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POProgram using Semaphores runs fine on Linux...unexpected results on Mac osX
 

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  1. POProgram using Semaphores runs fine on Linux...unexpected results on Mac osX
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    <p>I wrote a simple program solving the Readers-Writers problem using semaphores. It runs perfectly on Linux os, but when I run it on my Mac osX I get unexpected results and I can't figure out why. </p> <p>My Program:</p> <pre><code>#include &lt;semaphore.h&gt; #include &lt;sys/types.h&gt; #include &lt;stdio.h&gt; #include &lt;pthread.h&gt; #include &lt;unistd.h&gt; void* function1(void* val); void* function2(void* val); // shared values volatile int X; volatile int Y; // declare semaphores sem_t s1; sem_t s2; main() { void* status; pthread_t thread1; pthread_t thread2; srand(time(NULL)); // initialize semaphores to zero sem_init(&amp;s1, 0, 0); sem_init(&amp;s2, 0, 0); pthread_create(&amp;thread1, NULL, function1, NULL); pthread_create(&amp;thread2, NULL, function2, NULL); pthread_join(thread1, &amp;status); pthread_join(thread2, &amp;status); sem_destroy(&amp;s1); sem_destroy(&amp;s2); } void* function1(void* val) { while(1) { X = rand()%1000; // write printf("After thread ID A writes to X, X = %d\n", X); sem_post(&amp;s1); // signal sem_wait(&amp;s2); // wait printf("After thread ID A reads from Y, Y = %d\n", Y); // read sleep(3); } } void* function2(void* val) { while(1) { sem_wait(&amp;s1); // wait printf("After thread ID B reads from X, X = %d\n", X); // read Y = rand()%1000; // write printf("After thread ID B write to Y, Y = %d\n", Y); sem_post(&amp;s2); // signal sleep(3); } } </code></pre> <p>The output I receive on Linux (what it's supposed to look like): </p> <pre><code>After thread ID A writes to X, X = 100 After thread ID B reads from X, X = 100 After thread ID B write to Y, Y = 234 After thread ID A reads from Y, Y = 234 ... </code></pre> <p>The output on Mac osX (unexpected):</p> <pre><code>After thread ID A writes to X, X = 253 After thread ID A reads from Y, Y = 0 After thread ID B reads from X, X = 253 After thread ID B write to Y, Y = 728 ... </code></pre>
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    1. USAdam Soffer
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      1. POProgram using Semaphores runs fine on Linux...unexpected results on Mac osX
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    1. CONot a solution, but anytime a multi threaded system works fine in one location (and have you tried different persuasions of Linux?) but not fine in another location then I would be suspecting a race condition.
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      1. POProgram using Semaphores runs fine on Linux...unexpected results on Mac osX
      1. USPeter M
 

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