drd/tests/sem_as_mutex.c

   1 /* Use a semaphore to implement mutual exclusion. */
   2
   3
   4 #include <assert.h>
   5 #include <stdio.h>     /* printf() */
   6 #include <pthread.h>
   7 #include <semaphore.h>
   8 #include <unistd.h>    /* sleep() */
   9
  10
  11 /* Local functions declarations. */
  12
  13 static void* thread_func(void*);
  14
  15
  16 /* Local variables. */
  17
  18 /* s_sem protects s_d3. */
  19 static sem_t s_sem;
  20
  21 static double s_d1; /* accessed before thread creation and in the created */
  22                     /* thread (not a race). */
  23 static double s_d2; /* accessed in the created thread and after the join */
  24                     /* (not a race). */
  25 static double s_d3; /* accessed simultaneously from both threads (race). */
  26 static int    s_debug     = 0;
  27 static int    s_do_printf = 0;
  28 static int    s_do_mutual_exclusion = 0;
  29
  30
  31 /* Function definitions. */
  32
  33 int main(int argc, char** argv)
  34 {
  35   int optchar;
  36   pthread_t threadid;
  37
  38   while ((optchar = getopt(argc, argv, "dmp")) != EOF)
  39   {
  40     switch (optchar)
  41     {
  42     case 'd':
  43       s_debug = 1;
  44       break;
  45     case 'm':
  46       s_do_mutual_exclusion = 1;
  47       break;
  48     case 'p':
  49       s_do_printf = 1;
  50       break;
  51     default:
  52       assert(0);
  53     }
  54   }
  55
  56   sem_init(&s_sem, 0, 1);
  57
  58   /*
  59    * Switch to line-buffered mode, such that timing information can be
  60    * obtained for each printf() call with strace.
  61    */
  62   setlinebuf(stdout);
  63
  64   if (s_debug)
  65   {
  66     printf("&s_d1 = %p; &s_d2 = %p; &s_d3 = %p\n", &s_d1, &s_d2, &s_d3);
  67   }
  68
  69   s_d1 = 1;
  70   s_d3 = 3;
  71
  72   pthread_create(&threadid, 0, thread_func, 0);
  73
  74   sleep(1); /* Wait until thread_func() finished. */
  75
  76   {
  77     if (s_do_mutual_exclusion) sem_wait(&s_sem);
  78     s_d3++;
  79     if (s_do_mutual_exclusion) sem_post(&s_sem);
  80   }
  81
  82   /* Wait until the thread finished. */
  83   pthread_join(threadid, 0);
  84   if (s_do_printf) printf("s_d2 = %g (should be 2)\n", s_d2);
  85   if (s_do_printf) printf("s_d3 = %g (should be 5)\n", s_d3);
  86
  87   sem_destroy(&s_sem);
  88
  89   return 0;
  90 }
  91
  92 static void* thread_func(void* thread_arg)
  93 {
  94   if (s_do_printf)
  95   {
  96     printf("s_d1 = %g (should be 1)\n", s_d1);
  97   }
  98   s_d2 = 2;
  99   {
 100     if (s_do_mutual_exclusion) sem_wait(&s_sem);
 101     s_d3++;
 102     if (s_do_mutual_exclusion) sem_post(&s_sem);
 103   }
 104   return 0;
 105 }