wwbmmm commented on code in PR #2147:
URL: https://github.com/apache/brpc/pull/2147#discussion_r1127642318
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src/bthread/work_stealing_queue.h:
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@@ -115,15 +119,22 @@ class WorkStealingQueue {
// Returns true on stolen.
// May run in parallel with push() pop() or another steal().
bool steal(T* val) {
- size_t t = _top.load(butil::memory_order_acquire);
+ // no instructions before _top.store() must be aware
+ size_t t = _top.load(butil::memory_order_relaxed);
+
size_t b = _bottom.load(butil::memory_order_acquire);
if (t >= b) {
// Permit false negative for performance considerations.
return false;
}
do {
- butil::atomic_thread_fence(butil::memory_order_seq_cst);
+ // erased: butil::atomic_thread_fence(butil::memory_order_seq_cst);
+ // no instruction before _top.cas must be known to other pthreads
b = _bottom.load(butil::memory_order_acquire);
+
+ // If not get t again and another steal() happens
+ // after the first getting, it might stuck in a dead circle
+ t = _top.load(butil::memory_order_acquire);
Review Comment:
if compare_exchange_strong returns false, the current value of _top will be
stored in t. No need to load again here.
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