ZhengweiZhu commented on issue #2983: URL: https://github.com/apache/brpc/issues/2983#issuecomment-3388228204
> > Jumping precedes tracing, from the tracer's perspective the current implementation set m->traced = true first, then find its status TASK_STATUS_JUMPING and block at WaitForJumping(m). When the bthread is about to jumping to run, it finds it is traced so block at WaitForTracing(m). > > In this scenario, bthread first locks and sets status to TASK_STATUS_JUMPING. At this time, tracing=false, so WaitForTracing() will not be called. > > [brpc/src/bthread/task_tracer.cpp](https://github.com/apache/brpc/blob/4eeb5e260af165291f95f30f0fa64f9ff67ba192/src/bthread/task_tracer.cpp#L139-L163) > > Lines 139 to 163 in [4eeb5e2](/apache/brpc/commit/4eeb5e260af165291f95f30f0fa64f9ff67ba192) > > bool tracing; > { > BAIDU_SCOPED_LOCK(m->version_lock); > if (TASK_STATUS_UNKNOWN == m->status && TASK_STATUS_JUMPING == s) { > // Do not update status for jumping when bthread is ending. > return; > } > > tracing = m->traced; > // bthread is scheduled for the first time. > if (TASK_STATUS_READY == s || NULL == m->stack) { > m->status = TASK_STATUS_FIRST_READY; > } else { > m->status = s; > } > if (TASK_STATUS_CREATED == s) { > m->worker_tid = pthread_t{}; > } > } > > // Make sure bthread does not jump stack when it is being traced. > if (tracing && TASK_STATUS_JUMPING == s) { > WaitForTracing(m); > } > } To clarify this, assume the bthread to be traced is A. The status of A is TASK_STATUS_JUMPING when A is jumping from OR jumping to, which relates to cur_meta and next_meta in sched_to. https://github.com/apache/brpc/blob/4eeb5e260af165291f95f30f0fa64f9ff67ba192/src/bthread/task_group.cpp#L754-L756 The timeline is: t1: the first time as traced is false so g->_control->_task_tracer.set_status(TASK_STATUS_JUMPING, cur_meta) succeeds t2: the tracer starts to trace bthread A (which is in TASK_STATUS_JUMPING) and set A->traced to true and blocks at WaitForJumping t3: the A is jumping to and g->_control->_task_tracer.set_status(TASK_STATUS_JUMPING, next_meta) blocks at WaitForTracing as its traced is already set to true by tracer and its status is always TASK_STATUS_JUMPING. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
