two-headBoy commented on code in PR #3633:
URL: https://github.com/apache/brpc/pull/3633#discussion_r4399924127
##########
src/bthread/task_group_inl.h:
##########
@@ -93,11 +93,100 @@ inline void TaskGroup::push_rq(bthread_t tid) {
// brpc)
flush_nosignal_tasks();
LOG_EVERY_SECOND(ERROR) << "_rq is full, capacity=" << _rq.capacity();
- // TODO(gejun): May cause deadlock when all workers are spinning here.
- // A better solution is to pop and run existing bthreads, however which
- // make set_remained()-callbacks do context switches and need extensive
- // reviews on related code.
- ::usleep(1000);
+ if (is_current_pthread_task() && !is_current_main_task()) {
+ // A pthread-mode bthread runs on _main_stack and cannot be
+ // scheduled out, fall back to waiting.
+ ::usleep(1000);
+ continue;
+ }
+ const auto pop_task = [this](bthread_t* t) -> bool {
+#ifndef BTHREAD_FAIR_WSQ
+ return _rq.pop(t);
+#else
Review Comment:
Under BTHREAD_FAIR_WSQ, pop_task() uses _rq.steal() rather than an
owner-side pop. If steal() has different semantics (end of deque, fairness, or
concurrency assumptions) than the owner-consumption path, this may change
scheduling behavior in the overload path. Prefer using the owner pop API if it
exists in the fair-WSQ implementation; otherwise, add an explicit comment
explaining why steal() is the correct/safe choice for the owning worker here.
##########
src/bthread/task_group_inl.h:
##########
@@ -93,11 +93,100 @@ inline void TaskGroup::push_rq(bthread_t tid) {
// brpc)
flush_nosignal_tasks();
LOG_EVERY_SECOND(ERROR) << "_rq is full, capacity=" << _rq.capacity();
- // TODO(gejun): May cause deadlock when all workers are spinning here.
- // A better solution is to pop and run existing bthreads, however which
- // make set_remained()-callbacks do context switches and need extensive
- // reviews on related code.
- ::usleep(1000);
+ if (is_current_pthread_task() && !is_current_main_task()) {
+ // A pthread-mode bthread runs on _main_stack and cannot be
+ // scheduled out, fall back to waiting.
+ ::usleep(1000);
+ continue;
+ }
+ const auto pop_task = [this](bthread_t* t) -> bool {
+#ifndef BTHREAD_FAIR_WSQ
+ return _rq.pop(t);
+#else
Review Comment:
Under BTHREAD_FAIR_WSQ, pop_task() uses _rq.steal() rather than an
owner-side pop. If steal() has different semantics (end of deque, fairness, or
concurrency assumptions) than the owner-consumption path, this may change
scheduling behavior in the overload path. Prefer using the owner pop API if it
exists in the fair-WSQ implementation; otherwise, add an explicit comment
explaining why steal() is the correct/safe choice for the owning worker here.
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