tst-sem3.c 2.9 KB

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  1. /* Copyright (C) 2002, 2003 Free Software Foundation, Inc.
  2. This file is part of the GNU C Library.
  3. Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
  4. The GNU C Library is free software; you can redistribute it and/or
  5. modify it under the terms of the GNU Lesser General Public
  6. License as published by the Free Software Foundation; either
  7. version 2.1 of the License, or (at your option) any later version.
  8. The GNU C Library is distributed in the hope that it will be useful,
  9. but WITHOUT ANY WARRANTY; without even the implied warranty of
  10. MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  11. Lesser General Public License for more details.
  12. You should have received a copy of the GNU Lesser General Public
  13. License along with the GNU C Library; if not, see
  14. <http://www.gnu.org/licenses/>. */
  15. #include <errno.h>
  16. #include <semaphore.h>
  17. #include <stdint.h>
  18. #include <stdio.h>
  19. #include <stdlib.h>
  20. #include <string.h>
  21. #include <unistd.h>
  22. #include <sys/mman.h>
  23. #include <sys/wait.h>
  24. int
  25. main (void)
  26. {
  27. size_t ps = sysconf (_SC_PAGESIZE);
  28. char tmpfname[] = "/tmp/tst-sem3.XXXXXX";
  29. char data[ps];
  30. void *mem;
  31. int fd;
  32. sem_t *s;
  33. pid_t pid;
  34. char *p;
  35. fd = mkstemp (tmpfname);
  36. if (fd == -1)
  37. {
  38. printf ("cannot open temporary file: %m\n");
  39. exit (1);
  40. }
  41. /* Make sure it is always removed. */
  42. unlink (tmpfname);
  43. /* Create one page of data. */
  44. memset (data, '\0', ps);
  45. /* Write the data to the file. */
  46. if (write (fd, data, ps) != (ssize_t) ps)
  47. {
  48. puts ("short write");
  49. exit (1);
  50. }
  51. mem = mmap (NULL, ps, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  52. if (mem == MAP_FAILED)
  53. {
  54. printf ("mmap failed: %m\n");
  55. exit (1);
  56. }
  57. s = (sem_t *) (((uintptr_t) mem + __alignof (sem_t))
  58. & ~(__alignof (sem_t) - 1));
  59. p = (char *) (s + 1);
  60. if (sem_init (s, 1, 1) == -1)
  61. {
  62. puts ("init failed");
  63. exit (1);
  64. }
  65. if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1)
  66. {
  67. puts ("1st wait failed");
  68. exit (1);
  69. }
  70. errno = 0;
  71. if (TEMP_FAILURE_RETRY (sem_trywait (s)) != -1)
  72. {
  73. puts ("trywait succeeded");
  74. exit (1);
  75. }
  76. else if (errno != EAGAIN)
  77. {
  78. puts ("trywait didn't return EAGAIN");
  79. exit (1);
  80. }
  81. *p = 0;
  82. puts ("going to fork now");
  83. pid = fork ();
  84. if (pid == -1)
  85. {
  86. puts ("fork failed");
  87. exit (1);
  88. }
  89. else if (pid == 0)
  90. {
  91. /* Play some lock ping-pong. It's our turn to unlock first. */
  92. if ((*p)++ != 0)
  93. {
  94. puts ("child: *p != 0");
  95. exit (1);
  96. }
  97. if (sem_post (s) == -1)
  98. {
  99. puts ("child: 1st post failed");
  100. exit (1);
  101. }
  102. puts ("child done");
  103. }
  104. else
  105. {
  106. if (TEMP_FAILURE_RETRY (sem_wait (s)) == -1)
  107. {
  108. printf ("parent: 2nd wait failed: %m\n");
  109. exit (1);
  110. }
  111. if (*p != 1)
  112. {
  113. puts ("*p != 1");
  114. exit (1);
  115. }
  116. puts ("parent done");
  117. }
  118. exit (0);
  119. }