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• prevent race condition without using locks C++

  - by Hristo

  How do I prevent a race condition with locking or using mutexes/semaphors in C++? I'm dealing with a nested for loop in which I will be setting a value in an array: for (int i = 0; i < m; ++i) for (int j = 0; j < n; ++j) for (int k = 0; k < o; ++k) array[k] += foo(...); More or less, I want to deal with this so that I can ensure different threads running at the same time don't write to array[k] at the same time. Any suggestions on how to approach this? Thanks, Hristo

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• Are mathamatical Algorithms protected by copyright

  - by analogy

  I wish to implement an algorithm which i read in a journal paper in my software (commercial). I want to know if this is allowed or not. The algorithm in question is described in http://arxiv.org/abs/0709.2938 It is a very simple algorithm and a number of implementations exist in python (http://igraph.sourceforge.net/) and java. One of them is in gpl another which i got from a different researcher and had no license attached. There are significant differences in two implementations, e.g. second one uses threads and multiple cores. It is possible to rewrite/ (not translate) the algorithm. So can I use it in my software or on a server for commercial purpose. Thanks

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• Performance characteristics of pthreads vs ucontext

  - by Robert Mason

  I'm trying to port a library that uses ucontext over to a platform which supports pthreads but not ucontext. The code is pretty well written so it should be relatively easy to replace all the calls to the ucontext API with a call to pthread routines. However, does this introduce a significant amount of additional overhead? Or is this a satisfactory replacement. I'm not sure how ucontext maps to operating system threads, and the purpose of this facility is to make coroutine spawning fairly cheap and easy. So, question is: Does replacing ucontext calls with pthread calls significantly change the performance characteristics of a library?

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• AudioRecord doesn't work for Motorola Milestone

  - by hcpl

  I'm having this problem only on Motorola Milestone. Code: // init recorder recordInstance = new AudioRecord(MediaRecorder.AudioSource.MIC, 8000, AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT, 8000); recordInstance.startRecording(); //more code here recordInstance.stop(); The errorinformation I have (can't find more for the moment since I don't have a milestone myself for debugging): Uncaught handler: thread main exiting due to uncaught exception java.lang.IllegalStateException: stop() called on an uninitialized AudioRecord. at android.media.AudioRecord.stop(AudioRecord.java:51 6) Apparantly I'm not the only one with this problem. Some very similar threads I found (without solution): http://groups.google.com/group/android-developers/browse_thread/thread/6dd24aeb484b2e40 http://androidcommunity.com/forums/f2/problem-using-audiorecord-in-motorola-milestone-30935/ http://community.developer.motorola.com/t5/Android-App-Development-for/Problem-using-AudioRecord-on-Milestone-device/m-p/3889 http://www.fring.com/forums/showthread.php?t=16194

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• While using ConcurrentQueue, trying to dequeue while looping through in parallel

  - by James Black

  I am using the parallel data structures in my .NET 4 application and I have a ConcurrentQueue that gets added to while I am processing through it. I want to do something like: personqueue.AsParallel().WithDegreeOfParallelism(20).ForAll(i => ... ); as I make database calls to save the data, so I am limiting the number of concurrent threads. But, I expect that the ForAll isn't going to dequeue, and I am concerned about just doing ForAll(i => { personqueue.personqueue.TryDequeue(...); ... }); as there is no guarantee that I am popping off the correct one. So, how can I iterate through the collection and dequeue, in a parallel fashion. Or, would it be better to use PLINQ to do this processing, in parallel?

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• search engine (solr/sphinx) question

  - by noname

  i want to make my threads content searchable with full text search engines like solr. but i wonder one thing. should i index just the thread.title, thread.body and post.body or should i index username, created date, nr of posts, views, country, region and city too that belongs to thread? i mean when an user search for a thread he will get hits returned containing thread title, 2 lines of body, which user has posted it, creation date, tags, and so on. should i index all this information too? but then it would be pretty much the whole database. or should i just index the 3 first columns i mentioned for full text search. and another question. when an user post a new thread, then i have to immidiately tell solr to add that row? if im not, how would it be searchable?

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• Stack recommendations for small/medium-sized web application in Python

  - by reto

  I'm looking for some recommendations for a python web application. We have some memory restrictions and we try to keep it small and lean. We thought about using WSGI (and a python webserver) and build the rest ourself. We already have a template engine we'd like to use, but we are open for some suggestions regarding the whole request handling (the controller). The application has to run in a single process and the requests have to be processed with multiple threads. We've looked at django, but we are a not sure if it fits into our memory budget. Your feedback is very welcome! Cheers, Reto

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• Fire just once a Thread in Asp.net WebSite Global.asax

  - by Luís Custódio

  I've a legacy application using Asp.Net WebSite (winforms...) and I need run a background thread that collect periodically some files. But this thread must run just one time! My problem start when I put a method in Application_Start: void Application_Start(object sender, EventArgs e) { SetConnection(); SetNHibernate(); SetNinject(); SetExportThread(); } So I start my application on Visual Studio and three threads start to run. I need some singleton? or something?

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• Log RuntimeException thrown from thread created by Spring via the @Async annotation

  - by Eugen

  I'm having some difficulty logging RuntimeException from a thread. My system is: Java 7 (b118), Spring 3.0.5. The threads are not created by hand, but via Spring's @Async annotation, which creates it's own executor behind the scenes, so I don't really have the option of overriding any methods of the thread, FutureTask or anything low level. So my question is if Spring has any support or if there are any best practices for handling (logging) these type of exceptions? Any suggestions are appreciated. Thanks.

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• How to manage db connections on server?

  - by simpatico

  I have a severe problem with my database connection in my web application. Since I use a single database connection for the whole application from singleton Database class, if i try concurrent db operations (two users) the database rollsback the transactions. This is my static method used: All threads/servlets call static Database.doSomething(...) methods, which in turn call the the below method. private static /* synchronized*/ Connection getConnection(final boolean autoCommit) throws SQLException { if (con == null) { con = new MyRegistrationBean().getConnection(); } con.setAutoCommit(true); //TODO return con; } What's the recommended way to manage this db connection/s I have, so that I don't incurr in the same problem.

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• how much concurrent http request can erlang handle

  - by user209123

  I am developing a application for benchmarking purposes, for which I require to create large number of http connection in a short time, I created a program in java to test how much threads is java able to create, it turns out in my 2GB single core machine, the limit is variable between 5000 and 6000 with 1 GB of memory given to JVM after which it hits outofmemoryerror with heap limit reached. It is suggested around that erlang will be able to generate much more concurrent processes, I am willing to learn erlang if it is capable of solving the problem , although I am interested in knowing can erlang be able to say generate somewhere around 100000 processes which are essentially http requests waiting for responses, in a matter of few seconds without reaching any limit like memory error etc.,

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• My C# program running as Windows Service is blocking Windows XP from hibernation

  - by sherpa

  I have Windows Service written in C#. It starts two threads, one is pooling a Web Service, second is waiting on a Monitor object for a new job to arrive. Besides that, the main thread acts as a WCF service host using NetNamedPipeBinding. It lets the client application to register a callback and then sends notifications back. The problem I have is that when this Windows Service is running, I cannot hibernate or Standby my computer which is running on Windows XP, SP3. When I set Windows to hibernate or standby, nothing happens. Then, at the moment when I go to Service Manager and stop the service, the system hibernation starts immediately. The service class extending the ServiceBase has properties like CanHandlePowerEvent, CanPauseAndContinue, etc. set to true... That didn't make any difference. The question is: what can be blocking the Hibernation/Standby from proceeding? What should I take care about to avoid it?

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• Mutex takes a long while to unlock

  - by l.thee.a

  I have two threads. First one is something like this: while(1) { pthread_mutex_lock(&mutex); //DO WORK pthread_mutex_unlock(&mutex); pthread_yield(); } The second one locks the mutex on user event, change some settings and unlocks. Thread one does ~ 200 iterations a second. However on occasion it takes the second thread up to 3 seconds to get active (to unlock the mutex). How do I ensure faster response?

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• Can not open ports in iptables on CentOS 5??

  - by abszero

  I am trying to open up ports in CentOS's firewall and am having a terrible go at it. I have followed the "HowTo" here: http://wiki.centos.org/HowTos/Network/IPTables as well as a few other places on the Net but I still can't get the bloody thing to work. Basically I wanted to get two things working: VNC and Apache over the internal network. The problem is that the firewall is blocking all attempts to connect to these services. Now if I issue service iptables stop and then try to access the server via VNC or hit the webserver everything works as expected. However the moment I turn iptables back on all of my access is blocked. Below is a truncated version of my iptables file as it appears in vi -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 5801 -j ACCEPT -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 5901 -j ACCEPT -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 6001 -j ACCEPT -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 5900 -j ACCEPT -A RH-Firewall-1-INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT Really I would just be happy if I could get port 80 opened up for Apache since I can do most stuff via putty but if I could figure out VNC as well that would be cool. As far as VNC goes there is just a single/user desktop that I am trying to connect to via: [ipaddress]:1 Any help would be greatly appreciated!

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• zeromq installtion on mac os snow leopard

  - by Ashish

  I have installed zeromq 2.1.11 on mac os x using the steps given on http://www.zeromq.org/area:download Then i installed pyzmq (python bindings ) But i get the following error : import zmq Traceback (most recent call last): File "<pyshell#1>", line 1, in <module> import zmq File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/zmq/__init__.py", line 35, in <module> from zmq.utils import initthreads # initialize threads ImportError: dlopen(/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/zmq/utils/initthreads.so, 2): no suitable image found. Did find: /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/zmq/utils/initthreads.so: no matching architecture in universal wrapper

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• Connecting to an RMI object without registry

  - by Mark Probst

  I think I need to connect to a remote RMI object without going through the registry, but I don't know how. My situation is this: I'm implementing a simple job distribution service which consists of one distributor and multiple workers. The distributor has a registered RMI object to which clients connect to send jobs, and workers connect to accept jobs. Unfortunately the distributor and worker hosts are behind a firewall. To get to the distributor host I am tunneling two ports (one for the registry, one for the distributor object) via SSH, so I can get to the registry and the distributor from outside the firewall. To make that work I have to set "-Djava.rmi.server.hostname=localhost" on the distributor JVM so that the clients connect to their local, tunneled port, instead of the port on the actual distributor host, which is blocked. This creates a problem for the workers, though, because they need to connect to the distributor directly, but because of the "localhost" redirection they behave like clients and try to connect to a port on their own host, which is not available, because I'm not tunneling on the workers (it is impractical). Now, if I could connect to a remote object directly by giving the hostname and port, I could do away both with the registry on the distributor and the "localhost" hack, and make the workers connect properly. How do I do that? Or is there a different solution to this problem?

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• Injecting EntityManager Vs. EntityManagerFactory

  - by SB

  A long question, please bear with me. We are using Spring+JPA for a web application. My team is debating over injecting EntityManagerFactory in the GenericDAO(a DAO based on Generics something on the lines provided by APPFUSE, we do not use JpaDaosupport for some reason) over injecting an EntityManager. We are using "application managed persistence". The arguments against injecting a EntityManagerFactory is that its too heavy and so is not required, the EntityManager does what we need. Also, as Spring would create a new instance of a DAO for every web request(I doubt this) there are not going to be any concurrency issues as in the same EntityManager instance is shared by two threads. The argument for injecting EFM is that its a good practice over all its always good to have a handle to a factory. I am not sure which is the best approach, can someone please enlighten me? SB

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• Python Multiprocessing Question

  - by Avan

  My program has 2 parts divided into the core and downloader. The core handles all the app logic while the downloader just downloads urls. Right now, I am trying to use the python multiprocessing module to accomplish the task of the core as a process and the downloader as a process. The first problem I noticed was that if I spawn the downloader process from the core process so that the downloader is the child process and the core is the parent, the core process(parent) is blocked until the child is finished. I do not want this behaivor though. I would like to have a core process and a downloader process that are both able to execute their code and communicate between each other. example ... def main(): jobQueue = Queue() jobQueue.put("http://google.com) d = Downloader(jobQueue) p = Process(target=d.start()) p.start() if __name__ == '__main__': freeze_support() main() where Downloader's start() just takes the url out of the queue and downloads it. In order to have the 2 processes unblocked, would I need to create 2 processes from the parent process and then share something between them?

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• Implicit Memory Barriers

  - by foo

  let's say i have variables A, B and C that two threads (T1, T2) share. i have the following code: //T1 //~~ A = 1; B = 1; C = 1; InterlockedExchange(ref Foo, 1); //T2 (executes AFTER T1 calls InterlockedExchange) //~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ InterlockedExchange(ref Bar, 1); WriteLine(A); WriteLine(B); WriteLine(C); Question: does calling InterlockedExchange (implicit full fence) on T1 and T2, gurentess that T2 will "See" the write done by T1 before the fence? (A, B and C variables), even though those variables are not plance on the same cache-line as Foo and Bar?

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• Java Session Like Object

  - by scriptmonster

  I have been developing a project and in this project i have designed my code to do the same job after a specified time interval continuously. The job that wanted to be done has a lot of distinct cycles. The interval is small to execute them normally thus i used threads. Until that point everything is clear for me. To decrease the process and information transaction i wanted to put an session like object that holds the given data and provide it to any thread at anytime. With this object i plan to not query the same configuration information from database at everytime but if it exists on the session take it else query and store on session. I'm not sure how to implement this structure. Regards,

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• Using NSThread to solve waiting for image from URL on the iPhone

  - by james.ingham

  So I have the following code in a method which I want to set a UIImageView image to that of one from an online source: [NSThread detachNewThreadSelector:@selector(loadImage) toTarget:self withObject:nil]; Then in the method called by the thread I have this: - (void) loadImage { NSURL *url = [NSURL URLWithString:logoPath]; // logoPath is an NSString with path details NSData *data = [NSData dataWithContentsOfURL:url]; logoImage.image = [UIImage imageWithData:data]; } This works great however I get many warnings within the Debugger Console along the lines of: 2010-05-10 14:30:14.052 ProjectTitle[2930:633f] * _NSAutoreleaseNoPool(): Object 0x169d30 of class NSHTTPURLResponse autoreleased with no pool in place - just leaking This occurs many times each time I call the new thread and then eventually, under no pattern, after calling a few of these threads I get the classic 'EXC_BAD_ACCESS' run-time error. I understand that this is happening because I'm not retaining the object but how can I solve this with the code in 'loadImage' shown above? Thanks

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• How to Treat Race Condition of Session in Web Application?

  - by Morgan Cheng

  I was in a ASP.NET application has heavy traffic of AJAX requests. Once a user login our web application, a session is created to store information of this user's state. Currently, our solution to keep session data consistent is quite simple and brutal: each request needs to acquire a exclusive lock before being processed. This works fine for tradition web application. But, when the web application turns to support AJAX, it turns to not efficient. It is quite possible that multiple AJAX requests are sent to server at the same time without reloading the web page. If all AJAX requests are serialized by the exclusive lock, the response is not so quick. Anyway, many AJAX requests that doesn't access same session variables are blocked as well. If we don't have a exclusive lock for each requests, then we need to treat all race condition carefully to avoid dead lock. I'm afraid that would make the code complex and buggy. So, is there any best practice to keep session data consistent and keep code simple and clean?

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• Encoding with url and api

  - by user2950824

  So I have this web app set up and running and it works fine for any username that you request, but when i try http://mrcastelo.pythonanywhere.com/lol/euw/Nazaré, it simply doesnt work - the error that I get on the server is the following: iddata= getJSON(urllolbase+region+urlid+username) #SummonerID UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 5: ordinal not in range(128) It is annoying me greatly, I've tried some other threads but none of them came to a fix. The api that I am using (www.legendaryapi.com) does accept this because this works. Any idea on how to fix this?

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• Does my Dictionary must use locking mechanism?

  - by theateist

  Many threads have access to summary. Each thread will have an unique key for accessing the dictionary; Dictionary<string, List<Result>> summary; Do I need locking for following operations? summary[key] = new List<Result>() summary[key].Add(new Result()); It seems that I don't need locking because each thread will access dictionary with different key, but won't the (1) be problematic because of adding concurrently new record to dictionary with other treads?

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• FileReference.browse() stops playback on some Flash Players

  - by Christophe Herreman

  We have an issue were the server session associated with a Flex client times out when the browse file dialog is open for a time longer then the configured session timeout. It seems that on some players, the playback is stopped when browse or download on a FileReference is executing. This also causes remote calls to be blocked and hence our manual keep-alive messages are not sent to the server, resulting in a session timeout. I searched for some info on this in the docs and found a notice of it, but it does not explicitly list the players it does (not) work. Would anyone know were I could find a complete list? PS: here are the links that mention this behavior: http://livedocs.adobe.com/flex/3/html/help.html?content=17_Networking_and_communications_7.html While calls to the FileReference.browse(), FileReferenceList.browse(), or FileReference.download() method are executing, most players will continue SWF file playback. http://livedocs.adobe.com/flex/3/langref/flash/net/FileReference.html While calls to the FileReference.browse(), FileReferenceList.browse(), or FileReference.download() methods are executing, SWF file playback pauses in stand-alone and external versions of Flash Player and in AIR for Linux and Mac OS X 10.1 and earlier Anyone knows what is meant with an "external Flash Player"? PPS: we tested this on Linux (10.0.x and 10.1.x) in Firefox where it seems to stop playback and on Windows (10.0.x) in IE where playback seems to continue.

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