[Android] [PATCH] Implement fully pthread_rwlock*
Rafaël Carré
funman at videolan.org
Thu Mar 1 04:41:04 CET 2012
The code comes from Android ICS
ABI didn't change since it was committed in 2.2
Tested on ICS, and (not by me) on 2.2
I am not sure which functions are executed when those are present in libc.so
---
...rw_locks-needed-for-Android-2.2-and-below.patch | 143 --------
vlc-android/jni/Android.mk | 4 +-
vlc-android/jni/pthread-rwlocks.c | 364 ++++++++++++++++++++
3 files changed, 366 insertions(+), 145 deletions(-)
delete mode 100644 patches/0002-Implement-rw_locks-needed-for-Android-2.2-and-below.patch
create mode 100644 vlc-android/jni/pthread-rwlocks.c
diff --git a/patches/0002-Implement-rw_locks-needed-for-Android-2.2-and-below.patch b/patches/0002-Implement-rw_locks-needed-for-Android-2.2-and-below.patch
deleted file mode 100644
index 38ad628..0000000
--- a/patches/0002-Implement-rw_locks-needed-for-Android-2.2-and-below.patch
+++ /dev/null
@@ -1,143 +0,0 @@
-From 699c382047607310a892e019ecf16dc2f4d55937 Mon Sep 17 00:00:00 2001
-From: =?UTF-8?q?R=C3=A9mi=20Duraffort?= <ivoire at videolan.org>
-Date: Sun, 7 Nov 2010 19:11:51 +0100
-Subject: [PATCH 2/3] Implement rw_locks, needed for Android 2.2 and below
-
-Signed-off-by: Jean-Baptiste Kempf <jb at videolan.org>
----
- include/vlc_threads.h | 22 ++++++++++++++
- src/posix/thread.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++
- 2 files changed, 98 insertions(+), 0 deletions(-)
-
-diff --git a/include/vlc_threads.h b/include/vlc_threads.h
-index 7a6c6af..181f273 100644
---- a/include/vlc_threads.h
-+++ b/include/vlc_threads.h
-@@ -123,8 +123,30 @@ typedef pthread_mutex_t vlc_mutex_t;
- #define VLC_STATIC_MUTEX PTHREAD_MUTEX_INITIALIZER
- typedef pthread_cond_t vlc_cond_t;
- #define VLC_STATIC_COND PTHREAD_COND_INITIALIZER
-+#ifndef __ANDROID__
- typedef pthread_rwlock_t vlc_rwlock_t;
- #define VLC_STATIC_RWLOCK PTHREAD_RWLOCK_INITIALIZER
-+#else
-+typedef unsigned long DWORD;
-+
-+typedef struct
-+{
-+ vlc_mutex_t mutex;
-+ vlc_cond_t read_wait;
-+ vlc_cond_t write_wait;
-+ unsigned long readers;
-+ unsigned long writers;
-+ DWORD writer;
-+} vlc_rwlock_t;
-+
-+#define VLC_STATIC_RWLOCK { \
-+ .mutex = VLC_STATIC_MUTEX, \
-+ .read_wait = VLC_STATIC_COND, \
-+ .readers = 0, \
-+ .writers = 0, \
-+ .writer = 0, \
-+ }
-+#endif
- typedef pthread_key_t vlc_threadvar_t;
- typedef struct vlc_timer *vlc_timer_t;
-
-diff --git a/src/posix/thread.c b/src/posix/thread.c
-index 6cfe7a0..5781a94 100644
---- a/src/posix/thread.c
-+++ b/src/posix/thread.c
-@@ -574,6 +574,7 @@ void vlc_sem_wait (vlc_sem_t *sem)
- VLC_THREAD_ASSERT ("locking semaphore");
- }
-
-+#ifndef __ANDROID__
- /**
- * Initializes a read/write lock.
- */
-@@ -618,6 +619,81 @@ void vlc_rwlock_unlock (vlc_rwlock_t *lock)
- int val = pthread_rwlock_unlock (lock);
- VLC_THREAD_ASSERT ("releasing R/W lock");
- }
-+#endif
-+/*** Read/write locks */
-+/* SRW (Slim Read Write) locks are available in Vista+ only */
-+void vlc_rwlock_init (vlc_rwlock_t *lock)
-+{
-+ vlc_mutex_init (&lock->mutex);
-+ vlc_cond_init (&lock->read_wait);
-+ vlc_cond_init (&lock->write_wait);
-+ lock->readers = 0; /* active readers */
-+ lock->writers = 0; /* waiting or active writers */
-+ lock->writer = 0; /* ID of active writer */
-+}
-+
-+/**
-+ * Destroys an initialized unused read/write lock.
-+ */
-+void vlc_rwlock_destroy (vlc_rwlock_t *lock)
-+{
-+ vlc_cond_destroy (&lock->read_wait);
-+ vlc_cond_destroy (&lock->write_wait);
-+ vlc_mutex_destroy (&lock->mutex);
-+}
-+
-+/**
-+ * Acquires a read/write lock for reading. Recursion is allowed.
-+ */
-+void vlc_rwlock_rdlock (vlc_rwlock_t *lock)
-+{
-+ vlc_mutex_lock (&lock->mutex);
-+ while (lock->writer != 0)
-+ vlc_cond_wait (&lock->read_wait, &lock->mutex);
-+ if (lock->readers == ULONG_MAX)
-+ abort ();
-+ lock->readers++;
-+ vlc_mutex_unlock (&lock->mutex);
-+}
-+
-+/**
-+ * Acquires a read/write lock for writing. Recursion is not allowed.
-+ */
-+void vlc_rwlock_wrlock (vlc_rwlock_t *lock)
-+{
-+ vlc_mutex_lock (&lock->mutex);
-+ if (lock->writers == ULONG_MAX)
-+ abort ();
-+ lock->writers++;
-+ while ((lock->readers > 0) || (lock->writer != 0))
-+ vlc_cond_wait (&lock->write_wait, &lock->mutex);
-+ lock->writers--;
-+ lock->writer = 42;
-+ vlc_mutex_unlock (&lock->mutex);
-+}
-+
-+/**
-+ * Releases a read/write lock.
-+ */
-+void vlc_rwlock_unlock (vlc_rwlock_t *lock)
-+{
-+ vlc_mutex_lock (&lock->mutex);
-+ if (lock->readers > 0)
-+ lock->readers--; /* Read unlock */
-+ else
-+ lock->writer = 0; /* Write unlock */
-+
-+ if (lock->writers > 0)
-+ {
-+ if (lock->readers == 0)
-+ vlc_cond_signal (&lock->write_wait);
-+ }
-+ else
-+ vlc_cond_broadcast (&lock->read_wait);
-+ vlc_mutex_unlock (&lock->mutex);
-+}
-+
-+
-
- /**
- * Allocates a thread-specific variable.
---
-1.7.9.1
-
diff --git a/vlc-android/jni/Android.mk b/vlc-android/jni/Android.mk
index ff4c335..a0f1013 100644
--- a/vlc-android/jni/Android.mk
+++ b/vlc-android/jni/Android.mk
@@ -3,7 +3,7 @@ include $(CLEAR_VARS)
LOCAL_MODULE := libvlcjni
-LOCAL_SRC_FILES := libvlcjni.c aout.c thumbnailer.c
+LOCAL_SRC_FILES := libvlcjni.c aout.c thumbnailer.c pthread-rwlocks.c
LOCAL_C_INCLUDES := $(VLC_SRC_DIR)/include
@@ -28,7 +28,7 @@ LOCAL_LDLIBS := -L$(VLC_CONTRIB)/lib \
-ldvbpsi -lebml -lmatroska -ltag \
-logg -lFLAC -ltheora \
-lmpeg2 -ldca -la52 \
- -lavformat -lavcodec -lswscale -lavutil -lpostproc -lgsm -lopenjpeg \
+ -lavformat -lavcodec -lswscale -lavutil -lpostproc -lgsm -lopenjpeg -llua \
-lliveMedia -lUsageEnvironment -lBasicUsageEnvironment -lgroupsock \
-lspeex -lspeexdsp \
-lxml2 -lpng \
diff --git a/vlc-android/jni/pthread-rwlocks.c b/vlc-android/jni/pthread-rwlocks.c
new file mode 100644
index 0000000..3086fbd
--- /dev/null
+++ b/vlc-android/jni/pthread-rwlocks.c
@@ -0,0 +1,364 @@
+/*
+ * 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 <errno.h>
+#include <unistd.h>
+#include <pthread.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
+
+/* __get_thread and pthread_internal_t didn't change since introduced,
+ * up to ics */
+typedef struct pthread_internal_t
+{
+ struct pthread_internal_t* next;
+ struct pthread_internal_t** pref;
+ pthread_attr_t attr;
+ pid_t kernel_id;
+ pthread_cond_t join_cond;
+ int join_count;
+ void* return_value;
+ int intern;
+ __pthread_cleanup_t* cleanup_stack;
+ void** tls; /* thread-local storage area */
+} pthread_internal_t;
+
+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;
+}
--
1.7.9
More information about the Android
mailing list