Migrate pthread_rwlock implementation away from sys/atomics
Bug: 8133149
Bug: 14903517
Change-Id: Ib85987f53d7aeaec12a980ccb645c4a449c48503
diff --git a/libc/bionic/pthread_rwlock.cpp b/libc/bionic/pthread_rwlock.cpp
index 3a1b543..063137b 100644
--- a/libc/bionic/pthread_rwlock.cpp
+++ b/libc/bionic/pthread_rwlock.cpp
@@ -27,7 +27,6 @@
*/
#include <errno.h>
-#include <sys/atomics.h>
#include "pthread_internal.h"
#include "private/bionic_futex.h"
@@ -53,7 +52,7 @@
* write" cases and will deadlock in write after read case.
*
* TODO: VERY CAREFULLY convert this to use C++11 atomics when possible. All volatile
- * members of pthread_rwlock_t should be converted to atomics<> and __atomic_cmpxchg
+ * members of pthread_rwlock_t should be converted to atomics<> and __sync_bool_compare_and_swap
* should be changed to compare_exchange_strong accompanied by the proper ordering
* constraints (comments have been added with the intending ordering across the code).
*
@@ -147,17 +146,17 @@
int32_t cur_state = rwlock->state; // C++11 relaxed atomic read
if (__predict_true(cur_state >= 0)) {
// Add as an extra reader.
- done = __atomic_cmpxchg(cur_state, cur_state + 1, &rwlock->state) == 0; // C++11 memory_order_aquire
+ done = __sync_bool_compare_and_swap(&rwlock->state, cur_state, cur_state + 1); // C++11 memory_order_aquire
} else {
if (!timespec_from_absolute(rel_timeout, abs_timeout)) {
return ETIMEDOUT;
}
// Owner holds it in write mode, hang up.
// 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->pending_readers); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
+ // sequentially consistent. (currently enforced by __sync_fetch_and_add which creates a full barrier)
+ __sync_fetch_and_add(&rwlock->pending_readers, 1); // 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
+ __sync_fetch_and_sub(&rwlock->pending_readers, 1); // C++11 memory_order_relaxed
if (ret == -ETIMEDOUT) {
return ETIMEDOUT;
}
@@ -180,17 +179,17 @@
int32_t cur_state = rwlock->state;
if (__predict_true(cur_state == 0)) {
// Change state from 0 to -1.
- done = __atomic_cmpxchg(0 /* cur_state */, -1 /* new state */, &rwlock->state) == 0; // C++11 memory_order_aquire
+ done = __sync_bool_compare_and_swap(&rwlock->state, 0 /* cur state */, -1 /* new state */); // C++11 memory_order_aquire
} else {
if (!timespec_from_absolute(rel_timeout, abs_timeout)) {
return ETIMEDOUT;
}
// Failed to acquire, hang up.
// 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->pending_writers); // C++11 memory_order_relaxed (if the futex_wait ensures the ordering)
+ // sequentially consistent. (currently enforced by __sync_fetch_and_add which creates a full barrier)
+ __sync_fetch_and_add(&rwlock->pending_writers, 1); // 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
+ __sync_fetch_and_sub(&rwlock->pending_writers, 1); // C++11 memory_order_relaxed
if (ret == -ETIMEDOUT) {
return ETIMEDOUT;
}
@@ -211,14 +210,11 @@
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
- return EBUSY;
- }
- } else {
- return EBUSY;
+ if ((cur_state >= 0) &&
+ __sync_bool_compare_and_swap(&rwlock->state, cur_state, cur_state + 1)) { // C++11 memory_order_acquire
+ return 0;
}
- return 0;
+ return EBUSY;
}
int pthread_rwlock_wrlock(pthread_rwlock_t* rwlock) {
@@ -232,16 +228,12 @@
int pthread_rwlock_trywrlock(pthread_rwlock_t* rwlock) {
int tid = __get_thread()->tid;
int32_t cur_state = rwlock->state;
- if (cur_state == 0) {
- if(__atomic_cmpxchg(0, -1, &rwlock->state) != 0) { // C++11 memory_order_acquire
- return EBUSY;
- }
- } else {
- return EBUSY;
+ if ((cur_state == 0) &&
+ __sync_bool_compare_and_swap(&rwlock->state, 0 /* cur state */, -1 /* new state */)) { // C++11 memory_order_acquire
+ rwlock->writer_thread_id = tid;
+ return 0;
}
-
- rwlock->writer_thread_id = tid;
- return 0;
+ return EBUSY;
}
@@ -260,11 +252,11 @@
// We're no longer the owner.
rwlock->writer_thread_id = 0;
// Change state from -1 to 0.
- // We use __atomic_cmpxchg to achieve sequential consistency of the state store and
+ // We use __sync_bool_compare_and_swap to achieve sequential consistency of the state store and
// the following pendingX loads. A simple store with memory_order_release semantics
// is not enough to guarantee that the pendingX loads are not reordered before the
// store (which may lead to a lost wakeup).
- __atomic_cmpxchg(-1 /* cur_state*/, 0 /* new state */, &rwlock->state); // C++11 maybe memory_order_seq_cst?
+ __sync_bool_compare_and_swap( &rwlock->state, -1 /* cur state*/, 0 /* new state */); // C++11 maybe memory_order_seq_cst?
// Wake any waiters.
if (__predict_false(rwlock->pending_readers > 0 || rwlock->pending_writers > 0)) {
@@ -273,8 +265,8 @@
done = true;
} else { // cur_state > 0
// Reduce state by 1.
- // See the above comment on why we need __atomic_cmpxchg.
- done = __atomic_cmpxchg(cur_state, cur_state - 1, &rwlock->state) == 0; // C++11 maybe memory_order_seq_cst?
+ // See the comment above on why we need __sync_bool_compare_and_swap.
+ done = __sync_bool_compare_and_swap(&rwlock->state, cur_state, cur_state - 1); // 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->pending_readers > 0 || rwlock->pending_writers > 0)) {