为什么这个简单的线程C ++程序在退出时崩溃，除非我调用thread.join（）？

Question

The program below will end up failing with a message regarding abort() being called.

I'm starting a thread that simple prints to cout . If I use std::this_thread::sleep_for() , I get the error. If I remove this, I get the error. If I call join() on the thread, everything works fine.

Shouldn't the thread have terminated long before the 1000 ms delay was up? Why is this causing an error? I can't believe calling join() is a requirement for a thread.

#include <thread>
#include <iostream>

class ThreadTest
{
public:
    ThreadTest() : _t{ &ThreadTest::Run, this } {}
    void Wait() { _t.join(); }

private:

    void Run(){
        std::cout << "In thread" << std::endl;
    }

    std::thread _t;
};

int main(int argc, char *argv[])
{
    ThreadTest tt;

    std::this_thread::sleep_for(std::chrono::milliseconds(1000));
    // tt.Wait();

    return 0;
}

Answer 1

According to cppreference on thread class destructor :

~thread() : Destroys the thread object. If *this still has an associated running thread (ie joinable() == true ), std::terminate() is called.

And joinable() :

[...] A thread that has finished executing code, but has not yet been joined is still considered an active thread of execution and is therefore joinable.

So you have to call join() explicitely before your thread variable is automatically destroyed or use the detach() member function.

Answer 2

Check cppreference's std::thread page .

A thread that has finished executing code, but has not yet been joined is still considered an active thread of execution and is therefore joinable.

[ the destructor ] Destroys the thread object. If *this still has an associated running thread (ie joinable() == true ), std::terminate() is called .

To get the behavior you want, you'd need to call _t.detach() before exiting from main :

[ detach() ] Separates the thread of execution from the thread object, allowing execution to continue independently. Any allocated resources will be freed once the thread exits. After calling detach *this no longer owns any thread.