pthread_once.c 3.0 KB

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  1. /* Copyright (C) 2004, 2005 Free Software Foundation, Inc.
  2. This file is part of the GNU C Library.
  3. The GNU C Library is free software; you can redistribute it and/or
  4. modify it under the terms of the GNU Lesser General Public
  5. License as published by the Free Software Foundation; either
  6. version 2.1 of the License, or (at your option) any later version.
  7. The GNU C Library is distributed in the hope that it will be useful,
  8. but WITHOUT ANY WARRANTY; without even the implied warranty of
  9. MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  10. Lesser General Public License for more details.
  11. You should have received a copy of the GNU Lesser General Public
  12. License along with the GNU C Library; if not, see
  13. <http://www.gnu.org/licenses/>. */
  14. #include "pthreadP.h"
  15. #include <lowlevellock.h>
  16. unsigned long int __fork_generation attribute_hidden;
  17. static void
  18. clear_once_control (void *arg)
  19. {
  20. pthread_once_t *once_control = (pthread_once_t *) arg;
  21. *once_control = 0;
  22. lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  23. }
  24. int
  25. attribute_protected
  26. __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
  27. {
  28. for (;;)
  29. {
  30. int oldval;
  31. int newval;
  32. /* Pseudo code:
  33. newval = __fork_generation | 1;
  34. oldval = *once_control;
  35. if ((oldval & 2) == 0)
  36. *once_control = newval;
  37. Do this atomically.
  38. */
  39. do
  40. {
  41. newval = __fork_generation | 1;
  42. oldval = *once_control;
  43. if (oldval & 2)
  44. break;
  45. } while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval);
  46. /* Check if the initializer has already been done. */
  47. if ((oldval & 2) != 0)
  48. return 0;
  49. /* Check if another thread already runs the initializer. */
  50. if ((oldval & 1) == 0)
  51. break;
  52. /* Check whether the initializer execution was interrupted by a fork. */
  53. if (oldval != newval)
  54. break;
  55. /* Same generation, some other thread was faster. Wait. */
  56. lll_futex_wait (once_control, oldval, LLL_PRIVATE);
  57. }
  58. /* This thread is the first here. Do the initialization.
  59. Register a cleanup handler so that in case the thread gets
  60. interrupted the initialization can be restarted. */
  61. pthread_cleanup_push (clear_once_control, once_control);
  62. init_routine ();
  63. pthread_cleanup_pop (0);
  64. /* Say that the initialisation is done. */
  65. *once_control = __fork_generation | 2;
  66. /* Wake up all other threads. */
  67. lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  68. return 0;
  69. }
  70. weak_alias (__pthread_once, pthread_once)
  71. strong_alias (__pthread_once, __pthread_once_internal)
  72. #if defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__PIC__)
  73. /* When statically linked, if pthread_create is used, this file
  74. will be brought in. The exception handling code in GCC assumes
  75. that if pthread_create is available, so are these. */
  76. const void *include_pthread_getspecific attribute_hidden = pthread_getspecific;
  77. const void *include_pthread_setspecific attribute_hidden = pthread_setspecific;
  78. const void *include_pthread_key_create attribute_hidden = pthread_key_create;
  79. #endif