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POsimple testing of semaphores
 

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  1. POsimple testing of semaphores
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    <p>I am trying to create a simple program to test semaphores. I am forking the process and tormenting the value of variable c in the critical section of each process, but the value of c I get is still 1 not 2. Even with the mmap() uncommented. Can anyone please explain to me what I am doing wrong? Any help would be appreciated. I am a total newbie in this. Thank you very much for your time.</p> <pre><code>int main() { int c = 0; sem_t mutex; sem_t mutex1; // sem_t *mutex = (sem_t*)mmap(NULL, sizeof(sem_t*), PROT_READ|PROT_WRITE,MAP_SHARED|MAP_ANONYMOUS,-1, 0); sem_init(&amp;mutex, 0, 1); sem_init(&amp;mutex1, 0, 1); pid_t i; int id = fork(); if(id == -1) {} else if(id == 0) { sem_wait (&amp;mutex); c++; sem_post (&amp;mutex); } else { sem_wait (&amp;mutex); c++; sem_post (&amp;mutex); } cout&lt;&lt;c&lt;&lt;endl; //system("pause"); return 0; } </code></pre> <p>I tried it another way by making the pshared argument 1, but it still does not work. I have also tried it sem_op but it still does not work.</p> <pre><code> int main() { int c = 0; int sid =semget(1105,2, 0666 | IPC_CREAT); pid_t i; int id = fork(); if(id == -1) { } else if(id == 0) { struct sembuf sb; sb.sem_num = 0; sb.sem_op = -1; sb.sem_flg = 0; if((semop(sid, &amp;sb, 1)) == -1) cout&lt;&lt;"error"&lt;&lt;endl; c++; sb.sem_num = 0; sb.sem_op = -1; sb.sem_flg = 0; if((semop(sid, &amp;sb, 1)) == -1) cout&lt;&lt;"error"&lt;&lt;endl; } else if(id == 1) { struct sembuf sb; if((semop(sid, &amp;sb, 1)) == -1) cout&lt;&lt;"error"&lt;&lt;endl; c++; sb.sem_num = 0; sb.sem_op = -1; sb.sem_flg = 0; if((semop(sid, &amp;sb, 1)) == -1) cout&lt;&lt;"error"&lt;&lt;endl; } cout&lt;&lt;c&lt;&lt;endl; return 0; } </code></pre>
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    1. COPlease take the time to properly format the code you posted.
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    2. COI just edited it. Thank you.
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    3. COPlease run your code through [`indent(1)`](http://linux.die.net/man/1/indent) or a similar function from your IDE — your hand edits are still inconsistently formatted and hard to follow. Please include headers necessary for compilation. Please exclude extraneous code like `mutex1`.
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