1  /* Lock a semaphore if it does not require blocking.  Generic version.
       2     Copyright (C) 2005-2023 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 <semaphore.h>
      20  #include <errno.h>
      21  
      22  #include <pt-internal.h>
      23  
      24  int
      25  __sem_waitfast (struct new_sem *isem, int definitive_result)
      26  {
      27  #if __HAVE_64B_ATOMICS
      28    uint64_t d = atomic_load_relaxed (&isem->data);
      29  
      30    do
      31      {
      32        if ((d & SEM_VALUE_MASK) == 0)
      33  	break;
      34        if (atomic_compare_exchange_weak_acquire (&isem->data, &d, d - 1))
      35  	/* Successful down.  */
      36  	return 0;
      37      }
      38    while (definitive_result);
      39    return -1;
      40  #else
      41    unsigned v = atomic_load_relaxed (&isem->value);
      42  
      43    do
      44      {
      45        if ((v >> SEM_VALUE_SHIFT) == 0)
      46  	break;
      47        if (atomic_compare_exchange_weak_acquire (&isem->value,
      48  	    &v, v - (1 << SEM_VALUE_SHIFT)))
      49  	/* Successful down.  */
      50  	return 0;
      51      }
      52    while (definitive_result);
      53    return -1;
      54  #endif
      55  }