The AI company
While Google, Tesla, Uber and many other companies are fighting for the top place in the race for self driving cars, Facebook may come ahead as they focus on Augmented/Virtual Reality (AR/VR) technologies, that indirectly will solve a lot of problems in self driving car development.
In a recent article:
SLAM: Bringing art to life through technology
They showcase a lot of focused work in simultaneous localization and mapping area (SLAM), this is an ongoing challenge in computer vision and robotics research.
SLAM can be used to localize people (and cars or any other mobile robots) mainly using their phone camera, accelerometer/gyro and GPS (where available), while mapping in realtime new areas.
They already have pretty optimized algorithms that can achieve fast recognition of objects and their 3D structure:
An algorithm tailored to each device
Our SLAM library integrates features from multiple systems (ORB-SLAM, SVO, and LSD SLAM), but what really sets it apart is the library's performance optimization, down to the very last instruction. Having a SLAM system capable of running at 60 Hz on mobile devices is hard: every 16 milliseconds, your phone has to capture an image, find hundreds of interesting key points, match them with the same points in the previous frame, and then use trigonometry to determine where each of these points is in 3D space. Since there is so much going on, we needed to do lots of fine-grained optimization and rethinking of how these algorithms operate.
Hopefully they will open source some of their work in this area.
At OSSDC we will also be focusing on getting SLAM and 3D Reconstruction using stereo or multi camera setup, to help detect and avoid obstacle from very close to far away (needed to predict optimum motion path).
To learn more and contribute, I invite you to join the discussions at http://ossdc.org/
For fresh news about self driving cars, artificial intelligence and robotics, follow me on Twitter at @gtarobotics


I wrote some Ruby code to convert positive decimal integers (like 123
) or strings (like "123"
) into strings of Swedish (like "etthundratjugotre"
).
I was pleasantly surprised at how little code was needed. I suppose anything else would be odd (or contain redundant code), since it’s a system of predictable patterns.
The code shouldn’t be too hard to adapt for English or any other language with a similar numbers-to-words mapping to Swedish. Keep in mind that the names for large numbers vary even between American and British English.
The code was implemented as an Integer.to_swedish
class method (e.g. Integer.to_swedish("123")
), also available through an Integer
instance method (e.g. 123.to_swedish
).
Every named power of ten listed in Swedish Wikipedia is handled, except for googolplex and googolplexian, being too large to store within the known universe.
Numbers recurse if necessary, so whereas the highest named number is “centiljard” (10603), you can have any number of those, limited only by available memory.
The use of whitespace (between parts except within hundreds and tens) is obviously debatable.
The algorithm
The input is turned into a reverse array of digits, so "123"
becomes [3,2,1]
.
That array is turned into output (a list of strings, eventually joined together) starting at the beginning (the left-hand side) and moving towards the end.
Zeroes and empty input are given special treatment: the program bails early, returning the proper value, if they are present.
A private class method, Integer.below_thousand
handles the numbers 1–999. Its workings are rather obvious. If in the range 10–19, a stored “teen” value is chosen. If outside that range, singles and tens are appended to the output as appropriate. If there are any hundreds involved, those are appended to the output next.
The rest of the code basically consists of applying Integer.unit
to various named powers of ten and their ranges, in the right order. The input of this method is the entire number (in that reverse array representation), the name, and the positions of the number that this name ranges over. So e.g. thousands range from 103 to 105 (i.e. 1000–999 000 are some number of thousands). 106 to 108 is the range for millions, and so on. How many thousands, millions etc is determined recursively.
For the most part, it’s just ten to the power of some multiple of three, which is a reason you don’t need a lot of code. There is the odd exception, though, that needs special handling.
For the largest implemented named power of ten, “centiljarder”, the range is from 10603 to the end of the input.
After joining the output together into a string, two regular expression substitutions are applied, to fix gender and number agreement issues.
The code
The code (download):
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 |
|
outputs:
nil
noll
ett
en biljon tjugofyra miljarder niohundraåtta miljoner tvåhundrasextiosju tusen tvåhundratjugonio
en centiljard centiljarder ett


{# The first thing we do is call event data from the CMS. #}
{% set data = cms.events%}
{# Next we sort the data by publish_date. The true bit reverses it so it's newest first. Learn more: #}
{# http://www.webhook.com/docs/template-rules-and-filters/#sortproperty_reverseorder #}
{% set data = data|sort('publish_date', true) %}
{# This is how you set pagination. It's always important to do this after your sort. #}
{% set data = paginate(data, 5) %}
WELD Events
{# This forloop can use any data from http:localhost:2000/cms/#/form/event/ #}


HIV/AIDS Vaccine Passes Phase I Clinical Trial
2 min read
An HIV vaccine developed in Canada http:/
[caption id="attachment_386" align="alignright" width="420"]
provides little information on the effectiveness of the vaccine and is only designed to detect severe side effects or safety issues. The vaccine is a genetically modified killed whole virus vaccine, which means that it relies on a modified version of the HIV virus which is more capable of triggering an immune response that results in immunity than an unmodified virus. The researchers report finding increased antibody production, providing some evidence that the vaccine is indeed effective. As stated in the press release
The antibody against p24 capsid antigen increased as much as 64-fold in some vaccinees and antibody against gp120 surface antigen increased up to eight-fold after vaccination.
....
In particular, the antibody against gp120 surface antigen is considered to be very important, since some of these antibodies may represent the broadly neutralizing antibodies, which seem to be the most important parameter of an effective HIV vaccine for prevention of HIV-infection.
The researchers plan future trials to confirm that the vaccine is effective.
An effective vaccine would give public health officials a way to control the spread of AIDS.
#aids #canada #hiv #old #old #uncategorized #westernuniversity


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Style with Demelza de Burca: Versatile shirt dresses are a fashion classic for your winter wardrobe
Here’s our edit of some of the best on the high street for AW19
by Demelza De-BurcaShirt dresses are a fashion classic and the versatile piece is a must-have for your autumn winter wardrobe.
A workwear essential, a shirt dress is formal enough for big meetings in the office but it can also double up as a post-work dinner outfit too.
It’s easy to style up for every occasion.
Here’s our edit of some of the best on the high street for AW19.
How to follow the Irish Mirror on social media
You can like our main Facebook page here.
Our Irish Mirror Sports page - which brings you all your Irish and UK sports news - can be found here.
You can also check out our Irish Mirror GAA sports page.
The Irish Mirror Twitter account is @IrishMirror while our sports account is @MirrorSportIE.
Our Instagram account can be found here.


WKTPolygon Class Reference
| Inherits from | WKTGeometry : NSObject |
|---|---|
| Declared in | WKTPolygon.h |
Overview
This class represent Polygon Geometry on WKT Format.
Its String representation are:
2D Representation: POLYGON ((0 0, 10 0, 10 10, 0 0))
3D Representation: POLYGONZ ((0 0 0, 10 0 5, 10 10 5, 0 0 0))
At 3D representation may be POLYGON Z too.
Example of use:
WKTPoint *p1 = [[WKTPoint alloc] initWithDimensionX:5.0 andDimensionY:10.0];
WKTPoint *p2 = [[WKTPoint alloc] initWithDimensionX:10.0 andDimensionY:10.0];
WKTPoint *p3 = [[WKTPoint alloc] initWithDimensionX:10.0 andDimensionY:15.0];
WKTPoint *p4 = [[WKTPoint alloc] initWithDimensionX:5.0 andDimensionY:15.0];
WKTPointM *points = [[WKTPointM alloc] initWithPoints:@[p1, p2, p3, p4]];
WKTPolygon *p = [[WKTPolygon alloc] initWithMultiPoints:@[points]];
Example of MapKit Polygon creation:
MKPolygon *mapPolygon = [p toMapPolygon];
MKMapView *map = [[MKMapView alloc] init];
[map addOverlay: mapPolygon];
Example of WKT representation:
NSString *wktString = [p toWKT];
NSLog(@"WKT: %@", wktString);
> WKT: POLYGON ((5.000000 10.000000, 10.000000 10.000000, 10.000000 15.000000, 5.000000 15.000000))
Constructor
– init
Basic Constructor that set default values to new instance.
- (instancetype)init
Return Value
WKTPolygon instance
Declared In
WKTPolygon.h
– initWithMultiPoints:
Complex Constructor that set default values and points to new instance.
- (instancetype)initWithMultiPoints:(NSArray *)multiPoints
Parameters
multiPoints |
List of WKTPointM |
|---|
Return Value
WKTPolygon instance
Discussion
From this point of view, a polygon is similar to multi linestring.
This method is the same that init join setPolygons:
Declared In
WKTPolygon.h
Internal operations
– setPolygons:
Set and check Multi Points List internal property for after that to generate polygon correctly.
- (void)setPolygons:(NSArray *)multiPoints
Parameters
multiPoints |
List of WKTPointM |
|---|
Exceptions
WKTPolygon |
Parameter is nil, have a class that it is not Multi Point or these classes does not have same dimensions. |
|---|
Declared In
WKTPolygon.h
– removePolygons
Clear Multi Points List internal property
- (void)removePolygons
Declared In
WKTPolygon.h
– getPolygon
Return Multi Points List internal property.
- (NSArray *)getPolygon
Return Value
List of WKTPointM that its count always will be equal or greater than zero
Discussion
Multi Points List internal property never is nil.
Declared In
WKTPolygon.h
– getInteriorPolygons
Return Multi Points List which are internal polygons.
- (NSArray *)getInteriorPolygons
Return Value
List of WKTPointM that its count always will be equal or greater than zero
Declared In
WKTPolygon.h
– getExteriorPolygon
Return Multi Points which is external polygon.
- (WKTPointM *)getExteriorPolygon
Return Value
Declared In
WKTPolygon.h
WKTPolygon operations
– isEqual:
Check if two WKTPolygon are equal.
- (BOOL)isEqual:(WKTPolygon *)otherPolygon
Parameters
otherPolygon |
WKTPolygon to compare with itself |
|---|
Return Value
Boolean
Declared In
WKTPolygon.h
– copyTo:
Pass all properties from itself to other WKTPolygon reference.
- (void)copyTo:(WKTPolygon *)otherPolygon
Parameters
otherPolygon |
WKTPolygon to pass properties |
|---|
Exceptions
WKTPolygon |
Parameter is nil. |
|---|
Declared In
WKTPolygon.h
– toWKT
Return WKT representation.
- (NSString *)toWKT
Return Value
String like POLYGON (( …. )) or POLYGON EMPTY
Declared In
WKTPolygon.h
MapKit operations
– toMapPolygon
Return MKPolygon representation.
- (MKPolygon *)toMapPolygon
Return Value
MapKit Polygon for add overlay to map or nil if there is not valid polygon
Declared In
WKTPolygon.h


input type=week
week of birth
<label>week of birth <input type="week"></label>
HTML5 input type=week element


SOURCE-HIGHLIGHT(1) User Commands SOURCE-HIGHLIGHT(1) NAME Source-highlight - convert source code to syntax highlighted document SYNOPSIS source-highlight [OPTIONS]... < input_file > output_file DESCRIPTION GNU source-highlight 3.1.6 Highlight the syntax of a source file (e.g. Java) into a specific format (e.g. HTML) source-highlight [OPTIONS]... -i input_file -o output_file source-highlight [OPTIONS]... [FILES]... -h, --help Print help and exit --detailed-help Print help, including all details and hidden options, and exit -V, --version Print version and exit -i, --input=filename input file. default std input -o, --output=filename output file. default std output (when the third invocation form is used). If STDOUT is specified, the output is directed to standard output you can simply specify some files at the command line and also use regu‐ lar expressions (for instance *.java). In this case the name for the output files will be formed using the name of the source file with a .<ext> appended, where <ext> is the extension chosen according to the output format specified (for instance .html). -s, --src-lang=STRING source language (use --lang-list to get the complete list). If not specified, the source language will be guessed from the file extension. --lang-list list all the supported language and associated language definition file --outlang-list list all the supported output language and associated language definition file -f, --out-format=STRING output format (use --outlang-list to get the complete list) (default=`html') -d, --doc create an output file that can be used as a stand alone document (e.g., not to be included in another one) --no-doc cancel the --doc option even if it is implied (e.g., when css is given) -c, --css=filename the external style sheet filename. Implies --doc -T, --title=STRING give a title to the output document. Implies --doc -t, --tab=INT specify tab length. (default=`8') -H, --header=filename file to insert as header -F, --footer=filename file to insert as footer --style-file=filename specify the file containing format options (default=`default.style') --style-css-file=filename specify the file containing format options (in css syntax) --style-defaults=filename specify the file containing defaults for format options (default=`style.defaults') --outlang-def=filename output language definition file --outlang-map=filename output language map file (default=`outlang.map') --data-dir=path directory where language definition files and language maps are searched for. If not specified these files are searched for in the current directory and in the data dir installation directory --output-dir=path output directory --lang-def=filename language definition file --lang-map=filename language map file (default=`lang.map') --show-lang-elements=filename prints the language elements that are defined in the language definition file --infer-lang force to infer source script language (overriding given language specification) Lines: -n, --line-number[=padding] number all output lines, using the specified padding character (default=`0') --line-number-ref[=prefix] number all output lines and generate an anchor, made of the specified prefix + the line number (default=`line') Filtering output: Mode: linerange specifying line ranges --line-range=STRING generate only the lines in the specified range(s) --range-separator=STRING the optional separator to be printed among ranges (e.g., "...") --range-context=INT number of (context) lines generated even if not in range Mode: regexrange specifying regular expression delimited ranges --regex-range=STRING generate only the lines within the specified regular expressions reference generation: --gen-references=STRING generate references (possible values="inline", "postline", "post‐ doc" default=`inline') --ctags-file=filename specify the file generated by ctags that will be used to generate references (default=`tags') --ctags=cmd how to run the ctags command. If this option is not specified, ctags will be executed with the default value. If it is specified with an empty string, ctags will not be executed at all (default=`ctags --excmd=n --tag-relative=yes') testing: -v, --verbose verbose mode on -q, --quiet print no progress information --binary-output write output files in binary mode --statistics print some statistics (i.e., elapsed time) --gen-version put source-highlight version in the generated file (default=on) --check-lang=filename only check the correctness of a language definition file --check-outlang=filename only check the correctness of an output language definition file --failsafe if no language definition is found for the input, it is simply copied to the output -g, --debug-langdef[=type] debug a language definition. In dump mode just dumps all the steps; in interactive, at each step, waits for some input (press ENTER to step) (possible values="interactive", "dump" default=`dump') --show-regex=filename show the regular expression automaton corresponding to a language definition file Maintained by Lorenzo Bettini <http://www.lorenzobettini.it> REPORTING BUGS Report bugs to <bug-source-highlight at gnu.org> COPYRIGHT Copyright © 1999-2008 Lorenzo Bettini <http://www.lorenzobettini.it> This program comes with ABSOLUTELY NO WARRANTY. This is free software; you may redistribute copies of the program under the terms of the GNU General Public License. For more information about these matters, see the file named COPYING. SEE ALSO The full documentation for Source-highlight is maintained as a Texinfo manual. If the info and Source-highlight programs are properly installed at your site, the command info Source-highlight should give you access to the complete manual. Source-highlight 3.1.6 (library: 4December 2011 SOURCE-HIGHLIGHT(1)


Stay in touch with our dog walkers through the chat interface. This makes it easy to discuss arrangements and make bookings. Once the walk has been completed you can rate your walker and book again all through the chat.
That sounds great. I’d be happy with that.
Could you send over some pictures of your dog, please?
Here are a few pictures. She’s a happy girl!
Can you make it?
She looks so happy! The time we discussed works. How long shall I take her out for?
30 minute walk $29


PERLTHRTUT
Section: Perl Programmers Reference Guide (1)Updated: 2009-04-14
Index Return to Main Contents
NAME
perlthrtut - Tutorial on threads in PerlDESCRIPTION
This tutorial describes the use of Perl interpreter threads (sometimes referred to as ithreads) that was first introduced in Perl 5.6.0. In this model, each thread runs in its own Perl interpreter, and any data sharing between threads must be explicit. The user-level interface for ithreads uses the threads class.NOTE: There was another older Perl threading flavor called the 5.005 model that used the Threads class. This old model was known to have problems, is deprecated, and was removed for release 5.10. You are strongly encouraged to migrate any existing 5.005 threads code to the new model as soon as possible.
You can see which (or neither) threading flavour you have by running "perl -V" and looking at the "Platform" section. If you have "useithreads=define" you have ithreads, if you have "use5005threads=define" you have 5.005 threads. If you have neither, you don't have any thread support built in. If you have both, you are in trouble.
The threads and threads::shared modules are included in the core Perl distribution. Additionally, they are maintained as a separate modules on CPAN, so you can check there for any updates.
What Is A Thread Anyway?
A thread is a flow of control through a program with a single execution point.Sounds an awful lot like a process, doesn't it? Well, it should. Threads are one of the pieces of a process. Every process has at least one thread and, up until now, every process running Perl had only one thread. With 5.8, though, you can create extra threads. We're going to show you how, when, and why.
Threaded Program Models
There are three basic ways that you can structure a threaded program. Which model you choose depends on what you need your program to do. For many non-trivial threaded programs, you'll need to choose different models for different pieces of your program.Boss/Worker
The boss/worker model usually has one boss thread and one or more worker threads. The boss thread gathers or generates tasks that need to be done, then parcels those tasks out to the appropriate worker thread.This model is common in GUI and server programs, where a main thread waits for some event and then passes that event to the appropriate worker threads for processing. Once the event has been passed on, the boss thread goes back to waiting for another event.
The boss thread does relatively little work. While tasks aren't necessarily performed faster than with any other method, it tends to have the best user-response times.
Work Crew
In the work crew model, several threads are created that do essentially the same thing to different pieces of data. It closely mirrors classical parallel processing and vector processors, where a large array of processors do the exact same thing to many pieces of data.This model is particularly useful if the system running the program will distribute multiple threads across different processors. It can also be useful in ray tracing or rendering engines, where the individual threads can pass on interim results to give the user visual feedback.
Pipeline
The pipeline model divides up a task into a series of steps, and passes the results of one step on to the thread processing the next. Each thread does one thing to each piece of data and passes the results to the next thread in line.This model makes the most sense if you have multiple processors so two or more threads will be executing in parallel, though it can often make sense in other contexts as well. It tends to keep the individual tasks small and simple, as well as allowing some parts of the pipeline to block (on I/O or system calls, for example) while other parts keep going. If you're running different parts of the pipeline on different processors you may also take advantage of the caches on each processor.
This model is also handy for a form of recursive programming where, rather than having a subroutine call itself, it instead creates another thread. Prime and Fibonacci generators both map well to this form of the pipeline model. (A version of a prime number generator is presented later on.)
What kind of threads are Perl threads?
If you have experience with other thread implementations, you might find that things aren't quite what you expect. It's very important to remember when dealing with Perl threads that Perl Threads Are Not X Threads for all values of X. They aren't POSIX threads, or DecThreads, or Java's Green threads, or Win32 threads. There are similarities, and the broad concepts are the same, but if you start looking for implementation details you're going to be either disappointed or confused. Possibly both.This is not to say that Perl threads are completely different from everything that's ever come before --- they're not. Perl's threading model owes a lot to other thread models, especially POSIX. Just as Perl is not C, though, Perl threads are not POSIX threads. So if you find yourself looking for mutexes, or thread priorities, it's time to step back a bit and think about what you want to do and how Perl can do it.
However, it is important to remember that Perl threads cannot magically do things unless your operating system's threads allow it. So if your system blocks the entire process on "sleep()", Perl usually will, as well.
Thread-Safe Modules
The addition of threads has changed Perl's internals substantially. There are implications for people who write modules with XS code or external libraries. However, since Perl data is not shared among threads by default, Perl modules stand a high chance of being thread-safe or can be made thread-safe easily. Modules that are not tagged as thread-safe should be tested or code reviewed before being used in production code.Not all modules that you might use are thread-safe, and you should always assume a module is unsafe unless the documentation says otherwise. This includes modules that are distributed as part of the core. Threads are a relatively new feature, and even some of the standard modules aren't thread-safe.
Even if a module is thread-safe, it doesn't mean that the module is optimized to work well with threads. A module could possibly be rewritten to utilize the new features in threaded Perl to increase performance in a threaded environment.
If you're using a module that's not thread-safe for some reason, you can protect yourself by using it from one, and only one thread at all. If you need multiple threads to access such a module, you can use semaphores and lots of programming discipline to control access to it. Semaphores are covered in ``Basic semaphores''.
See also ``Thread-Safety of System Libraries''.
Thread Basics
The threads module provides the basic functions you need to write threaded programs. In the following sections, we'll cover the basics, showing you what you need to do to create a threaded program. After that, we'll go over some of the features of the threads module that make threaded programming easier.Basic Thread Support
Thread support is a Perl compile-time option --- it's something that's turned on or off when Perl is built at your site, rather than when your programs are compiled. If your Perl wasn't compiled with thread support enabled, then any attempt to use threads will fail.Your programs can use the Config module to check whether threads are enabled. If your program can't run without them, you can say something like:
use Config; $Config{useithreads} or die('Recompile Perl with threads to run this program.');
A possibly-threaded program using a possibly-threaded module might have code like this:
use Config; use MyMod; BEGIN { if ($Config{useithreads}) { # We have threads require MyMod_threaded; import MyMod_threaded; } else { require MyMod_unthreaded; import MyMod_unthreaded; } }
Since code that runs both with and without threads is usually pretty messy, it's best to isolate the thread-specific code in its own module. In our example above, that's what "MyMod_threaded" is, and it's only imported if we're running on a threaded Perl.
A Note about the Examples
In a real situation, care should be taken that all threads are finished executing before the program exits. That care has not been taken in these examples in the interest of simplicity. Running these examples as is will produce error messages, usually caused by the fact that there are still threads running when the program exits. You should not be alarmed by this.Creating Threads
The threads module provides the tools you need to create new threads. Like any other module, you need to tell Perl that you want to use it; "use threads;" imports all the pieces you need to create basic threads.The simplest, most straightforward way to create a thread is with "create()":
use threads; my $thr = threads->create(\&sub1); sub sub1 { print("In the thread\n"); }
The "create()" method takes a reference to a subroutine and creates a new thread that starts executing in the referenced subroutine. Control then passes both to the subroutine and the caller.
If you need to, your program can pass parameters to the subroutine as part of the thread startup. Just include the list of parameters as part of the "threads->create()" call, like this:
use threads; my $Param3 = 'foo'; my $thr1 = threads->create(\&sub1, 'Param 1', 'Param 2', $Param3); my @ParamList = (42, 'Hello', 3.14); my $thr2 = threads->create(\&sub1, @ParamList); my $thr3 = threads->create(\&sub1, qw(Param1 Param2 Param3)); sub sub1 { my @InboundParameters = @_; print("In the thread\n"); print('Got parameters >', join('<>', @InboundParameters), "<\n"); }
The last example illustrates another feature of threads. You can spawn off several threads using the same subroutine. Each thread executes the same subroutine, but in a separate thread with a separate environment and potentially separate arguments.
"new()" is a synonym for "create()".
Waiting For A Thread To Exit
Since threads are also subroutines, they can return values. To wait for a thread to exit and extract any values it might return, you can use the "join()" method:
use threads; my ($thr) = threads->create(\&sub1); my @ReturnData = $thr->join(); print('Thread returned ', join(', ', @ReturnData), "\n"); sub sub1 { return ('Fifty-six', 'foo', 2); }
In the example above, the "join()" method returns as soon as the thread ends. In addition to waiting for a thread to finish and gathering up any values that the thread might have returned, "join()" also performs any OS cleanup necessary for the thread. That cleanup might be important, especially for long-running programs that spawn lots of threads. If you don't want the return values and don't want to wait for the thread to finish, you should call the "detach()" method instead, as described next.
NOTE: In the example above, the thread returns a list, thus necessitating that the thread creation call be made in list context (i.e., "my ($thr)"). See "``$thr-'' in threadsjoin()"> and ``THREAD CONTEXT'' in threads for more details on thread context and return values.
Ignoring A Thread
"join()" does three things: it waits for a thread to exit, cleans up after it, and returns any data the thread may have produced. But what if you're not interested in the thread's return values, and you don't really care when the thread finishes? All you want is for the thread to get cleaned up after when it's done.In this case, you use the "detach()" method. Once a thread is detached, it'll run until it's finished; then Perl will clean up after it automatically.
use threads; my $thr = threads->create(\&sub1); # Spawn the thread $thr->detach(); # Now we officially don't care any more sleep(15); # Let thread run for awhile sub sub1 { $a = 0; while (1) { $a++; print("\$a is $a\n"); sleep(1); } }
Once a thread is detached, it may not be joined, and any return data that it might have produced (if it was done and waiting for a join) is lost.
"detach()" can also be called as a class method to allow a thread to detach itself:
use threads; my $thr = threads->create(\&sub1); sub sub1 { threads->detach(); # Do more work }
Process and Thread Termination
With threads one must be careful to make sure they all have a chance to run to completion, assuming that is what you want.An action that terminates a process will terminate all running threads. die() and exit() have this property, and perl does an exit when the main thread exits, perhaps implicitly by falling off the end of your code, even if that's not what you want.
As an example of this case, this code prints the message ``Perl exited with active threads: 2 running and unjoined'':
use threads; my $thr1 = threads->new(\&thrsub, "test1"); my $thr2 = threads->new(\&thrsub, "test2"); sub thrsub { my ($message) = @_; sleep 1; print "thread $message\n"; }
But when the following lines are added at the end:
$thr1->join(); $thr2->join();
it prints two lines of output, a perhaps more useful outcome.
Threads And Data
Now that we've covered the basics of threads, it's time for our next topic: Data. Threading introduces a couple of complications to data access that non-threaded programs never need to worry about.Shared And Unshared Data
The biggest difference between Perl ithreads and the old 5.005 style threading, or for that matter, to most other threading systems out there, is that by default, no data is shared. When a new Perl thread is created, all the data associated with the current thread is copied to the new thread, and is subsequently private to that new thread! This is similar in feel to what happens when a UNIX process forks, except that in this case, the data is just copied to a different part of memory within the same process rather than a real fork taking place.To make use of threading, however, one usually wants the threads to share at least some data between themselves. This is done with the threads::shared module and the ":shared" attribute:
use threads; use threads::shared; my $foo :shared = 1; my $bar = 1; threads->create(sub { $foo++; $bar++; })->join(); print("$foo\n"); # Prints 2 since $foo is shared print("$bar\n"); # Prints 1 since $bar is not shared
In the case of a shared array, all the array's elements are shared, and for a shared hash, all the keys and values are shared. This places restrictions on what may be assigned to shared array and hash elements: only simple values or references to shared variables are allowed - this is so that a private variable can't accidentally become shared. A bad assignment will cause the thread to die. For example:
use threads; use threads::shared; my $var = 1; my $svar :shared = 2; my %hash :shared; ... create some threads ... $hash{a} = 1; # All threads see exists($hash{a}) and $hash{a} == 1 $hash{a} = $var; # okay - copy-by-value: same effect as previous $hash{a} = $svar; # okay - copy-by-value: same effect as previous $hash{a} = \$svar; # okay - a reference to a shared variable $hash{a} = \$var; # This will die delete($hash{a}); # okay - all threads will see !exists($hash{a})
Note that a shared variable guarantees that if two or more threads try to modify it at the same time, the internal state of the variable will not become corrupted. However, there are no guarantees beyond this, as explained in the next section.
Thread Pitfalls: Races
While threads bring a new set of useful tools, they also bring a number of pitfalls. One pitfall is the race condition:
use threads; use threads::shared; my $a :shared = 1; my $thr1 = threads->create(\&sub1); my $thr2 = threads->create(\&sub2); $thr1->join(); $thr2->join(); print("$a\n"); sub sub1 { my $foo = $a; $a = $foo + 1; } sub sub2 { my $bar = $a; $a = $bar + 1; }
What do you think $a will be? The answer, unfortunately, is it depends. Both "sub1()" and "sub2()" access the global variable $a, once to read and once to write. Depending on factors ranging from your thread implementation's scheduling algorithm to the phase of the moon, $a can be 2 or 3.
Race conditions are caused by unsynchronized access to shared data. Without explicit synchronization, there's no way to be sure that nothing has happened to the shared data between the time you access it and the time you update it. Even this simple code fragment has the possibility of error:
use threads; my $a :shared = 2; my $b :shared; my $c :shared; my $thr1 = threads->create(sub { $b = $a; $a = $b + 1; }); my $thr2 = threads->create(sub { $c = $a; $a = $c + 1; }); $thr1->join(); $thr2->join();
Two threads both access $a. Each thread can potentially be interrupted at any point, or be executed in any order. At the end, $a could be 3 or 4, and both $b and $c could be 2 or 3.
Even "$a += 5" or "$a++" are not guaranteed to be atomic.
Whenever your program accesses data or resources that can be accessed by other threads, you must take steps to coordinate access or risk data inconsistency and race conditions. Note that Perl will protect its internals from your race conditions, but it won't protect you from you.
Synchronization and control
Perl provides a number of mechanisms to coordinate the interactions between themselves and their data, to avoid race conditions and the like. Some of these are designed to resemble the common techniques used in thread libraries such as "pthreads"; others are Perl-specific. Often, the standard techniques are clumsy and difficult to get right (such as condition waits). Where possible, it is usually easier to use Perlish techniques such as queues, which remove some of the hard work involved.Controlling access: lock()
The "lock()" function takes a shared variable and puts a lock on it. No other thread may lock the variable until the variable is unlocked by the thread holding the lock. Unlocking happens automatically when the locking thread exits the block that contains the call to the "lock()" function. Using "lock()" is straightforward: This example has several threads doing some calculations in parallel, and occasionally updating a running total:
use threads; use threads::shared; my $total :shared = 0; sub calc { while (1) { my $result; # (... do some calculations and set $result ...) { lock($total); # Block until we obtain the lock $total += $result; } # Lock implicitly released at end of scope last if $result == 0; } } my $thr1 = threads->create(\&calc); my $thr2 = threads->create(\&calc); my $thr3 = threads->create(\&calc); $thr1->join(); $thr2->join(); $thr3->join(); print("total=$total\n");
"lock()" blocks the thread until the variable being locked is available. When "lock()" returns, your thread can be sure that no other thread can lock that variable until the block containing the lock exits.
It's important to note that locks don't prevent access to the variable in question, only lock attempts. This is in keeping with Perl's longstanding tradition of courteous programming, and the advisory file locking that "flock()" gives you.
You may lock arrays and hashes as well as scalars. Locking an array, though, will not block subsequent locks on array elements, just lock attempts on the array itself.
Locks are recursive, which means it's okay for a thread to lock a variable more than once. The lock will last until the outermost "lock()" on the variable goes out of scope. For example:
my $x :shared; doit(); sub doit { { { lock($x); # Wait for lock lock($x); # NOOP - we already have the lock { lock($x); # NOOP { lock($x); # NOOP lockit_some_more(); } } } # *** Implicit unlock here *** } } sub lockit_some_more { lock($x); # NOOP } # Nothing happens here
Note that there is no "unlock()" function - the only way to unlock a variable is to allow it to go out of scope.
A lock can either be used to guard the data contained within the variable being locked, or it can be used to guard something else, like a section of code. In this latter case, the variable in question does not hold any useful data, and exists only for the purpose of being locked. In this respect, the variable behaves like the mutexes and basic semaphores of traditional thread libraries.
A Thread Pitfall: Deadlocks
Locks are a handy tool to synchronize access to data, and using them properly is the key to safe shared data. Unfortunately, locks aren't without their dangers, especially when multiple locks are involved. Consider the following code:
use threads; my $a :shared = 4; my $b :shared = 'foo'; my $thr1 = threads->create(sub { lock($a); sleep(20); lock($b); }); my $thr2 = threads->create(sub { lock($b); sleep(20); lock($a); });
This program will probably hang until you kill it. The only way it won't hang is if one of the two threads acquires both locks first. A guaranteed-to-hang version is more complicated, but the principle is the same.
The first thread will grab a lock on $a, then, after a pause during which the second thread has probably had time to do some work, try to grab a lock on $b. Meanwhile, the second thread grabs a lock on $b, then later tries to grab a lock on $a. The second lock attempt for both threads will block, each waiting for the other to release its lock.
This condition is called a deadlock, and it occurs whenever two or more threads are trying to get locks on resources that the others own. Each thread will block, waiting for the other to release a lock on a resource. That never happens, though, since the thread with the resource is itself waiting for a lock to be released.
There are a number of ways to handle this sort of problem. The best way is to always have all threads acquire locks in the exact same order. If, for example, you lock variables $a, $b, and $c, always lock $a before $b, and $b before $c. It's also best to hold on to locks for as short a period of time to minimize the risks of deadlock.
The other synchronization primitives described below can suffer from similar problems.
Queues: Passing Data Around
A queue is a special thread-safe object that lets you put data in one end and take it out the other without having to worry about synchronization issues. They're pretty straightforward, and look like this:
use threads; use Thread::Queue; my $DataQueue = Thread::Queue->new(); my $thr = threads->create(sub { while (my $DataElement = $DataQueue->dequeue()) { print("Popped $DataElement off the queue\n"); } }); $DataQueue->enqueue(12); $DataQueue->enqueue("A", "B", "C"); sleep(10); $DataQueue->enqueue(undef); $thr->join();
You create the queue with "Thread::Queue->new()". Then you can add lists of scalars onto the end with "enqueue()", and pop scalars off the front of it with "dequeue()". A queue has no fixed size, and can grow as needed to hold everything pushed on to it.
If a queue is empty, "dequeue()" blocks until another thread enqueues something. This makes queues ideal for event loops and other communications between threads.
 In their most basic form, they behave very much like lockable scalars, except that they can't hold data, and that they must be explicitly unlocked. In their advanced form, they act like a kind of counter, and can allow multiple threads to have the lock at any one time.Basic semaphores
Semaphores have two methods, "down()" and "up()": "down()" decrements the resource count, while "up()" increments it. Calls to "down()" will block if the semaphore's current count would decrement below zero. This program gives a quick demonstration:
use threads; use Thread::Semaphore; my $semaphore = Thread::Semaphore->new(); my $GlobalVariable :shared = 0; $thr1 = threads->create(\&sample_sub, 1); $thr2 = threads->create(\&sample_sub, 2); $thr3 = threads->create(\&sample_sub, 3); sub sample_sub { my $SubNumber = shift(@_); my $TryCount = 10; my $LocalCopy; sleep(1); while ($TryCount--) { $semaphore->down(); $LocalCopy = $GlobalVariable; print("$TryCount tries left for sub $SubNumber (\$GlobalVariable is $GlobalVariable)\n"); sleep(2); $LocalCopy++; $GlobalVariable = $LocalCopy; $semaphore->up(); } } $thr1->join(); $thr2->join(); $thr3->join();
The three invocations of the subroutine all operate in sync. The semaphore, though, makes sure that only one thread is accessing the global variable at once.
Advanced Semaphores
By default, semaphores behave like locks, letting only one thread "down()" them at a time. However, there are other uses for semaphores.Each semaphore has a counter attached to it. By default, semaphores are created with the counter set to one, "down()" decrements the counter by one, and "up()" increments by one. However, we can override any or all of these defaults simply by passing in different values:
use threads; use Thread::Semaphore; my $semaphore = Thread::Semaphore->new(5); # Creates a semaphore with the counter set to five my $thr1 = threads->create(\&sub1); my $thr2 = threads->create(\&sub1); sub sub1 { $semaphore->down(5); # Decrements the counter by five # Do stuff here $semaphore->up(5); # Increment the counter by five } $thr1->detach(); $thr2->detach();
If "down()" attempts to decrement the counter below zero, it blocks until the counter is large enough. Note that while a semaphore can be created with a starting count of zero, any "up()" or "down()" always changes the counter by at least one, and so "$semaphore->down(0)" is the same as "$semaphore->down(1)".
The question, of course, is why would you do something like this? Why create a semaphore with a starting count that's not one, or why decrement or increment it by more than one? The answer is resource availability. Many resources that you want to manage access for can be safely used by more than one thread at once.
For example, let's take a GUI driven program. It has a semaphore that it uses to synchronize access to the display, so only one thread is ever drawing at once. Handy, but of course you don't want any thread to start drawing until things are properly set up. In this case, you can create a semaphore with a counter set to zero, and up it when things are ready for drawing.
Semaphores with counters greater than one are also useful for establishing quotas. Say, for example, that you have a number of threads that can do I/O at once. You don't want all the threads reading or writing at once though, since that can potentially swamp your I/O channels, or deplete your process' quota of filehandles. You can use a semaphore initialized to the number of concurrent I/O requests (or open files) that you want at any one time, and have your threads quietly block and unblock themselves.
Larger increments or decrements are handy in those cases where a thread needs to check out or return a number of resources at once.
Waiting for a Condition
The functions "cond_wait()" and "cond_signal()" can be used in conjunction with locks to notify co-operating threads that a resource has become available. They are very similar in use to the functions found in "pthreads". However for most purposes, queues are simpler to use and more intuitive. See threads::shared for more details.Giving up control
There are times when you may find it useful to have a thread explicitly give up the CPU to another thread. You may be doing something processor-intensive and want to make sure that the user-interface thread gets called frequently. Regardless, there are times that you might want a thread to give up the processor.Perl's threading package provides the "yield()" function that does this. "yield()" is pretty straightforward, and works like this:
use threads; sub loop { my $thread = shift; my $foo = 50; while($foo--) { print("In thread $thread\n"); } threads->yield(); $foo = 50; while($foo--) { print("In thread $thread\n"); } } my $thr1 = threads->create(\&loop, 'first'); my $thr2 = threads->create(\&loop, 'second'); my $thr3 = threads->create(\&loop, 'third');
It is important to remember that "yield()" is only a hint to give up the CPU, it depends on your hardware, OS and threading libraries what actually happens. On many operating systems, yield() is a no-op. Therefore it is important to note that one should not build the scheduling of the threads around "yield()" calls. It might work on your platform but it won't work on another platform.
General Thread Utility Routines
We've covered the workhorse parts of Perl's threading package, and with these tools you should be well on your way to writing threaded code and packages. There are a few useful little pieces that didn't really fit in anyplace else.What Thread Am I In?
The "threads->self()" class method provides your program with a way to get an object representing the thread it's currently in. You can use this object in the same way as the ones returned from thread creation.Thread IDs
"tid()" is a thread object method that returns the thread ID of the thread the object represents. Thread IDs are integers, with the main thread in a program being 0. Currently Perl assigns a unique TID to every thread ever created in your program, assigning the first thread to be created a TID of 1, and increasing the TID by 1 for each new thread that's created. When used as a class method, "threads->tid()" can be used by a thread to get its own TID.Are These Threads The Same?
The "equal()" method takes two thread objects and returns true if the objects represent the same thread, and false if they don't.Thread objects also have an overloaded "==" comparison so that you can do comparison on them as you would with normal objects.
What Threads Are Running?
"threads->list()" returns a list of thread objects, one for each thread that's currently running and not detached. Handy for a number of things, including cleaning up at the end of your program (from the main Perl thread, of course):
# Loop through all the threads foreach my $thr (threads->list()) { $thr->join(); }
If some threads have not finished running when the main Perl thread ends, Perl will warn you about it and die, since it is impossible for Perl to clean up itself while other threads are running.
NOTE: The main Perl thread (thread 0) is in a detached state, and so does not appear in the list returned by "threads->list()".
A Complete Example
Confused yet? It's time for an example program to show some of the things we've covered. This program finds prime numbers using threads.
1 #!/usr/bin/perl 2 # prime-pthread, courtesy of Tom Christiansen 3 4 use strict; 5 use warnings; 6 7 use threads; 8 use Thread::Queue; 9 10 sub check_num { 11 my ($upstream, $cur_prime) = @_; 12 my $kid; 13 my $downstream = Thread::Queue->new(); 14 while (my $num = $upstream->dequeue()) { 15 next unless ($num % $cur_prime); 16 if ($kid) { 17 $downstream->enqueue($num); 18 } else { 19 print("Found prime: $num\n"); 20 $kid = threads->create(\&check_num, $downstream, $num); 21 if (! $kid) { 22 warn("Sorry. Ran out of threads.\n"); 23 last; 24 } 25 } 26 } 27 if ($kid) { 28 $downstream->enqueue(undef); 29 $kid->join(); 30 } 31 } 32 33 my $stream = Thread::Queue->new(3..1000, undef); 34 check_num($stream, 2);
This program uses the pipeline model to generate prime numbers. Each thread in the pipeline has an input queue that feeds numbers to be checked, a prime number that it's responsible for, and an output queue into which it funnels numbers that have failed the check. If the thread has a number that's failed its check and there's no child thread, then the thread must have found a new prime number. In that case, a new child thread is created for that prime and stuck on the end of the pipeline.
This probably sounds a bit more confusing than it really is, so let's go through this program piece by piece and see what it does. (For those of you who might be trying to remember exactly what a prime number is, it's a number that's only evenly divisible by itself and 1.)
The bulk of the work is done by the "check_num()" subroutine, which takes a reference to its input queue and a prime number that it's responsible for. After pulling in the input queue and the prime that the subroutine is checking (line 11), we create a new queue (line 13) and reserve a scalar for the thread that we're likely to create later (line 12).
The while loop from line 14 to line 26 grabs a scalar off the input queue and checks against the prime this thread is responsible for. Line 15 checks to see if there's a remainder when we divide the number to be checked by our prime. If there is one, the number must not be evenly divisible by our prime, so we need to either pass it on to the next thread if we've created one (line 17) or create a new thread if we haven't.
The new thread creation is line 20. We pass on to it a reference to the queue we've created, and the prime number we've found. In lines 21 through 24, we check to make sure that our new thread got created, and if not, we stop checking any remaining numbers in the queue.
Finally, once the loop terminates (because we got a 0 or "undef" in the queue, which serves as a note to terminate), we pass on the notice to our child, and wait for it to exit if we've created a child (lines 27 and 30).
Meanwhile, back in the main thread, we first create a queue (line 33) and queue up all the numbers from 3 to 1000 for checking, plus a termination notice. Then all we have to do to get the ball rolling is pass the queue and the first prime to the "check_num()" subroutine (line 34).
That's how it works. It's pretty simple; as with many Perl programs, the explanation is much longer than the program.
Different implementations of threads
Some background on thread implementations from the operating system viewpoint. There are three basic categories of threads: user-mode threads, kernel threads, and multiprocessor kernel threads.User-mode threads are threads that live entirely within a program and its libraries. In this model, the OS knows nothing about threads. As far as it's concerned, your process is just a process.
This is the easiest way to implement threads, and the way most OSes start. The big disadvantage is that, since the OS knows nothing about threads, if one thread blocks they all do. Typical blocking activities include most system calls, most I/O, and things like "sleep()".
Kernel threads are the next step in thread evolution. The OS knows about kernel threads, and makes allowances for them. The main difference between a kernel thread and a user-mode thread is blocking. With kernel threads, things that block a single thread don't block other threads. This is not the case with user-mode threads, where the kernel blocks at the process level and not the thread level.
 Threads that block performing I/O, for example, won't block threads that are doing other things. Each process still has only one thread running at once, though, regardless of how many CPUs a system might have.
Since kernel threading can interrupt a thread at any time, they will uncover some of the implicit locking assumptions you may make in your program. For example, something as simple as "$a = $a + 2" can behave unpredictably with kernel threads if $a is visible to other threads, as another thread may have changed $a between the time it was fetched on the right hand side and the time the new value is stored.
Multiprocessor kernel threads are the final step in thread support. With multiprocessor kernel threads on a machine with multiple CPUs, the OS may schedule two or more threads to run simultaneously on different CPUs.
This can give a serious performance boost to your threaded program, since more than one thread will be executing at the same time. As a tradeoff, though, any of those nagging synchronization issues that might not have shown with basic kernel threads will appear with a vengeance.
In addition to the different levels of OS involvement in threads, different OSes (and different thread implementations for a particular OS) allocate CPU cycles to threads in different ways.
Cooperative multitasking systems have running threads give up control if one of two things happen. If a thread calls a yield function, it gives up control. It also gives up control if the thread does something that would cause it to block, such as perform I/O. In a cooperative multitasking implementation, one thread can starve all the others for CPU time if it so chooses.
Preemptive multitasking systems interrupt threads at regular intervals while the system decides which thread should run next. In a preemptive multitasking system, one thread usually won't monopolize the CPU.
On some systems, there can be cooperative and preemptive threads running simultaneously. (Threads running with realtime priorities often behave cooperatively, for example, while threads running at normal priorities behave preemptively.)
Most modern operating systems support preemptive multitasking nowadays.
Performance considerations
The main thing to bear in mind when comparing Perl's ithreads to other threading models is the fact that for each new thread created, a complete copy of all the variables and data of the parent thread has to be taken. Thus, thread creation can be quite expensive, both in terms of memory usage and time spent in creation. The ideal way to reduce these costs is to have a relatively short number of long-lived threads, all created fairly early on --- before the base thread has accumulated too much data. Of course, this may not always be possible, so compromises have to be made. However, after a thread has been created, its performance and extra memory usage should be little different than ordinary code.Also note that under the current implementation, shared variables use a little more memory and are a little slower than ordinary variables.
Process-scope Changes
Note that while threads themselves are separate execution threads and Perl data is thread-private unless explicitly shared, the threads can affect process-scope state, affecting all the threads.The most common example of this is changing the current working directory using "chdir()". One thread calls "chdir()", and the working directory of all the threads changes.
Even more drastic example of a process-scope change is "chroot()": the root directory of all the threads changes, and no thread can undo it (as opposed to "chdir()").
Further examples of process-scope changes include "umask()" and changing uids and gids.
Thinking of mixing "fork()" and threads? Please lie down and wait until the feeling passes. Be aware that the semantics of "fork()" vary between platforms. For example, some UNIX systems copy all the current threads into the child process, while others only copy the thread that called "fork()". You have been warned!
Similarly, mixing signals and threads may be problematic. Implementations are platform-dependent, and even the POSIX semantics may not be what you expect (and Perl doesn't even give you the full POSIX API). For example, there is no way to guarantee that a signal sent to a multi-threaded Perl application will get intercepted by any particular thread. (However, a recently added feature does provide the capability to send signals between threads. See "``THREAD SIGNALLING'' in threads for more details.)
Thread-Safety of System Libraries
Whether various library calls are thread-safe is outside the control of Perl. Calls often suffering from not being thread-safe include: "localtime()", "gmtime()", functions fetching user, group and network information (such as "getgrent()", "gethostent()", "getnetent()" and so on), "readdir()", "rand()", and "srand()" --- in general, calls that depend on some global external state.If the system Perl is compiled in has thread-safe variants of such calls, they will be used. Beyond that, Perl is at the mercy of the thread-safety or -unsafety of the calls. Please consult your C library call documentation.
On some platforms the thread-safe library interfaces may fail if the result buffer is too small (for example the user group databases may be rather large, and the reentrant interfaces may have to carry around a full snapshot of those databases). Perl will start with a small buffer, but keep retrying and growing the result buffer until the result fits. If this limitless growing sounds bad for security or memory consumption reasons you can recompile Perl with "PERL_REENTRANT_MAXSIZE" defined to the maximum number of bytes you will allow.
Conclusion
A complete thread tutorial could fill a book (and has, many times), but with what we've covered in this introduction, you should be well on your way to becoming a threaded Perl expert.SEE ALSO
Annotated POD for threads: <http://annocpan.org/?mode=search&field=Module&name=threads>Lastest version of threads on CPAN: <http://search.cpan.org/search?module=threads>
Annotated POD for threads::shared: <http://annocpan.org/?mode=search&field=Module&name=threads%3A%3Ashared>
Lastest version of threads::shared on CPAN: <http://search.cpan.org/search?module=threads%3A%3Ashared>
Perl threads mailing list: <http://lists.cpan.org/showlist.cgi?name=iThreads>
Bibliography
Here's a short bibliography courtesy of JA~Xrgen Christoffel:Introductory Texts
Birrell, Andrew D. An Introduction to Programming with Threads. Digital Equipment Corporation, 1989, DEC-SRC Research Report #35 online as http://gatekeeper.dec.com/pub/DEC/SRC/research-reports/abstracts/src-rr-035.html (highly recommended)Robbins, Kay. A., and Steven Robbins. Practical Unix Programming: A Guide to Concurrency, Communication, and Multithreading. Prentice-Hall, 1996.
Lewis, Bill, and Daniel J. Berg. Multithreaded Programming with Pthreads. Prentice Hall, 1997, ISBN 0-13-443698-9 (a well-written introduction to threads).
Nelson, Greg (editor). Systems Programming with Modula-3. Prentice Hall, 1991, ISBN 0-13-590464-1.
Nichols, Bradford, Dick Buttlar, and Jacqueline Proulx Farrell. Pthreads Programming. O'Reilly & Associates, 1996, ISBN 156592-115-1 (covers POSIX threads).
OS-Related References
Boykin, Joseph, David Kirschen, Alan Langerman, and Susan LoVerso. Programming under Mach. Addison-Wesley, 1994, ISBN 0-201-52739-1.Tanenbaum, Andrew S. Distributed Operating Systems. Prentice Hall, 1995, ISBN 0-13-219908-4 (great textbook).
Silberschatz, Abraham, and Peter B. Galvin. Operating System Concepts, 4th ed. Addison-Wesley, 1995, ISBN 0-201-59292-4
Other References
Arnold, Ken and James Gosling. The Java Programming Language, 2nd ed. Addison-Wesley, 1998, ISBN 0-201-31006-6.comp.programming.threads FAQ, <http://www.serpentine.com/~bos/threads-faq/>
Le Sergent, T. and B. Berthomieu. ``Incremental MultiThreaded Garbage Collection on Virtually Shared Memory Architectures'' in Memory Management: Proc. of the International Workshop IWMM 92, St. Malo, France, September 1992, Yves Bekkers and Jacques Cohen, eds. Springer, 1992, ISBN 3540-55940-X (real-life thread applications).
Artur Bergman, ``Where Wizards Fear To Tread'', June 11, 2002, <http://www.perl.com/pub/a/2002/06/11/threads.html>
Acknowledgements
Thanks (in no particular order) to Chaim Frenkel, Steve Fink, Gurusamy Sarathy, Ilya Zakharevich, Benjamin Sugars, JA~Xrgen Christoffel, Joshua Pritikin, and Alan Burlison, for their help in reality-checking and polishing this article. Big thanks to Tom Christiansen for his rewrite of the prime number generator.AUTHOR
Dan Sugalski<EMAIL_ADDRESS>modified by Arthur Bergman to fit the new thread model/module.
Reworked slightly by JA~Xrg Walter<EMAIL_ADDRESS>to be more concise about thread-safety of Perl code.
Rearranged slightly by Elizabeth Mattijsen<EMAIL_ADDRESS>to put less emphasis on yield().
Copyrights
The original version of this article originally appeared in The Perl Journal #10, and is copyright 1998 The Perl Journal. It appears courtesy of Jon Orwant and The Perl Journal. This document may be distributed under the same terms as Perl itself.
Index
- NAME
- DESCRIPTION
- What Is A Thread Anyway?
- Threaded Program Models
- What kind of threads are Perl threads?
- Thread-Safe Modules
- Thread Basics
- Threads And Data
- Synchronization and control
- General Thread Utility Routines
- A Complete Example
- Different implementations of threads
- Performance considerations
- Process-scope Changes
- Thread-Safety of System Libraries
- Conclusion
- SEE ALSO
- Bibliography
- Acknowledgements
- AUTHOR
- Copyrights
This document was created by man2html, using the manual pages.
Time: 05:29:08 GMT, December 24, 2015


I've aways felt the default edit feature class / create feature class tool in ArcGIS Javascript API feels a bit too 'GIS nerdy' for the casual user. I'm not a big fan of creating the feature first and then populating the attribute table, and well the attribute table that appears to me just looks plain ugly. In this demo i'll show you how to create a custom form and to save it so it will be ready to be applied to a feature class or a graphic if needed. Of course, this demo will look ugly also, but it will show you how to create your own custom form, from there you can style and make it as nice as you want.
First lets set up our styling, we are going to need the main map div and a side pane that has some basic buttons and a basic form.
In the style script, lets add the following code:
It should look like this in your editor, or using the Sandbox
Now lets modify the HTML a bit for a crude display. Navigate to the body section in your HTML and replace with the following.
Sweet, it should look like this on your end
Now that we have the basic page set up, lets go ahead and start adding some javascript to our example to get this demo up and going. Lets go ahead and add in the modules or widgets we need for this examples.
What is going on here is we are now calling the modules located in the ESRI api. This will open up options for us in manipulating the data we will be working with. If you noticed in my screen shot my map object was a bit different so lets go ahead and update that too.
All we did in this step was set the map to Colorado's extent, and we zoomed out a bit so we can get a better perspective of where we are in the world. For the basemap there are plenty of options you can select besides "topo"; check out Basemaps Available
Next we want to add in our Feature Layer that we can edit. For this tutorial I have a Feature Service that is publicly available that we can use as a test. After the map object, add in the following code:
This will add in the FeatureService that has the ability to edit features through ArcGIS’s Rest API. We also added in the map.addLayer(featureLayer); which is adding the feature layer we defined into the map.
Now that we have our map object created, and our editable feature service added, lets create a standard shape for us to insert into the service. For this purpose we are going to use a circle. It can be any type of polygon, but I find using a the circle graphic easy and quick for this purpose. (To add lines or points, the service that we added via FeatureLayer object needs to be either a line or a point)
Lets first define the properties of the graphic we want to create.
All we are doing here is creating symbology for the circle. There are many options you could do here feel free to explore and try other options by using ESRI’s API Documentation.
Now that we have the basics set up, lets create the interactions between the form and the features. Since we want to use a form, lets go ahead and do this by using graphics first to get a visual confirmation and then we can submit, so this will be a two-step process, setting the properties and graphic, and then submitting to the Feature Service.
And that’s it, that’s all we must do to set up a basic form, of course there is a lot of styling and form validation that could be added to this.


The difference is how you spread your elements. In HTML we uses many different elements (text box or a picture or just a colored box) This elements is the companions of the web page as we know it.In this blog we will focus in two different concepts : inline Vs inline-block . Inline and inline-locks are two diffrent way we can lay out our elements. The best example is this:
In this example we can see that when we open our Google site, we have 8 option to go back to our history choices. The elements are organized in a unique way, they are organized in two lines which in each line they are laid out in 'display: inline-block' this mean that they are organized and coordinated one after another, the space between them is perfect, it is identical and equal. In the following example we can see that the images are lied out in the 'inline' system, which means that there are stack one next to the other.
As we can see, there is no repetitive distance between the pictures, every picture start right where the one before end.
Here is a good diagram that define the difference between 'inline' Vs 'inline-block'. I would say that in most cases, most pages would use 'inline-block' system because it is more organized and it's just look better. But there are many other examples we can find inline system too, if you are designing a website and you want to create less organized environments, in this case inline would be a preface solution for you.


About Me
Hello, my name is Jitendra Bajracharya. I'm a software development Engineer apprentice at Amazon and currently receiving training through code fellows. Previously, I graduated from another bootcamp MSSA in Cloud Application Development. Some of the development languages and tools that I am familiar with are C#, ASP.NET, Azure, SQL, html, and javascript.


Pariya’s death sad, says Tinubu - The Nation Newspaper
ALL Progressives Congress (APC) National stalwart Asiwaju Bola Ahmed Tinubu has described the death of Umar Pariya as sad.
In a tweet on his handle on Tuesday, he said: “I’m deeply saddened by the death of Umar Pariya. I knew him very well. He was very cerebral.
Read Also: David-West spoke truth to power, says Tinubu
“An excellent human being, Umar Pariya had a welcoming and accommodating spirit. May his soul rest in the bosom of the Lord.
“My condolences to Vice President Atiku Abubakar over the loss. May VP Atiku, family, friends and associates of the late Pariya find the strength to live through this sudden and untimely demise.”


WITNESS LIST Water Policy, Select Interim Committee November 3, 2004 - 1:30P Interim Charges ON: Christian, Debra (Self), Tyler, TX Flynn, Mark (Self), Whitehouse, TX Goss, Alan (Self), Troup, TX Goss, Teresa (Self), Troup, TX Hayes, Tommy (Self), East Texas, TX Houston, Jace General Counsel (Texas Groundwater District Coalition), Friendswood, TX Kitchens, Ron Executive Director (Texas Railroad Commission), Austin, TX Lynch, William Rancher/Farmer (Self), Dell City, TX Mahoney, Mike General Manager (Tx Groundwater District Coalition), Pleasanton, TX McCarthy, Edmond Attorney (Self), Austin, TX Middleton, Gary Chairman (Southcentral Water Advisory Committee), Victoria, TX Nabors, David Farmer / Rancher (Self), Paris, TX Nash, Barbara (Self), Troup, TX Sherman, Lynn President, Water Texas (Self), Austin, TX Shultz, Nanette (Self), Whitehouse, TX Sledge, Brian Attorney (Numerous groundwater districts with historic use periods), Austin, TX Williams, C.E. General Manager (Texas Groundwater District Coalition), White Deer, TX Registering, but not testifying: On: Langford, David (Texas Wildlife Association), Comfort, TX Marsh, Lila Attorney (Mesa Water), Dallas, TX Morgan, Gordon President (Headwaters Groundwater Conservation District), Kerrville, TX


This package Example circuits contains some useful examples to demonstrate how the library is working and how the models can be used.
| Name | Description |
|---|---|
| Inverter | Simple inverter circuit |
| InvertersApartRecord | Two inverters where transistor models use different modelcard instances |
| InvertersExtendedModel | Two inverters with MOS models defined by inheritance |
| FourInverters | Four inverters with MOSFET level 1, using private record as model card |
| Nand | MOS Nand gate circuit |
| Nor | MOS NOR gate circuit |
| Graetz | Graetz rectifier circuit |
| Oscillator | Oscillator circuit |
| CoupledInductors | |
| CascodeCircuit | |
| Spice3BenchmarkDifferentialPair | Simple differential pair |
| Spice3BenchmarkMosfetCharacterization | Mos output characteristics |
| Spice3BenchmarkRtlInverter | Simple RTL inverter |
| Spice3BenchmarkFourBitBinaryAdder | ADDER - 4 BIT ALL-NAND-GATE BINARY ADDER |


Id: 392
Name: Bearded Morty
Status: Alive
Species: Human
Type:
Gender: Male
OriginName: unknown
OriginUrl:
LocationName: Citadel of Ricks
LocationUrl: https://rickandmortyapi.com/api/location/3
Image: https://rickandmortyapi.com/api/character/avatar/392.jpeg
Episode: ['https://rickandmortyapi.com/api/episode/28']
Url: https://rickandmortyapi.com/api/character/392
Created: 2018-01-14T14:48:05.977Z


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Job Experience
RetailMeNot
- Jan 2020 - Present
- Software Engineer I
- Full-Stack Development (Typescript, React, Python, Kubernetes, and more)
Audible
- Summer 2019
- Incoming Software Development Engineering Intern
- Digital Asset Management Team (ADAM)
J.P. Morgan Chase & Co.
- Summer 2018
- Software Engineering Intern
- Experience with Python and Flask.
Texas A&M College of Engineering IT
- May 2017 - Present
- Co-Lead Full-Stack Application Developer
- Ruby on Rails
- AWS - Elastic Beanstalk, EC2, S3, RDS, Lambda


UTTT for people with friends. Since it's quite likely you don't have any, I might make a bot one day.
Design based off PullJosh's pen version


{% extends 'company/base.html' %} {% block page %} Company Profile Statistics Page Order page
| Driver_id | Date Hired | ssn | Date of Birth | License | Other License | Wage Plan | ||
|---|---|---|---|---|---|---|---|---|
| {{ driver_id.company_id }} | {{ driver.driver_id }} | {{ driver.date_hired }} | {{ driver.ssn }} | {{ driver.date_of_birth}} | {{ driver.license }} | {{ driver.other_license}} | {{ driver.wage_plan }} | {% if driver.wage_plan == "Hourly" %} {% endif %} |


Appointments
To make an appointment please call the practice between 9am and 6pm Monday to Friday. Saturday 9.00am to 12.30pm. Outside these hours you can leave a message on our answer machine. Contact us here >>
Emergencies
If you are in acute pain we will do our best to offer you an appointment on the day you call. The message on the reception answer phone will have the current out of hours number.
Cancellations
Please give at least 24 hours notice for a cancellation or the full appointment fee will be payable.
Your first appointment
When you first visit the practice we will take a detailed case history about your present complaint, medical history and general health/lifestyle. We will also examine you and treat you. Using this information and a detailed knowledge of anatomy and physiology we will explain to you why the symptoms have presented themselves in the way that they have. A treatment plan, the likely time scale and expected outcome will be discussed.
Please feel free to ask us any questions, no matter how trivial they seem. It is your body and if you understand why your symptoms exist this will aid in your return to recovery.
Medical insurance
The osteopaths at Kane and Ross are recognised by all the major health insurers. But please note patients are no longer reimbursed by AXA PPP Healthcare and BUPA (UK) as their terms have substantially restricted the level of service osteopathic practices are able to offer. Treatment with us can be covered by all the other major health insurances, including BUPA International and AXA PPP International. Please check with your insurers to establish your level of cover and any requirements they may have, such as a referral letter from your doctor. We will provide all relevant paperwork to ease the process of having your fees reimbursed.
For more about the petition against BUPA (UK): http://www.save-osteopathy-on-bupa.org


At BCIT, two of the courses I took were Discrete Mathematics and Computer Architecture. Both of those courses got into the Boolean logic and gates. We talked about a few different circuits: adders, multiplexers and decoders, memory circuits, an ALU. Inevitably, one of the tasks I had to do was trace the path a signal took through a circuit and identify which outputs would be asserted. It felt very tedious, it had very strict set of rules, and it was error-prone. Perfect job for a computer to do.
So I started building a program to calculate the output of circuits for me, with some interactive possibilities. This required some way to represent the different circuits to the computer, so I decided to take it farther and make a reusable node API for circuits. After some though about what I wanted it to be able to do, I came up with this set of goals for what the user would be able to do:
- See a graphical representation of each gate and the links
- Indicate which gates/wires were activated
- Pan across the circuit
- Zoom in and out
- Click an input to activate/deactivate it
- Switch between prebuilt circuits via a drop-down menu
- Auto-focus (zoom/pan) on the circuit based on the area of interest it covers
Programmatically, I wanted to be able to write a circuit by typing something like:
- andgate = new GateAnd(x, y)
- input1 = new Input(x, y)
- input2 = new Input(x, y)
- output1 = new Output(x, y)
- Link(input1, andgate)
- Link(input2, andgate)
- Link(andgate, output1)
So I set that as my mission and started programming. The resulting function signatures were a little longer, to be able to specify specific gate ports, scale factors, and link path shapes. The actual code equivalent to the above, looks like this:
- input1 = new GateInput(0, 0, 3, GateState.OFF);
- input2 = new GateInput(0, 100, 3, GateState.ON);
- andgate = new GateAnd(150, 50, 3);
- output1 = new GatePin(300, 50, 3);
- Gate.connect(input1, -1, andgate, 0, Link.HVH);
- Gate.connect(input2, -1, andgate, 1, Link.HVH);
- Gate.connect(andgate, -1, output1, -1);
- output1.setLabel("Output");
- output1.setLabelSide(GatePin.NW);
Specifying my goal at the outset really helped me achieve what I wanted, and design something usable. I feel proud of the API I ended up with, and I reused it once already creating a binary tree visualizer.
Download the jar file here


The aim of ABACUS is to promote and celebrate Eastern and Western cultural exchange. We host a number of diverse events throughout the year that centre on socialising, meeting new people and having fun. The society prides itself on being incredibly inclusive and welcoming to new faces, whether you may be a BBC (British Born Chinese), an international student or someone who would like to partake in our range of fun events, you are more than welcome to join us!
Our flagship event is the annual ABACUS Boat Party hosted in London (in collaboration with the Oxford University Asia-Pacific Society) during the end of Michaelmas1. Our members are invited to join us in a night of luxury and grandeur as we sail down the Thames against the backdrop of the glistening London skyline. There will be a myriad of food, drink and entertainment options during the evening so make sure you don’t miss out!
In addition to our annual boat party, we host several other events ranging from club nights to non-drinking events such as Funkyard (the biggest Asian club night in Cambridge), and the Garden Party, as well as a number of smaller events, such as dim sum meetups, karaoke nights and formals. We promise that there is something for everyone! The society is also extremely proactive with regards to increasing the cohesion of the Asian community within Cambridge and we host several inter-society events that encourage the appreciation of a diverse range of cultures and, of course, allow our members to meet a wider range of people across the university.
One of the best things about Cambridge ABACUS is the strong sense of community between our members and the lasting friendships that are formed as a result. The society acts as a home away from home for many of our members and allows you to establish a sense of belonging in the new environment that you are faced with when coming to university. We set up ‘ABACUS families’ early in the year and host a number of family formals so that new members are easily integrated into the community and have ‘parents’, who are more settled at the university, to be there to offer you guidance and support, whilst also providing a source of familiar faces at our events. We not only care about your welfare in our society, but also your future beyond university too, providing information when we can about exciting career opportunities that may be of interest.
We strongly encourage you to come along to our events, whether this may be with friends or by yourself, to become a part of our flourishing community here in Cambridge and, most importantly, to have a good time!
1. Dates for the 2020/21 academic year subject to change


Butterfly Technique
• Every multiplication has 2 basic operations : Vertical and Crosswise.
• Starting from the bottom-right, perform vertical multiplication first and crosswise next.
• In case of carry in current operation, add forward to next operation.
Example : 64x41 = ?


Hello, I am writing this report about mixing alcohol with 2C-T-21. I have tried combining alcohol with 2C-I, AMT, 2C-T-2, and a few others, and the second that the alcohol hit my stomach with those substances, I and several others that I regularly tripped with immediately felt nausea and/or vomited. So it was known to be a bad idea to drink while tripping in my group or circle of psychonauts.
So anyway, one day I introduced a friend who is a very heavy drinker to 2c-t-21 and he loved it, but he told me that he drank a lot of Jack Daniels during the trip and it intensified the effects for him. I just thought that he had an iron stomach from drinking all the time and the effects were all in his head, but I eventually tried this combo with an moderately strong dose of 2c-t-21(I never used an accurate scale as I am very familiar with how 2c-t-21 effects me), and found his statement to be true. I started drinking shots of whiskey in the middle of my trip and the alcohol didn't cause any nausea at all like the two went together perfectly.
Shortly after drinking a few shots I got this burst of tripping really hard, and the strange thing is that the alcohol added like a very strong speeding sensation like I just downed a bunch of amphetamines, huge waves of tingly energy. I couldn't believe how hard this combination made me trip, it's like the alcohol multiplied the effects of the 2c-t-21 in the same manner as with opiates or benzodiazepines.
The trip lasted the same amount of time maybe a little less than usual as it seems that the liquor pushed the chemical through my system faster. I just thought that this combo would be interesting to note because alcohol does not seem to have this effect with most other tryptamines and phenethylamines.
Experience Reports are the writings and opinions of the individual authors who submit them.
Some of the activities described are dangerous and/or illegal and none are recommended by Erowid.