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  • boost scoped_lock mutex crashes

    - by JahSumbar
    hello, I have protected a std::queue's access functions, push, pop, size, with boost::mutexes and boost::mutex::scoped_lock in these functions from time to time it crashes in a scoped lock the call stack is this: 0 0x0040f005 boost::detail::win32::interlocked_bit_test_and_set include/boost/thread/win32/thread_primitives.hpp 361 1 0x0040e879 boost::detail::basic_timed_mutex::timed_lock include/boost/thread/win32/basic_timed_mutex.hpp 68 2 0x0040e9d3 boost::detail::basic_timed_mutex::lock include/boost/thread/win32/basic_timed_mutex.hpp 64 3 0x0040b96b boost::unique_lock<boost::mutex>::lock include/boost/thread/locks.hpp 349 4 0x0040b998 unique_lock include/boost/thread/locks.hpp 227 5 0x00403837 MyClass::inboxSize - this is my inboxSize function that uses this code: MyClass::inboxSize () { boost::mutex::scoped_lock scoped_lock(m_inboxMutex); return m_inbox.size(); } and the mutex is declared like this: boost::mutex m_inboxMutex; it crashes at the last pasted line in this function: inline bool interlocked_bit_test_and_set(long* x,long bit) { long const value=1<<bit; long old=*x; and x has this value: 0xababac17 Thanks for the help

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  • Should mutex.WaitOne() inside or before the try/finally block.

    - by chillitom
    Hi Guys, I was wondering which of the following was the suggested pattern when using Mutex (or Semaphores or ReadWriteLockSlims etc.). Should the initial lock happen inside or outside of the try statement? Is it unimportant? _mutex.WaitOne() try { // critical code } finally { _mutex.ReleaseMutex(); } or try { _mutex.WaitOne() // critical code } finally { _mutex.ReleaseMutex(); }

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  • C++ Unlocking a std::mutex before calling std::unique_lock wait

    - by Sant Kadog
    I have a multithreaded application (using std::thread) with a manager (class Tree) that executes some piece of code on different subtrees (embedded struct SubTree) in parallel. The basic idea is that each instance of SubTree has a deque that store objects. If the deque is empty, the thread waits until a new element is inserted in the deque or the termination criteria is reached. One subtree can generate objects and push them in the deque of another subtree. For convenience, all my std::mutex, std::locks and std::variable_condition are stored in a struct called "locks". The class Tree creates some threads that run the following method (first attempt) : void Tree::launch(SubTree & st, Locks & locks ) { /* some code */ std::lock_guard<std::mutex> deque_lock(locks.deque_mutex_[st.id_]) ; // lock the access to the deque of subtree st if (st.deque_.empty()) // check that the deque is still empty { // some threads are still running, wait for them to terminate std::unique_lock<std::mutex> wait_lock(locks.restart_mutex_[st.id_]) ; locks.restart_condition_[st.id_].wait(wait_lock) ; } /* some code */ } The problem is that "deque_lock" is still locked while the thread is waiting. Hence no object can be added in the deque of the current thread by a concurrent one. So I turned the lock_guard into a unique_lock and managed the lock/unlock manually : void launch(SubTree & st, Locks & locks ) { /* some code */ std::unique_lock<std::mutex> deque_lock(locks.deque_mutex_[st.id_]) ; // lock the access to the deque of subtree st if (st.deque_.empty()) // check that the deque is still empty { deque_lock.unlock() ; // unlock the access to the deque to enable the other threads to add objects // DATA RACE : nothing must happen to the unprotected deque here !!!!!! // some threads are still running, wait for them to terminate std::unique_lock<std::mutex> wait_lock(locks.restart_mutex_[st.id_]) ; locks.restart_condition_[st.id_].wait(wait_lock) ; } /* some code */ } The problem now, is that there is a data race, and I would like to make sure that the "wait" instruction is performed directly after the "deque_lock.unlock()" one. Would anyone know a way to create such a critical instruction sequence with the standard library ? Thanks in advance.

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  • Write-Only Reference in C++?

    - by Robert Mason
    Is there a way to code a write-only reference to an object? For example, suppose there was a mutex class: template <class T> class mutex { protected: T _data; public: mutex(); void lock(); //locks the mutex void unlock(); //unlocks the mutex T& data(); //returns a reference to the data, or throws an exception if lock is unowned }; Is there a way to guarantee that one couldn't do this: mutex<type> foo; T& ref; foo.lock(); ref = foo.data(); foo.unlock(); //I have a unguarded reference to foo now On the other hand, is it even worth it? I know that some people assume that programmers won't deliberately clobber the system, but then, why do we have private variables in the first place, eh? It'd be nice to just say it's "Undefined Behavior", but that just seems a little bit too insecure.

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  • SQLVDI error - attempt to release mutex not owned by caller

    - by Chris W
    I've started getting some errors in the App event log of one of our database servers (Windows 2003 & SQL Server 2005). The nightly full database backups are completing successfully however immediately after the job success is written to the event log there is a run of entries that say: SQLVDI: Loc=CVDS. Desc=Release(ClientAliveMutex). ErrorCode=(288)Attempt to release mutex not owned by caller. There's five of these logged - the server itself has more than 20 databases on it which are all backed up successfully. The server is backed up by Bacula using a VSS backup. Has anyone got any ideas what would be causing the errors? They seem to have started after a re-boot on Friday to install some patches which included KB960089. Edit: After getting the errors for a few days they've now stopped without any action on my part other than letting the backups continue as they were. It may be a coincidence but they stopped after Bacula completed its weekly full rather than the daily incremental backup.

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  • SQLVDI error - attempt to release mutex not owned by caller

    - by Chris W
    I've started getting some errors in the App event log of one of our database servers (Windows 2003 & SQL Server 2005). The nightly full database backups are completing successfully however immediately after the job success is written to the event log there is a run of entries that say: SQLVDI: Loc=CVDS. Desc=Release(ClientAliveMutex). ErrorCode=(288)Attempt to release mutex not owned by caller. There's five of these logged - the server itself has more than 20 databases on it which are all backed up successfully. The server is backed up by Bacula using a VSS backup. Has anyone got any ideas what would be causing the errors? They seem to have started after a re-boot on Friday to install some patches which included KB960089. Edit: After getting the errors for a few days they've now stopped without any action on my part other than letting the backups continue as they were. It may be a coincidence but they stopped after Bacula completed its weekly full rather than the daily incremental backup.

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  • How do you protect a common resource using mutexes?

    - by Steve
    I have a common resource, which I want 1 and only 1 instance of my application (or it's COM API) to have access to at any time. I have tried to protect this resource using mutexes, but when multiple threads of a host dotnet application try to access the COM object, the mutex doesn't seem to be released. This is the code I have used to protect my resource. repeat Mutex := CreateMutex(nil, True, PChar('Connections')); until (Mutex <> 0) and (GetLastError <> ERROR_ALREADY_EXISTS); try //use resource here! finally CloseHandle(Mutex); end; If I run the threads simultaneously, the first thread get's through (obviously, being the first one to create the mutex), but subsequent threads are caught in the repeat loop. If I run each thread at 5 second intervals, then all is ok. I suspect I'm not using mutexes correctly here, but I have found very little documentation about how to do this. Any ideas?

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  • How can I synchronize database access between a write-thread and a read-thread?

    - by Runcible
    My program has two threads: Main execution thread that handles user input and queues up database writes A utility thread that wakes up every second and flushes the writes to the database Inside the main thread, I occasionally need to make reads on the database. When this happens, performance is not important, but correctness is. (In a perfect world, I would be reading from a cache, not making a round-trip to the database - but let's put that aside for the sake of discussion.) How do I make sure that the main thread sees a correct / quiescent database? A standard mutex won't work, since I run the risk of having the main thread grab the mutex before the data gets flushed to the database. This would be a big race condition. What I really want is some sort of mutex that lets the main thread of execution proceed only AFTER the mutex has been grabbed and released once. Does such a thing exist? What's the best way to solve this problem?

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  • Lock a mutex multiple times in the same thread

    - by Megacan
    Hi, I'm developing an application on an embedded linux OS (uClinux) and I need to be able to lock the mutex more than once (by the same thread). I have a mutex and a mutexattr defined and initialized as follows: pthread_mutexattr_t waiting_barcode_mutexattr; pthread_mutex_t waiting_barcode_mutex; pthread_mutexattr_init(&waiting_barcode_mutexattr); pthread_mutexattr_settype(&waiting_barcode_mutexattr, PTHREAD_MUTEX_RECURSIVE); pthread_mutex_init(&waiting_barcode_mutex, &waiting_barcode_mutexattr); But when I try to acquire the lock twice it blocks on the second lock: pthread_mutex_lock(&waiting_barcode_mutex); pthread_mutex_lock(&waiting_barcode_mutex); Am I initializing it wrong or is there a better way of accomplishing the same? Thanks in advance.

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  • Using many mutex locks

    - by hanno
    I have a large tree structure on which several threads are working at the same time. Ideally, I would like to have an individual mutex lock for each cell. I looked at the definition of pthread_mutex_t in bits/pthreadtypes.h and it is fairly short, so the memory usage should not be an issue in my case. However, is there any performance penalty when using many (let's say a few thousand) different pthread_mutex_ts for only 8 threads?

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  • Should I use Mutex OR Critical Section for Windows Mobile RIL

    - by afriza
    Hi, I am using a Radio Layer Interface (RIL) Native API in Windows Mobile application. In this API, the return values / results of most functions are not returned immediately but are passed through a callback function which is passed to the RIL API. Some usage examples are found at XDA Develompent Tools and Google Gears Geolocation API. My question is, in these two examples, a mutex is used to guard the data instead of other synchronization objects. Now, will Critical Section do fine here in the use cases described by both examples? Which thread or process will actually call the callback functions?

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  • What mutex/locking/waiting mechanism to use when writing a Chat application with Tornado Web Framewo

    - by user272973
    We're implementing a Chat server using Tornado. The premise is simple, a user makes open an HTTP ajax connection to the Tornado server, and the Tornado server answers only when a new message appears in the chat-room. Whenever the connection closes, regardless if a new message came in or an error/timeout occurred, the client reopens the connection. Looking at Tornado, the question arises of what library can we use to allow us to have these calls wait on some central object that would signal them - A_NEW_MESSAGE_HAS_ARRIVED_ITS_TIME_TO_SEND_BACK_SOME_DATA. To describe this in Win32 terms, each async call would be represented as a thread that would be hanging on a WaitForSingleObject(...) on some central Mutex/Event/etc. We will be operating in a standard Python environment (Tornado), is there something built-in we can use, do we need an external library/server, is there something Tornado recommends? Thanks

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  • Compiler reordering around mutex boundaries?

    - by shojtsy
    Suppose I have my own non-inline functions LockMutex and UnlockMutex, which are using some proper mutex - such as boost - inside. How will the compiler know not to reorder other operations with regard to calls to the LockMutex and UnlockMutex? It can not possibly know how will I implement these functions in some other compilation unit. void SomeClass::store(int i) { LockMutex(_m); _field = i; // could the compiler move this around? UnlockMutex(_m); } ps: One is supposed to use instances of classes for holding locks to guarantee unlocking. I have left this out to simplify the example.

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  • Should I make my MutexLock volatile?

    - by sje397
    I have some code in a function that goes something like this: void foo() { { // scope the locker MutexLocker locker(&mutex); // do some stuff.. } bar(); } The function call bar() also locks the mutex. I am having an issue whereby the program crashes (for someone else, who has not as yet provided a stack trace or more details) unless the mutex lock inside bar is disabled. Is it possible that some optimization is messing around with the way I have scoped the locker instance, and if so, would making it volatile fix it? Is that a bad idea? Thanks.

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  • Subtle C++ mistake, can you spot it?

    - by aaa
    I ran into a subtle C++ gotcha, took me while to resolve it. Can you spot it? class synchronized_container { boost::mutex mutex_; std::vector <T> container_; void push_back(const T &value) { boost::scoped_lock(mutex_); // raii mutex lock container_.push_back(value); } ... }; scoped lock is a raii mutex lock, obtains lock on constructor, release lock in destructor. The program will work as expected in serial, but will may occasionally produce weird stuff with more than one thread.

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  • Problems doing asynch operations in C# using Mutex.

    - by firoso
    I've tried this MANY ways, here is the current iteration. I think I've just implemented this all wrong. What I'm trying to accomplish is to treat this Asynch result in such a way that until it returns AND I finish with my add-thumbnail call, I will not request another call to imageProvider.BeginGetImage. To Clarify, my question is two-fold. Why does what I'm doing never seem to halt at my Mutex.WaitOne() call, and what is the proper way to handle this scenario? /// <summary> /// re-creates a list of thumbnails from a list of TreeElementViewModels (directories) /// </summary> /// <param name="list">the list of TreeElementViewModels to process</param> public void BeginLayout(List<AiTreeElementViewModel> list) { // *removed code for canceling and cleanup from previous calls* // Starts the processing of all folders in parallel. Task.Factory.StartNew(() => { thumbnailRequests = Parallel.ForEach<AiTreeElementViewModel>(list, options, ProcessFolder); }); } /// <summary> /// Processes a folder for all of it's image paths and loads them from disk. /// </summary> /// <param name="element">the tree element to process</param> private void ProcessFolder(AiTreeElementViewModel element) { try { var images = ImageCrawler.GetImagePaths(element.Path); AsyncCallback callback = AddThumbnail; foreach (var image in images) { Console.WriteLine("Attempting Enter"); synchMutex.WaitOne(); Console.WriteLine("Entered"); var result = imageProvider.BeginGetImage(callback, image); } } catch (Exception exc) { Console.WriteLine(exc.ToString()); // TODO: Do Something here. } } /// <summary> /// Adds a thumbnail to the Browser /// </summary> /// <param name="result">an async result used for retrieving state data from the load task.</param> private void AddThumbnail(IAsyncResult result) { lock (Thumbnails) { try { Stream image = imageProvider.EndGetImage(result); string filename = imageProvider.GetImageName(result); string imagePath = imageProvider.GetImagePath(result); var imageviewmodel = new AiImageThumbnailViewModel(image, filename, imagePath); thumbnailHash[imagePath] = imageviewmodel; HostInvoke(() => Thumbnails.Add(imageviewmodel)); UpdateChildZoom(); //synchMutex.ReleaseMutex(); Console.WriteLine("Exited"); } catch (Exception exc) { Console.WriteLine(exc.ToString()); // TODO: Do Something here. } } }

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  • Boost threading/mutexs, why does this work?

    - by Flamewires
    Code: #include <iostream> #include "stdafx.h" #include <boost/thread.hpp> #include <boost/thread/mutex.hpp> using namespace std; boost::mutex mut; double results[10]; void doubler(int x) { //boost::mutex::scoped_lock lck(mut); results[x] = x*2; } int _tmain(int argc, _TCHAR* argv[]) { boost::thread_group thds; for (int x = 10; x>0; x--) { boost::thread *Thread = new boost::thread(&doubler, x); thds.add_thread(Thread); } thds.join_all(); for (int x = 0; x<10; x++) { cout << results[x] << endl; } return 0; } Output: 0 2 4 6 8 10 12 14 16 18 Press any key to continue . . . So...my question is why does this work(as far as i can tell, i ran it about 20 times), producing the above output, even with the locking commented out? I thought the general idea was: in each thread: calculate 2*x copy results to CPU register(s) store calculation in correct part of array copy results back to main(shared) memory I would think that under all but perfect conditions this would result in some part of the results array having 0 values. Is it only copying the required double of the array to a cpu register? Or is it just too short of a calculation to get preempted before it writes the result back to ram? Thanks.

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  • N processes and M types of processes - enter and exit cs

    - by sarit
    i was asked to write: enter function and exit function for the following case: there are N processes and M types of processes (NM) tere is a critical section in which all processes with the same type can enter. for example: if type A is in cs, type B cannot enter cs. but all processes with type A can enter. i can use only mutex and "type" which is the type of the process. deadlock is not allowed. do you think this is ok? shared: this.type = -1; mutex m, m1=1; enter{ down(m) if (this.type == process.type) up(m1) down(m1) this.type= process.type up(m) } exit { this.type = -1 up(m1) } thanks! (by the way, this is not HW... i have an exam and im solvig tests from previous years)

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  • Detecting a stale Mutex

    - by sum1stolemyname
    Is there any technique or tool available to detect this kind of a deadlock during runtime? picture this in a worker thread (one of several, normally 4-6) try WaitForSingleObject(myMutex); DoSTuffThatMightCauseAnException; Except ReleaseMutex(myMutex); end; or more generally is there a design-pattern to avoid these kind of bugs? I coded the above code in the little hous after a longer hacking run

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  • How is spin lock implemented under the hood?

    - by httpinterpret
    This is a lock that can be held by only one thread of execution at a time. An attempt to acquire the lock by another thread of execution makes the latter loop until the lock is released. How does it handle the case when two threads try to acquire the lock exactly the same time? I think this question also applies to various of other mutex implementation.

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  • Multiuser XML document "database" for asp.net app

    - by Pierreten
    I was thinking about a way to allow multiple users to get CRUD access to an XML document in an asp.net app. The operations would obviously have to be made under the assumption of a multithreaded environment. For perf reasons, would it make sense to cache the document, and use a mutex on that cached version? When would changes be flushed to the physical XML document? Any and all recommendations are appreciated (also "use a database" isn't an option at this point unfortunately)

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  • What is the correct way to create a single instance application?

    - by Nidonocu
    Using C# and WPF under .net (rather than WindowsForms or console), what is the correct way to create an application that can only be run as a single instance? I know it has something to do with some mythical thing called a mutex, rarely can I find someone that bothers to stop and explain what one of these are. The code needs to also inform the already running instance that the user tried to start a second one, and maybe also pass any command line arguments if any existed.

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