关于timer的删除问题

[yinghaoyu]

TimerQueue::cancelInLoop和TimerQueue::handleRead都是在同一个线程loop里执行的，在TimerQueue::cancelInLoop删除timer的时候，请问什么情况下callingExpiredTimers_会触发？

[chenshuo]

gdb 调试 bin/timerqueue_unittest，在第 158 行设断点，

  156   else if (callingExpiredTimers_)
  157   {
  158     cancelingTimers_.insert(timer);
  159   }

然后

(gdb) bt

#0  std::set<>::insert () at /usr/include/c++/11/bits/stl_set.h:509
#1  muduo::net::TimerQueue::cancelInLoop (this=, timerId=...) at TimerQueue.cc:158
#2  in muduo::net::TimerQueue::cancel (this=, timerId=...) at /usr/include/c++/11/tuple:1090
#3  in cancel (timer=...) at TimerQueue_unittest.cc:31
#4  in std::function<void ()>::operator()() const (this=) at std_function.h:586
#5  muduo::net::Timer::run (this=) at Timer.h:39
#6  muduo::net::TimerQueue::handleRead (this=) at TimerQueue.cc:176
#7  in std::function<void (muduo::Timestamp)>::operator()(muduo::Timestamp) const () at /usr/include/c++/11/bits/std_function.h:586
#8  muduo::net::Channel::handleEventWithGuard (this=, receiveTime=...) at Channel.cc:107
#9  in muduo::net::Channel::handleEvent (this=, receiveTime=...) at Channel.cc:79
#10 in muduo::net::EventLoop::loop (this=) at EventLoop.cc:125
#11 in main () at TimerQueue_unittest.cc:55

[yinghaoyu]

在一个Eventloop里面，handleEvent是在doPendingFunctors之前的，既然这样，一定是先执行handleRead直到结束，才会执行cancelInLoop的吧？我实在没想明白这个触发条件，求点拨

[chenshuo]

EventLoop::loop
  -> Channel::handleEvent 
    -> TimerQueue::handleRead
      callingExpiredTimers_ = true;
      -> Timer::run
        -> **user timer cancels another timer**
          -> TimerQueue::cancel
            -> TimerQueue::cancelInLoop
              if (callingExpiredTimers_) 成立
      callingExpiredTimers_ = false;

[yinghaoyu]

我悟了，user timer cancels another timer，这两个function都是在handleEvent里处理的！Thanks a lot !

[chenshuo]

You are welcome.