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am 3fd88ebe: am 0f79a2f4: Merge "Cleaned up pthread rwlocks implementation."

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* commit '3fd88ebe0f881438ed07b62d991e46e7f9adab83':
  Cleaned up pthread rwlocks implementation.
This commit is contained in:
Elliott Hughes 2014-05-23 01:56:05 +00:00 committed by Android Git Automerger
commit 236130cd8d
3 changed files with 83 additions and 81 deletions
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127
libc/bionic/pthread_rwlock.cpp
View File

@ -57,7 +57,7 @@
* should be changed to compare_exchange_strong accompanied by the proper ordering
* constraints (comments have been added with the intending ordering across the code).
*
* TODO: As it stands now, pendingReaders and pendingWriters could be merged into a
* TODO: As it stands now, pending_readers and pending_writers could be merged into a
* a single waiters variable. Keeping them separate adds a bit of clarity and keeps
* the door open for a writer-biased implementation.
*
@ -66,24 +66,30 @@
#define RWLOCKATTR_DEFAULT 0
#define RWLOCKATTR_SHARED_MASK 0x0010
#define RWLOCK_IS_SHARED(rwlock) ((rwlock)->attr == PTHREAD_PROCESS_SHARED)
static inline bool rwlock_is_shared(const pthread_rwlock_t* rwlock) {
return rwlock->attr == PTHREAD_PROCESS_SHARED;
}
extern pthread_internal_t* __get_thread(void);
static bool timespec_from_absolute(timespec* rel_timeout, const timespec* abs_timeout) {
if (abs_timeout != NULL) {
if (__timespec_from_absolute(rel_timeout, abs_timeout, CLOCK_REALTIME) < 0) {
return false;
}
}
return true;
}
int pthread_rwlockattr_init(pthread_rwlockattr_t *attr)
{
int pthread_rwlockattr_init(pthread_rwlockattr_t* attr) {
*attr = PTHREAD_PROCESS_PRIVATE;
return 0;
}
int pthread_rwlockattr_destroy(pthread_rwlockattr_t *attr)
{
int pthread_rwlockattr_destroy(pthread_rwlockattr_t* attr) {
*attr = -1;
return 0;
}
int pthread_rwlockattr_setpshared(pthread_rwlockattr_t *attr, int pshared)
{
int pthread_rwlockattr_setpshared(pthread_rwlockattr_t* attr, int pshared) {
switch (pshared) {
case PTHREAD_PROCESS_PRIVATE:
case PTHREAD_PROCESS_SHARED:
@ -99,9 +105,8 @@ int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t* attr, int* pshared
return 0;
}
int pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
{
if (attr) {
int pthread_rwlock_init(pthread_rwlock_t* rwlock, const pthread_rwlockattr_t* attr) {
if (attr != NULL) {
switch (*attr) {
case PTHREAD_PROCESS_SHARED:
case PTHREAD_PROCESS_PRIVATE:
@ -113,30 +118,30 @@ int pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *at
}
rwlock->state = 0;
rwlock->pendingReaders = 0;
rwlock->pendingWriters = 0;
rwlock->writerThreadId = 0;
rwlock->pending_readers = 0;
rwlock->pending_writers = 0;
rwlock->writer_thread_id = 0;
return 0;
}
int pthread_rwlock_destroy(pthread_rwlock_t *rwlock)
{
int pthread_rwlock_destroy(pthread_rwlock_t* rwlock) {
if (rwlock->state != 0) {
return EBUSY;
}
return 0;
}
static int __pthread_rwlock_timedrdlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
if (__predict_false(__get_thread()->tid == rwlock->writerThreadId)) {
if (__predict_false(__get_thread()->tid == rwlock->writer_thread_id)) {
return EDEADLK;
}
timespec ts;
timespec* rel_timeout = (abs_timeout == NULL) ? NULL : &ts;
bool done = false;
do {
// This is actually a race read as there's nothing that guarantees the atomicity of integers
// This is actually a race read as there's nothing that guarantees the atomicity of integer
// reads / writes. However, in practice this "never" happens so until we switch to C++11 this
// should work fine. The same applies in the other places this idiom is used.
int32_t cur_state = rwlock->state; // C++11 relaxed atomic read
@ -144,26 +149,19 @@ static int __pthread_rwlock_timedrdlock(pthread_rwlock_t* rwlock, const timespec
// Add as an extra reader.
done = __atomic_cmpxchg(cur_state, cur_state + 1, &rwlock->state) == 0; // C++11 memory_order_aquire
} else {
timespec ts;
timespec* tsp = NULL;
if (abs_timeout != NULL) {
if (__timespec_from_absolute(&ts, abs_timeout, CLOCK_REALTIME) < 0) {
if (!timespec_from_absolute(rel_timeout, abs_timeout)) {
return ETIMEDOUT;
}
tsp = &ts;
}
// Owner holds it in write mode, hang up.
// To avoid loosing wake ups the pendingReaders update and the state read should be
// To avoid losing wake ups the pending_readers update and the state read should be
// sequentially consistent. (currently enforced by __atomic_inc which creates a full barrier)
__atomic_inc(&rwlock->pendingReaders); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
if (__futex_wait_ex(&rwlock->state, RWLOCK_IS_SHARED(rwlock), cur_state, tsp) != 0) {
if (errno == ETIMEDOUT) {
__atomic_dec(&rwlock->pendingReaders); // C++11 memory_order_relaxed
__atomic_inc(&rwlock->pending_readers); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
int ret = __futex_wait_ex(&rwlock->state, rwlock_is_shared(rwlock), cur_state, rel_timeout);
__atomic_dec(&rwlock->pending_readers); // C++11 memory_order_relaxed
if (ret == -ETIMEDOUT) {
return ETIMEDOUT;
}
}
__atomic_dec(&rwlock->pendingReaders); // C++11 memory_order_relaxed
}
} while (!done);
return 0;
@ -171,10 +169,12 @@ static int __pthread_rwlock_timedrdlock(pthread_rwlock_t* rwlock, const timespec
static int __pthread_rwlock_timedwrlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
int tid = __get_thread()->tid;
if (__predict_false(tid == rwlock->writerThreadId)) {
if (__predict_false(tid == rwlock->writer_thread_id)) {
return EDEADLK;
}
timespec ts;
timespec* rel_timeout = (abs_timeout == NULL) ? NULL : &ts;
bool done = false;
do {
int32_t cur_state = rwlock->state;
@ -182,29 +182,22 @@ static int __pthread_rwlock_timedwrlock(pthread_rwlock_t* rwlock, const timespec
// Change state from 0 to -1.
done = __atomic_cmpxchg(0 /* cur_state */, -1 /* new state */, &rwlock->state) == 0; // C++11 memory_order_aquire
} else {
timespec ts;
timespec* tsp = NULL;
if (abs_timeout != NULL) {
if (__timespec_from_absolute(&ts, abs_timeout, CLOCK_REALTIME) < 0) {
if (!timespec_from_absolute(rel_timeout, abs_timeout)) {
return ETIMEDOUT;
}
tsp = &ts;
}
// Failed to acquire, hang up.
// To avoid loosing wake ups the pendingWriters update and the state read should be
// To avoid losing wake ups the pending_writers update and the state read should be
// sequentially consistent. (currently enforced by __atomic_inc which creates a full barrier)
__atomic_inc(&rwlock->pendingWriters); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
if (__futex_wait_ex(&rwlock->state, RWLOCK_IS_SHARED(rwlock), cur_state, tsp) != 0) {
if (errno == ETIMEDOUT) {
__atomic_dec(&rwlock->pendingWriters); // C++11 memory_order_relaxed
__atomic_inc(&rwlock->pending_writers); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
int ret = __futex_wait_ex(&rwlock->state, rwlock_is_shared(rwlock), cur_state, rel_timeout);
__atomic_dec(&rwlock->pending_writers); // C++11 memory_order_relaxed
if (ret == -ETIMEDOUT) {
return ETIMEDOUT;
}
}
__atomic_dec(&rwlock->pendingWriters); // C++11 memory_order_relaxed
}
} while (!done);
rwlock->writerThreadId = tid;
rwlock->writer_thread_id = tid;
return 0;
}
@ -212,8 +205,11 @@ int pthread_rwlock_rdlock(pthread_rwlock_t* rwlock) {
return __pthread_rwlock_timedrdlock(rwlock, NULL);
}
int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock)
{
int pthread_rwlock_timedrdlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
return __pthread_rwlock_timedrdlock(rwlock, abs_timeout);
}
int pthread_rwlock_tryrdlock(pthread_rwlock_t* rwlock) {
int32_t cur_state = rwlock->state;
if (cur_state >= 0) {
if(__atomic_cmpxchg(cur_state, cur_state + 1, &rwlock->state) != 0) { // C++11 memory_order_acquire
@ -225,16 +221,15 @@ int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock)
return 0;
}
int pthread_rwlock_timedrdlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
return __pthread_rwlock_timedrdlock(rwlock, abs_timeout);
}
int pthread_rwlock_wrlock(pthread_rwlock_t* rwlock) {
return __pthread_rwlock_timedwrlock(rwlock, NULL);
}
int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock)
{
int pthread_rwlock_timedwrlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
return __pthread_rwlock_timedwrlock(rwlock, abs_timeout);
}
int pthread_rwlock_trywrlock(pthread_rwlock_t* rwlock) {
int tid = __get_thread()->tid;
int32_t cur_state = rwlock->state;
if (cur_state == 0) {
@ -245,16 +240,12 @@ int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock)
return EBUSY;
}
rwlock->writerThreadId = tid;
rwlock->writer_thread_id = tid;
return 0;
}
int pthread_rwlock_timedwrlock(pthread_rwlock_t* rwlock, const timespec* abs_timeout) {
return __pthread_rwlock_timedwrlock(rwlock, abs_timeout);
}
int pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
{
int pthread_rwlock_unlock(pthread_rwlock_t* rwlock) {
int tid = __get_thread()->tid;
bool done = false;
do {
@ -263,11 +254,11 @@ int pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
return EPERM;
}
if (cur_state == -1) {
if (rwlock->writerThreadId != tid) {
if (rwlock->writer_thread_id != tid) {
return EPERM;
}
// We're no longer the owner.
rwlock->writerThreadId = 0;
rwlock->writer_thread_id = 0;
// Change state from -1 to 0.
// We use __atomic_cmpxchg to achieve sequential consistency of the state store and
// the following pendingX loads. A simple store with memory_order_release semantics
@ -276,8 +267,8 @@ int pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
__atomic_cmpxchg(-1 /* cur_state*/, 0 /* new state */, &rwlock->state); // C++11 maybe memory_order_seq_cst?
// Wake any waiters.
if (__predict_false(rwlock->pendingReaders > 0 || rwlock->pendingWriters > 0)) {
__futex_wake_ex(&rwlock->state, RWLOCK_IS_SHARED(rwlock), INT_MAX);
if (__predict_false(rwlock->pending_readers > 0 || rwlock->pending_writers > 0)) {
__futex_wake_ex(&rwlock->state, rwlock_is_shared(rwlock), INT_MAX);
}
done = true;
} else { // cur_state > 0
@ -286,8 +277,8 @@ int pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
done = __atomic_cmpxchg(cur_state, cur_state - 1, &rwlock->state) == 0; // C++11 maybe memory_order_seq_cst?
if (done && (cur_state - 1) == 0) {
// There are no more readers, wake any waiters.
if (__predict_false(rwlock->pendingReaders > 0 || rwlock->pendingWriters > 0)) {
__futex_wake_ex(&rwlock->state, RWLOCK_IS_SHARED(rwlock), INT_MAX);
if (__predict_false(rwlock->pending_readers > 0 || rwlock->pending_writers > 0)) {
__futex_wake_ex(&rwlock->state, rwlock_is_shared(rwlock), INT_MAX);
}
}
}

21
libc/include/pthread.h
View File

@ -94,17 +94,28 @@ typedef long pthread_condattr_t;
typedef long pthread_rwlockattr_t;
typedef struct {
#if !defined(__LP64__)
pthread_mutex_t __unused_lock;
pthread_cond_t __unused_cond;
#endif
volatile int32_t state; // 0=unlock, -1=writer lock, +n=reader lock
volatile int32_t writerThreadId;
volatile int32_t pendingReaders;
volatile int32_t pendingWriters;
volatile int32_t writer_thread_id;
volatile int32_t pending_readers;
volatile int32_t pending_writers;
int32_t attr;
void* __reserved[3];
#ifdef __LP64__
char __reserved[36];
#else
char __reserved[12];
#endif
} pthread_rwlock_t;
#define PTHREAD_RWLOCK_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, 0, 0, 0, 0, 0, { NULL, NULL, NULL } }
#ifdef __LP64__
#define PTHREAD_RWLOCK_INITIALIZER { 0, 0, 0, 0, 0, { 0 } }
#else
#define PTHREAD_RWLOCK_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, 0, 0, 0, 0, 0, { 0 } }
#endif
typedef int pthread_key_t;
typedef long pthread_t;