1  /* pthread_once.  Generic version.
       2     Copyright (C) 2002-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library;  if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <pthread.h>
      20  #include <atomic.h>
      21  
      22  #include <pt-internal.h>
      23  
      24  static void
      25  clear_once_control (void *arg)
      26  {
      27    pthread_once_t *once_control = arg;
      28    __pthread_spin_unlock (&once_control->__lock);
      29  }
      30  
      31  int
      32  __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
      33  {
      34    ASSERT_TYPE_SIZE (pthread_once_t, __SIZEOF_PTHREAD_ONCE_T);
      35  
      36    atomic_full_barrier ();
      37    if (once_control->__run == 0)
      38      {
      39        __pthread_spin_wait (&once_control->__lock);
      40  
      41        if (once_control->__run == 0)
      42  	{
      43  	  pthread_cleanup_push (clear_once_control, once_control);
      44  	  init_routine ();
      45  	  pthread_cleanup_pop (0);
      46  
      47  	  atomic_full_barrier ();
      48  	  once_control->__run = 1;
      49  	}
      50  
      51        __pthread_spin_unlock (&once_control->__lock);
      52      }
      53  
      54    return 0;
      55  }
      56  weak_alias (__pthread_once, pthread_once);