sysdeps/htl/pt-spin.c

   1 /* Spin locks.
   2    Copyright (C) 2000-2018 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    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <pthread.h>
  20 #include <sched.h>
  21
  22 /* The default for single processor machines; don't spin, it's
  23    pointless.  */
  24 #ifndef __PTHREAD_SPIN_COUNT
  25 # define __PTHREAD_SPIN_COUNT 1
  26 #endif
  27
  28 /* The number of times to spin while trying to lock a spin lock object
  29    before yielding the processor. */
  30 int __pthread_spin_count = __PTHREAD_SPIN_COUNT;
  31
  32
  33 /* Lock the spin lock object LOCK.  If the lock is held by another
  34    thread spin until it becomes available.  */
  35 int
  36 _pthread_spin_lock (__pthread_spinlock_t *lock)
  37 {
  38   int i;
  39
  40   while (1)
  41     {
  42       for (i = 0; i < __pthread_spin_count; i++)
  43         {
  44           if (__pthread_spin_trylock (lock) == 0)
  45             return 0;
  46         }
  47
  48       __sched_yield ();
  49     }
  50 }