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glibc  2.9
Functions | Variables
pthread_once.c File Reference
#include "pthreadP.h"
#include <lowlevellock.h>

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Functions

static void clear_once_control (void *arg)
int __pthread_once (pthread_once_t *once_control, void(*init_routine)(void))

Variables

unsigned long int __fork_generation attribute_hidden

Function Documentation

int __pthread_once ( pthread_once_t once_control,
void(*)(void)  init_routine 
)

Definition at line 35 of file pthread_once.c.

{
  for (;;)
    {
      int oldval;
      int newval;
      int tmp;

      /* Pseudo code:
        newval = __fork_generation | 1;
        oldval = *once_control;
        if ((oldval & 2) == 0)
          *once_control = newval;
        Do this atomically.
      */
      newval = __fork_generation | 1;
      __asm __volatile (
              "1:    ldl_l  %0, %2\n"
              "      and    %0, 2, %1\n"
              "      bne    %1, 2f\n"
              "      mov    %3, %1\n"
              "      stl_c  %1, %2\n"
              "      beq    %1, 1b\n"
              "2:    mb"
              : "=&r" (oldval), "=&r" (tmp), "=m" (*once_control)
              : "r" (newval), "m" (*once_control));

      /* Check if the initializer has already been done.  */
      if ((oldval & 2) != 0)
       return 0;

      /* Check if another thread already runs the initializer. */
      if ((oldval & 1) == 0)
       break;

      /* Check whether the initializer execution was interrupted by a fork.  */
      if (oldval != newval)
       break;

      /* Same generation, some other thread was faster. Wait.  */
      lll_futex_wait (once_control, oldval, LLL_PRIVATE);
    }

  /* This thread is the first here.  Do the initialization.
     Register a cleanup handler so that in case the thread gets
     interrupted the initialization can be restarted.  */
  pthread_cleanup_push (clear_once_control, once_control);

  init_routine ();

  pthread_cleanup_pop (0);

  /* Add one to *once_control to take the bottom 2 bits from 01 to 10.  */
  atomic_increment (once_control);

  /* Wake up all other threads.  */
  lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);

  return 0;
}

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static void clear_once_control ( void *  arg) [static]

Definition at line 26 of file pthread_once.c.

{
  pthread_once_t *once_control = (pthread_once_t *) arg;

  *once_control = 0;
  lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
}

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Variable Documentation

unsigned long int __fork_generation attribute_hidden

Definition at line 23 of file pthread_once.c.