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

Go to the source code of this file.

Functions

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

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 38 of file pthread_once.c.

{
  while (1)
    {
      int oldval;
      int newval;

      /* Pseudo code:
          oldval = *once_control;
          if ((oldval & 2) == 0)
           {
             newval = (oldval & 3) | __fork_generation | 1;
             *once_control = newval;
           }
        Do this atomically.  */
      __asm __volatile ("   l       %1,%0\n"
                     "0: lhi        %2,2\n"
                     "   tml        %1,2\n"
                     "   jnz        1f\n"
                     "   nr  %2,%1\n"
                     "   ahi        %2,1\n"
                     "   o   %2,%3\n"
                     "   cs  %1,%2,%0\n"
                     "   jl  0b\n"
                     "1:"
                     : "=Q" (*once_control), "=&d" (oldval), "=&d" (newval)
                     : "m" (__fork_generation), "m" (*once_control)
                     : "cc" );
      /* Check if the initialized has already been done.  */
      if ((oldval & 2) != 0)
         break;
      /* Check if another thread already runs the initializer. */
      if ((oldval & 1) != 0)
       {
         /* Check whether the initializer execution was interrupted
            by a fork.       */
         if (((oldval ^ newval) & -4) == 0)
           {
             /* Same generation, some other thread was faster. Wait.  */
             lll_futex_wait (once_control, newval, LLL_PRIVATE);
             continue;
           }
       }

      /* 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.  */
      __asm __volatile ("   l       %1,%0\n"
                     "0: lr  %2,%1\n"
                     "   ahi        %2,1\n"
                     "   cs  %1,%2,%0\n"
                     "   jl  0b\n"
                     : "=Q" (*once_control), "=&d" (oldval), "=&d" (newval)
                     : "m" (*once_control) : "cc" );

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

  return 0;
}

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static void clear_once_control ( void *  arg) [static]

Definition at line 28 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 24 of file pthread_once.c.