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POWhy this thread safe queue, creates a deadlock?
 

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  1. POWhy this thread safe queue, creates a deadlock?
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    <p>I've written my own version of thread safe queue. However, when I run this program, it hangs/deadlocks itself.</p> <p>Wondering, why is this locks/hangs forever.</p> <pre><code>void concurrentqueue::addtoQueue(const int number) { locker currentlock(lock_for_queue); numberlist.push(number); pthread_cond_signal(&amp;queue_availability_condition); } int concurrentqueue::getFromQueue() { int number = 0; locker currentlock(lock_for_queue); if ( empty() ) { pthread_cond_wait(&amp;queue_availability_condition,&amp;lock_for_queue); } number = numberlist.front(); numberlist.pop(); return number; } bool concurrentqueue::empty() { return numberlist.empty(); } </code></pre> <p>I've written, the class locker as RAII.</p> <pre><code>class locker { public: locker(pthread_mutex_t&amp; lockee): target(lockee) { pthread_mutex_lock(&amp;target); } ~locker() { pthread_mutex_unlock(&amp;target); } private: pthread_mutex_t target; }; </code></pre> <p>My writer/reader thread code is very simple. Writer thread, adds to the queue and reader thread, reads from the queue.</p> <pre><code>void * writeintoqueue(void* myqueue) { void *t = 0; concurrentqueue *localqueue = (concurrentqueue *) myqueue; for ( int i = 0; i &lt; 10 ; ++i) { localqueue-&gt;addtoQueue(i*10); } pthread_exit(t); } void * readfromqueue(void* myqueue) { void *t = 0; concurrentqueue *localqueue = (concurrentqueue *) myqueue; int number = 0; for ( int i = 0 ; i &lt; 10 ; ++i) { number = localqueue-&gt;getFromQueue(); std::cout &lt;&lt; "The number from the queue is " &lt;&lt; number &lt;&lt; std::endl; } pthread_exit(t); } </code></pre>
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    1. COI'm not a `pthreads` expert my any means, but I don't think you want to copy your `pthread_mutex_t` by value into `target` in your `locker` class. Make `target` a `pthread_mutex_t &` or `pthread_mutex_t *`.
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      1. USmsandiford
    2. CO@spong I am certain this is the problem. By making a copy the locking and the signaling are not dealing with the same structure anymore, and this would cause many pthread implementations to go wonky. You should add your comment as an answer.
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      1. USLogan Capaldo
    3. COWhy reinvent the wheel. This is the implementation I use. http://gist.github.com/482342
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      1. USMichael Anderson
 

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