/* Copyright (C) 2003-2012 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library; if not, see <http://www.gnu.org/licenses/>. */ #include <errno.h> #include <sysdep.h> #include <lowlevellock.h> #include <pthread.h> #include <pthreadP.h> #include <stap-probe.h> /* Acquire read lock for RWLOCK. */ int __pthread_rwlock_rdlock (rwlock) pthread_rwlock_t *rwlock; { int result = 0; LIBC_PROBE (rdlock_entry, 1, rwlock); /* Make sure we are alone. */ lll_lock (rwlock->__data.__lock, rwlock->__data.__shared); while (1) { /* Get the rwlock if there is no writer... */ if (rwlock->__data.__writer == 0 /* ...and if either no writer is waiting or we prefer readers. */ && (!rwlock->__data.__nr_writers_queued || PTHREAD_RWLOCK_PREFER_READER_P (rwlock))) { /* Increment the reader counter. Avoid overflow. */ if (__builtin_expect (++rwlock->__data.__nr_readers == 0, 0)) { /* Overflow on number of readers. */ --rwlock->__data.__nr_readers; result = EAGAIN; } else LIBC_PROBE (rdlock_acquire_read, 1, rwlock); break; } /* Make sure we are not holding the rwlock as a writer. This is a deadlock situation we recognize and report. */ if (__builtin_expect (rwlock->__data.__writer == THREAD_GETMEM (THREAD_SELF, tid), 0)) { result = EDEADLK; break; } /* Remember that we are a reader. */ if (__builtin_expect (++rwlock->__data.__nr_readers_queued == 0, 0)) { /* Overflow on number of queued readers. */ --rwlock->__data.__nr_readers_queued; result = EAGAIN; break; } int waitval = rwlock->__data.__readers_wakeup; /* Free the lock. */ lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); /* Wait for the writer to finish. */ lll_futex_wait (&rwlock->__data.__readers_wakeup, waitval, rwlock->__data.__shared); /* Get the lock. */ lll_lock (rwlock->__data.__lock, rwlock->__data.__shared); --rwlock->__data.__nr_readers_queued; } /* We are done, free the lock. */ lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared); return result; } weak_alias (__pthread_rwlock_rdlock, pthread_rwlock_rdlock) hidden_def (__pthread_rwlock_rdlock)