[英]Unexpected behavior using std::map with std::thread
So I need a thread pool for my application, which led me to create a std::map<int, std::thread>
object. 因此,我需要为我的应用程序创建一个线程池,这导致我创建了一个std::map<int, std::thread>
对象。 I've encountered some very unexpected behavior, which can be simplified to this: 我遇到了一些非常意外的行为,可以将其简化为:
std::map<int, std::thread> threads;
threads.insert(std::pair<int, std::thread>(1, std::thread([]() {
std::cout << "I'm the first thread and I'm gonna work\n";
})));
threads[1].join();
std::cout << "Thread 1 joinable? " << threads[1].joinable() << "\n";
threads.insert(std::pair<int, std::thread>(1, std::thread([]() {
std::cout << "I'm not gonna work at all\n";
})));
threads[1].join();
The output is 输出是
I'm the first thread and I'm gonna work
Thread 1 joinable? 0
Right after, std::terminate()
is called and program receives SIGABRT signal. 之后,将调用std::terminate()
,程序将接收SIGABRT信号。
Live debugging suggested that terminate
is being called because joinable()
is true, but I just checked and figured it's not! 实时调试表明正在调用terminate
,因为joinable()
为true,但是我只是检查了一下,发现不是这样!
Moreover, the way to overcome it was simply to add the following line after join()
ing: 而且,克服它的方法就是在join()
之后添加以下行:
threads.erase(1);
That leaves me a bit confused, as it looks like a new instance of std::thread
was created just before my insert
call... Can someone hint me about this unexpected behavior? 这让我有些困惑,因为它看起来像是在我的insert
调用之前创建的std::thread
的新实例...有人可以提示我这种意外行为吗?
From http://en.cppreference.com/w/cpp/container/map/insert : 从http://en.cppreference.com/w/cpp/container/map/insert中 :
Inserts element(s) into the container, if the container doesn't already contain an element with an equivalent key. 如果容器尚未包含具有等效键的元素,则将其插入容器。
Your map already contains an element at key 1
so the second threads.insert
doesn't do anything. 您的地图已经在键1
处包含一个元素,因此第二个threads.insert
不执行任何操作。 You are simply trying to join twice on the same std::thread
. 您只是想在同一std::thread
上加入两次。 This is why threads.erase(1);
这就是为什么threads.erase(1);
solves the problem, your map no longer contains a thread at key 1
. 解决了问题,您的地图不再在键1
处包含线程。
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