1 /* Try to acquire a rwlock for reading. Generic version. 2 Copyright (C) 2002-2022 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 pthread_rwlock_tryrdlock(struct __pthread_rwlock * rwlock)26pthread_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 } 56