Arbitrum V2
Transcript By: Bryan Bishop
Tags: Smart contracts, Layer 2
Category: Conference
Arbitrum 2.0: Faster Off-Chain Contracts with On-Chain Security
Ed Felten, Off-chain Labs
https://twitter.com/kanzure/status/1230191734375628802
Introduction
Thank you, good morning everybody. I’m going to talk about our latest version of our Abitrum system. The first version was discussed in a paper in 2018. Since then, there’s a lot of advances in my technology and a real running system has been made. This is the first working roll-up system for general smart contracts.
First I will set the scene to provide some context on what we’re talking about and how what we’re doing fits into the larger picture. Then I’ll talk about how the system works, what has changed since the last paper, and some lessons learned from building and deploying it.
Layer 2 protocols
So what about layer 2 systems that support smart contracts? They generally rely on having a set of parties like validators that are responsible for tracking the state of the layer 2 chain and taking action to make sure it develops correctly.
What is the assumption about how many validators you trust? There’s usually k-of-n validator honesty requirement, like (n+1)/n. On the right, you have systems where you assume only 1/n validators are honest. That one validator wins out against n-1 malicious validators.
Today we will be talking about 1/n trust assumption.
The next branch here is whether there’s a fixed validator set, or a situation where anyone can be a validator. When there’s anyone that can be a validator, that’s typically called a roll-up protocol. The alternative is to have a fixed validator set. At any given time, there’s a single enumerated set of validators. In that subset, the best known type is a state channel approach.
In state channels, you operate entirely off-chain. If all the validators agree unanimously, then they all mutually sign and move on, and only at the end of the period of agreement do you have to take a signed receipt and cash out on chain. State channels are incredibly efficient when everyone agres and participates, but if there’s any validator that stops, then you have to fall back to doing everything on the main chain.
In our 2018 paper, we introduced Arbitrum channels which is a hybrid of state channels and a fixed set of validators– when they are all operating by unanimous agreement you operate off-chain like a state channel. But when you lose unanmity, you fallback to a roll-up permissioned chain.
I am going to be talking about Arbitrum channels- the roll-up part of the protocol, which is the most interesting and complex part of the Arbitrum channel protocols.
Drilling down
Let me drill down into how a system like ours and similar ones work. So you have some amount of source code that represents a smart contract, it might be some legacy Solidity code or something out. You’re going ot take that source code, run it through a custom compiler, and generate an executable program that runs on a virtual machine that the Layer 2 system is implementing. Once you have that layer 2 executable, then you can launch your chain by launching a set of validators. Each validator has an emulator for emulating the VM and it can emulate programs in that VM architecture. You run the program on that virtual machine.
If all goes well, and all the validators are honest, then all the validators will have equivalent replicas of that VM as it runs. Dishonest validators will do what they do. But honest validators if the protocol is correct will always agree and have a replication of the state. They will agree and make progress quickly.
If they don’t agree, then they interact with an on-chain contract and that contract is responsible for the ultimate abjudication for any dispute betwee nvalidators. So the special sauce is how to make this on-chain manager contract as small and fast as possible, while still getting generality.
Design goal
Our first goal was to run general-purpose code and contracts. We want it fast and cheap, even with a slower layer 1. We want that any any-trust guarantees of safety, liveness and finality. Any one party acting alone can ensure that this property holds. Safety means that no bad state change will occur. Safety means that no bad thing will happen. Liveness means that some good thing will eventually happen, which combined with safety means some good thing will eventually happen. Finality means that if a valid state change is proposed and it’s pending, then it will eventually be confirmed, which allows parties as “fated to be confirmed” even before they are confirmed by the protocol, which allows faster responses for users.
We want to interop with the layer one chain so that you can make calls back and forth between contracts, or you want to move tokens back and forth. And we want censorship resistance as the underlying layer one chain.
Approach
The approach we took in building this is first of all, we did obvious stuff to minimize on-chain work and try to go fast. But in particula,r here are some distinguishing factors.
We wanted to run many separate layer 2 chains, which gives you more parallelism so that you can go faster in aggregate. It offers better incentives with respect to who is going to be a validator and who is going to pay for a chain. If your application is munched together with 10 other applications, then if you’re validating then you’re validating the things you care about but also the things from those 9 other applications. So coherent communities of interest has a better incentive structure than a single large chain.
On each chain, we run a single virtual machine instance. We don’t have a separate virtual machine per contract. All the activities on-chain should be run in a single program. So all the separate contracts and libraries thta might be runninng on the chain. We also need to have a runtime system built into that system able to do bookkeeping, check signatures, check formats, and various other things you would do in a runtime system or operating system on a conventional machine. The role of that runtime system is important for both efficiency and correctness. Having that runtime system is a big benefit.
We want to create incentives to keep the validators in the fastest mode.
We also pay attention to the safe speed limit, which is the speed at which you can allow activity to happen without outrunning the ability of validators to keep up. Validators need to be able to check on everything that is happening. It’s possible to propose stuff faster than validators can check it. The safe speed limit is based on how fast the validators can operate. So we want to make sure validators can always run at full speed.
Two use cases, two protocols
There’s the Arbitrum Rollup protocol in which anyone can be a validator. As in any roll-up protocol, if you want anyone to be a validator then you need to make sure they can get the information to become a validator. They need to find this information on the main chain so they can get up to date. If someone gives them a recent checkpoint of the state of the system, then there needs to be enough information on-chain to verify that. In roll-up protocols, we have a protocol based on proposals, and proposals are challengeable, and if they are challenged then there’s a dispute.
In the Arbitrum Channel protocol, there’s an enumerated set of validators, it can be private so that only validators know the full state. It’s just like a state channel, and when they aren’t in cooperation, then they fallback to the Arbitrum Rollup protocol.
I’ll talk about the roll-p protocol, resisting delay attacks with a branch-and-prune state management. And then how to handle time, messages and interoperability in a layer 2 situation.
Roll-up protocol
We have something called a roll-up block or assertion. It’s a claim about the execution of a VM in a chain. This might cover many transactions worth of work. Any validator can post an on-chain assertion which is a claim about what the chain will do or has done. It consists of a set of messages that the chain is consuming from the head of its inbox. These are things like requests to the contract to execute transactions, or incoming transfers of currency. There’s a number of steps that can be executed by the chain’s VM. It includes a root hash of the state machine after those steps are executed. The entire machine is organized in a merkle tree so you can summarize its state in a single hash. Then it asserts a set of outputs that are allegedly produced by the execution, like events, payments, log items made by those contracts. The arbitrum protocol decides after an assertion is made, whether to accept or reject an assertion.
How does that work? Well, there’s a state tree. I’m going to start by storing in this state… you can imagine that the history of this chain extends way off to the left. There’s a long history back to some genesis state. Alice places a stake on her assertion, claiming that the state will eventually be confirmed. The rules of the protocol say that if and when that state is confirmed, Alice can get her stake back. If the state is rejected, then Alice will lose her stake and it will go somewhere else. Once she has staked, a challenge period begins and every validator has some amount of time to check the assertion, decide if it is right, and if it is wrong then to challenge the assertion from Alice.
Say a validator sees that the assertion is correct. The validator can choose to stake on that same state node. The rules of his stake are going to be the same: if the assertion is confirmed, then he gets his stake back. The deadline runs out, let’s say, and nobody else can stake for or against that assertion. The system looks at this and says everyone who has stake is staked on the same branch, therefore we have unanimous agreement, so we’re going to go ahead and confirm that node. The top node will be confirmed, Alice and Bob gets their stake back, and time goes on.
But another thing that can happen is that another validator can stake on a state where Alice’s assertion is rejected. So now we have a disagreement between Alice and Bob on one hand, and Charlie on the other. So they enter into a dispute, and they execute an efficient dispute resolution which involves an interactive protocol where they use bisections to narrow down the scope of the dispute to a single instruction and then an on-chain instruction evaluates that single instruction. Then the dispute can be resolved on-chain. When Charlie loses, half the stake goes to Alice, the other stake gets burned, and then Charlie gets booted from the system. Then the protocol runs again and Alice and Bob are in agreement and the state gets turned green.
What happens when the challenge interval is running? We’d like to be able to pipeline these assertions. While Alice’s assertion is under consideration, Bob can make another assertion on top of Alice’s. He can pick any leaf from the tree, and make an assertion, and cause two leafs to sprout from that. By staking on that state node, he’s also implicitly staking on the correctness of Alice’s assertions because Bob’s stake cannot be confirmed unless Alice’s have been confirmed place. So he’s not undoing any commitments he has made before, he’s just committing to more stuff. Bob has made a new assertion, he moved his stake, and Alice might make another assertion on top of Bob’s even though her first one is still under consideration, and she is still required to stake.
The normal state of an operating chain is like this: you have a linear pipeline sequence of assertions and nobody wants to lose stake by asserting something false… They aren’t challenged, because nobody wants to lose their stake. So you have a frontier of assertions marching along, and behind you have a frontier of confirmations marching along. By having a pipeline, we can keep the validators always busy, and we don’t hav to keep the system waiting.
So we can make progress even when there’s disputes people can keep working out the truthful branch. Honest validators can always continue building the truthful branch. Dishonest validators can build out a false branch, but everyone else can ignore it knowing that eventually that branch will be proven away.
Efficient on-chain tracking
This might sound expensive to track this on-chain, but there are some tricks to reduce those costs. You can summarize the state. You have to track the hash of every leaf of the tree. If you have the hash of a leaf and the root of the tree, then you can prove any node is a member of the tree by using a set of merkle proofs. For each staker, you need the identity and the hash of the staking action.
This gives you trustless finality. You get the trustless properties I was talking about, happy to explain why out-of-band later.
Why time is hard to handle in layer two
The problem is that legacy programs like in Solidity it likes to ask what’s the current block number in the first layer? The result of this is determined when the transaction is put on-chain. But in the layer 2 transaction, you have to propose what happens in the transaction. It can’t be determined later when it gets adopted on-chain. So the outcome of the assertion has to be unique, and it can’t change over time. Also, layer 2 execution is asynchronous from the layer one clock.
In a previous paper, we talked about using time as a precondition where you label each assertion with lower and upper bounds about when the assertion can be accepted. The assumption is kept as moot outside those bounds. The application can ask, what are the current time bounds? That’s deterministic, and always correct. Because the assertion is moot outside those time bounds, it will always be true at the time that the assertion is accepted. Execution is deterministic. You’re given an interval, but real applications want a single scalar time.
So what do you do when the app asks for the time? One good solution is to take the max over the lower time bounds of all the assertions you’ve seen so far, and tell that to the application as the current time. It will never decrease, and it’s always within the time bounds. But the layer 2 runtime has to prevent the application from seeing anomalies. This might lag behind the real itme. There might be incoming messages that are timestamped after that, and you don’t want messages to appear to becomng from the future.
The l2 runtime system can see the current timebounds but also messages pegged in the future. We know what we’re doing; the l2 runtime is able to show a consistent and sensible notion of time to the application. So this is another example of how the use of an l2 runtime is pretty beneficial.
Takeaways
The branch-and-prune approach to state management allows high performance and strong guarantees of safety, liveness and finality. There’s significant advantages for compiling everything into a single L2 program per chain, consisting of a substantial runtime component in that. There’s also a surprising amount of “systems problem solving” needed to make this work. You have to solve a bunch of difficult problems to get this to work.
Arbitrum
Arbitrum Rollup is a commercial product. We have plugins for the standard front-end system so you can port existing applications to run in L2 and get those benefits. We have easy tooling for launching your dApp. This is the first roll-up for general contracts to be working on testnet. Also, we’re hiring. Thank you.
Sponsorship: These transcripts are sponsored by Blockchain Commons.
Disclaimer: These are unpaid transcriptions, performed in real-time and in-person during the actual source presentation. Due to personal time constraints they are usually not reviewed against the source material once published. Errors are possible. If the original author/speaker or anyone else finds errors of substance, please email me at<EMAIL_ADDRESS>for corrections or contribute online via github/git. I sometimes add annotations to the transcription text. These will always be denoted by a standard editor’s note in parenthesis brackets ((like this)), or in a numbered footnote. I welcome feedback and discussion of these as well.
Tweet: Transcript: “Arbitrum 2.0: Faster Off-Chain Contracts with On-Chain Security” https://diyhpl.us/wiki/transcripts/stanford-blockchain-conference/2020/aribtrum-v2/ @EdFelten @CBRStanford #SBC20


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public interface RemoteObject
ObjectSpace.getRemoteObject(com.esotericsoftware.kryonet.Connection, int, Class...)
| Modifier and Type | Method and Description |
|---|---|
void |
close()
Causes this RemoteObject to stop listening to the connection for method invocation response messages.
|
Connection |
getConnection()
Returns the local connection for this remote object.
|
byte |
getLastResponseID()
Gets the ID of response for the last method invocation.
|
void |
setNonBlocking(boolean nonBlocking)
Sets the blocking behavior when invoking a remote method.
|
void |
setResponseTimeout(int timeoutMillis)
Sets the milliseconds to wait for a method to return value.
|
void |
setTransmitExceptions(boolean transmit)
Sets whether exceptions are sent back when invoking a remote method.
|
void |
setTransmitReturnValue(boolean transmit)
Sets whether return values are sent back when invoking a remote method.
|
java.lang.Object |
waitForLastResponse()
Waits for the response to the last method invocation to be received or the response timeout to be reached.
|
java.lang.Object |
waitForResponse(byte responseID)
Waits for the specified method invocation response to be received or the response timeout to be reached.
|
void setResponseTimeout(int timeoutMillis)
void setNonBlocking(boolean nonBlocking)
nonBlocking
- If false, the invoking thread will wait for the remote method to return or timeout (default). If true,
the invoking thread will not wait for a response. The method will return immediately and the return value should
be ignored. If they are being transmitted, the return value or any thrown exception can later be retrieved with
waitForLastResponse()
or waitForResponse(byte)
. The responses will be stored until retrieved, so
each method call should have a matching retrieve.void setTransmitReturnValue(boolean transmit)
transmit
- If true, then the return value for non-blocking method invocations can be retrieved with
waitForLastResponse()
or waitForResponse(byte)
. If false, then non-primitive return values for
remote method invocations are not sent by the remote side of the connection and the response can never be
retrieved. This can also be used to save bandwidth if you will not check the return value of a blocking remote
invocation. Note that an exception could still be returned by waitForLastResponse()
or
waitForResponse(byte)
if setTransmitExceptions(boolean)
is true.void setTransmitExceptions(boolean transmit)
transmit
- If false, exceptions will be unhandled and rethrown as RuntimeExceptions inside the invoking thread. This is
the legacy behavior. If true, behavior is dependent on whether setNonBlocking(boolean)
. If non-blocking
is true, the exception will be serialized and sent back to the call site of the remotely invoked method, where it
will be re-thrown. If non-blocking is false, an exception will not be thrown in the calling thread but instead can
be retrieved with waitForLastResponse()
or waitForResponse(byte)
, similar to a return value.java.lang.Object waitForLastResponse()
byte getLastResponseID()
java.lang.Object waitForResponse(byte responseID)
void close()
Connection getConnection()


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An awk program can be used to retrieve information from a database, the database basically being any kind of text file. The more structured the text file, the easier it is to work with, although the structure might be no more than a line consisting of individual words.
The list of acronyms below is a simple database.
$cat acronyms
BASIC Beginner's All-Purpose Symbolic Instruction Code CICS Customer Information Control System COBOL Common Business Oriented Language DBMS Data Base Management System GIGO Garbage In, Garbage Out GIRL Generalized Information Retrieval Language
A tab is used as the field separator. We're going to look at a program that takes an acronym as input and displays the appropriate line from the database as output. (In the next chapter, we're going to look at two other programs that use the acronym database. One program reads the list of acronyms and then finds occurrences of these acronyms in another file. The other program locates the first occurrence of these acronyms in a text file and inserts the description of the acronym.)
The shell script that we develop is named acro. It takes the first argument from the command line (the name of the acronym) and passes it to the awk script. The acro script follows:
$cat acro
#! /bin/sh # assign shell's $1 to awk search variable awk '$1 == search' search=$1 acronyms
The first argument specified on the shell command line ($1) is assigned to the variable named search; this variable is passed as a parameter into the awk program. Parameters passed to an awk program are specified after the script section. (This gets somewhat confusing, because $1 inside the awk program represents the first field of each input line, while $1 in the shell represents the first argument supplied on the command line.)
The example below demonstrates how this program can be used to find a particular acronym on our list.
$acro CICS
CICS Customer Information Control System
Notice that we tested the parameter as a string ($1 == search). We could also have written this as a regular expression match ($1 ~ search).
A net posting was once forwarded to one of us because it contained a problem that could be solved using awk. Here's the original posting by Emmett Hogan:
I have been trying to rewrite a sed/tr/fgrep script that we use quite a bit here in Perl, but have thus far been unsuccessful...hence this posting. Having never written anything in perl, and not wishing to wait for the Nutshell Perl Book, I figured I'd tap the knowledge of this group. Basically, we have several files which have the format: item info line 1 info line 2 . . . info line n Where each info line refers to the item and is indented by either spaces or tabs. Each item "block" is separated by a blank line. What I need to do, is to be able to type: info glitch filename Where info is the name of the perl script, glitch is what I want to find out about, and filename is the name of the file with the information in it. The catch is that I need it to print the entire "block" if it finds glitch anywhere in the file, i.e.: machine Sun 3/75 8 meg memory Prone to memory glitches more info more info would get printed if you looked for "glitch" along with any other "blocks" which contained the word glitch. Currently we are using the following script: #!/bin/csh -f # sed '/^ /\!s/^/@/' $2 | tr '\012@' '@\012' | fgrep -i $1 | tr '@' '\012' Which is in a word....SLOW. I am sure Perl can do it faster, better, etc...but I cannot figure it out. Any, and all, help is greatly appreciated. Thanks in advance, Emmett ------------------------------------------------------------------- Emmett Hogan Computer Science Lab, SRI International
The problem yielded a solution based on awk. You may want to try to tackle the problem yourself before reading any further. The solution relies on awk's multiline record capability and requires that you be able to pass the search string as a command-line parameter.
Here's the info script using awk:
awk 'BEGIN { FS = "\n"; RS = "" } $0 ~ search { print $0 }' search=$1 $2
Given a test file with multiple entries, info was tested to see if it could find the word "glitch."
$info glitch glitch.test
machine Sun 3/75 8 meg memory Prone to memory glitches more info more info
In the next chapter, we look at conditional and looping constructs, and arrays.


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Fernando Pessoa
...one of the most significant literary figures of the 20th century
Early life and carrer:
- Pessoa was born in Lisbon on 13 June 1888. When Pessoa was five, his father, Joaquim de Seabra Pessôa, died of tuberculosis and on 2 January of the following year, his younger brother Jorge, aged one, also died.
- Fernando sailed with his mother for South Africa in early 1896 to join his stepfather, a military officer appointed Portuguese consul in Durban, capital of the former British Colony of Natal.
- He moved to the Durban High School in April 1899, becoming fluent in English and developing an appreciation for English literature.
- At the age of sixteen, The Natal Mercury[3] (edition of 6 July 1904) published his poem "Hillier did first usurp the realms of rhyme...", under the name of C. R. Anon (anonymous), along with a brief introductory text: "I read with great amusement...".
- Ten years after his arrival, he sailed for Lisbon via the Suez Canal on board the "Herzog", leaving Durban for good at the age of seventeen.
- In 1912, Fernando Pessoa entered the literary world with a critical essay, published in the cultural journal A Águia, which triggered one of the most important literary debates in the Portuguese intellectual world of the 20th century: the polemic regarding a super-Camões.
- In 1915 a group of artists and poets, including Fernando Pessoa, Mário de Sá-Carneiro and Almada Negreiros, created the literary magazine Orpheu, which introduced modernist literature to Portugal.
- Along with the artist Ruy Vaz, Pessoa also founded the art journal Athena (1924–25), in which he published verses under the heteronyms Alberto Caeiro and Ricardo Reis.


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Structures
The following structures are available globally.
-
An efficient variable-size FIFO queue of elements of type “Element.”
See moreDeclaration
Swift
public struct RVS_FIFOQueue<Element> : OLEB_Queue
extension RVS_FIFOQueue: ExpressibleByArrayLiteral
extension RVS_FIFOQueue: MutableCollection
-
This enum defines the base for the OBD diagnostic trouble codes (DTCs). Each instance of this struct is a single DTC.
Declaration
Swift
public struct RVS_BTDriver_OBD_DTC
-
This struct will contain a transaction for an OBD device. OBD transactions are atomic and single-threaded. There can only be one going to a device at a time.
See moreDeclaration
Swift
public struct RVS_BTDriver_OBD_Device_TransactionStruct


Used to find all matching records by indexing a field in each record.
For instance if you have a RecordArray of students and you want to find out how many are living in the USA:
// "students" is a RecordArray of students' information. const studentsUSA = students.findBy('homeCountryName', 'USA'); console.log(`There are ${studentsUSA.length} students from USA.`);


{% extends "description.html" %} {% set id="ln-watchtowers"%} {# id must be unique and follow the rules for ids in css https://www.w3.org/TR/CSS21/syndata.html#characters #} {% set project="Lightning" %} {# Use proper-case (ex. Bitcoin, not bitcoin) #} {% set sub_project="Watchtowers" %} {# set to False or "" if not using #} {% set simple_desc="Keeps your BTC secure on Lightning by monitoring the Bitcoin network" %} {# Keep this short (~50 characters) #} {% set details=True %} {% set further_reading=True %} {% block at_a_glance %}
All Lightning transactions are essentially multisignature bitcoin transactions (ie. requiring a predefined number of keys to spend, rather than just one). Typically these transactions are 2-of-2 multisigs with a timelock (aka. a withdrawal delay). When you move BTC around on the Lightning Network you're essentially sharing IOUs with people. When you eventually want to turn those IOUs into BTC in your wallet you need to ""close"" your Lightning channel.
There's two general ways to move BTC out of a Lightning channel:
Watchtowers cover the second case, watching the Bitcoin network and making sure that the wrong transactions don't end up on the network sending money to the wrong people.
{% endblock at_a_glance %} {% block status %}Watchtowers are already in a few wallets but they're still in alpha development
{% endblock status %} {% block future %}Eventually Watchtowers will be available everywhere and making fraudulent Lightning transactions by giving the Bitcoin network old IOUs will be practically impossible.
{% endblock future %} {% block vs_alts %}Currently Lightning channels are not yet easy to monitor, while the rate of fraud is low it is still feasible and does occasionally happen.
{% endblock vs_alts %} {% block further_reading %} Radar.tech {% endblock further_reading %}


| static | Clock() |
| private | Clock() |
| public static Clock& | Instance() |
| public void | Start() |
| public void | Stop() |
| private void | Tick() |
| public const long | tick = 50 |
| private static UniquePtr<Clock> | instance |
| private Machine& | machine |
| private RecursiveMutex | mtx |
| private bool | started |
| private ConditionVariable | stop |
| private bool | stopping |
| private Thread | thread |


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| “OFF AND RUNNING” | ||
| $2,000 WEEKLY MINIMUM | ||
| Michael H "A" Team | 4,614.00 | 7 |
| Dawn D Sales Machine | 4,490.00 | 7 |
| Damion C Road Warriors | 4,392.00 | 6 |
| Rares S Home Office | 4,348.00 | 3 |
| Michael R Road Warriors | 4,265.00 | 5 |
| Tyler L Sales Machine | 4,250.00 | 6 |
| Kelly H Sales Machine | 4,149.00 | 6 |
| John B Road Warriors | 4,123.00 | 5 |
| Rebecca G Fire N Reign | 4,104.00 | 8 |
| Terry B Fire N Reign | 4,084.00 | 7 |
| Vincent S Slayers | 4,029.00 | 1 |
| Juan M Tigers | 3,847.00 | 9 |
| Shirlin M "A" Team | 3,821.00 | 3 |
| Stephen S Sales Machine | 3,699.00 | 3 |
| Jonathan H Fire N Reign | 3,611.00 | 6 |
| Angela H Home Office | 3,448.00 | 5 |
| Todd S "A" Team | 3,281.00 | 4 |
| Ricky A Tigers | 3,275.00 | 3 |
| Kevin F Road Warriors | 3,262.00 | 5 |
| George J Fire N Reign | 3,254.00 | 3 |
| David R Transformers | 3,078.00 | 3 |
| Donald M Road Warriors | 3,069.00 | 1 |
| William C Fire N Reign | 2,761.00 | 4 |
| Jeorge H Road Warriors | 2,726.00 | 4 |
| Clint C Home Office | 2,666.00 | 3 |
| Karen E Sales Machine | 2,617.00 | 4 |
| “OFF AND RUNNING” | ||
| $2,000 WEEKLY MINIMUM | ||
| Allan C Road Warriors | 2,530.00 | 8 |
| Joseph D Road Warriors | 2,484.00 | 2 |
| Kevin C Sales Machine | 2,470.00 | 3 |
| Edward E Rebels | 2,430.00 | 3 |
| David S Fire N Reign | 2,296.00 | 6 |
| Tony J Road Warriors | 2,278.00 | 3 |
| Ronald P Road Warriors | 2,249.00 | 2 |
| Kenneth B Home Office | 2,193.00 | 1 |
| Elbert L Home Office | 2,112.00 | 3 |
| Bruce W "A" Team | 2,106.00 | 3 |
| Carlton T "A" Team | 2,080.00 | 2 |
| Zachary R The Dream Team | 2,024.00 | 3 |
| Chris B Sales Machine | 2,000.00 | 2 |
| “ON THE HIGH HORSE” | |
| CONSECUTIVE WEEKS OF $2000 OR MORE OF SUBMITTED PREMIUM | |
| Lloyd M Road Warriors | 29 |
| Michael R Road Warriors | 16 |
| Todd S "A" Team | 8 |
| Angela H Home Office | 7 |
| Ronald P Road Warriors | 7 |
| Patricia C Road Warriors | 6 |
| Bruce W "A" Team | 5 |
| Jonathan H Fire N Reign | 5 |
| Joseph D Road Warriors | 5 |
| Tim W Storm | 4 |
| George J Fire N Reign | 3 |
| John B Road Warriors | 3 |
| Kelly H Sales Machine | 3 |
| Kevin C Sales Machine | 3 |
| Rebecca G Fire N Reign | 3 |
| Stephen S Sales Machine | 3 |
| Terry B Fire N Reign | 3 |
| Clint C Home Office | 2 |
| Dedrick P Sales Machine | 2 |
| Juan M Tigers | 2 |
| Zachary R The Dream Team | 2 |
| PONY UP | ||
| MINIMUM OF 5 APPS IN A WEEK | ||
| Julienne W Sales Machine | 4,724.00 | 12 |
| Dedrick P Sales machine | 5,070.00 | 10 |
| Juan M Tigers | 3,847.00 | 9 |
| Lloyd M Road Warriors | 7,178.00 | 8 |
| Rebecca G Fire N Reign | 4,104.00 | 8 |
| Allan C Road Warriors | 2,530.00 | 8 |
| Michael H "A" Team | 4,614.00 | 7 |
| Dawn D Sales Machine | 4,490.00 | 7 |
| Terry B Fire N Reign | 4,084.00 | 7 |
| Anthony S Sales Machine | 7,214.00 | 6 |
| Patricia C Road Warriors | 5,013.00 | 6 |
| Damion C Road Warriors | 4,392.00 | 6 |
| Tyler L Sales Machine | 4,250.00 | 6 |
| Kelly H Sales Machine | 4,149.00 | 6 |
| Jonathan H Fire N Reign | 3,611.00 | 6 |
| David S Fire N Reign | 2,296.00 | 6 |
| William R Sales Machine | 1,736.00 | 6 |
| John M Road Warriors | 6,500.00 | 5 |
| Tim W Storm | 5,128.00 | 5 |
| Michael R Road Warriors | 4,265.00 | 5 |
| John B Road Warriors | 4,123.00 | 5 |
| Angela H Home Office | 3,448.00 | 5 |
| Kevin F Road Warriors | 3,262.00 | 5 |
| Steven S Home Office | 1,551.00 | 5 |
| Larry K Tigers | 1,130.00 | 5 |
| “THE WINNERS CIRCLE” | |
| 5 OR MORE APPS FOR CONSECUTIVE WEEKS | |
| Lloyd M Road Warriors | 16 |
| Michael R Road Warriors | 6 |
| Patricia C Road Warriors | 5 |
| John B Road Warriors | 3 |
| Rebecca G Fire N Reign | 3 |
| Terry B Fire N Reign | 3 |
| Dedrick P Sales Machine | 2 |
| Juan M Tigers | 2 |


Hello, world!
Hello, world!
Hello
, world!
This is
paragraph
text
One
Two
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One
Two
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numbers
1
2
3
4
5
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Send


(#) Using obsolete ProGuard configuration
!!! ERROR: Using obsolete ProGuard configuration
This is an error, and is also enforced at build time when
supported by the build system. For Android this means it will
run during release builds.
Id
: `Proguard`
Summary
: Using obsolete ProGuard configuration
Severity
: Fatal
Category
: Correctness
Platform
: Android
Vendor
: Android Open Source Project
Feedback
: https://issuetracker.google.com/issues/new?component=192708
Affects
: Shrinking configuration files
Editing
: This check runs on the fly in the IDE editor
See
: https://issuetracker.google.com/36928077
Implementation
: [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/ProguardDetector.java)
Tests
: [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/ProguardDetectorTest.kt)
Copyright Year
: 2011
Using `-keepclasseswithmembernames` in a proguard config file is not
correct; it can cause some symbols to be renamed which should not be.
Earlier versions of ADT used to create proguard.cfg files with the wrong
format. Instead of `-keepclasseswithmembernames` use
`-keepclasseswithmembers`, since the old flags also implies "allow
shrinking" which means symbols only referred to from XML and not Java
(such as possibly CustomViews) can get deleted.
(##) Example
Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
proguard.cfg:21:Error: Obsolete ProGuard file; use
-keepclasseswithmembers instead of -keepclasseswithmembernames
[Proguard]
-keepclasseswithmembernames class * {
^
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here is the source file referenced above:
`proguard.cfg`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ linenumbers
-optimizationpasses 5
-dontusemixedcaseclassnames
-dontskipnonpubliclibraryclasses
-dontpreverify
-verbose
-optimizations !code/simplification/arithmetic,!field/*,!class/merging/*
-keep public class * extends android.app.Activity
-keep public class * extends android.app.Application
-keep public class * extends android.app.Service
-keep public class * extends android.content.BroadcastReceiver
-keep public class * extends android.content.ContentProvider
-keep public class * extends android.app.backup.BackupAgentHelper
-keep public class * extends android.preference.Preference
-keep public class com.android.vending.licensing.ILicensingService
-keepclasseswithmembernames class * {
native


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Start-ups and solutions
We help entrepreneurs, start-ups and enterprises shape their ideas into products
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We help entrepreneurs, start-ups and enterprises shape their ideas into products


Modern day has been dramatically changed because of the evolution of technology. Life was burdensome and everyday chores consumed too much of our time before the technology was here. Due to the technology we have, the access to education, medicine, industry, transportation etc. has been simplified. One of the thing that everyone use on a daily basis is internet.
How do we connect to the internet? Majority of the people use internet through WiFi. A facility allowing computers, smartphones, or other devices to connect to the Internet or communicate with one another wirelessly within a particular area.
However, there are 2 different kinds of WiFi main frequencies and not everyone know their similarity and differences. One of them is 2.4 GHz WiFi. The 2.4 GHz is a ratio that cycles 2.4 billion times per second. There are many devices that we use on a daily basis use the same frequencies as the 2.4 GHz WiFi. These devices include microwave, any video devices that use FM carrier, car alarm, bluetooth, and of course the 2.4 GHz WiFi.The 2.4 GHz is the most used radio frequencies in the US. And the WiFi that uses it will have a large range and long waves. It is able to get through walls and solid objects easily. On the other hand, because of its large range and long waves, it will definitely get a slower speed to the internet and will have some drop connections. In fact, the Purple writer once written “The 2.4 Ghz extended range meant that an increasing number of devices (from baby monitors to bluetooth) were using the same frequency, causing it to become overcrowded and slower. “(The History of WiFi, 2014)
On the other hand, the second main frequency for WiFi, the 5GHz has a totally opposite characteristic. It has a smaller range but a faster connection to the internet. As you can tell the meaning of GHz is a billion cycle per second. The 5Ghz ratio cycles 5 billion times per second. It is about 2 times faster than the 2.4 GHz and about half of the range of the 2.4 Ghz. Its higher frequencies allow data to be transmitted faster and stay with a stable connection.
Also giving credit for 5 Ghz, 5 Ghz allow us to use a new technology called beamforming. It does not work as the traditional radio signal that goes in every directions. The beamforming is a strong point to point connection. It reduce the direction where the signal is going and empower the signal strength to a direction which create a larger range and stronger connection to a device.
While the 2.4 GHz covers about 20-30 ft, the 5 GHz only covers 10-15ft. But with the beamforming, the 5 Ghz can reach a range of 40 ft. Also the maximum speed for the 2.4 band is 600 Mbps and the maximum speed for the 5 band is 1300 Mbps.
Both of the bands uses radio waves to transmit information across a network. Devices that uses WiFi will include a wireless adapter that can translate data sent into a radio signal. The same signal will be transmitted to a decoder known as the router. Once the data is decoded, the data will be sent to the Internet through a wired Ethernet connection.
Both wireless network works as a two way traffic, the data received form the internet will also pass through the router to be coded into a radio signal that will be received by the devices. Therefore, both WiFi bands are not actually wireless. They need to be connection to a router through radio signal, and the router need to be connection to the wired internet for you to use the internet.


Skeleton :skull:
An easy way to create sliding CAGradientLayer
animations! Works great for creating skeleton screens for loading content.
I plan on expanding this library with functionality that allows easily converting a regular UITableViewCell
or UICollectionViewCell
to it’s skeleton screen equivalent, hence the name Skeleton. I just haven’t figured out exactly how I want to do that yet! :sweat_smile:
Overview
In essence, the entire library comes down to just one extension:
public extension CAGradientLayer {
public func slide(to dir: Direction, group: ((CAAnimationGroup) -> CAAnimationGroup) = { $0 })
public func stopSliding()
}
Everything else is there to help you out and provide convenience! You can check out the documentation for more.
Example
To run the example project, clone the repo, and run pod install
from the Example directory first.
Installation
Skeleton is available through CocoaPods. To install it, simply add the following line to your Podfile:
pod "Skeleton"
Author
Gonzalo Nuñez<EMAIL_ADDRESS>License
Skeleton is available under the MIT license. See the LICENSE file for more info.


Nothing But Net - 2587z: "Klay"
Nothing But Net Awards: Science Division Finalists | Science Division First Seed | Texas State Championship Finalists | Texas State Championship Excellence | Texas State Championship Robot Skills
Watch Reveal Video


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{{urec.iou_label}}
{{urec.layer}} {{urec.unit}}
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Seeds to generate To transfer activations from one pixel to another (1) click on a source pixel on the left image and (2) click on a target pixel on a right image, then (3) choose a set of units to insert in the palette. #{{ ex.id }}
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Contains util methods to interact with Hadoop from Spark.
Executable utility for starting and terminating drivers inside of a standalone cluster.
A main class used by spark-submit to launch Python applications.
Main gateway of launching a Spark application.


{% extends 'base.html' %} {% block content %}
It is a long established fact that a reader will be distracted by the readable content of a page when looking at its layout. The point of using Lorem Ipsum is that it has a more-or-less normal distribution of letters, as opposed to using 'Content here, content here', making it look like readable English. Many desktop publishing packages and web page editors now use Lorem Ipsum as their default model text, and a search for 'lorem ipsum' will uncover many web sites still in their infancy. Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like).
Time: {{api_item.time}}


Ballarat Alstom crisis: Workers to rally at MP's office, demanding answers
by Alex FordUnions have organised a protest outside state Wendouree MP Juliana Addison's office for Tuesday, calling on the Labor member to stand up for jobs at the Ballarat Alstom train facility.
Workers have been waiting for months for word from the state government about the X'Trapolis 2.0 project, which, if approved, will create new metropolitan trains for Melbourne and keep at least 70 workers directly employed, and hundreds more indirectly.
However, once work on the current order of trains is finished, there is no certainty the workforce will be retained by the factory.
READ MORE ON ALSTOM:
Unions to call motion at ALP state conference
Ballarat Alstom workers protest state government
Ballarat Alstom jobs still at risk, no action from state government
Design work has been completed by Alstom on the X'Trapolis 2.0 project, and the state government is reviewing the designs.
On Friday, before he spoke at the state Labor conference on Saturday, Alstom worker and Rail, Tram and Bus Union member Luke Cornish told The Courier workers wanted answers from a state government which had promised more work during the election campaign.
The union moved a motion at the conference, passed unanimously, "encouraging" a "substantive order of trains that will provide security and certainty".
Ms Addison will be in Melbourne and Shepparton on Tuesday on parliamentary committee business, helping conduct an inquiry into sustainable employment for long term and disadvantaged job seekers, and had informed Alstom's Combined Union Secretaries.
In a statement, she said the state government will continue to negotiate in good faith with Alstom to continue to support local jobs.
"The Andrews Labor Government invested $103.5 million in five new six-carriage X'Trapolis trains in the 2018-19 Victorian Budget to meet growing passenger demand on Melbourne's rail network, while retaining jobs and skills in Ballarat until at least the middle of next year," she said.
The rally begins on Lydiard Street at noon.


--- layout: post title: 'XP Day: Nat Pryce, TDD and asynchronous systems' date: 2008-12-11 00:00:00 category: software-development ---
XP Day: Nat Pryce, TDD and asynchronous systems
Case study of 3 different systems, dealing with asynchrony on system development and TDD.
Symptoms this can lead to in tests:
Example: system for administering loans. For regulatory reasons certain transactions had to be conducted by fax. Agent watches system, posts events to a JMS queue, consumer picks up events, triggers client to take actions.
Couldn't test many components automatically, had to do unit tests and manual QA. System uses multiple processes, loosely joined.
They built their own system: a framework for testing the Swing GUIs, using probes sent into Swing, running withing Swing threads, taking data out of GUI data structures and back onto test threads. Probes hide behind an API based on assertions.
Second case study: device receiving data from a GPS, doing something with this info, translating it into a semantically richer form and using it to get, e.g. weather data from a web service.
System structured around an event message bus. Poke an event in, you expect to get an event out: lots of concurrency between producers and consumers.
Tested with a single process running entire message bus (different from deployed architecture); tests sent events onto message bus, the testbed captured events in a buffer and the test could make assertions based on these captured events. Web services were faked out. Again, all synchronisation was hidden behind an API of assertions with timeouts to detect test failure.
Third case study: grid computing system for a bank. Instead of probing a swing app, used WebDriver to probe a web browser running out-of-process. Probes repeat, time out, etc. Slow tests only occur when failures happen, which should be rare. Assertion-based API hides these timeouts, and stops accidental race conditions caused by data being queried whilst it's being changed.
Question: the fact that you use a DSL to hide the nasties of synchronisation doesn't help solve the symptoms in the first slide, does it?
Polling can miss updates in state changes. Event traces effectively let you log all events so you don't miss anything. Assertions need to be sure that they're testing the up-to-date state of the system. You need to check for state changes.
Question: what about tests when states don't change? Tests pass immediately.
You need to use an idiom to test that nothing happens.
It's difficult to test timer-based stuff ("do X in a second") reliably. Pull out these parts into third party services. Pulled out scheduler, tested carefully, gave it a simple API, developed a fake scheduler for tests. To test timer-based events you need to fake out the scheduler.


Web developer able to build a polished web application with full database backend from designing the wireframe to pushing to production. Exceptional at working with diverse teams to deploy projects.
Interests: cooking, traveling, trendy coffee shops, photography


Wakhi Anglicized keyboard based on English (US). To produce letters with the tilde sign c̃, type first the letter, then the tilde sign. The grave accent sign ` is produced by typing twice the ̃ (tilde) sign.
See this document for more information.
Unshifted
Shifted
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