pthread_once.c 2.5 KB

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  1. /* Copyright (C) 2003-2013 Free Software Foundation, Inc.
  2. Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
  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. __pthread_once (once_control, init_routine)
  26. pthread_once_t *once_control;
  27. void (*init_routine) (void);
  28. {
  29. while (1)
  30. {
  31. int oldval, val, newval;
  32. val = *once_control;
  33. do
  34. {
  35. /* Check if the initialized has already been done. */
  36. if ((val & 2) != 0)
  37. return 0;
  38. oldval = val;
  39. newval = (oldval & 3) | __fork_generation | 1;
  40. val = atomic_compare_and_exchange_val_acq (once_control, newval,
  41. oldval);
  42. }
  43. while (__builtin_expect (val != oldval, 0));
  44. /* Check if another thread already runs the initializer. */
  45. if ((oldval & 1) != 0)
  46. {
  47. /* Check whether the initializer execution was interrupted
  48. by a fork. */
  49. if (((oldval ^ newval) & -4) == 0)
  50. {
  51. /* Same generation, some other thread was faster. Wait. */
  52. lll_futex_wait (once_control, newval, LLL_PRIVATE);
  53. continue;
  54. }
  55. }
  56. /* This thread is the first here. Do the initialization.
  57. Register a cleanup handler so that in case the thread gets
  58. interrupted the initialization can be restarted. */
  59. pthread_cleanup_push (clear_once_control, once_control);
  60. init_routine ();
  61. pthread_cleanup_pop (0);
  62. /* Add one to *once_control. */
  63. atomic_increment (once_control);
  64. /* Wake up all other threads. */
  65. lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  66. break;
  67. }
  68. return 0;
  69. }
  70. weak_alias (__pthread_once, pthread_once)
  71. strong_alias (__pthread_once, __pthread_once_internal)