chenBright commented on code in PR #3539:
URL: https://github.com/apache/brpc/pull/3539#discussion_r3998908107
##########
src/bthread/parking_lot.h:
##########
@@ -69,13 +105,23 @@ class BAIDU_CACHELINE_ALIGNMENT ParkingLot {
// Fast path, no need to futex_wait.
return;
}
- if (_no_signal_when_no_waiter) {
- _waiter_num.fetch_add(1, butil::memory_order_relaxed);
+ if (!_no_signal_when_no_waiter) {
+ futex_wait_private(&_pending_signal, expected_state.val, NULL);
+ return;
}
- futex_wait_private(&_pending_signal, expected_state.val, nullptr);
- if (_no_signal_when_no_waiter) {
- _waiter_num.fetch_sub(1, butil::memory_order_relaxed);
+
+ _waiter_num.fetch_add(1, butil::memory_order_relaxed);
+ // Matching StoreLoad fence for the signal-side fence above. It
publishes
+ // this waiter before _pending_signal is checked below.
+ butil::atomic_thread_fence(butil::memory_order_seq_cst);
+ // Re-check _pending_signal with a real atomic load, which closes the
Dekker
+ // pattern at the C++ memory model level(the check inside futex_wait
is done
Review Comment:
fixed.
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