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glibc  2.9
Functions
tst-sem3.c File Reference
#include <errno.h>
#include <semaphore.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/wait.h>

Go to the source code of this file.

Functions

int main (void)

Function Documentation

int main ( void  )

Definition at line 32 of file tst-sem3.c.

{
  size_t ps = sysconf (_SC_PAGESIZE);
  char tmpfname[] = "/tmp/tst-sem3.XXXXXX";
  char data[ps];
  void *mem;
  int fd;
  sem_t *s;
  pid_t pid;
  char *p;

  fd = mkstemp (tmpfname);
  if (fd == -1)
    {
      printf ("cannot open temporary file: %m\n");
      exit (1);
    }

  /* Make sure it is always removed.  */
  unlink (tmpfname);

  /* Create one page of data.  */
  memset (data, '\0', ps);

  /* Write the data to the file.  */
  if (write (fd, data, ps) != (ssize_t) ps)
    {
      puts ("short write");
      exit (1);
    }

  mem = mmap (NULL, ps, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  if (mem == MAP_FAILED)
    {
      printf ("mmap failed: %m\n");
      exit (1);
    }

  s = (sem_t *) (((uintptr_t) mem + __alignof (sem_t))
               & ~(__alignof (sem_t) - 1));
  p = (char *) (s + 1);

  if (sem_init (s, 1, 1) == -1)
    {
      puts ("init failed");
      exit (1);
    }

  if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1)
    {
      puts ("1st wait failed");
      exit (1);
    }

  errno = 0;
  if (TEMP_FAILURE_RETRY (sem_trywait (s)) != -1)
    {
      puts ("trywait succeeded");
      exit (1);
    }
  else if (errno != EAGAIN)
    {
      puts ("trywait didn't return EAGAIN");
      exit (1);
    }

  *p = 0;

  puts ("going to fork now");
  pid = fork ();
  if (pid == -1)
    {
      puts ("fork failed");
      exit (1);
    }
  else if (pid == 0)
    {
      /* Play some lock ping-pong.  It's our turn to unlock first.  */
      if ((*p)++ != 0)
       {
         puts ("child: *p != 0");
         exit (1);
       }

      if (sem_post (s) == -1)
       {
         puts ("child: 1st post failed");
         exit (1);
       }

      puts ("child done");
    }
  else
    {
      if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1)
       {
         printf ("parent: 2nd wait failed: %m\n");
         exit (1);
       }

      if (*p != 1)
       {
         puts ("*p != 1");
         exit (1);
       }

      puts ("parent done");
    }

  exit (0);
}

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