fbtl/tst-sem3.c

   1 /* Copyright (C) 2002-2013 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <semaphore.h>
  21 #include <stdint.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26 #include <sys/mman.h>
  27 #include <sys/wait.h>
  28
  29
  30 int
  31 main (void)
  32 {
  33   size_t ps = sysconf (_SC_PAGESIZE);
  34   char tmpfname[] = "/tmp/tst-sem3.XXXXXX";
  35   char data[ps];
  36   void *mem;
  37   int fd;
  38   sem_t *s;
  39   pid_t pid;
  40   char *p;
  41
  42   fd = mkstemp (tmpfname);
  43   if (fd == -1)
  44     {
  45       printf ("cannot open temporary file: %m\n");
  46       exit (1);
  47     }
  48
  49   /* Make sure it is always removed.  */
  50   unlink (tmpfname);
  51
  52   /* Create one page of data.  */
  53   memset (data, '\0', ps);
  54
  55   /* Write the data to the file.  */
  56   if (write (fd, data, ps) != (ssize_t) ps)
  57     {
  58       puts ("short write");
  59       exit (1);
  60     }
  61
  62   mem = mmap (NULL, ps, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  63   if (mem == MAP_FAILED)
  64     {
  65       printf ("mmap failed: %m\n");
  66       exit (1);
  67     }
  68
  69   s = (sem_t *) (((uintptr_t) mem + __alignof (sem_t))
  70                  & ~(__alignof (sem_t) - 1));
  71   p = (char *) (s + 1);
  72
  73   if (sem_init (s, 1, 1) == -1)
  74     {
  75       puts ("init failed");
  76       exit (1);
  77     }
  78
  79   if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1)
  80     {
  81       puts ("1st wait failed");
  82       exit (1);
  83     }
  84
  85   errno = 0;
  86   if (TEMP_FAILURE_RETRY (sem_trywait (s)) != -1)
  87     {
  88       puts ("trywait succeeded");
  89       exit (1);
  90     }
  91   else if (errno != EAGAIN)
  92     {
  93       puts ("trywait didn't return EAGAIN");
  94       exit (1);
  95     }
  96
  97   *p = 0;
  98
  99   puts ("going to fork now");
 100   pid = fork ();
 101   if (pid == -1)
 102     {
 103       puts ("fork failed");
 104       exit (1);
 105     }
 106   else if (pid == 0)
 107     {
 108       /* Play some lock ping-pong.  It's our turn to unlock first.  */
 109       if ((*p)++ != 0)
 110         {
 111           puts ("child: *p != 0");
 112           exit (1);
 113         }
 114
 115       if (sem_post (s) == -1)
 116         {
 117           puts ("child: 1st post failed");
 118           exit (1);
 119         }
 120
 121       puts ("child done");
 122     }
 123   else
 124     {
 125       if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1)
 126         {
 127           printf ("parent: 2nd wait failed: %m\n");
 128           exit (1);
 129         }
 130
 131       if (*p != 1)
 132         {
 133           puts ("*p != 1");
 134           exit (1);
 135         }
 136
 137       puts ("parent done");
 138     }
 139
 140   exit (0);
 141 }