std :: promise< void>抛出未知错误，除非调用sleep [英] std::promise<void> throws Unknown error, unless calling sleep

问题描述

我有此代码:

#include <future>
#include <thread>

int main()
{
    std::promise<void> p;
    p.set_value();
    p.get_future().get();

    return 0;
}

然后用 gcc 编译后，它会抛出 std :: system_error :

And after compiling it with gcc it throws std::system_error:

$ g++ -o foo foo.cpp -std=c++11 -lpthread
$ ./foo
terminate called after throwing an instance of 'std::system_error'
  what():  Unknown error -1

奇怪的是，在创建承诺之前，先添加零秒睡眠 ，以防止出现异常情况

What is weird, adding zero-second sleep before creating the promise, prevents the exception:

int main()
{
    std::this_thread::sleep_for(std::chrono::milliseconds(0));
    std::promise<void> p;
    p.set_value();
    p.get_future().get();

    return 0;
}

$ g++ -o foo foo.cpp -std=c++11 -lpthread
$ ./foo
$ 

我尝试了 gcc 4.8.5和5.4.0，结果相同.为什么会这样呢?

I tried gcc 4.8.5 and 5.4.0, same results. Why does it behave like that?

推荐答案

此错误来自您的编译.应该是:

This error comes from your compilation. It should be:

 g++ -o foo foo.cpp -std=c++11 -pthread

< thread> 库需要此特殊标志 -pthread ，但是您提供了 -lpthread .前者使用全线程支持来编译您的翻译单元.后者仅链接库，而没有定义所需的宏和所需的工具.

The <thread> library needs this special flag -pthread but you provided -lpthread. The former compile your translation unit with the full thread support. The later only links the library, without defining the needed macros and needed tools.

关于大肠菌:

• 带有 -pthread : http://coliru.stacked-crooked.com/a/a53bed6696bb8d83
• 不包含: http://coliru.stacked-crooked.com/a/fd972e1556f8c060

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