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• C++ Thread Safe Integer

  - by Paul Ridgway

  Hello everyone, I have currently created a C++ class for a thread safe integer which simply stores an integer privately and has public get a set functions which use a boost::mutex to ensure that only one change at a time can be applied to the integer. Is this the most efficient way to do it, I have been informed that mutexes are quite resource intensive? The class is used a lot, very rapidly so it could well be a bottleneck... Googleing C++ Thread Safe Integer returns unclear views and oppinions on the thread safety of integer operations on different architectures. Some say that a 32bit int on a 32bit arch is safe, but 64 on 32 isn't due to 'alignment' Others say it is compiler/OS specific (which I don't doubt). I am using Ubuntu 9.10 on 32 bit machines, some have dual cores and so threads may be executed simultaneously on different cores in some cases and I am using GCC 4.4's g++ compiler. Thanks in advance...

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• Are memory barriers necessary for atomic reference counting shared immutable data?

  - by Dietrich Epp

  I have some immutable data structures that I would like to manage using reference counts, sharing them across threads on an SMP system. Here's what the release code looks like: void avocado_release(struct avocado *p) { if (atomic_dec(p->refcount) == 0) { free(p->pit); free(p->juicy_innards); free(p); } } Does atomic_dec need a memory barrier in it? If so, what kind of memory barrier? Additional notes: The application must run on PowerPC and x86, so any processor-specific information is welcomed. I already know about the GCC atomic builtins. As for immutability, the refcount is the only field that changes over the duration of the object.

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• mkmapview cpu usage on iphone 3G

  - by mozveren

  Hello all, I have some troubles with iphone 3G and Mkmapview. After a certain random time, my application freeze. When I launch with performances tool, I can see that the application a lot of time to retrieve map tiles in cache. 19.6 7006 Foundation +[NSURLConnection(NSURLConnectionReallyInternal) 18.5 6613 GMM GMM::TileCachePrivate::runCacheThread() Its seems that the MkMapView component launch several threads to load the tiles in caches. How I can avoid this behavior ? The behavior seems to not make troubles on 3GS. Thanks

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• which layout engine for finding coordinates of html elements on the web page?

  - by Mexx

  I am doing some web data classification task and was thinking if I could get the co-ordinates of html elements as they would appear on a web-browser without taking into consideration any css or javascript being referred in the web page. My language of programming is c++ and the need results for a couple million of pages, so it has to be fast. I know there is a Microsoft COM component which renders the page in a web browser control and then can be queried for position of different html tags. But this is not suitable in my case as it first renders the whole page which takes up a lot of time. So as I found out, there are open-source layout engines WebKit, Gecko that can probably be used for this. But that's a huge piece of code and I need someone to direct me to the right classes or right modules to look into or any previous/similar work someone has done previously. Also, please let me know what you guys think is a good choice if I want to customize the existing code for use with multiple threads to make it faster. Thanks

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• java statistics collection for performance evaluation

  - by user384706

  What is the most efficient way to collect and report performance statistic analysis from an application? If I have an application that uses a series of network apis, and I want to report statistics at runtime, e.g. Method doA() was called 3 times and consumed on avg 500ms Method doB() was called 5 times and consumed on avg 1200ms etc Then, I thought of using a well defined data structure (of collection) that each thread updates per remote call, and this can be used for the report. But I think that it will make the performance worse, for the time spend for statistics collection. Am I correct? How would I procceed if I used a background thread for this, and the other threads that did the remote calls were unaware of this collection gathering? Thanks

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• Performing time consuming operation on STL container within a lock

  - by Ashley

  I have an unordered_map of an unordered_map which stores a pointer of objects. The unordered map is being shared by multiple threads. I need to iterate through each object and perform some time consuming operation (like sending it through network etc) . How could I lock the multiple unordered_map so that it won't blocked for too long? typedef std::unordered_map<string, classA*>MAP1; typedef std::unordered_map<int, MAP1*>MAP2; MAP2 map2; pthread_mutex_lock(&mutexA) //how could I lock the maps? Could I reduce the lock granularity? for(MAP2::iterator it2 = map2.begin; it2 != map2.end; it2++) { for(MAP1::iterator it1 = *(it2->second).begin(); it1 != *(it2->second).end(); it1++) { //perform some time consuming operation on it1->second eg sendToNetwork(*(it1->second)); } } pthread_mutex_unlock(&mutexA)

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• Regular expression help parsing SQLIO output

  - by jaspernygaard

  Hi I've been working on a regular expression to parse the output of a series of SQLIO runs. I've gotten pretty far, but not quite there yet. I'm seeking a 100% regex solution and no pre-manipulation of the input. Could anyone assist with a little guidance with the following regular expression: .*v(?<SQLIOVersion>\d\.\d).*\n.*\n(?<threads>\d*)\s.*for\s(?<Seconds>\d+).*\n.*using\s(?<clustersize>[0-9]*)KB.*\n.*\n.*size:\s(?<currentfilesize>\d+).*\n.*\n.*\n.*\n.*\s(?<IOs>\d*\.\d*).*\n.*\s(?<MBs>\d*\.\d*).*\n.*\n.*\s(?<MinLatency_ms>\d+).*\n.*\s(?<AvgLatency_ms>\d+).*\n.*\s(?<MaxLatency_ms>\d+).*\n.*\n.*\n\%\:..(?<ms>\d*\s+)* Here's a snippet of the output - note the headers, which change during the SQLIO batch run: File

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• passing parameters to a thread

  - by assassin

  I want to pass a function that takes a parameter to the ThreadStart Constructor in C#. But, it seems that this is not possible, as I get a syntax error it I try to do something like this Thread t1 = new Thread(new Thread Start(func1(obj1)); where obj1 is an object of type List<string> (say). If I want a thread to execute this function that takes in an object as a parameter, and I plan to create 2 such threads simultaneously with different parameter values what is the best method to achieve this?

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• optimize python code

  - by user283405

  i have code that uses BeautifulSoup library for parsing. But it is very slow. The code is written in such a way that threads cannot be used. Can anyone help me about this? I am using beautifulsoup library for parsing and than save in DB. if i comment the save statement, than still it takes time so there is no problem with database. def parse(self,text): soup = BeautifulSoup(text) arr = soup.findAll('tbody') for i in range(0,len(arr)-1): data=Data() soup2 = BeautifulSoup(str(arr[i])) arr2 = soup2.findAll('td') c=0 for j in arr2: if str(j).find("<a href=") > 0: data.sourceURL = self.getAttributeValue(str(j),'<a href="') else: if c == 2: data.Hits=j.renderContents() #and few others... #... c = c+1 data.save() Any suggestions? Note: I already ask this question here but that was closed due to incomplete information.

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• Need help understanding .net ThreadPool

  - by Meredith

  I am trying to understand what ThreadPool does, I have this .NET example: class Program { static void Main() { int c = 2; // Use AutoResetEvent for thread management AutoResetEvent[] arr = new AutoResetEvent[50]; for (int i = 0; i < arr.Length; ++i) { arr[i] = new AutoResetEvent(false); } // Set the number of minimum threads ThreadPool.SetMinThreads(c, 4); // Enqueue 50 work items that run the code in this delegate function for (int i = 0; i < arr.Length; i++) { ThreadPool.QueueUserWorkItem(delegate(object o) { Thread.Sleep(100); arr[(int)o].Set(); // Signals completion }, i); } // Wait for all tasks to complete WaitHandle.WaitAll(arr); } } Does this run 50 "tasks", in groups of 2 (int c) until they all finish? Or I am not understanding what it really does.

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• Secondary thread causes startup delay

  - by JK

  In my didFinishLaunchingWithOptions method I spawn a thread to perform some maintenance on my core data store. However, this increases the startup time by half a second. The startup view is a tableview which draws its content from the same store. If I let the thread sleep for a second, the startup time improves drastically. I would like to understand why the second thread is blocking/delaying the main thread. Is it because both are trying to access the store (The second thread has its own store coordinator and context) or another reason (e.g. dont spawn threads in didFinishLaunching)?

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• Ideal way to set global uncaught exception Handler in Android

  - by Samuh

  I want to set a global uncaught exception handler for all the threads in my Android application. So, in my Application subclass I set an implementation of Thread.UncaughtExceptionHandler as default handler for uncaught exceptions. Thread.setDefaultUncaughtExceptionHandler( new DefaultExceptionHandler(this)); In my implementation, I am trying to display an AlertDialog displaying appropriate exception message. However, this doesn't seem to work. Whenever, an exception is thrown for any thread which goes un-handled, I get the stock, OS-default dialog (Sorry!-Application-has-stopped-unexpectedly dialog). What is the correct and ideal way to set a default handler for uncaught exceptions? Thanks.

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• Why doesn't Perl threading work when I call readdir beforehand?

  - by Kevin

  Whenever I call readdir before I create a thread, I get an error that looks like this: perl(2820,0x7fff70c33ca0) malloc: * error for object 0x10082e600: pointer being freed was not allocated * set a breakpoint in malloc_error_break to debug Abort trap What's strange is that it happens when I call readdir before I create a thread (i.e. readdir is not called in any concurrent code). I don't even use the results from readdir, just making the call to it seems to screw things up. When I get rid of it, things seem to work fine. Some example code is below: opendir(DIR, $someDir); my @allFiles = readdir(DIR); close(DIR); my $thread = threads-create(\&sub1); $thread-join(); sub sub1 { print "in thread\n" }

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• Can in-memory SQLite databases be used concurrently?

  - by Kent Boogaart

  In order to prevent a SQLite in-memory database from being cleaned up, one must use the same connection to access the database. However, using the same connection causes SQLite to synchronize access to the database. Thus, if I have many threads performing reads against an in-memory database, it is slower on a multi-core machine than the exact same code running against a file-backed database. Is there any way to get the best of both worlds? That is, an in-memory database that permits multiple, concurrent calls to the database?

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• problem with HttpWebRequest.GetResponse perfomance in multithread applcation

  - by Nikita

  I have very bad perfomance of HttpWebRequest.GetResponse method when it is called from different thread for different URLs. For example if we have one thread and execute url1 it requires 3sec. If we ececute url1 and url2 in parallet it requires 10sec, first request ended after 8sec and second after 10sec. If we exutet 10 URLs url1, url2, ... url0 it requires 1min 4 sec!!! first request ended after 50 secs! I use GetResponse method. I tried te set DefaultConnectionLimit but it doesn't help. If use BeginGetRequest/EndGetResponse methods it works very fast but only if this methods called from one thread. If from different it is also very slowly. I need to execute Http requests from many threads at one time. ?an anyone ever encountered such a problem? Thank you for any suggestions.

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• networking application and GUI in python

  - by pygabriel

  I'm writing an application that sends files over network, I want to develop a custom protocol to not limit myself in term on feature richness (http wouldn't be appropriate, the nearest thing is the bittorrent protocol maybe). I've tried with twisted, I've built a good app but there's a bug that makes my GUI blocking, so I've to switch to another framework/strategy. What do you suggest? Using raw sockets and using gtk mainloop (there are select-like functions in the toolkit) is too much difficult? It's viable running two mainloops in different threads? Asking for suggestions

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• Multithreading with STL container

  - by Steven

  I have an unordered map which stores a pointer of objects. I am not sure whether I am doing the correct thing to maintain the thread safety. typedef std::unordered_map<string, classA*>MAP1; MAP1 map1; pthread_mutex_lock(&mutexA) if(map1.find(id) != map1.end()) { pthread_mutex_unlock(&mutexA); //already exist, not adding items } else { classA* obj1 = new classA; map1[id] = obj1; obj1->obtainMutex(); //Should I create a mutex for each object so that I could obtain mutex when I am going to update fields for obj1? pthread_mutex_unlock(&mutexA); //release mutex for unordered_map so that other threads could access other object obj1->field1 = 1; performOperation(obj1); //takes some time obj1->releaseMutex(); //release mutex after updating obj1 }

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• python unit testing os.remove fails file system

  - by hwjp

  Am doing a bit of unit testing on a function which attempts to open a new file, but should fail if the file already exists. when the function runs sucessfully, the new file is created, so i want to delete it after every test run, but it doesn't seem to be working: class MyObject_Initialisation(unittest.TestCase): def setUp(self): if os.path.exists(TEMPORARY_FILE_NAME): try: os.remove(TEMPORARY_FILE_NAME) except WindowsError: #TODO: can't figure out how to fix this... #time.sleep(3) #self.setUp() #this just loops forever pass def tearDown(self): self.setUp() any thoughts? The Windows Error thrown seems to suggest the file is in use... could it be that the tests are run in parallel threads? I've read elsewhere that it's 'bad practice' to use the filesystem in unit testing, but really? Surely there's a way around this that doesn't invole dummying the filesystem?

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• Java: serial thread confinement question

  - by denis

  Assume you have a Collection(ConcurrentLinkedQueue) of Runnables with mutable state. Thread A iterates over the Collection and hands the Runnables to an ExecutorService. The run() method changes the Runnables state. The Runnable has no internal synchronization. The above is a repetitive action and the worker threads need to see the changes made by previous iterations. So a Runnable gets processed by one worker thread after another, but is never accessed by more than one thread at a time - a case of serial thread confinement(i hope ;)). The question: Will it work just with the internal synchronization of the ConcurrentLinkedQueue/ExecutorSerivce? To be more precise: If Thread A hands Runnable R to worker thread B and B changes the state of R, and then A hands R to worker thread C..does C see the modifications done by B?

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• Inherit appenders from calling instance in log4j or logback

  - by Lord.Quackstar

  In my program I have 2 separate streams of logging events (calling them streams for simplicity, in reality its 2 appenders). Stream1 contains client logging and Stream2 contains control logging. Now this might seem easy, except that certain classes can be both in the client logging and server logging, depending on the situation. Complicating this further is the fact that a command that a client wants takes place in 2 separate threads (one being fetched randomly from a thread pool), so any kind of tracking with MDC or NDC isn't possible. What would really simplify this is if the logger could inherit the appenders from the calling instance. That way I can setup 2 appenders for 2 loggers and be done. However I have no idea how to do it cleanly or easily. Can anyone offer any advice on how to do so? Note: If something needs to be passed around, I do have a event bean that gets passed to everything in the chain that can be used if necessary.

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• How to implement HeightMap smoothing using Thrust

  - by igal k

  I'm trying to implement height map smoothing using Thrust. Let's say I have a big array ( around 1 million floats). A known graphics algorithm to implement the above problem is to calculate the average around a given cell. If for example I need to calculate the value at a given cell[i,j] what I will basically do is: cell[i,j] = cell[i-1,j-1] + cell[i-1,j] + cell[i-1,j+1] + cell[i,j-1] + cell[i,j+1] + cell[i+1,j -1] + cell[i+1,j] + cell[i+1,j+1] cell[i,j] /=9 That's the CPU code. Is there a way to implement it using thrust? I know that I could use the transform algorithm. But I'm not sure it's correct to access different cells which are occupied but different threads (banks conflicts and so on).

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• Threading errors with Application.LoadComponent (key already exists)

  - by Kellls

  MSDN says that public static members of System.Windows.Application are thread safe. But when I try to run my app with multiple threads I get the following exception: ArgumentException: An entry with the same key already exists. at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) at System.Collections.Generic.SortedList`2.Add(TKey key, TValue value) at System.IO.Packaging.Package.AddIfNoPrefixCollisionDetected(ValidatedPartUri partUri, PackagePart part) at System.IO.Packaging.Package.GetPartHelper(Uri partUri) at System.IO.Packaging.Package.GetPart(Uri partUri) at System.Windows.Application.GetResourceOrContentPart(Uri uri) at System.Windows.Application.LoadComponent(Uri resourceLocator, Boolean bSkipJournaledProperties) at System.Windows.Application.LoadComponent(Uri resourceLocator) The application works fine on a single thread and even on two or three. When I get up past 5 then I get the error every time. Am I doing something wrong? What can I do to fix this?

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• how to get apache mod_cache work with mod_wsgi (django)?

  - by harmv

  I thought i'd speed up my django projects, by letting apache doing some caching for me. Unfortunately I see that apache never caches my dynamic pages. Has mod_cache problems with mod_wsgi served code ? My apache config: <VirtualHost *:80 ServerName myserver.com CacheEnable mem / # for testing only CacheIgnoreQueryString On CacheIgnoreCacheControl On WSGIDaemonProcess aname processes=1 threads=25 WSGIProcessGroup aname Alias /media/ /home/harm/projects/test/media/ WSGIScriptAlias / /home/harm/projects/test/wsgi.py The response does have the correct caching headers: Content-Length 2647 Content-Encoding gzip Vary Accept-Encoding Cache-Control public, max-age=3600 Keep-Alive timeout=15, max=100 Connection Keep-Alive Content-Type application/x-javascript Am I missing something ?

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• Are static delegates thread-safe?

  - by leypascua

  Consider this code snippet: public static class ApplicationContext { private static Func<TService> Uninitialized<TService>() { throw new InvalidOperationException(); } public static Func<IAuthenticationProvider> AuthenticationProvider = Uninitialized<IAuthenticationProvider>(); public static Func<IUnitOfWorkFactory> UnitOfWorkFactory = Uninitialized<IUnitOfWorkFactory>(); } //can also be in global.asax if used in a web app. public static void Main(string[] args) { ApplicationContext.AuthenticationProvider = () => new LdapAuthenticationProvider(); ApplicationContext.UnitOfWorkFactory = () => new EFUnitOfWorkFactory(); } //somewhere in the code.. say an ASP.NET MVC controller ApplicationContext.AuthenticationProvider().SignIn(username, true); Are delegates in the static class ApplicationContext thread-safe in the sense that multiple-threads can invoke them? What potential problems will I face if I pursue this approach?

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• Pushing app to heroku error

  - by Ryan Max

  Hello, I am getting the following error when I try to push my app to heroku. I saw a similar thread on here, but the issues seemed related to OSX. I am running windows 7 $ git push heroku master Counting objects: 1652, done. Delta compression using up to 4 threads. fatal: object 91f5d3ee9e2edcd42e961ed2eb254d5181cbc734 inconsistent object lengt h (476 vs 8985) error: pack-objects died with strange error error: failed to push some refs to '[email protected]:floating-stone-94.git I'm not sure what this means. I can't find any consistent answers on the internet. I tried re-creating my ssh public key but still the same.

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