EventLoop::loop中quit_标志位被清掉导致程序无法退出的问题

[hbzzhtt]

这个问题应该作者发现了，标注了FIXME。
一种容易出现的场景是muduo/net/tests/EventLoopThreadPool_unittest.cc 之中，EventLoopThread对象刚创建时 创建了一个线程 在那个线程里面call loop ，但是那个线程还没走到loop，结果本线程的EventLoopThread对象发生了析构，导致quit先调用，loop后调用，本应退出的EventLoop::quit_标志位在EventLoop::loop之中被清除，程序无法退出。

Three threads:
logging 20200308 04:22:15.927503Z 32735 DEBUG EventLoop EventLoop created 0x7FD7C719E9E0 in thread 32735 - EventLoop.cc:77
logging 20200308 04:22:15.927513Z 32735 DEBUG threadFunc three0 call callback - EventLoopThread.cc:66
init(): pid = 32733, tid = 32735, loop = 0x7fd7c719e9e0
logging 20200308 04:22:15.927603Z 32735 DEBUG threadFunc three0 call loop - EventLoopThread.cc:75
logging 20200308 04:22:15.927661Z 32736 DEBUG EventLoop EventLoop created 0x7FD7C699D9E0 in thread 32736 - EventLoop.cc:77
logging 20200308 04:22:15.927669Z 32736 DEBUG threadFunc three1 call callback - EventLoopThread.cc:66
init(): pid = 32733, tid = 32736, loop = 0x7fd7c699d9e0
logging 20200308 04:22:15.927762Z 32736 DEBUG threadFunc three1 call loop - EventLoopThread.cc:75
logging 20200308 04:22:15.927803Z 32737 DEBUG EventLoop EventLoop created 0x7FD7C619C9E0 in thread 32737 - EventLoop.cc:77
logging 20200308 04:22:15.927809Z 32737 DEBUG threadFunc three2 call callback - EventLoopThread.cc:66
init(): pid = 32733, tid = 32737, loop = 0x7fd7c619c9e0
logging 20200308 04:22:15.927824Z 32733 DEBUG ~EventLoopThread three0 call loop->quit  - EventLoopThread.cc:35
logging 20200308 04:22:15.927828Z 32733 DEBUG ~EventLoopThread three0 call thread->join - EventLoopThread.cc:37
main(): pid = 32733, tid = 32735, loop = 0x7fd7c719e9e0
logging 20200308 04:22:15.927839Z 32735 DEBUG threadFunc three0 quit loop - EventLoopThread.cc:79
logging 20200308 04:22:15.927842Z 32735 DEBUG ~EventLoop EventLoop 0x7FD7C719E9E0 of thread 32735 destructs in thread 32735 - EventLoop.cc:95
logging 20200308 04:22:15.927868Z 32733 DEBUG ~EventLoopThread three1 call loop->quit  - EventLoopThread.cc:35
logging 20200308 04:22:15.927874Z 32733 DEBUG ~EventLoopThread three1 call thread->join - EventLoopThread.cc:37
logging 20200308 04:22:15.927891Z 32736 DEBUG threadFunc three1 quit loop - EventLoopThread.cc:79
logging 20200308 04:22:15.927894Z 32736 DEBUG ~EventLoop EventLoop 0x7FD7C699D9E0 of thread 32736 destructs in thread 32736 - EventLoop.cc:95
logging 20200308 04:22:15.927912Z 32733 DEBUG ~EventLoopThread three2 call loop->quit  - EventLoopThread.cc:35
logging 20200308 04:22:15.927917Z 32733 DEBUG ~EventLoopThread three2 call thread->join - EventLoopThread.cc:37
logging 20200308 04:22:15.927928Z 32737 DEBUG threadFunc three2 call loop - EventLoopThread.cc:75

Ubuntu 18.04 , cpp11 , gcc 7.4.0

[lys861205]

直接在使用构造函数中对quit_的赋值，在call loop 不需要对quit_赋值；还在call loop 赋值quit_的目的是什么