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Diffstat (limited to 'nptl/pthread_rwlock_rdlock.c')
-rw-r--r--nptl/pthread_rwlock_rdlock.c95
1 files changed, 95 insertions, 0 deletions
diff --git a/nptl/pthread_rwlock_rdlock.c b/nptl/pthread_rwlock_rdlock.c
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index 0000000000..e225d7030d
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+++ b/nptl/pthread_rwlock_rdlock.c
@@ -0,0 +1,95 @@
+/* Copyright (C) 2003, 2004 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, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+#include <errno.h>
+#include <sysdep.h>
+#include <lowlevellock.h>
+#include <pthread.h>
+#include <pthreadP.h>
+
+
+/* Acquire read lock for RWLOCK. */
+int
+__pthread_rwlock_rdlock (rwlock)
+ pthread_rwlock_t *rwlock;
+{
+ int result = 0;
+
+ /* Make sure we are along. */
+ lll_mutex_lock (rwlock->__data.__lock);
+
+ 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
+ || rwlock->__data.__flags == 0))
+ {
+ /* 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;
+ }
+
+ 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_mutex_unlock (rwlock->__data.__lock);
+
+ /* Wait for the writer to finish. */
+ lll_futex_wait (&rwlock->__data.__readers_wakeup, waitval);
+
+ /* Get the lock. */
+ lll_mutex_lock (rwlock->__data.__lock);
+
+ --rwlock->__data.__nr_readers_queued;
+ }
+
+ /* We are done, free the lock. */
+ lll_mutex_unlock (rwlock->__data.__lock);
+
+ return result;
+}
+
+weak_alias (__pthread_rwlock_rdlock, pthread_rwlock_rdlock)
+strong_alias (__pthread_rwlock_rdlock, __pthread_rwlock_rdlock_internal)