C++ 中分离线程的资源释放

Question

我正在经历 this post 堆栈溢出，其中接受的答案是：

what happens to a detached thread when main() exits is:
It continues running (because the standard doesn't say it is stopped), and that's well-defined, as long as it touches neither (automatic|thread_local) variables of other threads nor static objects.

虽然在 post 中接受的答案是：

Process terminates when main() exits, and all threads are killed.

为了查看行为，我在 g++ (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4 上测试了以下代码，这表明一旦主线程退出，其他分离线程也会退出。

#include <iostream>       
#include <thread>         
#include <unistd.h>
#include <fstream>
using namespace std;

void foo()
{
std::cout<<"Inside foo\n";
int i=0;
ofstream myfile;


while(i<10)
{
    std::cout<<"Inside while\n";
    myfile.open ("/home/abc/example.txt",ios::app);
    myfile << "Writing this to a file.\n";
    myfile.close();
    i++;
    sleep(1);
}}

int main()
{
    std::thread first (foo);     
    first.detach();
    sleep(5);
    return 0;
}

那么，为什么在堆栈溢出的许多 post 中，即使主线程退出，分离线程也会在后台继续运行ning？在什么情况下，分离线程在主程序退出时继续在后台运行以及以上哪一个陈述是正确的？

提前致谢。

Answer 1

标准将线程的范围定义为程序：

1.10/1: A thread of execution (also known as a thread) is a single flow of control within a program (...) The execution of the entire program consists of an execution of all of its threads.

标准关于分离线程的说法：

30.3.3/1: A thread of execution is detached when no thread object represents that thread.

所以标准中没有任何内容表明线程可以在其程序中存活下来。

如果你想在程序结束后在后台保留一些东西运行ning，你必须分叉或创建一个单独的进程，该进程将运行在后台使用自己的资源和线程。

C++ 中分离线程的资源释放

Resource deallocation for Detach thread in C++

c++

multithreading

detach

c++11

stdthread