sysdeps/htl/pt-rwlock-tryrdlock.c

   1 /* Try to acquire a rwlock for reading.  Generic version.
   2    Copyright (C) 2002-2020 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 <assert.h>
  21
  22 #include <pt-internal.h>
  23
  24 /* Try to acquire RWLOCK.  */
  25 int
  26 pthread_rwlock_tryrdlock (struct __pthread_rwlock *rwlock)
  27 {
  28   __pthread_spin_wait (&rwlock->__lock);
  29   if (__pthread_spin_trylock (&rwlock->__held) == 0)
  30     /* Successfully acquired the lock.  */
  31     {
  32       assert (rwlock->__readerqueue == 0);
  33       assert (rwlock->__writerqueue == 0);
  34       assert (rwlock->__readers == 0);
  35
  36       rwlock->__readers = 1;
  37       __pthread_spin_unlock (&rwlock->__lock);
  38       return 0;
  39     }
  40   else
  41     /* Lock is held, but is held by a reader?  */
  42   if (rwlock->__readers > 0)
  43     {
  44       assert (rwlock->__readerqueue == 0);
  45       rwlock->__readers++;
  46       __pthread_spin_unlock (&rwlock->__lock);
  47       return 0;
  48     }
  49
  50   /* The lock is busy.  */
  51
  52   __pthread_spin_unlock (&rwlock->__lock);
  53
  54   return EBUSY;
  55 }