
extendName(string $fullyQualifiedName)
Same as extend() but accepts a fully qualified class name for convenience.
at line 110
public ObjectDefinitionBuilder
implement(ObjectDefinition $objectDefinition)
An interface that this object will implement.
You can call this method multiple times to implement multiple interfaces.
at line 118
public ObjectDefinitionBuilder
implementName(string $fullyQualifiedName)
Same as implement() but accepts a fully qualified class name for convenience.
at line 135
public ObjectDefinitionBuilder
objectVariable($scope, ObjectDefinition $objectDefinition)
Adds a variable into the class to represent the specified object.
For scope, specify "private", "protected" or "public". You may also prefix scope with "final" if desired.
This function will take the name of the specified object, strip out any generally undesired words (Interface, Class, etc.) and create a pretty variable name that will be defined in the class.
E.g.: An object named "UserRepositoryInterface" would be defined in the class as "$userRepository"
at line 144
public ObjectDefinitionBuilder
objectVariableName($scope, $fullyQualifiedName)
Same as objectVariable() but accepts a fully qualified name string in place of an object definition for convenience.
at line 152
public ObjectDefinitionBuilder
defineVariable(VariableDefinition $variableDefinition)
Very simply defines the specified variable inside the object.
at line 162
public ObjectDefinitionBuilder
defineVariableName($scope, $name, $type, $description = null)
Same as defineVariable but takes a series of parameters and constructs the VariableDefinition object rather than requiring the object to be pre-defined.
at line 170
public ObjectDefinition
make()
Returns the object definition containing all of the parameters captured by the builder.
at line 178
public ObjectPresenter
present()
Returns the presenter that represents the object made by the builder.


|
EmberZNet API Reference: For the STM32F103RET Host platform
EmberZNet <IP_ADDRESS>
For the EFR32 and EM3xx Platforms
|
Example host common SPI Protocol implementation for interfacing with a NCP. More...
Functions | |
| void | halNcpSerialInit (void) |
| Initializes the SPI Protocol. More... | |
| void | halNcpSerialPowerup (void) |
| Reinitializes the SPI Protocol when coming out of sleep (powerdown). More... | |
| void | halNcpSerialPowerdown (void) |
| Shuts down the SPI Protocol when entering sleep (powerdown). More... | |
| EzspStatus | halNcpHardReset (void) |
| Forcefully resets the NCP by pulling on the nRESET line; waits for the NCP to boot; verifies that is has booted; verifies the NCP is active; verifies the SPI Protocol version. When this function returns, the NCP is ready to accept all commands. More... | |
| EzspStatus | halNcpHardResetReqBootload (bool requestBootload) |
| Forcefully resets the NCP by pulling on the nRESET line; sets the nWAKE signal based upon the state of the requestBootload bool; waits for the NCP to boot; verifies that is has booted; verifies the NCP is active; verifies the SPI Protocol version. When this function returns, the NCP is ready to accept all commands. More... | |
| void | halNcpWakeUp (void) |
| If the Host thinks that the NCP is sleeping and wants to wake it up, the EZSP calls halNcpWakeUp(). More... | |
| void | halNcpSendCommand (void) |
| The EZSP writes a command into the command buffer and then calls halNcpSendCommand(). More... | |
| void | halNcpSendRawCommand (void) |
| The upper layer writes a command into the command buffer and then calls halNcpSendRawCommand(). More... | |
| EzspStatus | halNcpPollForResponse (void) |
| After sending a Command with halNcpSendCommand(), the upper layer repeatedly calls this function until the SPI Protocol has finished reception of a Response. More... | |
| void | halNcpIsAwakeIsr (bool isAwake) |
| The SPI Protocol calls halNcpIsAwakeIsr() once the wakeup handshaking is complete and the NCP is ready to accept a command. More... | |
| bool | halNcpHasData (void) |
| If the Host wants to find out whether the NCP has a pending callback, the EZSP calls halNcpHasData(). If this function returns true then the EZSP will send a callback command. More... | |
| bool | halNcpVerifySpiProtocolVersion (void) |
| Transmits the SPI Protocol Version Command and checks the response against a literal value to verify the SPI Protocol version. More... | |
| bool | halNcpVerifySpiProtocolActive (void) |
| Transmits the SPI Status Command and checks the response against a literal value to verify the SPI Protocol is active. More... | |
| int | halNcpGetIntFd (void) |
| Retrieves the file descriptor for the nHOST_INT line, which is what the NCP pulls low when it has something to transmit to the host. More... | |
Variables | |
| uint8_t * | halNcpFrame |
| uint8_t | halNcpSpipErrorByte |
Example host common SPI Protocol implementation for interfacing with a NCP.
For complete documentation of the SPI Protocol, refer to the NCP docs.
See spi-protocol-common.h for source code.
| int halNcpGetIntFd | ( | void | ) |
Retrieves the file descriptor for the nHOST_INT line, which is what the NCP pulls low when it has something to transmit to the host.
| EzspStatus halNcpHardReset | ( | void | ) |
Forcefully resets the NCP by pulling on the nRESET line; waits for the NCP to boot; verifies that is has booted; verifies the NCP is active; verifies the SPI Protocol version. When this function returns, the NCP is ready to accept all commands.
This function is the same as halNcpHardResetReqBootload(), except that the NCP cannot be told to enter bootload mode through the nWAKE signal.
| EzspStatus halNcpHardResetReqBootload | ( | bool | requestBootload | ) |
Forcefully resets the NCP by pulling on the nRESET line; sets the nWAKE signal based upon the state of the requestBootload bool; waits for the NCP to boot; verifies that is has booted; verifies the NCP is active; verifies the SPI Protocol version. When this function returns, the NCP is ready to accept all commands.
This function is the same as halNcpHardReset(), except that the ability to request the NCP enter bootload mode through the nWAKE signal is made available.
| bool halNcpHasData | ( | void | ) |
If the Host wants to find out whether the NCP has a pending callback, the EZSP calls halNcpHasData(). If this function returns true then the EZSP will send a callback command.
| void halNcpIsAwakeIsr | ( | bool | isAwake | ) |
The SPI Protocol calls halNcpIsAwakeIsr() once the wakeup handshaking is complete and the NCP is ready to accept a command.
| isAwake | true if the wake handshake completed and the NCP is awake. false is the wake handshake failed and the NCP is unresponsive. |
| EzspStatus halNcpPollForResponse | ( | void | ) |
After sending a Command with halNcpSendCommand(), the upper layer repeatedly calls this function until the SPI Protocol has finished reception of a Response.
| void halNcpSendCommand | ( | void | ) |
The EZSP writes a command into the command buffer and then calls halNcpSendCommand().
This function assumes the command being sent is an EZSP frame and therefore sets the SPI Byte for an EZSP Frame. If sending a command other than EZSP, use halNcpSendRawCommand(). This function returns immediately after transmission of the Command has completed and the transaction has entered the Wait section. The EZSP must now call halNcpPollForResponse() until the Response is received.
| void halNcpSendRawCommand | ( | void | ) |
The upper layer writes a command into the command buffer and then calls halNcpSendRawCommand().
This function makes no assumption about the data in the SpipBuffer, it will just faithly try to perform the transaction. This function returns immediately after transmission of the Command has completed and the transaction has entered the Wait section. The upper layer must now call halNcpPollForResponse() until the the Response is received.
| void halNcpSerialInit | ( | void | ) |
Initializes the SPI Protocol.
| void halNcpSerialPowerdown | ( | void | ) |
Shuts down the SPI Protocol when entering sleep (powerdown).
| void halNcpSerialPowerup | ( | void | ) |
Reinitializes the SPI Protocol when coming out of sleep (powerdown).
| bool halNcpVerifySpiProtocolActive | ( | void | ) |
Transmits the SPI Status Command and checks the response against a literal value to verify the SPI Protocol is active.
| bool halNcpVerifySpiProtocolVersion | ( | void | ) |
Transmits the SPI Protocol Version Command and checks the response against a literal value to verify the SPI Protocol version.
| void halNcpWakeUp | ( | void | ) |
If the Host thinks that the NCP is sleeping and wants to wake it up, the EZSP calls halNcpWakeUp().
Waking up can take some time (milliseconds) so halNcpWakeUp() returns immediately and the SPI Protocol calls halNcpIsAwakeIsr() once the wakeup handshaking is complete and the NCP is ready to accept commands.
| uint8_t* halNcpFrame |
A pointer to the length byte at the start of the Payload. Upper layers will write the command to this location before starting a transaction. The upper layer will read the response from this location after a transaction completes. This pointer is the upper layers' primary access into the command/response buffer.
| uint8_t halNcpSpipErrorByte |
This error byte is the third byte found in a special SPI Protocol error case. It provides more detail concerning the error. Refer to the NCP docs for a more detailed description of this byte. The application does not need to work with this byte, but it can be useful information when developing.


Multi-threading
GDAL API: re-entrant, but not thread-safe
The exact meaning of the terms thread-safe
or re-entrant
is not fully
standardized. We will use here the QT definitions.
In particular, a C function or C++ method is said to be re-entrant if it can
be called simultaneously from multiple threads, but only if each invocation
uses its own data.
All GDAL public C functions and C++ methods are re-entrant, except:
the general initialization functions, like
GDALAllRegister()
.the general cleanup functions like
GDALDestroy()
orOSRCleanup()
.
Those functions should not be called concurrently from several threads, and it is general best practice to call them from the main thread of the program at program initialization and termination.
Unless otherwise stated, no GDAL public C functions and C++ methods should be
assumed to be thread-safe. That is you should not call simultaneously GDAL
functions from multiple threads on the same data instance, or even instances
that are closely related through ownership relationships. For example, for a
multi-band raster dataset, it is not safe to call concurrently GDAL functions
on different GDALRasterBand
instances owned by the same
GDALDataset
instance (each thread should instead manipulate a
distinct GDALDataset). Similarly for a GDALDataset owning several OGRLayer
.
Those restrictions apply to the C and C++ ABI, and all languages bindings (unless they would take special precautions to serialize calls)
GDAL block cache and multi-threading
The current design of the GDAL raster block cache make it appropriate to read several datasets from several threads. However performance issues may arise when writing several datasets from several threads, due to lock contention in the global structures of the block cache mechanism.
RAM fragmentation and multi-threading
It has been observed that scenarios that involve multi-threading reading or writing of raster datasets are prone to cause a high RAM usage, in particular when using the default dynamic memory allocator of Linux. Using the alternate tcmalloc memory allocator helps reducing the amount of virtual and resident memory used.
For example, with Debian/Ubuntu distributions, this can be done by
installing the libtcmalloc-minimal4
package and running the binary that
executes GDAL with:
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libtcmalloc_minimal.so.4 ./binary
GDAL and multi-processing
POSIX fork() API should not be called during the middle of a GDAL operation, otherwise some structures like mutexes might appear to be locked forever in the forked process. If multi-processing is done, we recommend that processes are forked before any GDAL operation is done. Operating on the same GDALDataset instance in several sub-processes will generally lead to wrong results due to the underlying file descriptors being shared.