drd/tests/sem_open.c

   1 /* Use a semaphore to implement mutual exclusion. */
   2
   3 #include <assert.h>
   4 #include <fcntl.h>     /* O_CREAT */
   5 #include <pthread.h>
   6 #include <semaphore.h>
   7 #include <stdio.h>     /* printf() */
   8 #include <stdlib.h>    /* exit()  */
   9 #include <unistd.h>    /* sleep() */
  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   char semaphore_name[32];
  38
  39   while ((optchar = getopt(argc, argv, "dmp")) != EOF)
  40   {
  41     switch (optchar)
  42     {
  43     case 'd':
  44       s_debug = 1;
  45       break;
  46     case 'm':
  47       s_do_mutual_exclusion = 1;
  48       break;
  49     case 'p':
  50       s_do_printf = 1;
  51       break;
  52     default:
  53       assert(0);
  54     }
  55   }
  56
  57   /*
  58    * Use the ipcs and ipcrm commands to clean up named semaphores left by
  59    * aborted instances of this process.
  60    */
  61   snprintf(semaphore_name, sizeof(semaphore_name), "/drd-sem-open-test-%d",
  62            getpid());
  63   s_sem = sem_open(semaphore_name, O_CREAT | O_EXCL, 0600, 1);
  64   if (s_sem == SEM_FAILED)
  65   {
  66     fprintf(stderr, "Failed to create a semaphore with name %s\n",
  67             semaphore_name);
  68     exit(1);
  69   }
  70
  71   /*
  72    * Switch to line-buffered mode, such that timing information can be
  73    * obtained for each printf() call with strace.
  74    */
  75   setlinebuf(stdout);
  76
  77   if (s_debug)
  78   {
  79     printf("&s_d1 = %p; &s_d2 = %p; &s_d3 = %p\n", &s_d1, &s_d2, &s_d3);
  80   }
  81
  82   s_d1 = 1;
  83   s_d3 = 3;
  84
  85   pthread_create(&threadid, 0, thread_func, 0);
  86
  87   sleep(1); /* Wait until thread_func() finished. */
  88
  89   {
  90     if (s_do_mutual_exclusion) sem_wait(s_sem);
  91     s_d3++;
  92     if (s_do_mutual_exclusion) sem_post(s_sem);
  93   }
  94
  95   /* Wait until the thread finished. */
  96   pthread_join(threadid, 0);
  97   if (s_do_printf) printf("s_d2 = %g (should be 2)\n", s_d2);
  98   if (s_do_printf) printf("s_d3 = %g (should be 5)\n", s_d3);
  99
 100   sem_close(s_sem);
 101   sem_unlink(semaphore_name);
 102
 103   return 0;
 104 }
 105
 106 static void* thread_func(void* thread_arg)
 107 {
 108   if (s_do_printf)
 109   {
 110     printf("s_d1 = %g (should be 1)\n", s_d1);
 111   }
 112   s_d2 = 2;
 113   {
 114     if (s_do_mutual_exclusion) sem_wait(s_sem);
 115     s_d3++;
 116     if (s_do_mutual_exclusion) sem_post(s_sem);
 117   }
 118   return 0;
 119 }