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    <p>Copied from an <a href="https://stackoverflow.com/questions/4258283/waiting-win32-threads/4258377#4258377">answer</a> to <a href="https://stackoverflow.com/questions/4258283/waiting-win32-threads/">one of my earlier questions</a>. My question concerns Win32 threads but the described consept pretty much the same with pthreads.</p> <ol> <li>Use a semaphore in your queue to indicate whether there are elements ready to be processed.</li> <li>Every time you add an item, call <code>sem_post()</code> to increment the count associated with the semaphore</li> <li>In the loop in your thread process, call <code>sem_wait()</code> on the handle of your semaphore object</li> </ol> <p>Here is a tutorial for <a href="http://www.csc.villanova.edu/~mdamian/threads/posixsem.html" rel="nofollow noreferrer">POSIX Semaphores</a></p> <p>But first like the other guy said, you have to make Q thread-safe.</p> <pre><code>void *func(void *newWorker) { struct workerType* worker = (struct workerType*) newWorker; while(numServed &lt; maxJobs) { //if(!Q.empty()) { // No need to ask if Q is empty. // If a thread passes the sem_wait function // there has to be at least one job in the Q sem_wait(&amp;semaphore); pthread_mutex_lock(&amp;mutex); struct jobType* job = Q.front(); numServed++; cout &lt;&lt; job-&gt;jobNum &lt;&lt; " was served by " &lt;&lt; worker-&gt;workerNum &lt;&lt; endl; Q.pop(); pthread_mutex_unlock(&amp;mutex); //sleep(worker-&gt;runTime); No need to sleep also //} } } void *job(void *jobdata) { struct jobType *job = (struct jobType*) jobdata; //sleep(job-&gt;arrivtime); pthread_mutex_lock(&amp;mutex); Q.push(job); pthread_mutex_unlock(&amp;mutex); sem_post(&amp;semaphore); // Inform the workers that another job is pushed. } </code></pre>
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    1. COThanks, I'll try this. Would the initial semaphore value be 0?
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    2. CO@user623982: Yes, 0 would be fine. In this case the value of the semaphore is equal to the current number of jobs in the Q.
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    3. COWhat if I need both functions to sleep? Jobs sleep their respective arrival times before being pushed onto the queue, workers sleep their run time after acquiring a job. I tried doing this several ways but I get incorrect results.
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