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• How to check the backtrace of a "USER process" in the Linux Kernel Crash Dump

  - by Biswajit

  I was trying to debug a USER Process in Linux Crash Dump. The normal steps to go to the crash dump are: Go to the path where the dump is located. Use the command crash kernel_link dump.201104181135. Where kernel_link is a soft link I have created for vmlinux image. Now you will be in the CRASH prompt. If you run the command foreach <PID Of the process> bt Eg: crash> **foreach 6920 bt** **PID: 6920 TASK: ffff88013caaa800 CPU: 1 COMMAND: **"**climmon**"**** #0 [ffff88012d2cd9c8] **schedule** at ffffffff8130b76a #1 [ffff88012d2cdab0] **schedule_timeout** at ffffffff8130bbe7 #2 [ffff88012d2cdb50] **schedule_timeout_uninterruptible** at ffffffff8130bc2a #3 [ffff88012d2cdb60] **__alloc_pages_nodemask** at ffffffff810b9e45 #4 [ffff88012d2cdc60] **alloc_pages_curren**t at ffffffff810e1c8c #5 [ffff88012d2cdc90] **__page_cache_alloc** at ffffffff810b395a #6 [ffff88012d2cdcb0] **__do_page_cache_readahead** at ffffffff810bb592 #7 [ffff88012d2cdd30] **ra_submit** at ffffffff810bb6ba #8 [ffff88012d2cdd40] **filemap_fault** at ffffffff810b3e4e #9 [ffff88012d2cdda0] **__do_fault** at ffffffff810caa5f #10 [ffff88012d2cde50] **handle_mm_fault** at ffffffff810cce69 #11 [ffff88012d2cdf00] **do_page_fault** at ffffffff8130f560 #12 [ffff88012d2cdf50] **page_fault** at ffffffff8130d3f5 RIP: 00007fd02b7e9071 RSP: 0000000040e86ea0 RFLAGS: 00010202 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007fd02b7e9071 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000040e86ec0 RBP: 0000000040e87140 R8: 0000000000000800 R9: 0000000000000000 R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff16ec43d0 R13: 00007fd02bcadf00 R14: 0000000040e87950 R15: 0000000000001000 ORIG_RAX: ffffffffffffffff CS: 0033 SS: 002b If you check the above backtrace it shows the kernel functions used for scheduling/handling page fault but not the functions that were executed in the USER process (here eg. climmon). So I am not able to debug this process as I am not able to see the functions executed in that process. Can any one help me with this case?

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• Java Client .class File Protection

  - by Zac

  I am in the requirements phase of building a JEE application that will most likely run on a GlassFish/JBoss backend (doesn't matter for now). I know I shouldn't be thinking about architecture at requirements time, but one can't help but start to imagine how the components would all snap together :-) Here are some hard, non-flexible requirements on the client-side: (1) The client application will be a Swing box (2) The client is free to download, but will use a subscription model (thus requiring a login mechanism with server-side authentication/authorization, etc.) (3) Yes, Java is the best platform solution for the problem at hand for reasons outside the scope of this post (4) The client-side .class files need safeguarding against decompiling That last (4th) requirement is the basis of this post. I'm not really worried about someone actually decompiling and getting at my source code: in the end, it's just Swing controls driven by some lightweight business logic. I'm worried about a scenario where someone decompiles my code, modifies it to exploit/attack the server, re-compiles, and fires it up. I've envisioned all sorts of nasty solutions, but didn't know if this was a common problem with a common solution for JEE developers. Any thoughts? Not interested in "code obfuscation" techniques! Thanks for any input!

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• Strategy for animating a lot of "LED's" - thread?, UIView animations? NSOperation? (iPhone)

  - by RickiG

  Hi I have to do some different views containing 72 LED lights. I built an LED Class so I can loop through the LED's and set them to different colors (Green, Red, Orange, Blue None etc.). The LED then loads the appropriate .png. This works fine, I loop over the LED's and set them. Now I know that at some time they will need to not just turn on/off change color, but will have to turn on with a small delay. Like an equalizer. I have a 5-10 views containing the 72 LED's and I would like to achieve the above with the minimum amount of memory/CPU strain. for(LED *l in self.ledArray) { [l display:Green]; } I simply loop as shown above and inside the LED is a switch case that does the correct logic. If this were actual LED's and a microController I would use sleep(100) or similar in the loop, but I would really like to avoid stuff like that for obvious reasons. I was thinking that doing a performOnThread withDelay would really be consuming, so would UIView animation changing the alpha and NSOperation would also be a lot of lifting for a small feature. Is there a both efficient and clever way to go around this? Thanks for any inspiration given:)

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• Building a CMS in PHP: Development tools

  - by TRiG

  I'm planning to build a CMS in PHP and MySQL, mainly for my own amusement and education. (Though who knows, I may come up with something useful and cool. Anything's possible.) I'll be asking questions about code architecture etc. later. For now, I'm more interested in development tools. So far, all my playing with code has been done on a web server, and I've edited over FTP. I was thinking it might be quicker to use a localhost. Also, that way, I could use version control (which I've never done before). So, A. How do I set up a localhost server with many subdomains on an Ubuntu 9.10 computer. Is XAMPP for Linux the way to go, or should I use a standard Apache distro? (Or another webserver altogether?) For that matter, is it possible to set up more than one webserver on the same computer, and to use them for different localhost subdomains? B. How do I set up a version control thingy covering all the code (which will be on several subdomains of localhost, and in a few shared folders)? I've read Joel Spolsky's HgInt tutorial, and it makes Mercurial look good. And simple, especially if you're working on your own. C. Should I continue to use gEdit to write HTML/CSS/JS/PHP, or is there a better free editor out there for these languages?

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• Is there a way to get number of connections in Signalr hub group?

  - by pajo

  Here is my problem, I want to track if user is online or offline and notify other clients about it. I'm using hubs and implemented both IConnected and IDisconnect interfaces. My idea was to send notification to all clients when hub detects connect or disconnect. By default when user refreshes page he will get new connection id and eventually previous connection will call disconnect notifying other clients user is offline even though he's actually online. I tired to use my own ConnectionIdFactory returning username for connection id but with multiple tabs opened at some point it will detect user connectionid disconnected and after that client side hub will try to unsuccessfully connect to the hub in endless loop wasting memory and cpu making browser almost unusable. I needed to fix it fast so I removed my factory and now I add every new connection to the group using username, so I can easily notify single user on all connections, but then I have problem of detecting if user is online or offline as I don't know how many active connection user is having. So I'm wondering is there a way to get number of connections in one group? Or if anybody has some better idea how to track when user goes offline? I'm using Signalr 0.4

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• Using SVN post-commit hook to update only files that have been commited

  - by fondie

  I am using an SVN repository for my web development work. I have a development site set up which holds a checkout of the repository. I have set up an SVN post-commit hook so that whenever a commit is made to the repository the development site is updated: cd /home/www/dev_ssl /usr/bin/svn up This works fine but due to the size of the repository the updates take a long time (approx. 3 minutes) which is rather frustrating when making regular commits. What I'd like is to change the post-commit hook to only update those files/directories that have been committed but I don't know how to go about doing this. Updating the "lowest common directory" would probably be the best solution, e.g. If committing the follow files: /branches/feature_x/images/logo.jpg /branches/feature_x/css/screen.css It would update the directory: /branches/feature_x/ Can anyone help me create a solution that achieves this please? Thanks! Update: The repository and development site are located on the same server so network issues shouldn't be involved. CPU usage is very low, and I/O should be ok (it's running on hi-spec dedicated server) The development site is approx. 7.5GB in size and contains approx. 600,000 items, this is mainly due to having multiple branches/tags

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• How to get resultset with stored procedure calls over two linked servers?

  - by räph

  I have problems filling a temporary table with the resultset from a procedure call on a linked server, in which again a procedure on another server is called. I have a Stored Procedure sproc1 with the following code, which calls another procedure sproc2 on a linked server. SET @sqlCommand = 'INSERT INTO #tblTemp ( ModuleID, ParamID) ' + '( SELECT * FROM OPENQUERY(' + @targetServer + ', ' + '''SET FMTONLY OFF; EXEC ' + @targetDB + '.usr.sproc2 ' + @param + ''' ) )' exec ( @sqlCommand ) Now in the called sproc2 I again call a third procedure sproc3 on another linked server, which returns my resultset. SET @sqlCommand = 'EXEC ' + @targetServer +'.database.usr.sproc3 ' + @param exec ( @sqlCommand ) The whole thing doen't work, as I get an SQL error 7391 The operation could not be performed because OLE DB provider "%ls" for linked server "%ls" was unable to begin a distributed transaction. I already checked the hints at this microsoft article, but without success. But maybe, I can change the code in sproc1. Would there be some alternative to the temp table and the open query? Just calling stored procedures from server A to B to C and returning the resultset is working (I do this often in the application). But this special case with the temp table and openquery doesn't work! Or is it just not possible what I am trying to do? The microsft article states: Check the object you refer on the destination server. If it is a view or a stored procedure, or causes an execution of a trigger, check whether it implicitly references another server. If so, the third server is the source of the problem. Run the query directly on the third server. If you cannot run the query directly on the third server, the problem is not actually with the linked server query. Resolve the underlying problem first. Is this my case? PS: I can't avoid the architecture with the three servers.

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• Interesting questions related to lighttpd on Amazon EC2

  - by terence410

  This problem appeared today and I have no idea what is going on. Please share you ideas. I have 1 EC2 DB server (MYSQL + NFS File Sharing + Memcached). And I have 3 EC2 Web servers (lighttpd) where it will mounted the NFS folders on the DB server. Everything going smoothly for months but suddenly there is an interesting phenomenon. In every 8 minutes to 10 minutes, PHP file will be unreachable. This will last about 1 minute and then back to normal. Normal files like .html file are unaffected. All servers have the same problem exactly at the same time. I have spent one whole day to analysis the reason. Finally, I find out when the problem appear, the file descriptor of lighttpd suddenly increased a lot. I used ls /proc/1234/fd | wc -l to check the number of fd. The # of fd is around 250 in normal time. However, when the problem appeared, it will be raised to 1500 and then back to normal. It sounds funny, right? Do you have any idea what's going on? ======================== The CPU graph of one of the web server.

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• Wait on multiple condition variables on Linux without unnecessary sleeps?

  - by Joseph Garvin

  I'm writing a latency sensitive app that in effect wants to wait on multiple condition variables at once. I've read before of several ways to get this functionality on Linux (apparently this is builtin on Windows), but none of them seem suitable for my app. The methods I know of are: Have one thread wait on each of the condition variables you want to wait on, which when woken will signal a single condition variable which you wait on instead. Cycling through multiple condition variables with a timed wait. Writing dummy bytes to files or pipes instead, and polling on those. #1 & #2 are unsuitable because they cause unnecessary sleeping. With #1, you have to wait for the dummy thread to wake up, then signal the real thread, then for the real thread to wake up, instead of the real thread just waking up to begin with -- the extra scheduler quantum spent on this actually matters for my app, and I'd prefer not to have to use a full fledged RTOS. #2 is even worse, you potentially spend N * timeout time asleep, or your timeout will be 0 in which case you never sleep (endlessly burning CPU and starving other threads is also bad). For #3, pipes are problematic because if the thread being 'signaled' is busy or even crashes (I'm in fact dealing with separate process rather than threads -- the mutexes and conditions would be stored in shared memory), then the writing thread will be stuck because the pipe's buffer will be full, as will any other clients. Files are problematic because you'd be growing it endlessly the longer the app ran. Is there a better way to do this? Curious for answers appropriate for Solaris as well.

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• Which software for intranet CMS - Django or Joomla?

  - by zalun

  In my company we are thinking of moving from wiki style intranet to a more bespoke CMS solution. Natural choice would be Joomla, but we have a specific architecture. There is a few hundred people who will use the system. System should be self explainable (easier than wiki). We use a lot of tools web, applications and integrated within 3rd party software. The superior element which is a glue for all of them is API. In example for the intranet tools we do use Django, but it's used without ORM, kind of limited to templates and url - every application has an adequate methods within our API. We do not use the Django admin interface, because it is hardly dependent on ORM. Because of that Joomla may be hard to integrate. Every employee should be able to edit most of the pages, authentication and privileges have to be managed by our API. How hard is it to plug Joomla to use a different authentication process? (extension only - no hacks) If one knows Django better than Joomla, should Django be used?

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• ACL architechture for a Software As a service in Sprgin 3.0

  - by geoaxis

  I am making a software as a service using Spring 3.0 (Spring MVC, Spring Security, Spring Roo, Hibernate) I have to come up with a flexible access control list mechanism.I have three different kinds of users System (who can do any thing to the system, includes admin and internal daemons) Operations (who can add and delete users, organizations, and do maintenance work on behalf of users and organizations) End Users (they belong to one or more organization, for each organization, the user can have one or more roles, like being organization admin, or organization read-only member) (role like orgadmin can also add users for that organization) Now my question is, how should i model the entity of User? If I just take the End User, it can belong to one or more organizations, so each user can contain a set of references to its organizations. But how do we model the users role for each organization, So for example User UX belongs to organizations og1, og2 and og3, and for og1 he is both orgadmin, and org-read-only-user, where as for og2 he is only orgadmin and for og3 he is only org-read-only-user I have the possibility of making each user belong to one organization alone, but that's making the system bounded and I don't like that idea (although i would still satisfy the requirement) If you have a better extensible ACL architecture, please suggest it. Since its a software as a service, one would expect that alot of different organizations would be part if the same system. I had one concern that it is not a good idea to keep og1 and og2 data on the same DB (if og1 decides to spawn a 100 reports on the system, og2 should not suffer) But that is some thing advanced for now and is not directly related to ACL but to the physical distribution of data and setup of services based on those ACLs This is a community Wiki question, please correct any thing which you wish to do so. Thanks

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• How to use Data aware controls "correctly"?

  - by lyborko

  Hi, I would like to ask experienced users, if you prefer to use data aware controls to add, insert, delete and edit data in DB or you favor to do it manualy. I developed some DB applications, in which for the sake of "user friendly policy" I run into complicated web of table events (afterinsert, afteredit, after... and beforeedit, beforeinsert, before...). After that it was a quite nasty work to debug the application. Aware of this risk (later by another application) I tried to avoid this problem, so I paid increased attention to write code well, readable and comprehensive. It seemed everything all right from the beginning, but as I needed to handle some preprocessing stuff before sending and loading data etc, I run into the same problems again, "slowly and inevitably". Sometime I could not use dataaware controls anyway, and what seemed to be a "cool" feature of DAControl at the beginning it turned to an obstacle on the end. I "had to" write special routine for non-dataaware controls, in order to behave as dataaware. Then I asked myself, why on earth should I use dataaware controls? Is it better to found application architecture on non-dataaware controls? It requires more time to write bug-proof code, of course, but does it worth of it? I do not know... I happened to me several times, like jinxed : paradise on the beginning hell on the end... I do not know, if I use wrong method to write DB program, if there is some standard common practice how to proceed. Or if it is common problem to everybody? Thanx for advices and your experiences

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• JAVASCRIPT ENABLED [closed]

  - by kirchoffs415

  HI, I hope somebody can help, i keep getting the following message when i log on-- Your Javascript is disabled. Limited functionality is available. it will stay for maybe a day sometimes two.I have uninstalled javascript and reinstalled but still the same. Iam using chrome. any help would be gratefull many thanks Dominic p.s. my system spec is as follows System InformationOS Name Microsoft® Windows Vista™ Home Premium Version 6.0.6002 Service Pack 2 Build 6002 Other OS Description Not Available OS Manufacturer Microsoft Corporation System Name DOM-PC System Manufacturer Dell Inc. System Model Inspiron 1545 System Type X86-based PC Processor Pentium(R) Dual-Core CPU T4200 @ 2.00GHz, 2000 Mhz, 2 Core(s), 2 Logical Processor(s) BIOS Version/Date Dell Inc. A05, 25/02/2009 SMBIOS Version 2.4 Windows Directory C:\Windows System Directory C:\Windows\system32 Boot Device \Device\HarddiskVolume3 Locale United Kingdom Hardware Abstraction Layer Version = "6.0.6002.18005" User Name DOM-PC\DOM Time Zone GMT Standard Time Installed Physical Memory (RAM) 3.00 GB Total Physical Memory 2.96 GB Available Physical Memory 1.38 GB Total Virtual Memory 5.89 GB Available Virtual Memory 4.25 GB Page File Space 3.00 GB Page File C:\pagefile.sys My System Specs

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• how would you like computer science classes to be taught?

  - by aaa

  hello I am a graduate student now, and hopefully someday I will teach. my interests are C++, Python, embedded languages, and scientific computing. Meanwhile I daydream about how I would teach. I was not quite happy with my undergraduate university as I found many computer science classes lacking. so I would like to ask you, if you were a student, how would you like your computer science classes to be taught? I understand it is a very subjective question, but nevertheless I think it's important to know what people want. Some specific points I am interested in: should computer languages be taught explicitly, or should students be required to pick up language on their own? what is better for learning, tests, projects, some sort of take-home exam? how do you think classtime should be used? theory, introduction, explanations, etc.? do you think the group projects are important? how much about computer architecture do you want to learn in computer science class, not necessarily assembler class. should particular operating system/editor be mandated or encouraged? Thanks thank you for your comments. Question has been closed because it is a discussion question rather than Q&A. If you know appropriate website for discussions of such sort with low noise ratio, please let me know.

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• When is a good time to start thinking about scaling?

  - by Slokun

  I've been designing a site over the past couple days, and been doing some research into different aspects of scaling a site horizontally. If things go as planned, in a few months (years?) I know I'd need to worry about scaling the site up and out, since the resources it would end up consuming would be huge. So, this got me to thinking, when is the best time to start thinking about, and designing for, scalability? If you start too early on, you could easily over complicate your design, and make it impossible to actually build. You could also get too caught up in the details, the architecture, whatever, and wind up getting nothing done. Also, if you do get it working, but the site never takes off, you may have wasted a good chunk of extra effort. On the other hand, you could be saving yourself a ton of effort down the road. Designing it from the ground up to be big would make it much easier later on to let it grow big, with very little rewriting going on. I know for what I'm working on, I've decided to make at least a few choices now on the side of scaling, but I'm not going to do a complete change of thinking to get it to scale completely. Notably, I've redesigned my database from a conventional relational design to one similar to what was suggested on the Reddit site linked below, and I'm going to give memcache a try. So, the basic question, when is a good time to start thinking or worrying about scaling, and what are some good designs, tips, etc. for when doing so? A couple of things I've been reading, for those who are interested: http://www.codinghorror.com/blog/2009/06/scaling-up-vs-scaling-out-hidden-costs.html http://highscalability.com/blog/2010/5/17/7-lessons-learned-while-building-reddit-to-270-million-page.html http://developer.yahoo.com/performance/rules.html

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• Should a setter return immediately if assigned the same value?

  - by Andrei Rinea

  In classes that implement INotifyPropertyChanged I often see this pattern : public string FirstName { get { return _customer.FirstName; } set { if (value == _customer.FirstName) return; _customer.FirstName = value; base.OnPropertyChanged("FirstName"); } } Precisely the lines if (value == _customer.FirstName) return; are bothering me. I've often did this but I am not that sure it's needed nor good. After all if a caller assigns the very same value I don't want to reassign the field and, especially, notify my subscribers that the property has changed when, semantically it didn't. Except saving some CPU/RAM/etc by freeing the UI from updating something that will probably look the same on the screen/whatever_medium what do we obtain? Could some people force a refresh by reassigning the same value on a property (NOT THAT THIS WOULD BE A GOOD PRACTICE HOWEVER)? 1. Should we do it or shouldn't we? 2. Why?

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• rest and client rights integration, and backbone.js

  - by Francois

  I started to be more and more interested in the REST architecture style and client side development and I was thinking of using backbone.js on the client and a REST API (using ASP.NET Web API) for a little meeting management application. One of my requirements is that users with admin rights can edit meetings and other user can only see them. I was then wondering how to integrate the current user rights in the response for a given resource? My problem is beyond knowing if a user is authenticated or not, I want to know if I need to render the little 'edit' button next to the meeting (let's say I'm listing the current meetings in a grid) or not. Let's say I'm GETing /api/meetings and this is returning a list of meetings with their respective individual URI. How can I add if the user is able to edit this resource or not? This is an interesting passage from one of Roy's blog posts: A REST API should be entered with no prior knowledge beyond the initial URI (bookmark) and set of standardized media types that are appropriate for the intended audience (i.e., expected to be understood by any client that might use the API). From that point on, all application state transitions must be driven by client selection of server-provided choices that are present in the received representations or implied by the user’s manipulation of those representations It states that all transitions must be driven by the choices that are present in the representation. Does that mean that I can add an 'editURI' and a 'deleteURI' to each of the meeting i'm returning? if this information is there I can render the 'edit' button and if it's not there I just don't? What's the best practices on how to integrate the user's rights in the entity's representation? Or is this a super bad idea and another round trip is needed to fetch that information?

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• .NET multithreading, volatile and memory model

  - by fedor-serdukov

  Assume that we have the following code: class Program { static volatile bool flag1; static volatile bool flag2; static volatile int val; static void Main(string[] args) { for (int i = 0; i < 10000 * 10000; i++) { if (i % 500000 == 0) { Console.WriteLine("{0:#,0}",i); } flag1 = false; flag2 = false; val = 0; Parallel.Invoke(A1, A2); if (val == 0) throw new Exception(string.Format("{0:#,0}: {1}, {2}", i, flag1, flag2)); } } static void A1() { flag2 = true; if (flag1) val = 1; } static void A2() { flag1 = true; if (flag2) val = 2; } } } It's fault! The main quastion is Why... I suppose that CPU reorder operations with flag1 = true; and if(flag2) statement, but variables flag1 and flag2 marked as volatile fields...

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• Create a new app pool and assign it to a site subfolder on a remote host, using C# and IIS7

  - by Soeren

  I have a web site running on IIS7 on a remote server. I would like to do the following: Create a new subfolder under the root virtual directory. Create a new app pool. Add this new app pool to the new subfolder Normally, I would do this manually in IIS by first creating the app pool, and then right-clicking the sub folder an choose "add application", but I need to do this programmatically in C#. I've managed to make the above points 1 and 2 work, but I can't find the way to adding the application to the sub folder. This is the code I have used so far for 1 and 2: ServerManager mgr = new ServerManager(); ApplicationPool myAppPool = mgr.ApplicationPools.Add("MyAppPool"); myAppPool.AutoStart = true; myAppPool.Cpu.Action = ProcessorAction.KillW3wp; myAppPool.ManagedPipelineMode = ManagedPipelineMode.Integrated; myAppPool.ManagedRuntimeVersion = "V4.0"; myAppPool.ProcessModel.IdentityType = ProcessModelIdentityType.NetworkService; mgr.CommitChanges(); if (!Directory.Exists(@"D:\webroot\TestSite\NytSite")) { Directory.CreateDirectory(@"D:\webroot\TestSite\NytSite"); } So, I need to add "MyAppPool" to the "NytSite" folder... Is this even the correct way to do this? Any experiences out there? Thnx

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• x86_64 assembler: only one call per subroutine?

  - by zneak

  Hello everyone, I decided yesterday to start doing assembler. Most of it is okay (well, as okay as assembler can be), but I'm getting some problems with gas. It seems that I can call functions only once. After that, any subsequent call opcode with the same function name will fail. I must be doing something terribly wrong, though I can't see what. Take this small C function for instance: void path_free(path_t path) { if (path == NULL) return; free(((point_list_t*)path)->points); free(path); } I "translated" it to assembler like that: .globl _path_free _path_free: push rbp mov rbp, rsp cmp rdi, 0 jz byebye push rdi mov rdi, qword ptr [rdi] call _free pop rdi sub rsp, 8 call _free byebye: leave ret This triggers the following error for the second call _free: suffix or operands invalid for ``call''. And if I change it to something else, like free2, everything works (until link time, that is). Assembler code gcc -S gave me looks very similar to what I've done (except it's in AT&T syntax), so I'm kind of lost. I'm doing this on Mac OS X under the x86_64 architecture.

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• 500 Worker Threads, what kind of thread pool?

  - by Submerged

  I am wondering if this is the best way to do this. I have about 500 threads that run indefinitely, but Thread.sleep for a minute when done one cycle of processing. ExecutorService es = Executors.newFixedThreadPool(list.size()+1); for (int i = 0; i < list.size(); i++) { es.execute(coreAppVector.elementAt(i)); //coreAppVector is a vector of extends thread objects } The code that is executing is really simple and basically just this class aThread extends Thread { public void run(){ while(true){ Thread.sleep(ONE_MINUTE); //Lots of computation every minute } } } I do need a separate threads for each running task, so changing the architecture isn't an option. I tried making my threadPool size equal to Runtime.getRuntime().availableProcessors() which attempted to run all 500 threads, but only let 8 (4xhyperthreading) of them execute. The other threads wouldn't surrender and let other threads have their turn. I tried putting in a wait() and notify(), but still no luck. If anyone has a simple example or some tips, I would be grateful! Well, the design is arguably flawed. The threads implement Genetic-Programming or GP, a type of learning algorithm. Each thread analyzes advanced trends makes predictions. If the thread ever completes, the learning is lost. That said, I was hoping that sleep() would allow me to share some of the resources while one thread isn't "learning"

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• multi-core processing in R on windows XP - via doMC and foreach

  - by Jan

  Hi guys, I'm posting this question to ask for advice on how to optimize the use of multiple processors from R on a Windows XP machine. At the moment I'm creating 4 scripts (each script with e.g. for (i in 1:100) and (i in 101:200), etc) which I run in 4 different R sessions at the same time. This seems to use all the available cpu. I however would like to do this a bit more efficient. One solution could be to use the "doMC" and the "foreach" package but this is not possible in R on a Windows machine. e.g. library("foreach") library("strucchange") library("doMC") # would this be possible on a windows machine? registerDoMC(2) # for a computer with two cores (processors) ## Nile data with one breakpoint: the annual flows drop in 1898 ## because the first Ashwan dam was built data("Nile") plot(Nile) ## F statistics indicate one breakpoint fs.nile <- Fstats(Nile ~ 1) plot(fs.nile) breakpoints(fs.nile) # , hpc = "foreach" --> It would be great to test this. lines(breakpoints(fs.nile)) Any solutions or advice? Thanks, Jan

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• implement SIMD in C++

  - by Hristo

  I'm working on a bit of code and I'm trying to optimize it as much as possible, basically get it running under a certain time limit. The following makes the call... static affinity_partitioner ap; parallel_for(blocked_range<size_t>(0, T), LoopBody(score), ap); ... and the following is what is executed. void operator()(const blocked_range<size_t> &r) const { int temp; int i; int j; size_t k; size_t begin = r.begin(); size_t end = r.end(); for(k = begin; k != end; ++k) { // for each trainee temp = 0; for(i = 0; i < N; ++i) { // for each sample int trr = trRating[k][i]; int ei = E[i]; for(j = 0; j < ei; ++j) { // for each expert temp += delta(i, trr, exRating[j][i]); } } myscore[k] = temp; } } I'm using Intel's TBB to optimize this. But I've also been reading about SIMD and SSE2 and things along that nature. So my question is, how do I store the variables (i,j,k) in registers so that they can be accessed faster by the CPU? I think the answer has to do with implementing SSE2 or some variation of it, but I have no idea how to do that. Any ideas? Thanks, Hristo

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• Acceessing some aggregate functions in a linq datasource in a GridView

  - by Stephen Pellicer

  I am working on a traditional WebForms project. In the project I am trying out some Linq datasources with plans to eventually migrate to an MVC architecture. I am still very new to Linq. I have a GridView using a Linq datasource. The entities I am showing has a to many relationship and I would like to get the maximum value of a column in the many side of the relationship. I can show properties of the base entity in the gridview: <asp:TemplateField HeaderText="Number" SortExpression="tJobBase.tJob.JobNumber"> <ItemTemplate> <asp:Label ID="Label1" runat="server" Text='<%# Bind("tJobBase.tJob.JobNumber") %>'> </asp:Label> </ItemTemplate> </asp:TemplateField> I can also show the count of the many related property: <asp:TemplateField HeaderText="Number" SortExpression="tJobBase.tJob.tHourlies.Count"> <ItemTemplate> <asp:Label ID="Label1" runat="server" Text='<%# Bind("tJobBase.tJob.tHourlies.Count") %>'> </asp:Label> </ItemTemplate> </asp:TemplateField> Is there a way to get the max value of a column called WeekEnding in the tHourlies collection to show in the GridView?

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• Is there a way to easily convert a series of tarballs of a source tree into a git repository?

  - by Hotei

  I'm new to git and I have a moderately large number of weekly tarballs from a long running project. Each tarball has on average a few hundred files in it. I'm looking for a git strategy that will allow me to add the expanded contents of each tarball to a new git repository, starting from version 1.001 and going through version 1.650. As of this stage of the project 99.5% of tarball(n) is just a copy of version(n-1) - in other words, a perfect candidate for git. The desired end result is to have only the master branch remaining at the end of the process. I think I know git well enough to do this "by hand". As I understand it there is no possibility of a merge conflict since there will be no opportunity to change the master before the next version is added and committed. A shell script is my first guess, but I'm not sure how well bash will like it when git checkout branch_n gets processed while bash is executing in branch_n-1. For the purposes of this project the host environment is Ubuntu 10.4, resources available are 8 Gig RAM, 500 Gig Disk space free and 4 CPU processor at 3.ghz . I don't need someone else to solve the problem but I could use a nudge in the right direction as to how a git expert would approach it. Any advice from someone who's "been there done that" would be appreciated. Hotei PS: I have looked at site's suggested "related questions" and found nothing relevant.

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