c++ - 从通过 std::async 启动的函数抛出的异常会发生什么

Question

通过 std::async 启动的函数抛出的异常会怎样？

#include <future>
#include <iostream>
#include <stdexcept>

void foo()
{
  std::cout << "foo()" << std::endl;
  throw std::runtime_error("Error");
}

int main()
{
  try
  {
    std::cout << "1" << std::endl;
    auto f = std::async(std::launch::async, foo);
    f.get();
    std::cout << "2" << std::endl;
  }
  catch (const std::exception& ex)
  {
    std::cerr << ex.what() << std::endl;
  }
}

MSVC 给我以下输出:

1
foo()
Error

调用get函数在函数外捕获这样的异常是不是对的？

Answer 1

来自 cppreference :

[...] if the function f returns a value or throws an exception, it is stored in the shared state accessible through the std::future that async returns to the caller.

并在关于 std::future::get() 的引用中:

If an exception was stored in the shared state referenced by the future (e.g. via a call to std::promise::set_exception()) then that exception will be thrown.

所以是的，如果您的函数抛出异常，该异常基本上会被推迟到将来并在 get() 上重新抛出。