1  /* Try to acquire a rwlock for reading.  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 <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  }