pthread_once.c 2.7 KB

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  1. /* Copyright (C) 2003, 2004, 2007 Free Software Foundation, Inc.
  2. This file is part of the GNU C Library.
  3. Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
  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, write to the Free
  14. Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  15. 02111-1307 USA. */
  16. #include "pthreadP.h"
  17. #include <lowlevellock.h>
  18. unsigned long int __fork_generation attribute_hidden;
  19. static void
  20. clear_once_control (void *arg)
  21. {
  22. pthread_once_t *once_control = (pthread_once_t *) arg;
  23. *once_control = 0;
  24. lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  25. }
  26. int
  27. __pthread_once (once_control, init_routine)
  28. pthread_once_t *once_control;
  29. void (*init_routine) (void);
  30. {
  31. while (1)
  32. {
  33. int oldval, val, newval;
  34. val = *once_control;
  35. do
  36. {
  37. /* Check if the initialized has already been done. */
  38. if ((val & 2) != 0)
  39. return 0;
  40. oldval = val;
  41. newval = (oldval & 3) | __fork_generation | 1;
  42. val = atomic_compare_and_exchange_val_acq (once_control, newval,
  43. oldval);
  44. }
  45. while (__builtin_expect (val != oldval, 0));
  46. /* Check if another thread already runs the initializer. */
  47. if ((oldval & 1) != 0)
  48. {
  49. /* Check whether the initializer execution was interrupted
  50. by a fork. */
  51. if (((oldval ^ newval) & -4) == 0)
  52. {
  53. /* Same generation, some other thread was faster. Wait. */
  54. lll_futex_wait (once_control, newval, LLL_PRIVATE);
  55. continue;
  56. }
  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. /* Add one to *once_control. */
  65. atomic_increment (once_control);
  66. /* Wake up all other threads. */
  67. lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
  68. break;
  69. }
  70. return 0;
  71. }
  72. weak_alias (__pthread_once, pthread_once)
  73. strong_alias (__pthread_once, __pthread_once_internal)