Std :: thread.join () deadlock

Question

I don't understand why this simple snippet has a dead lock:

#include <atomic> #include <thread> #include <memory> using namespace std; class Test { public: Test() : mExit( false ) { mThread = thread( bind( &Test::func, this ) ); } ~Test() { if ( mThread.joinable() ) { mExit = true; mThread.join(); } } private: void func() { while ( !mExit ) { // do something } } private: atomic< bool > mExit; thread mThread; }; typedef unique_ptr< Test > TestPtr; TestPtr gTest; int main() { gTest = TestPtr( new Test ); return 0; } 

Edit I typed the wrong set of counterstructors mExit = true

Edit 2 I am using msvc2012 with the v110_xp toolkit.

Edit 3 The problem disappears if I explain the call to gTest.release () inside the main

Answer 1

I just had this problem, so I am posting a real answer to others.

In the visual studio, at least there is an “exit lock” that blocks when the thread enters the exit code (that is, after main() for the main thread and after f() for std::thread(f) ).

Since your test class is destroyed only after main() , blocking the output is blocked. Only after that will you set mExit = true; and another thread will be completed. Then this other thread waits for an “exit lock” that is already taken by the main thread, while the main thread waits in mThread.join(); leading to a deadlock.

So yes, you need to attach all your threads before the main thread completes.

Answer 2

For me, the code looks fine, if it's fine with the local dut bad with global, I suspect the class is associated with a deinite sequence. Joining takes place deep in the outlet, and the implementation may have already eliminated some structures. It should not be, but it is possible.

In any case, I always avoid running the thread in front of main and leave either end of the end. I believe that only asking for trouble. If you can rearrange it to force a connection at an earlier point, the whole problem may evaporate.

Also you should probably use atom_flag over the atom.

Answer 3

Change code from

gTest = TestPtr (new test);

to

auto gTest = std :: make_unique ();

to solve a problem.

the problem is like the point above with a global object.