7

To my surprise, a C++11 std::thread object that has finished executing, but has not yet been joined is still considered an active thread of execution. This is illustrated in the following code example (built on Xubuntu 13.03 with g++ 4.7.3). Does anyone know if the C++11 standard provides a means to detect if a std::thread object is still actively running code?

#include <thread>
#include <chrono>
#include <iostream>
#include <pthread.h>
#include <functional>
int main() {
    auto lambdaThread = std::thread([](){std::cout<<"Excuting lambda thread"<<std::endl;});
    std::this_thread::sleep_for(std::chrono::milliseconds(250));
    if(lambdaThread.joinable()) {
        std::cout<<"Lambda thread has exited but is still joinable"<<std::endl;
        lambdaThread.join();
    }
    return 0;
}
4

2 回答 2

8

No, I don't think that this is possible. I would also try to think about your design and if such a check is really necessary, maybe you are looking for something like the interruptible threads from boost.

However, you can use std::async - which I would do anyway - and then rely on the features std::future provides you.

Namely, you can call std::future::wait_for with something like std::chrono::seconds(0). This gives you a zero-cost check and enables you to compare the std::future_status returned by wait_for.

auto f = std::async(foo);
...
auto status = f.wait_for(std::chrono::seconds(0));
if(status == std::future_status::timeout) {
    // still computing
}
else if(status == std::future_status::ready) {
    // finished computing
}
else {
    // There is still std::future_status::defered
}
于 2013-08-05T17:47:31.833 回答
2

对于“主动运行的代码”的定义是什么？不是我所知道的，我不确定线程​​变为可连接后处于什么状态，在大多数情况下，我认为您实际上需要细粒度控制，例如由在该线程中运行的代码设置的标志， 反正

对于特定于平台的解决方案，您可以使用 GetThreadTimes

于 2013-08-05T17:41:47.463 回答