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  • Overused or abused programming techniques

    - by Anto
    Are there any techniques in programming that you find to be overused (IE used way more excessively than what they should be) or abused, or used a bit for everything, while not being a really good solution to many of the problems which people attempt to solve with it. It could be regular expressions, some kind of design pattern or maybe an algorithm, or something completely different. Maybe you think people abuse multiple inheritance etc.

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  • The Truth About Google's PR

    Have many times have you heard of the term Page Rank? Also known as PR, page rank is an algorithm and a trademark used by the most popular search engine in the world: Google. The goal of PR in websites is to measure the importance of the links pointing to a website.

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  • Should I expect to know a lot about every language I put on my resume as a college student?

    - by Newbie_code
    If I am asked to program an algorithm, say binary search, in languages other than Java during an interview, I will have a hard time trying to remember the syntax. Is it okay to tell my interviewer that I can only code this in Java, because I have worked with other languages before but have not used them for a while? If not, what suggestions do you have (i.e. what languages and parts of those languages among these should I pick up the syntax of before my interview)?

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  • How can I implement a matchmaker?

    - by csiz
    I'm making a multiplayer game, where players are separated in to rooms that would ideally have about 20 players. So I need a few pointers on an algorithm to distribute the players in to these rooms. A few more constraints: When a players gets in to a room, he should stay there until he decides to exit (the room itself changes levels) There may be more room servers, every server should create more rooms until near full capacity There's a central server that manages all the room servers, and directs the players towards their room

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  • Search Engine and How it Works

    What is a Search Engine and how does it work? A search engine is a primary tool of navigation which looks like a directory but does more than that. It not just displays the website matching with the keywords entered by a user but uses a complex algorithm that ranks them and displays them in an order of relevance.

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  • How to Use SEO Services to Have a Successful Website

    Essentially the optimization of web pages in a site is required because search engines are software programs based on a specific algorithm that is used at the time of its crawling into your website. Each website has numerous web pages and it is practically difficult to index and crawl each and every web page. No search engine can perform this function.

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  • How Relevant Are You?

    When searching for "van insurance" through a search engine, you will find millions of results in order of what the search engine believes are relevant to the inquiry. A search engine like Google has created a particular algorithm in order to list the relevance of each search weighing a variety of different aspects.

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  • SEO Copywriting - Embracing Google's Mayday Update

    SEO copywriting has changed dramatically over the past two or three years. Then, it was all meta tags and keyword density. Now, SEO copywriting is more about quality inbound links and useful content that reads smoothly. Google's 2010 Mayday algorithm update also emphasises quality content at the expense of 'long-tail keywords' whose demise is spelt in a single, simple term: 'irrelevance'.

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  • Link Building - The Right Way

    The idea of link building is to generate quality inbound links pointed towards your websites. Nowadays search engines use this as a part of their algorithm with the help of which they can determine the significance of their websites.

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  • Recommendations for distributed processing/distributed storage systems

    - by Eddie
    At my organization we have a processing and storage system spread across two dozen linux machines that handles over a petabyte of data. The system right now is very ad-hoc; processing automation and data management is handled by a collection of large perl programs on independent machines. I am looking at distributed processing and storage systems to make it easier to maintain, evenly distribute load and data with replication, and grow in disk space and compute power. The system needs to be able to handle millions of files, varying in size between 50 megabytes to 50 gigabytes. Once created, the files will not be appended to, only replaced completely if need be. The files need to be accessible via HTTP for customer download. Right now, processing is automated by perl scripts (that I have complete control over) which call a series of other programs (that I don't have control over because they are closed source) that essentially transforms one data set into another. No data mining happening here. Here is a quick list of things I am looking for: Reliability: These data must be accessible over HTTP about 99% of the time so I need something that does data replication across the cluster. Scalability: I want to be able to add more processing power and storage easily and rebalance the data on across the cluster. Distributed processing: Easy and automatic job scheduling and load balancing that fits with processing workflow I briefly described above. Data location awareness: Not strictly required but desirable. Since data and processing will be on the same set of nodes I would like the job scheduler to schedule jobs on or close to the node that the data is actually on to cut down on network traffic. Here is what I've looked at so far: Storage Management: GlusterFS: Looks really nice and easy to use but doesn't seem to have a way to figure out what node(s) a file actually resides on to supply as a hint to the job scheduler. GPFS: Seems like the gold standard of clustered filesystems. Meets most of my requirements except, like glusterfs, data location awareness. Ceph: Seems way to immature right now. Distributed processing: Sun Grid Engine: I have a lot of experience with this and it's relatively easy to use (once it is configured properly that is). But Oracle got its icy grip around it and it no longer seems very desirable. Both: Hadoop/HDFS: At first glance it looked like hadoop was perfect for my situation. Distributed storage and job scheduling and it was the only thing I found that would give me the data location awareness that I wanted. But I don't like the namename being a single point of failure. Also, I'm not really sure if the MapReduce paradigm fits the type of processing workflow that I have. It seems like you need to write all your software specifically for MapReduce instead of just using Hadoop as a generic job scheduler. OpenStack: I've done some reading on this but I'm having trouble deciding if it fits well with my problem or not. Does anyone have opinions or recommendations for technologies that would fit my problem well? Any suggestions or advise would be greatly appreciated. Thanks!

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  • Ipsec config problem // openswan

    - by user90696
    I try to configure Ipsec on server with openswan as client. But receive error - possible, it's auth error. What I wrote wrong in config ? Thank you for answers. #1: STATE_MAIN_I2: sent MI2, expecting MR2 003 "f-net" #1: received Vendor ID payload [Cisco-Unity] 003 "f-net" #1: received Vendor ID payload [Dead Peer Detection] 003 "f-net" #1: ignoring unknown Vendor ID payload [ca917959574c7d5aed4222a9df367018] 003 "f-net" #1: received Vendor ID payload [XAUTH] 108 "f-net" #1: STATE_MAIN_I3: sent MI3, expecting MR3 003 "f-net" #1: discarding duplicate packet; already STATE_MAIN_I3 010 "f-net" #1: STATE_MAIN_I3: retransmission; will wait 20s for response 003 "f-net" #1: discarding duplicate packet; already STATE_MAIN_I3 003 "f-net" #1: discarding duplicate packet; already STATE_MAIN_I3 003 "f-net" #1: discarding duplicate packet; already STATE_MAIN_I3 010 "f-net" #1: STATE_MAIN_I3: retransmission; will wait 40s for response 031 "f-net" #1: max number of retransmissions (2) reached STATE_MAIN_I3. Possible authentication failure: no acceptable response to our first encrypted message 000 "f-net" #1: starting keying attempt 2 of at most 3, but releasing whack other side - Cisco ASA. parameters for my connection on our Linux server : VPN Gateway 8.*.*.* (Cisco ) Phase 1 Exchange Type Main Mode Identification Type IP Address Local ID 4.*.*.* (our Linux server IP) Remote ID 8.*.*.* (VPN server IP) Authentication PSK Pre Shared Key Diffie-Hellman Key Group DH 5 (1536 bit) or DH 2 (1024 bit) Encryption Algorithm AES 256 HMAC Function SHA-1 Lifetime 86.400 seconds / no volume limit Phase 2 Security Protocol ESP Connection Mode Tunnel Encryption Algorithm AES 256 HMAC Function SHA-1 Lifetime 3600 seconds / 4.608.000 kilobytes DPD / IKE Keepalive 15 seconds PFS off Remote Network 192.168.100.0/24 Local Network 1 10.0.0.0/16 ............... Local Network 5 current openswan config : # config setup klipsdebug=all plutodebug="control parsing" protostack=netkey nat_traversal=no virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12 oe=off nhelpers=0 conn f-net type=tunnel keyexchange=ike authby=secret auth=esp esp=aes256-sha1 keyingtries=3 pfs=no aggrmode=no keylife=3600s ike=aes256-sha1-modp1024 # left=4.*.*.* leftsubnet=10.0.0.0/16 leftid=4.*.*.* leftnexthop=%defaultroute right=8.*.*.* rightsubnet=192.168.100.0/24 rightid=8.*.*.* rightnexthop=%defaultroute auto=add

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  • All websites migrated from server running IIS6 to IIS7

    - by Leah
    Hi, I hope someone will be able to help me with this. We have recently migrated all of our clients' sites to a new server running IIS7 - all the sites were originally running on a server running IIS6. Ever since the migration, lots of our clients are reporting error messages. There seems to be quite a number of issues related to sending emails and also, we have had the following error message reported by several different clients: Server Error in '/' Application. -------------------------------------------------------------------------------- Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Web.HttpException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. I have read elsewhere that this error can appear if a button is clicked before the whole page has finished loading. But as this error has now appeared on multiple sites and only since the server migration, it seems to me that it must be something else. I was wondering if someone could tell me if there is something specific which needs to be changed for .NET sites when sites are moved from a server running IIS6 to a server running IIS7? I don't deal with the actual servers very much so I'm afraid this is very much a grey area for me. Any help would be very much appreciated.

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  • Test A SSH Connection from Windows commandline

    - by IguanaMinstrel
    I am looking for a way to test if a SSH server is available from a Windows host. I found this one-liner, but it requires the a Unix/Linux host: ssh -q -o "BatchMode=yes" user@host "echo 2>&1" && echo "UP" || echo "DOWN" Telnet'ing to port 22 works, but that's not really scriptable. I have also played around with Plink, but I haven't found a way to get the functionality of the one-liner above. Does anyone know Plink enough to make this work? Are there any other windows based tools that would work? Please note that the SSH servers in question are behind a corporate firewall and are NOT internet accessible. Arrrg. Figured it out: C:\>plink -batch -v user@host Looking up host "host" Connecting to 10.10.10.10 port 22 We claim version: SSH-2.0-PuTTY_Release_0.62 Server version: SSH-2.0-OpenSSH_4.7p1-hpn12v17_q1.217 Using SSH protocol version 2 Server supports delayed compression; will try this later Doing Diffie-Hellman group exchange Doing Diffie-Hellman key exchange with hash SHA-256 Host key fingerprint is: ssh-rsa 1024 aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa:aa Initialised AES-256 SDCTR client->server encryption Initialised HMAC-SHA1 client->server MAC algorithm Initialised AES-256 SDCTR server->client encryption Initialised HMAC-SHA1 server->client MAC algorithm Using username "user". Using SSPI from SECUR32.DLL Attempting GSSAPI authentication GSSAPI authentication initialised GSSAPI authentication initialised GSSAPI authentication loop finished OK Attempting keyboard-interactive authentication Disconnected: Unable to authenticate C:\>

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  • Estimating compressed file size using a list parameter

    - by Sai
    I am currently compressing a list of files from a directory in the following format: tar -cvjf test_1.tar.gz -T test_1.lst --no-recursion The above command will compress only those files mentioned in the list. I am doing this because this list is generated such that it fits a DVD. However, during compression the compression rate decreases the estimated file size and there is abundant space left in the DVD. This is something like a Knapsack algorithm. I would like to estimate the compressed file size and add some more files to the list. I found that it is possible to estimate file size using the following command: tar -cjf - Folder/ | wc -c This command does not take a list parameter. Is there a way to estimate compressed file size? I am also looking into options like perl scripts etc. Edit: I think I should provide more information since I have been doing a lot of web search. I came across a perl script(Link)that sort of emulates the Knapsack algorithm. The current problem with the above mentioned script is that it splits the files in their original state. When I compress the files after splitting them, there are opportunities for adding more files which I consider to be inefficient. There are 2 ways I could resolve the inefficiency: a) Compress individual files and save them in a directory using a script. The compressed file could provide a best estimate. I could generate a script using a folder of compressed files and use them on the uncompressed ones. b) Check whether the compressed file's size is less than the required size. If so, I should keep adding files until I meet the requirement. However, the addition of new files to the compressed file is an optimization problem by itself.

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  • EFS Remote Encryption

    - by Apoulet
    We have been trying to setup EFS across our domain. Unfortunately Reading/Writing file over network share does not work, we get an "Access Denied" error. Another worrying fact is that I managed to get it working for 1 machine but no other would work. The machines are all Windows 2008R2, running as VM under ESXi host. According to: http://technet.microsoft.com/en-us/library/bb457116.aspx#EHAA We setup the involved machine to be trusted for delegation The user are not restricted and can be trusted for delegation. The users have logged-in on both side and can read/write encrypted files without issues locally. I enabled Kerberos logging in the registry and this is the relevant logs that I get on the machine that has the encrypted files. In order for all certificate that the user possess (Only Key Name changes): Event ID 5058: Audit Success, "Other System Events" Key file operation. Subject: Security ID: {MyDOMAIN}\{MyID} Account Name: {MyID} Account Domain: {MyDOMAIN} Logon ID: 0xbXXXXXXX Cryptographic Parameters: Provider Name: Microsoft Software Key Storage Provider Algorithm Name: Not Available. Key Name: {CE885431-9B4F-47C2-8415-2D766B999999} Key Type: User key. Key File Operation Information: File Path: C:\Users\{MyID}\AppData\Roaming\Microsoft\Crypto\RSA\S-1-5-21-4585646465656-260371901-2912106767-1207\66099999999991e891f187e791277da03d_dfe9ecd8-31c4-4b0f-9b57-6fd3cab90760 Operation: Read persisted key from file. Return Code: 0x0[/code] Event ID 5061: Audit Faillure, "System Intergrity" [code]Cryptographic operation. Subject: Security ID: {MyDOMAIN}\{MyID} Account Name: {MyID} Account Domain: {MyDOMAIN} Logon ID: 0xbXXXXXXX Cryptographic Parameters: Provider Name: Microsoft Software Key Storage Provider Algorithm Name: RSA Key Name: {CE885431-9B4F-47C2-8415-2D766B999999} Key Type: User key. Cryptographic Operation: Operation: Open Key. Return Code: 0x8009000b Could this be related to this error from the CryptAcquireContext function NTE_BAD_KEY_STATE 0x8009000BL The user password has changed since the private keys were encrypted. The problem is that the users I using at the moment can not change their password.

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  • How does Windows 7 taskbar "color hot-tracking" feature calculate the colour to use?

    - by theyetiman
    This has intrigued me for quite some time. Does anyone know the algorithm Windows 7 Aero uses to determine the colour to use as the hot-tracking hover highlight on taskbar buttons for currently-running apps? It is definitely based on the icon of the app, but I can't see a specific pattern of where it's getting the colour value from. It doesn't seem to be any of the following: An average colour value from the entire icon, otherwise you would get brown all the time with multi-coloured icons like Chrome. The colour used the most in the image, otherwise you'd get yellow for the SQL Server Management Studio icon (6th from left). Also, the Chrome icon used red, green and yellow in equal measure. A colour located at certain pixel coordinates within the icon, because Chrome is red -indicating the top of the icon - and Notepad++ (2nd from right) is green - indicating the bottom of the icon. I asked this question on ux.stackoverflow.com and it got closed as off-topic, but someone answered with the following: As described by Raymond Chen in this MSDN blog article: Some people ask how it's done. It's really nothing special. The code just looks for the predominant color in the icon. (And, since visual designers are sticklers for this sort of thing, black, white, and shades of gray are not considered "colors" for the purpose of this calculation.) However I wasn't really satisfied with that answer because it doesn't explain how the "predominant" colour is calculated. Surely on the SQL Management Studio icon, the predominant colour, to my eyes at least, is yellow. Yet the highlight is green. I want to know, specifically, what the algorithm is.

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  • Windows media scaling/interpolation method

    - by MichaelH
    Usually in Windows, if videos or other media is upscaled from a certain resolution to a higher resolution (e.g. "monitor size"), a bilinear filtering algorithm or similar is used, such that the upscaled material doesn't look blocky. On my system however, the used interpolation algorithm changed from 'bilinear' to 'nearest neighbor' at some point, with the effect that upscaled videos (e.g. viewed in MPC or WMP, and also Skype video streams) and games (e.g. from PopCap) appear rather blocky. Not sure what the common factor between those is, could be DirectShow(?). I am not aware of having changed any setting that could have affected this state, in fact I am not even aware such a setting exists. I'm guesing that some installed software must have changed something on my computer. My computer is running Windows 7, but I had already experienced the same effect on an XP machine some while ago, where it changed back again to the more pleasing bilinear interpolation after a while, as magically as the first time. What could be wrong with this installation, and how can I change this upscaling interpolation behavior?

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  • How many guesses per second are possible against an encrypted disk? [closed]

    - by HappyDeveloper
    I understand that guesses per second depends on the hardware and the encryption algorithm, so I don't expect an absolute number as answer. For example, with an average machine you can make a lot (thousands?) of guesses per second for a hash created with a single md5 round, because md5 is fast, making brute force and dictionary attacks a real danger for most passwords. But if instead you use bcrypt with enough rounds, you can slow the attack down to 1 guess per second, for example. 1) So how does disk encryption usually work? This is how I imagine it, tell me if it is close to reality: When I enter the passphrase, it is hashed with a slow algorithm to generate a key (always the same?). Because this is slow, brute force is not a good approach to break it. Then, with the generated key, the disk is unencrypted on the fly very fast, so there is not a significant performance lose. 2) How can I test this with my own machine? I want to calculate the guesses per second my machine can make. 3) How many guesses per second are possible against an encrypted disk with the fastest PC ever so far?

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  • Silverlight Recruiting Application Part 4 - Navigation and Modules

    After our brief intermission (and the craziness of Q1 2010 release week), we're back on track here and today we get to dive into how we are going to navigate through our applications as well as how to set up our modules. That way, as I start adding the functionality- adding Jobs and Applicants, Interview Scheduling, and finally a handy Dashboard- you'll see how everything is communicating back and forth. This is all leading up to an eventual webinar, in which I'll dive into this process and give a honest look at the current story for MVVM vs. Code-Behind applications. (For a look at the future with SL4 and a little thing called MEF, check out what Ross is doing over at his blog!) Preamble... Before getting into really talking about this app, I've done a little bit of work ahead of time to create a ton of files that I'll need. Since the webinar is going to cover the Dashboard, it's not here, but otherwise this is a look at what the project layout looks like (and remember, this is both projects since they share the .Web): So as you can see, from an architecture perspective, the code-behind app is much smaller and more streamlined- aka a better fit for the one man shop that is me. Each module in the MVVM app has the same setup, which is the Module class and corresponding Views and ViewModels. Since the code-behind app doesn't need a go-between project like Infrastructure, each MVVM module is instead replaced by a single Silverlight UserControl which will contain all the logic for each respective bit of functionality. My Very First Module Navigation is going to be key to my application, so I figured the first thing I would setup is my MenuModule. First step here is creating a Silverlight Class Library named MenuModule, creatingthe View and ViewModel folders, and adding the MenuModule.cs class to handle module loading. The most important thing here is that my MenuModule inherits from IModule, which runs an Initialize on each module as it is created that, in my case, adds the views to the correct regions. Here's the MenuModule.cs code: public class MenuModule : IModule { private readonly IRegionManager regionManager; private readonly IUnityContainer container; public MenuModule(IUnityContainer container, IRegionManager regionmanager) { this.container = container; this.regionManager = regionmanager; } public void Initialize() { var addMenuView = container.Resolve<MenuView>(); regionManager.Regions["MenuRegion"].Add(addMenuView); } } Pretty straightforward here... We inject a container and region manager from Prism/Unity, then upon initialization we grab the view (out of our Views folder) and add it to the region it needs to live in. Simple, right? When the MenuView is created, the only thing in the code-behind is a reference to the set the MenuViewModel as the DataContext. I'd like to achieve MVVM nirvana and have zero code-behind by placing the viewmodel in the XAML, but for the reasons listed further below I can't. Navigation - MVVM Since navigation isn't the biggest concern in putting this whole thing together, I'm using the Button control to handle different options for loading up views/modules. There is another reason for this- out of the box, Prism has command support for buttons, which is one less custom command I had to work up for the functionality I would need. This comes from the Microsoft.Practices.Composite.Presentation assembly and looks as follows when put in code: <Button x:Name="xGoToJobs" Style="{StaticResource menuStyle}" Content="Jobs" cal:Click.Command="{Binding GoModule}" cal:Click.CommandParameter="JobPostingsView" /> For quick reference, 'menuStyle' is just taking care of margins and spacing, otherwise it looks, feels, and functions like everyone's favorite Button. What MVVM's this up is that the Click.Command is tying to a DelegateCommand (also coming fromPrism) on the backend. This setup allows you to tie user interaction to a command you setup in your viewmodel, which replaces the standard event-based setup you'd see in the code-behind app. Due to databinding magic, it all just works. When we get looking at the DelegateCommand in code, it ends up like this: public class MenuViewModel : ViewModelBase { private readonly IRegionManager regionManager; public DelegateCommand<object> GoModule { get; set; } public MenuViewModel(IRegionManager regionmanager) { this.regionManager = regionmanager; this.GoModule = new DelegateCommand<object>(this.goToView); } public void goToView(object obj) { MakeMeActive(this.regionManager, "MainRegion", obj.ToString()); } } Another for reference, ViewModelBase takes care of iNotifyPropertyChanged and MakeMeActive, which switches views in the MainRegion based on the parameters. So our public DelegateCommand GoModule ties to our command on the view, that in turn calls goToView, and the parameter on the button is the name of the view (which we pass with obj.ToString()) to activate. And how do the views get the names I can pass as a string? When I called regionManager.Regions[regionname].Add(view), there is an overload that allows for .Add(view, "viewname"), with viewname being what I use to activate views. You'll see that in action next installment, just wanted to clarify how that works. With this setup, I create two more buttons in my MenuView and the MenuModule is good to go. Last step is to make sure my MenuModule loads in my Bootstrapper: protected override IModuleCatalog GetModuleCatalog() { ModuleCatalog catalog = new ModuleCatalog(); // add modules here catalog.AddModule(typeof(MenuModule.MenuModule)); return catalog; } Clean, simple, MVVM-delicious. Navigation - Code-Behind Keeping with the history of significantly shorter code-behind sections of this series, Navigation will be no different. I promise. As I explained in a prior post, due to the one-project setup I don't have to worry about the same concerns so my menu is part of MainPage.xaml. So I can cheese-it a bit, though, since I've already got three buttons all set I'm just copying that code and adding three click-events instead of the command/commandparameter setup: <!-- Menu Region --> <StackPanel Grid.Row="1" Orientation="Vertical"> <Button x:Name="xJobsButton" Content="Jobs" Style="{StaticResource menuStyleCB}" Click="xJobsButton_Click" /> <Button x:Name="xApplicantsButton" Content="Applicants" Style="{StaticResource menuStyleCB}" Click="xApplicantsButton_Click" /> <Button x:Name="xSchedulingModule" Content="Scheduling" Style="{StaticResource menuStyleCB}" Click="xSchedulingModule_Click" /> </StackPanel> Simple, easy to use events, and no extra assemblies required! Since the code for loading each view will be similar, we'll focus on JobsView for now.The code-behind with this setup looks something like... private JobsView _jobsView; public MainPage() { InitializeComponent(); } private void xJobsButton_Click(object sender, RoutedEventArgs e) { if (MainRegion.Content.GetType() != typeof(JobsView)) { if (_jobsView == null) _jobsView = new JobsView(); MainRegion.Content = _jobsView; } } What am I doing here? First, for each 'view' I create a private reference which MainPage will hold on to. This allows for a little bit of state-maintenance when switching views. When a button is clicked, first we make sure the 'view' typeisn't active (why load it again if it is already at center stage?), then we check if the view has been created and create if necessary, then load it up. Three steps to switching views and is easy as pie. Part 4 Results The end result of all this is that I now have a menu module (MVVM) and a menu section (code-behind) that load their respective views. Since I'm using the same exact XAML (except with commands/events depending on the project), the end result for both is again exactly the same and I'll show a slightly larger image to show it off: Next time, we add the Jobs Module and wire up RadGridView and a separate edit page to handle adding and editing new jobs. That's when things get fun. And somewhere down the line, I'll make the menu look slicker. :) Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Quartz.Net Windows Service Configure Logging

    - by Tarun Arora
    In this blog post I’ll be covering, Logging for Quartz.Net Windows Service 01 – Why doesn’t Quartz.Net Windows Service log by default 02 – Configuring Quartz.Net windows service for logging to eventlog, file, console, etc 03 – Results: Logging in action If you are new to Quartz.Net I would recommend going through, A brief Introduction to Quartz.net Walkthrough of Installing & Testing Quartz.Net as a Windows Service Writing & Scheduling your First HelloWorld job with Quartz.Net   01 – Why doesn’t Quartz.Net Windows Service log by default If you are trying to figure out why… The Quartz.Net windows service isn’t logging The Quartz.Net windows service isn’t writing anything to the event log The Quartz.Net windows service isn’t writing anything to a file How do I configure Quartz.Net windows service to use log4Net How do I change the level of logging for Quartz.Net Look no further, This blog post should help you answer these questions. Quartz.NET uses the Common.Logging framework for all of its logging needs. If you navigate to the directory where Quartz.Net Windows Service is installed (I have the service installed in C:\Program Files (x86)\Quartz.net, you can find out the location by looking at the properties of the service) and open ‘Quartz.Server.exe.config’ you’ll see that the Quartz.Net is already set up for logging to ConsoleAppender and EventLogAppender, but only ‘ConsoleAppender’ is set up as active. So, unless you have the console associated to the Quartz.Net service you won’t be able to see any logging. <log4net> <appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender"> <layout type="log4net.Layout.PatternLayout"> <conversionPattern value="%d [%t] %-5p %l - %m%n" /> </layout> </appender> <appender name="EventLogAppender" type="log4net.Appender.EventLogAppender"> <layout type="log4net.Layout.PatternLayout"> <conversionPattern value="%d [%t] %-5p %l - %m%n" /> </layout> </appender> <root> <level value="INFO" /> <appender-ref ref="ConsoleAppender" /> <!-- uncomment to enable event log appending --> <!-- <appender-ref ref="EventLogAppender" /> --> </root> </log4net> Problem: In the configuration above Quartz.Net Windows Service only has ConsoleAppender active. So, no logging will be done to EventLog. More over the RollingFileAppender isn’t setup at all. So, Quartz.Net will not log to an application trace log file. 02 – Configuring Quartz.Net windows service for logging to eventlog, file, console, etc Let’s change this behaviour by changing the config file… In the below config file, I have added the RollingFileAppender. This will configure Quartz.Net service to write to a log file. (<appender name="GeneralLog" type="log4net.Appender.RollingFileAppender">) I have specified the location for the log file (<arg key="configFile" value="Trace/application.log.txt"/>) I have enabled the EventLogAppender and RollingFileAppender to be written to by Quartz. Net windows service Changed the default level of logging from ‘Info’ to ‘All’. This means all activity performed by Quartz.Net Windows service will be logged. You might want to tune this back to ‘Debug’ or ‘Info’ later as logging ‘All’ will produce too much data to the logs. (<level value="ALL"/>) Since I have changed the logging level to ‘All’, I have added applicationSetting to remove logging log4Net internal debugging. (<add key="log4net.Internal.Debug" value="false"/>) <?xml version="1.0" encoding="utf-8" ?> <configuration> <configSections> <section name="quartz" type="System.Configuration.NameValueSectionHandler, System, Version=1.0.5000.0,Culture=neutral, PublicKeyToken=b77a5c561934e089" /> <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" /> <sectionGroup name="common"> <section name="logging" type="Common.Logging.ConfigurationSectionHandler, Common.Logging" /> </sectionGroup> </configSections> <common> <logging> <factoryAdapter type="Common.Logging.Log4Net.Log4NetLoggerFactoryAdapter, Common.Logging.Log4net"> <arg key="configType" value="INLINE" /> <arg key="configFile" value="Trace/application.log.txt"/> <arg key="level" value="ALL" /> </factoryAdapter> </logging> </common> <appSettings> <add key="log4net.Internal.Debug" value="false"/> </appSettings> <log4net> <appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender"> <layout type="log4net.Layout.PatternLayout"> <conversionPattern value="%d [%t] %-5p %l - %m%n" /> </layout> </appender> <appender name="EventLogAppender" type="log4net.Appender.EventLogAppender"> <layout type="log4net.Layout.PatternLayout"> <conversionPattern value="%d [%t] %-5p %l - %m%n" /> </layout> </appender> <appender name="GeneralLog" type="log4net.Appender.RollingFileAppender"> <file value="Trace/application.log.txt"/> <appendToFile value="true"/> <maximumFileSize value="1024KB"/> <rollingStyle value="Size"/> <layout type="log4net.Layout.PatternLayout"> <conversionPattern value="%d{HH:mm:ss} [%t] %-5p %c - %m%n"/> </layout> </appender> <root> <level value="ALL" /> <appender-ref ref="ConsoleAppender" /> <appender-ref ref="EventLogAppender" /> <appender-ref ref="GeneralLog"/> </root> </log4net> </configuration>   Note – Please ensure you restart the Quartz.Net Windows service for the config changes to be picked up by the service   03 – Results: Logging in action Once you start the Quartz.Net Windows Service up, the logging should be initiated to write all activities in the Console, EventLog and File… See screen shots below… Figure – Quartz.Net Windows Service logging all activity to the event log Figure – Quartz.Net Windows Service logging all activity to the application log file Where is the output from log4Net ConsoleAppender? As a default behaviour, the console isn't available in windows services, web services, windows forms. The output will simply be dismissed. Unless you are running the process interactively. Which you can do by firing up Quartz.Server.exe –i to see the output   This was fourth in the series of posts on enterprise scheduling using Quartz.net, in the next post I’ll be covering troubleshooting why a scheduled task hasn’t fired on Quartz.net windows service. All Quartz.Net specific blog posts can listed here. Thank you for taking the time out and reading this blog post. If you enjoyed the post, remember to subscribe to http://feeds.feedburner.com/TarunArora. Stay tuned!

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  • Thread placement policies on NUMA systems - update

    - by Dave
    In a prior blog entry I noted that Solaris used a "maximum dispersal" placement policy to assign nascent threads to their initial processors. The general idea is that threads should be placed as far away from each other as possible in the resource topology in order to reduce resource contention between concurrently running threads. This policy assumes that resource contention -- pipelines, memory channel contention, destructive interference in the shared caches, etc -- will likely outweigh (a) any potential communication benefits we might achieve by packing our threads more densely onto a subset of the NUMA nodes, and (b) benefits of NUMA affinity between memory allocated by one thread and accessed by other threads. We want our threads spread widely over the system and not packed together. Conceptually, when placing a new thread, the kernel picks the least loaded node NUMA node (the node with lowest aggregate load average), and then the least loaded core on that node, etc. Furthermore, the kernel places threads onto resources -- sockets, cores, pipelines, etc -- without regard to the thread's process membership. That is, initial placement is process-agnostic. Keep reading, though. This description is incorrect. On Solaris 10 on a SPARC T5440 with 4 x T2+ NUMA nodes, if the system is otherwise unloaded and we launch a process that creates 20 compute-bound concurrent threads, then typically we'll see a perfect balance with 5 threads on each node. We see similar behavior on an 8-node x86 x4800 system, where each node has 8 cores and each core is 2-way hyperthreaded. So far so good; this behavior seems in agreement with the policy I described in the 1st paragraph. I recently tried the same experiment on a 4-node T4-4 running Solaris 11. Both the T5440 and T4-4 are 4-node systems that expose 256 logical thread contexts. To my surprise, all 20 threads were placed onto just one NUMA node while the other 3 nodes remained completely idle. I checked the usual suspects such as processor sets inadvertently left around by colleagues, processors left offline, and power management policies, but the system was configured normally. I then launched multiple concurrent instances of the process, and, interestingly, all the threads from the 1st process landed on one node, all the threads from the 2nd process landed on another node, and so on. This happened even if I interleaved thread creating between the processes, so I was relatively sure the effect didn't related to thread creation time, but rather that placement was a function of process membership. I this point I consulted the Solaris sources and talked with folks in the Solaris group. The new Solaris 11 behavior is intentional. The kernel is no longer using a simple maximum dispersal policy, and thread placement is process membership-aware. Now, even if other nodes are completely unloaded, the kernel will still try to pack new threads onto the home lgroup (socket) of the primordial thread until the load average of that node reaches 50%, after which it will pick the next least loaded node as the process's new favorite node for placement. On the T4-4 we have 64 logical thread contexts (strands) per socket (lgroup), so if we launch 48 concurrent threads we will find 32 placed on one node and 16 on some other node. If we launch 64 threads we'll find 32 and 32. That means we can end up with our threads clustered on a small subset of the nodes in a way that's quite different that what we've seen on Solaris 10. So we have a policy that allows process-aware packing but reverts to spreading threads onto other nodes if a node becomes too saturated. It turns out this policy was enabled in Solaris 10, but certain bugs suppressed the mixed packing/spreading behavior. There are configuration variables in /etc/system that allow us to dial the affinity between nascent threads and their primordial thread up and down: see lgrp_expand_proc_thresh, specifically. In the OpenSolaris source code the key routine is mpo_update_tunables(). This method reads the /etc/system variables and sets up some global variables that will subsequently be used by the dispatcher, which calls lgrp_choose() in lgrp.c to place nascent threads. Lgrp_expand_proc_thresh controls how loaded an lgroup must be before we'll consider homing a process's threads to another lgroup. Tune this value lower to have it spread your process's threads out more. To recap, the 'new' policy is as follows. Threads from the same process are packed onto a subset of the strands of a socket (50% for T-series). Once that socket reaches the 50% threshold the kernel then picks another preferred socket for that process. Threads from unrelated processes are spread across sockets. More precisely, different processes may have different preferred sockets (lgroups). Beware that I've simplified and elided details for the purposes of explication. The truth is in the code. Remarks: It's worth noting that initial thread placement is just that. If there's a gross imbalance between the load on different nodes then the kernel will migrate threads to achieve a better and more even distribution over the set of available nodes. Once a thread runs and gains some affinity for a node, however, it becomes "stickier" under the assumption that the thread has residual cache residency on that node, and that memory allocated by that thread resides on that node given the default "first-touch" page-level NUMA allocation policy. Exactly how the various policies interact and which have precedence under what circumstances could the topic of a future blog entry. The scheduler is work-conserving. The x4800 mentioned above is an interesting system. Each of the 8 sockets houses an Intel 7500-series processor. Each processor has 3 coherent QPI links and the system is arranged as a glueless 8-socket twisted ladder "mobius" topology. Nodes are either 1 or 2 hops distant over the QPI links. As an aside the mapping of logical CPUIDs to physical resources is rather interesting on Solaris/x4800. On SPARC/Solaris the CPUID layout is strictly geographic, with the highest order bits identifying the socket, the next lower bits identifying the core within that socket, following by the pipeline (if present) and finally the logical thread context ("strand") on the core. But on Solaris on the x4800 the CPUID layout is as follows. [6:6] identifies the hyperthread on a core; bits [5:3] identify the socket, or package in Intel terminology; bits [2:0] identify the core within a socket. Such low-level details should be of interest only if you're binding threads -- a bad idea, the kernel typically handles placement best -- or if you're writing NUMA-aware code that's aware of the ambient placement and makes decisions accordingly. Solaris introduced the so-called critical-threads mechanism, which is expressed by putting a thread into the FX scheduling class at priority 60. The critical-threads mechanism applies to placement on cores, not on sockets, however. That is, it's an intra-socket policy, not an inter-socket policy. Solaris 11 introduces the Power Aware Dispatcher (PAD) which packs threads instead of spreading them out in an attempt to be able to keep sockets or cores at lower power levels. Maximum dispersal may be good for performance but is anathema to power management. PAD is off by default, but power management polices constitute yet another confounding factor with respect to scheduling and dispatching. If your threads communicate heavily -- one thread reads cache lines last written by some other thread -- then the new dense packing policy may improve performance by reducing traffic on the coherent interconnect. On the other hand if your threads in your process communicate rarely, then it's possible the new packing policy might result on contention on shared computing resources. Unfortunately there's no simple litmus test that says whether packing or spreading is optimal in a given situation. The answer varies by system load, application, number of threads, and platform hardware characteristics. Currently we don't have the necessary tools and sensoria to decide at runtime, so we're reduced to an empirical approach where we run trials and try to decide on a placement policy. The situation is quite frustrating. Relatedly, it's often hard to determine just the right level of concurrency to optimize throughput. (Understanding constructive vs destructive interference in the shared caches would be a good start. We could augment the lines with a small tag field indicating which strand last installed or accessed a line. Given that, we could augment the CPU with performance counters for misses where a thread evicts a line it installed vs misses where a thread displaces a line installed by some other thread.)

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  • Massive Silverlight Giveaway! DevExpress , Syncfusion, Crypto Obfuscator and SL Spy!

    - by mbcrump
    Oh my, have we grown! Maybe I should change the name to Multiple Silverlight Giveaways. So far, my Silverlight giveaways have been such a success that I’m going to be able to give away more than one Silverlight product every month. Last month, we gave away 3 great products. 1) ComponentOne Silverlight Controls 2)  ComponentOne XAP Optimizer (with obfuscation) and 3) Silverlight Spy. This month, we will give away 4 great Silverlight products and have 4 different winners. This way the Silverlight community can grow with more than just one person winning all the prizes. This month we will be giving away: DevExpress Silverlight Controls – Over 50+ Silverlight Controls Syncfusion User Interface Edition - Create stunning line of business silverlight applications with a wide range of components including a high performance grid, docking manager, chart, gauge, scheduler and much more. Crypto Obfuscator – Works for all .NET including Silverlight/Windows Phone 7. Silverlight Spy – provides a license EVERY month for this giveaway. ----------------------------------------------------------------------------------------------------------------------------------------------------------- Win a FREE developer’s license of one of the products listed above! 4 winners will be announced on April 1st, 2011! To be entered into the contest do the following things: Subscribe to my feed. – Use Google Reader, email or whatever is best for you.  Leave a comment below with a valid email account (I WILL NOT share this info with anyone.) Retweet the following : I just entered to win free #Silverlight controls from @mbcrump . Register here: http://mcrump.me/fTSmB8 ! Don’t change the URL because this will allow me to track the users that Tweet this page. Don’t forget to visit each of the vendors sites because they made this possible. MichaelCrump.Net provides Silverlight Giveaways every month. You can also see the latest giveaway by bookmarking http://giveaways.michaelcrump.net . ---------------------------------------------------------------------------------------------------------------------------------------------------------- DevExpress Silverlight Controls Let’s take a quick look at some of the software that is provided in this giveaway. Before we get started with the Silverlight Controls, here is a couple of links to bookmark for the DevExpress Silverlight Controls: The Live Demos of the Silverlight Controls is located here. Great Video Tutorials of the Silverlight Controls are here. One thing that I liked about the DevExpress is how easy it was to find demos of each control. After you install the controls the following Program Group appears complete with “demos” that include full-source.   So, the first question that you may ask is, “What is included?” Here is the official list below. I wanted to show several of the controls that I think developers will use the most. The Book – Very rich animation between switching pages. Very easy to add your own images and custom text. The Menu – This is another control that just looked great. You can easily add images to the menu items with a few lines of XAML. The Window / Dialog Box – You can use this control to make a very beautiful “Wizard” to help your users navigate between pages. This is useful in setup or installation. Calculator – This would be useful for any type of Banking app. Also a first that I’ve seen from a 3rd party Control company. DatePicker – This controls feels a lot smoother than the one provided by Microsoft. It also provides the ability to “Clear” the selection. Overall the DevExpress Silverlight Controls feature a lot of quality controls that you should check out. You can go ahead and download a trial version of it right now by clicking here. If you win the contest you can simply enter your registration key and continue using the product without reinstalling. Syncfusion User Interface Edition Before we get started with the Syncfusion User Interface Edition, here is a couple of links to bookmark. The Live Demos can be found here. You can download a demo of it now at http://www.syncfusion.com/downloads/evalstart. After you install the Syncfusion, you can view the dashboard to run locally installed samples. You may also download the documentation to your local machine if needed. Since the name of the package is “User Interface Edition”, I decided to share several samples that struck me as “awesome”. Dashboard Gauges – I was very impressed with the various gauges they have included. The digital clock also looks very impressive. Diagram – The diagrams are also very easy to build. In the sample project below you can drag/drop the shapes onto the content pane. More complex lines like the Bezier lines are also easy to create using Syncfusion. Scheduling – Another strong component was the Scheduling with built-in support for Themes. Tools – If all of that wasn’t enough, it also comes with a nice pack of essential tools. Syncfusion has a nice variety of Silverlight Controls that you should check out. You can go ahead and download a trial version of it right now by clicking here. Crypto Obfuscator The following feature set is what is important to me in an Obfuscator since I am a Silverlight/WP7 Developer: And thankfully this is what you get in Crypto Obfuscator. You can download a trial version right now if you want to go ahead and play with it. Let’s spend a few moments taking a look at the application. After you have installed Crypto Obfuscator you will see the following screen: After you click on Assemblies you have the option to add your .XAP file in: I went ahead and loaded my .xap file from a Silverlight Application. At this point, you can simply save your project and hit “Obfuscate” and your done. You don’t have to mess with any of the other settings if you don’t want too. Of course, you can change the settings and add obfuscation rules, watermarks and signing if you wish.  After Obfuscation, it looks like this in .NET Reflector: I was trying to browse through methods and it actually crashed Reflector. This confirms the level of protection the obfuscator is providing. If this were a commercial application that my team built, I would have a huge smile on my face right now. Crypto Obfuscator is a great product and I hope you will spend the time learning more about it. Silverlight Spy Silverlight Spy is a runtime inspector tool that will tell you pretty much everything that is going on with the application. Basically, you give it a URL that contains a Silverlight application and you can explore the element tree, events, xaml and so much more. This has already been reviewed on MichaelCrump.net. _________________________________________________________________________________________ Thanks for reading and don’t forget to leave a comment below in order to win one of the four prizes available! Subscribe to my feed

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  • Implementation of ZipCrypto / Zip 2.0 encryption in java

    - by gomesla
    I'm trying o implement the zipcrypto / zip 2.0 encryption algoritm to deal with encrypted zip files as discussed in http://www.pkware.com/documents/casestudies/APPNOTE.TXT I believe I've followed the specs but just can't seem to get it working. I'm fairly sure the issue has to do with my interpretation of the crc algorithm. The documentation states CRC-32: (4 bytes) The CRC-32 algorithm was generously contributed by David Schwaderer and can be found in his excellent book "C Programmers Guide to NetBIOS" published by Howard W. Sams & Co. Inc. The 'magic number' for the CRC is 0xdebb20e3. The proper CRC pre and post conditioning is used, meaning that the CRC register is pre-conditioned with all ones (a starting value of 0xffffffff) and the value is post-conditioned by taking the one's complement of the CRC residual. Here is the snippet that I'm using for the crc32 public class PKZIPCRC32 { private static final int CRC32_POLYNOMIAL = 0xdebb20e3; private int crc = 0xffffffff; private int CRCTable[]; public PKZIPCRC32() { buildCRCTable(); } private void buildCRCTable() { int i, j; CRCTable = new int[256]; for (i = 0; i <= 255; i++) { crc = i; for (j = 8; j > 0; j--) if ((crc & 1) == 1) crc = (crc >>> 1) ^ CRC32_POLYNOMIAL; else crc >>>= 1; CRCTable[i] = crc; } } private int crc32(byte buffer[], int start, int count, int lastcrc) { int temp1, temp2; int i = start; crc = lastcrc; while (count-- != 0) { temp1 = crc >>> 8; temp2 = CRCTable[(crc ^ buffer[i++]) & 0xFF]; crc = temp1 ^ temp2; } return crc; } public int crc32(int crc, byte buffer) { return crc32(new byte[] { buffer }, 0, 1, crc); } } Below is my complete code. Can anyone see what I'm doing wrong. package org.apache.commons.compress.archivers.zip; import java.io.IOException; import java.io.InputStream; public class ZipCryptoInputStream extends InputStream { public class PKZIPCRC32 { private static final int CRC32_POLYNOMIAL = 0xdebb20e3; private int crc = 0xffffffff; private int CRCTable[]; public PKZIPCRC32() { buildCRCTable(); } private void buildCRCTable() { int i, j; CRCTable = new int[256]; for (i = 0; i <= 255; i++) { crc = i; for (j = 8; j > 0; j--) if ((crc & 1) == 1) crc = (crc >>> 1) ^ CRC32_POLYNOMIAL; else crc >>>= 1; CRCTable[i] = crc; } } private int crc32(byte buffer[], int start, int count, int lastcrc) { int temp1, temp2; int i = start; crc = lastcrc; while (count-- != 0) { temp1 = crc >>> 8; temp2 = CRCTable[(crc ^ buffer[i++]) & 0xFF]; crc = temp1 ^ temp2; } return crc; } public int crc32(int crc, byte buffer) { return crc32(new byte[] { buffer }, 0, 1, crc); } } private static final long ENCRYPTION_KEY_1 = 0x12345678; private static final long ENCRYPTION_KEY_2 = 0x23456789; private static final long ENCRYPTION_KEY_3 = 0x34567890; private InputStream baseInputStream = null; private final PKZIPCRC32 checksumEngine = new PKZIPCRC32(); private long[] keys = null; public ZipCryptoInputStream(ZipArchiveEntry zipEntry, InputStream inputStream, String passwd) throws Exception { baseInputStream = inputStream; // Decryption // ---------- // PKZIP encrypts the compressed data stream. Encrypted files must // be decrypted before they can be extracted. // // Each encrypted file has an extra 12 bytes stored at the start of // the data area defining the encryption header for that file. The // encryption header is originally set to random values, and then // itself encrypted, using three, 32-bit keys. The key values are // initialized using the supplied encryption password. After each byte // is encrypted, the keys are then updated using pseudo-random number // generation techniques in combination with the same CRC-32 algorithm // used in PKZIP and described elsewhere in this document. // // The following is the basic steps required to decrypt a file: // // 1) Initialize the three 32-bit keys with the password. // 2) Read and decrypt the 12-byte encryption header, further // initializing the encryption keys. // 3) Read and decrypt the compressed data stream using the // encryption keys. // Step 1 - Initializing the encryption keys // ----------------------------------------- // // Key(0) <- 305419896 // Key(1) <- 591751049 // Key(2) <- 878082192 // // loop for i <- 0 to length(password)-1 // update_keys(password(i)) // end loop // // Where update_keys() is defined as: // // update_keys(char): // Key(0) <- crc32(key(0),char) // Key(1) <- Key(1) + (Key(0) & 000000ffH) // Key(1) <- Key(1) * 134775813 + 1 // Key(2) <- crc32(key(2),key(1) >> 24) // end update_keys // // Where crc32(old_crc,char) is a routine that given a CRC value and a // character, returns an updated CRC value after applying the CRC-32 // algorithm described elsewhere in this document. keys = new long[] { ENCRYPTION_KEY_1, ENCRYPTION_KEY_2, ENCRYPTION_KEY_3 }; for (int i = 0; i < passwd.length(); ++i) { update_keys((byte) passwd.charAt(i)); } // Step 2 - Decrypting the encryption header // ----------------------------------------- // // The purpose of this step is to further initialize the encryption // keys, based on random data, to render a plaintext attack on the // data ineffective. // // Read the 12-byte encryption header into Buffer, in locations // Buffer(0) thru Buffer(11). // // loop for i <- 0 to 11 // C <- buffer(i) ^ decrypt_byte() // update_keys(C) // buffer(i) <- C // end loop // // Where decrypt_byte() is defined as: // // unsigned char decrypt_byte() // local unsigned short temp // temp <- Key(2) | 2 // decrypt_byte <- (temp * (temp ^ 1)) >> 8 // end decrypt_byte // // After the header is decrypted, the last 1 or 2 bytes in Buffer // should be the high-order word/byte of the CRC for the file being // decrypted, stored in Intel low-byte/high-byte order. Versions of // PKZIP prior to 2.0 used a 2 byte CRC check; a 1 byte CRC check is // used on versions after 2.0. This can be used to test if the password // supplied is correct or not. byte[] encryptionHeader = new byte[12]; baseInputStream.read(encryptionHeader); for (int i = 0; i < encryptionHeader.length; i++) { encryptionHeader[i] ^= decrypt_byte(); update_keys(encryptionHeader[i]); } } protected byte decrypt_byte() { byte temp = (byte) (keys[2] | 2); return (byte) ((temp * (temp ^ 1)) >> 8); } @Override public int read() throws IOException { // // Step 3 - Decrypting the compressed data stream // ---------------------------------------------- // // The compressed data stream can be decrypted as follows: // // loop until done // read a character into C // Temp <- C ^ decrypt_byte() // update_keys(temp) // output Temp // end loop int read = baseInputStream.read(); read ^= decrypt_byte(); update_keys((byte) read); return read; } private final void update_keys(byte ch) { keys[0] = checksumEngine.crc32((int) keys[0], ch); keys[1] = keys[1] + (byte) keys[0]; keys[1] = keys[1] * 134775813 + 1; keys[2] = checksumEngine.crc32((int) keys[2], (byte) (keys[1] >> 24)); } }

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  • What is the fastest cyclic synchronization in Java (ExecutorService vs. CyclicBarrier vs. X)?

    - by Alex Dunlop
    Which Java synchronization construct is likely to provide the best performance for a concurrent, iterative processing scenario with a fixed number of threads like the one outlined below? After experimenting on my own for a while (using ExecutorService and CyclicBarrier) and being somewhat surprised by the results, I would be grateful for some expert advice and maybe some new ideas. Existing questions here do not seem to focus primarily on performance, hence this new one. Thanks in advance! The core of the app is a simple iterative data processing algorithm, parallelized to the spread the computational load across 8 cores on a Mac Pro, running OS X 10.6 and Java 1.6.0_07. The data to be processed is split into 8 blocks and each block is fed to a Runnable to be executed by one of a fixed number of threads. Parallelizing the algorithm was fairly straightforward, and it functionally works as desired, but its performance is not yet what I think it could be. The app seems to spend a lot of time in system calls synchronizing, so after some profiling I wonder whether I selected the most appropriate synchronization mechanism(s). A key requirement of the algorithm is that it needs to proceed in stages, so the threads need to sync up at the end of each stage. The main thread prepares the work (very low overhead), passes it to the threads, lets them work on it, then proceeds when all threads are done, rearranges the work (again very low overhead) and repeats the cycle. The machine is dedicated to this task, Garbage Collection is minimized by using per-thread pools of pre-allocated items, and the number of threads can be fixed (no incoming requests or the like, just one thread per CPU core). V1 - ExecutorService My first implementation used an ExecutorService with 8 worker threads. The program creates 8 tasks holding the work and then lets them work on it, roughly like this: // create one thread per CPU executorService = Executors.newFixedThreadPool( 8 ); ... // now process data in cycles while( ...) { // package data into 8 work items ... // create one Callable task per work item ... // submit the Callables to the worker threads executorService.invokeAll( taskList ); } This works well functionally (it does what it should), and for very large work items indeed all 8 CPUs become highly loaded, as much as the processing algorithm would be expected to allow (some work items will finish faster than others, then idle). However, as the work items become smaller (and this is not really under the program's control), the user CPU load shrinks dramatically: blocksize | system | user | cycles/sec 256k 1.8% 85% 1.30 64k 2.5% 77% 5.6 16k 4% 64% 22.5 4096 8% 56% 86 1024 13% 38% 227 256 17% 19% 420 64 19% 17% 948 16 19% 13% 1626 Legend: - block size = size of the work item (= computational steps) - system = system load, as shown in OS X Activity Monitor (red bar) - user = user load, as shown in OS X Activity Monitor (green bar) - cycles/sec = iterations through the main while loop, more is better The primary area of concern here is the high percentage of time spent in the system, which appears to be driven by thread synchronization calls. As expected, for smaller work items, ExecutorService.invokeAll() will require relatively more effort to sync up the threads versus the amount of work being performed in each thread. But since ExecutorService is more generic than it would need to be for this use case (it can queue tasks for threads if there are more tasks than cores), I though maybe there would be a leaner synchronization construct. V2 - CyclicBarrier The next implementation used a CyclicBarrier to sync up the threads before receiving work and after completing it, roughly as follows: main() { // create the barrier barrier = new CyclicBarrier( 8 + 1 ); // create Runable for thread, tell it about the barrier Runnable task = new WorkerThreadRunnable( barrier ); // start the threads for( int i = 0; i < 8; i++ ) { // create one thread per core new Thread( task ).start(); } while( ... ) { // tell threads about the work ... // N threads + this will call await(), then system proceeds barrier.await(); // ... now worker threads work on the work... // wait for worker threads to finish barrier.await(); } } class WorkerThreadRunnable implements Runnable { CyclicBarrier barrier; WorkerThreadRunnable( CyclicBarrier barrier ) { this.barrier = barrier; } public void run() { while( true ) { // wait for work barrier.await(); // do the work ... // wait for everyone else to finish barrier.await(); } } } Again, this works well functionally (it does what it should), and for very large work items indeed all 8 CPUs become highly loaded, as before. However, as the work items become smaller, the load still shrinks dramatically: blocksize | system | user | cycles/sec 256k 1.9% 85% 1.30 64k 2.7% 78% 6.1 16k 5.5% 52% 25 4096 9% 29% 64 1024 11% 15% 117 256 12% 8% 169 64 12% 6.5% 285 16 12% 6% 377 For large work items, synchronization is negligible and the performance is identical to V1. But unexpectedly, the results of the (highly specialized) CyclicBarrier seem MUCH WORSE than those for the (generic) ExecutorService: throughput (cycles/sec) is only about 1/4th of V1. A preliminary conclusion would be that even though this seems to be the advertised ideal use case for CyclicBarrier, it performs much worse than the generic ExecutorService. V3 - Wait/Notify + CyclicBarrier It seemed worth a try to replace the first cyclic barrier await() with a simple wait/notify mechanism: main() { // create the barrier // create Runable for thread, tell it about the barrier // start the threads while( ... ) { // tell threads about the work // for each: workerThreadRunnable.setWorkItem( ... ); // ... now worker threads work on the work... // wait for worker threads to finish barrier.await(); } } class WorkerThreadRunnable implements Runnable { CyclicBarrier barrier; @NotNull volatile private Callable<Integer> workItem; WorkerThreadRunnable( CyclicBarrier barrier ) { this.barrier = barrier; this.workItem = NO_WORK; } final protected void setWorkItem( @NotNull final Callable<Integer> callable ) { synchronized( this ) { workItem = callable; notify(); } } public void run() { while( true ) { // wait for work while( true ) { synchronized( this ) { if( workItem != NO_WORK ) break; try { wait(); } catch( InterruptedException e ) { e.printStackTrace(); } } } // do the work ... // wait for everyone else to finish barrier.await(); } } } Again, this works well functionally (it does what it should). blocksize | system | user | cycles/sec 256k 1.9% 85% 1.30 64k 2.4% 80% 6.3 16k 4.6% 60% 30.1 4096 8.6% 41% 98.5 1024 12% 23% 202 256 14% 11.6% 299 64 14% 10.0% 518 16 14.8% 8.7% 679 The throughput for small work items is still much worse than that of the ExecutorService, but about 2x that of the CyclicBarrier. Eliminating one CyclicBarrier eliminates half of the gap. V4 - Busy wait instead of wait/notify Since this app is the primary one running on the system and the cores idle anyway if they're not busy with a work item, why not try a busy wait for work items in each thread, even if that spins the CPU needlessly. The worker thread code changes as follows: class WorkerThreadRunnable implements Runnable { // as before final protected void setWorkItem( @NotNull final Callable<Integer> callable ) { workItem = callable; } public void run() { while( true ) { // busy-wait for work while( true ) { if( workItem != NO_WORK ) break; } // do the work ... // wait for everyone else to finish barrier.await(); } } } Also works well functionally (it does what it should). blocksize | system | user | cycles/sec 256k 1.9% 85% 1.30 64k 2.2% 81% 6.3 16k 4.2% 62% 33 4096 7.5% 40% 107 1024 10.4% 23% 210 256 12.0% 12.0% 310 64 11.9% 10.2% 550 16 12.2% 8.6% 741 For small work items, this increases throughput by a further 10% over the CyclicBarrier + wait/notify variant, which is not insignificant. But it is still much lower-throughput than V1 with the ExecutorService. V5 - ? So what is the best synchronization mechanism for such a (presumably not uncommon) problem? I am weary of writing my own sync mechanism to completely replace ExecutorService (assuming that it is too generic and there has to be something that can still be taken out to make it more efficient). It is not my area of expertise and I'm concerned that I'd spend a lot of time debugging it (since I'm not even sure my wait/notify and busy wait variants are correct) for uncertain gain. Any advice would be greatly appreciated.

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