Add pthread_rwlock_t implementation to the C library (DO NOT MERGE)
Change-Id: I756d8c26afc37cd7b71117ddbaa02a2cb40fdecb
diff --git a/libc/Android.mk b/libc/Android.mk
index 590afbe..0271f10 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -322,6 +322,7 @@
# up any thumb code.
libc_common_src_files += \
bionic/pthread.c.arm \
+ bionic/pthread-rwlocks.c.arm \
bionic/pthread-timers.c.arm \
bionic/ptrace.c.arm
@@ -356,6 +357,7 @@
arch-x86/string/strncmp_wrapper.S \
arch-x86/string/strlen.S \
bionic/pthread.c \
+ bionic/pthread-rwlocks.c \
bionic/pthread-timers.c \
bionic/ptrace.c
@@ -393,6 +395,7 @@
string/strlen.c \
bionic/eabi.c \
bionic/pthread.c \
+ bionic/pthread-rwlocks.c \
bionic/pthread-timers.c \
bionic/ptrace.c \
unistd/socketcalls.c
diff --git a/libc/bionic/pthread-rwlocks.c b/libc/bionic/pthread-rwlocks.c
new file mode 100644
index 0000000..ca3e95c
--- /dev/null
+++ b/libc/bionic/pthread-rwlocks.c
@@ -0,0 +1,347 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "pthread_internal.h"
+#include <errno.h>
+
+/* Technical note:
+ *
+ * Possible states of a read/write lock:
+ *
+ * - no readers and no writer (unlocked)
+ * - one or more readers sharing the lock at the same time (read-locked)
+ * - one writer holding the lock (write-lock)
+ *
+ * Additionally:
+ * - trying to get the write-lock while there are any readers blocks
+ * - trying to get the read-lock while there is a writer blocks
+ * - a single thread can acquire the lock multiple times in the same mode
+ *
+ * - Posix states that behaviour is undefined it a thread tries to acquire
+ * the lock in two distinct modes (e.g. write after read, or read after write).
+ *
+ * - This implementation tries to avoid writer starvation by making the readers
+ * block as soon as there is a waiting writer on the lock. However, it cannot
+ * completely eliminate it: each time the lock is unlocked, all waiting threads
+ * are woken and battle for it, which one gets it depends on the kernel scheduler
+ * and is semi-random.
+ *
+ */
+
+#define __likely(cond) __builtin_expect(!!(cond), 1)
+#define __unlikely(cond) __builtin_expect(!!(cond), 0)
+
+#define RWLOCKATTR_DEFAULT 0
+#define RWLOCKATTR_SHARED_MASK 0x0010
+
+extern pthread_internal_t* __get_thread(void);
+
+/* Return a global kernel ID for the current thread */
+static int __get_thread_id(void)
+{
+ return __get_thread()->kernel_id;
+}
+
+int pthread_rwlockattr_init(pthread_rwlockattr_t *attr)
+{
+ if (!attr)
+ return EINVAL;
+
+ *attr = PTHREAD_PROCESS_PRIVATE;
+ return 0;
+}
+
+int pthread_rwlockattr_destroy(pthread_rwlockattr_t *attr)
+{
+ if (!attr)
+ return EINVAL;
+
+ *attr = -1;
+ return 0;
+}
+
+int pthread_rwlockattr_setpshared(pthread_rwlockattr_t *attr, int pshared)
+{
+ if (!attr)
+ return EINVAL;
+
+ switch (pshared) {
+ case PTHREAD_PROCESS_PRIVATE:
+ case PTHREAD_PROCESS_SHARED:
+ *attr = pshared;
+ return 0;
+ default:
+ return EINVAL;
+ }
+}
+
+int pthread_rwlockattr_getpshared(pthread_rwlockattr_t *attr, int *pshared)
+{
+ if (!attr || !pshared)
+ return EINVAL;
+
+ *pshared = *attr;
+ return 0;
+}
+
+int pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
+{
+ pthread_mutexattr_t* lock_attr = NULL;
+ pthread_condattr_t* cond_attr = NULL;
+ pthread_mutexattr_t lock_attr0;
+ pthread_condattr_t cond_attr0;
+ int ret;
+
+ if (rwlock == NULL)
+ return EINVAL;
+
+ if (attr && *attr == PTHREAD_PROCESS_SHARED) {
+ lock_attr = &lock_attr0;
+ pthread_mutexattr_init(lock_attr);
+ pthread_mutexattr_setpshared(lock_attr, PTHREAD_PROCESS_SHARED);
+
+ cond_attr = &cond_attr0;
+ pthread_condattr_init(cond_attr);
+ pthread_condattr_setpshared(cond_attr, PTHREAD_PROCESS_SHARED);
+ }
+
+ ret = pthread_mutex_init(&rwlock->lock, lock_attr);
+ if (ret != 0)
+ return ret;
+
+ ret = pthread_cond_init(&rwlock->cond, cond_attr);
+ if (ret != 0) {
+ pthread_mutex_destroy(&rwlock->lock);
+ return ret;
+ }
+
+ rwlock->numLocks = 0;
+ rwlock->pendingReaders = 0;
+ rwlock->pendingWriters = 0;
+ rwlock->writerThreadId = 0;
+
+ return 0;
+}
+
+int pthread_rwlock_destroy(pthread_rwlock_t *rwlock)
+{
+ int ret;
+
+ if (rwlock == NULL)
+ return EINVAL;
+
+ if (rwlock->numLocks > 0)
+ return EBUSY;
+
+ pthread_cond_destroy(&rwlock->cond);
+ pthread_mutex_destroy(&rwlock->lock);
+ return 0;
+}
+
+/* Returns TRUE iff we can acquire a read lock. */
+static __inline__ int read_precondition(pthread_rwlock_t *rwlock, int thread_id)
+{
+ /* We can't have the lock if any writer is waiting for it (writer bias).
+ * This tries to avoid starvation when there are multiple readers racing.
+ */
+ if (rwlock->pendingWriters > 0)
+ return 0;
+
+ /* We can have the lock if there is no writer, or if we write-own it */
+ /* The second test avoids a self-dead lock in case of buggy code. */
+ if (rwlock->writerThreadId == 0 || rwlock->writerThreadId == thread_id)
+ return 1;
+
+ /* Otherwise, we can't have it */
+ return 0;
+}
+
+/* returns TRUE iff we can acquire a write lock. */
+static __inline__ int write_precondition(pthread_rwlock_t *rwlock, int thread_id)
+{
+ /* We can get the lock if nobody has it */
+ if (rwlock->numLocks == 0)
+ return 1;
+
+ /* Or if we already own it */
+ if (rwlock->writerThreadId == thread_id)
+ return 1;
+
+ /* Otherwise, not */
+ return 0;
+}
+
+/* This function is used to waken any waiting thread contending
+ * for the lock. One of them should be able to grab it after
+ * that.
+ */
+static void _pthread_rwlock_pulse(pthread_rwlock_t *rwlock)
+{
+ if (rwlock->pendingReaders > 0 || rwlock->pendingWriters > 0)
+ pthread_cond_broadcast(&rwlock->cond);
+}
+
+
+int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock)
+{
+ return pthread_rwlock_timedrdlock(rwlock, NULL);
+}
+
+int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock)
+{
+ int ret = 0;
+
+ if (rwlock == NULL)
+ return EINVAL;
+
+ pthread_mutex_lock(&rwlock->lock);
+ if (__unlikely(!read_precondition(rwlock, __get_thread_id())))
+ ret = EBUSY;
+ else
+ rwlock->numLocks ++;
+ pthread_mutex_unlock(&rwlock->lock);
+
+ return ret;
+}
+
+int pthread_rwlock_timedrdlock(pthread_rwlock_t *rwlock, const struct timespec *abs_timeout)
+{
+ int thread_id, ret = 0;
+
+ if (rwlock == NULL)
+ return EINVAL;
+
+ pthread_mutex_lock(&rwlock->lock);
+ thread_id = __get_thread_id();
+ if (__unlikely(!read_precondition(rwlock, thread_id))) {
+ rwlock->pendingReaders += 1;
+ do {
+ ret = pthread_cond_timedwait(&rwlock->cond, &rwlock->lock, abs_timeout);
+ } while (ret == 0 && !read_precondition(rwlock, thread_id));
+ rwlock->pendingReaders -= 1;
+ if (ret != 0)
+ goto EXIT;
+ }
+ rwlock->numLocks ++;
+EXIT:
+ pthread_mutex_unlock(&rwlock->lock);
+ return ret;
+}
+
+
+int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock)
+{
+ return pthread_rwlock_timedwrlock(rwlock, NULL);
+}
+
+int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock)
+{
+ int thread_id, ret = 0;
+
+ if (rwlock == NULL)
+ return EINVAL;
+
+ pthread_mutex_lock(&rwlock->lock);
+ thread_id = __get_thread_id();
+ if (__unlikely(!write_precondition(rwlock, thread_id))) {
+ ret = EBUSY;
+ } else {
+ rwlock->numLocks ++;
+ rwlock->writerThreadId = thread_id;
+ }
+ pthread_mutex_unlock(&rwlock->lock);
+ return ret;
+}
+
+int pthread_rwlock_timedwrlock(pthread_rwlock_t *rwlock, const struct timespec *abs_timeout)
+{
+ int thread_id, ret = 0;
+
+ if (rwlock == NULL)
+ return EINVAL;
+
+ pthread_mutex_lock(&rwlock->lock);
+ thread_id = __get_thread_id();
+ if (__unlikely(!write_precondition(rwlock, thread_id))) {
+ /* If we can't read yet, wait until the rwlock is unlocked
+ * and try again. Increment pendingReaders to get the
+ * cond broadcast when that happens.
+ */
+ rwlock->pendingWriters += 1;
+ do {
+ ret = pthread_cond_timedwait(&rwlock->cond, &rwlock->lock, abs_timeout);
+ } while (ret == 0 && !write_precondition(rwlock, thread_id));
+ rwlock->pendingWriters -= 1;
+ if (ret != 0)
+ goto EXIT;
+ }
+ rwlock->numLocks ++;
+ rwlock->writerThreadId = thread_id;
+EXIT:
+ pthread_mutex_unlock(&rwlock->lock);
+ return ret;
+}
+
+
+int pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
+{
+ int ret = 0;
+
+ if (rwlock == NULL)
+ return EINVAL;
+
+ pthread_mutex_lock(&rwlock->lock);
+
+ /* The lock must be held */
+ if (rwlock->numLocks == 0) {
+ ret = EPERM;
+ goto EXIT;
+ }
+
+ /* If it has only readers, writerThreadId is 0 */
+ if (rwlock->writerThreadId == 0) {
+ if (--rwlock->numLocks == 0)
+ _pthread_rwlock_pulse(rwlock);
+ }
+ /* Otherwise, it has only a single writer, which
+ * must be ourselves.
+ */
+ else {
+ if (rwlock->writerThreadId != __get_thread_id()) {
+ ret = EPERM;
+ goto EXIT;
+ }
+ if (--rwlock->numLocks == 0) {
+ rwlock->writerThreadId = 0;
+ _pthread_rwlock_pulse(rwlock);
+ }
+ }
+EXIT:
+ pthread_mutex_unlock(&rwlock->lock);
+ return ret;
+}
diff --git a/libc/docs/CHANGES.TXT b/libc/docs/CHANGES.TXT
index 9080685..a66e737 100644
--- a/libc/docs/CHANGES.TXT
+++ b/libc/docs/CHANGES.TXT
@@ -1,7 +1,12 @@
Bionic ChangeLog:
-----------------
-Differences between current and Android 2.1:
+Differences between current and Android 2.2:
+
+- <pthread.h>: Add reader/writer locks implementation.
+
+-------------------------------------------------------------------------------
+Differences between Android 2.2. and Android 2.1:
- Add support for SH-4 CPU architecture !
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index eb2d169..33039b9 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -219,6 +219,41 @@
*/
int pthread_mutex_lock_timeout_np(pthread_mutex_t *mutex, unsigned msecs);
+/* read-write lock support */
+
+typedef int pthread_rwlockattr_t;
+
+typedef struct {
+ pthread_mutex_t lock;
+ pthread_cond_t cond;
+ int numLocks;
+ int writerThreadId;
+ int pendingReaders;
+ int pendingWriters;
+ void* reserved[4]; /* for future extensibility */
+} pthread_rwlock_t;
+
+#define PTHREAD_RWLOCK_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, 0, NULL, 0, 0 }
+
+int pthread_rwlockattr_init(pthread_rwlockattr_t *attr);
+int pthread_rwlockattr_destroy(pthread_rwlockattr_t *attr);
+int pthread_rwlockattr_setpshared(pthread_rwlockattr_t *attr, int pshared);
+int pthread_rwlockattr_getpshared(pthread_rwlockattr_t *attr, int *pshared);
+
+int pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr);
+int pthread_rwlock_destroy(pthread_rwlock_t *rwlock);
+
+int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
+int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
+int pthread_rwlock_timedrdlock(pthread_rwlock_t *rwlock, const struct timespec *abs_timeout);
+
+int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
+int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
+int pthread_rwlock_timedwrlock(pthread_rwlock_t *rwlock, const struct timespec *abs_timeout);
+
+int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
+
+
int pthread_key_create(pthread_key_t *key, void (*destructor_function)(void *));
int pthread_key_delete (pthread_key_t);
int pthread_setspecific(pthread_key_t key, const void *value);