diff options
Diffstat (limited to 'runtime/base/mutex-inl.h')
| -rw-r--r-- | runtime/base/mutex-inl.h | 29 |
1 files changed, 16 insertions, 13 deletions
diff --git a/runtime/base/mutex-inl.h b/runtime/base/mutex-inl.h index 1890181..3e5cdba 100644 --- a/runtime/base/mutex-inl.h +++ b/runtime/base/mutex-inl.h @@ -23,7 +23,6 @@ #define ATRACE_TAG ATRACE_TAG_DALVIK -#include "cutils/atomic-inline.h" #include "cutils/trace.h" #include "base/stringprintf.h" @@ -152,20 +151,20 @@ inline void ReaderWriterMutex::SharedLock(Thread* self) { #if ART_USE_FUTEXES bool done = false; do { - int32_t cur_state = state_; + int32_t cur_state = state_.LoadRelaxed(); if (LIKELY(cur_state >= 0)) { // Add as an extra reader. - done = android_atomic_acquire_cas(cur_state, cur_state + 1, &state_) == 0; + done = state_.CompareExchangeWeakAcquire(cur_state, cur_state + 1); } else { // Owner holds it exclusively, hang up. ScopedContentionRecorder scr(this, GetExclusiveOwnerTid(), SafeGetTid(self)); - android_atomic_inc(&num_pending_readers_); - if (futex(&state_, FUTEX_WAIT, cur_state, NULL, NULL, 0) != 0) { + ++num_pending_readers_; + if (futex(state_.Address(), FUTEX_WAIT, cur_state, NULL, NULL, 0) != 0) { if (errno != EAGAIN) { PLOG(FATAL) << "futex wait failed for " << name_; } } - android_atomic_dec(&num_pending_readers_); + --num_pending_readers_; } } while (!done); #else @@ -184,14 +183,18 @@ inline void ReaderWriterMutex::SharedUnlock(Thread* self) { #if ART_USE_FUTEXES bool done = false; do { - int32_t cur_state = state_; + int32_t cur_state = state_.LoadRelaxed(); if (LIKELY(cur_state > 0)) { - // Reduce state by 1. - done = android_atomic_release_cas(cur_state, cur_state - 1, &state_) == 0; - if (done && (cur_state - 1) == 0) { // cas may fail due to noise? - if (num_pending_writers_.LoadRelaxed() > 0 || num_pending_readers_ > 0) { + // Reduce state by 1 and impose lock release load/store ordering. + // Note, the relaxed loads below musn't reorder before the CompareExchange. + // TODO: the ordering here is non-trivial as state is split across 3 fields, fix by placing + // a status bit into the state on contention. + done = state_.CompareExchangeWeakSequentiallyConsistent(cur_state, cur_state - 1); + if (done && (cur_state - 1) == 0) { // Weak CAS may fail spuriously. + if (num_pending_writers_.LoadRelaxed() > 0 || + num_pending_readers_.LoadRelaxed() > 0) { // Wake any exclusive waiters as there are now no readers. - futex(&state_, FUTEX_WAKE, -1, NULL, NULL, 0); + futex(state_.Address(), FUTEX_WAKE, -1, NULL, NULL, 0); } } } else { @@ -233,7 +236,7 @@ inline bool ReaderWriterMutex::IsExclusiveHeld(const Thread* self) const { inline uint64_t ReaderWriterMutex::GetExclusiveOwnerTid() const { #if ART_USE_FUTEXES - int32_t state = state_; + int32_t state = state_.LoadRelaxed(); if (state == 0) { return 0; // No owner. } else if (state > 0) { |