Add pthread_rwlock_t implementation to the C library (DO NOT MERGE)

Change-Id: I756d8c26afc37cd7b71117ddbaa02a2cb40fdecb

libc/Android.mk

@@ -322,6 +322,7 @@ libc_common_src_files += \
 # 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 @@ libc_common_src_files += \
 	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 @@ libc_common_src_files += \
 	string/strlen.c \
 	bionic/eabi.c \
 	bionic/pthread.c \
+	bionic/pthread-rwlocks.c \
 	bionic/pthread-timers.c \
 	bionic/ptrace.c \
 	unistd/socketcalls.c

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;
+}

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 !
 

libc/include/pthread.h

@@ -219,6 +219,41 @@ int pthread_cond_timeout_np(pthread_cond_t *cond,
  */
 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);