/***********************************************************************
 * sempahore.c --- Concise illustration of POSIX unnamed semaphore
 *                 operations.
 *
 * To compile:
 *
 *    gcc -o semaphore semaphore.c -lpthread
 *
 * (Semaphores are implemented as an extension of the Pthreads library,
 * hence the inclusion of the library.)
 ***********************************************************************/


/* Must include this header file. */
#include <semaphore.h>


int main()
{
   /* Declaring a semaphore. */
   sem_t semaphore;

   /* Note that semaphores are passed by address. */

   /* Semaphores must be initialized before first use.  The first parameter
    * is the address of the semaphore to initialize.  For us, the
    * second parameter should always be 0.  The third parameter is the
    * semaphore's initial value: 0 or 1 for a binary semaphore;
    * 0 to n for a counting semaphore.
    */
   sem_init(&semaphore, 0, 0);

   /* sem_post() is the semaphore signal operation */
   sem_post(&semaphore);

   /* The semaphore wait operation, of course */
   sem_wait(&semaphore);

   return 0;
}