并行函数调用与异步
问题描述:
需要创建并运行线程,在一个循环中。这里是编译/运行的代码,但它不会并行创建/运行线程,即形成此代码,我期望三个线程并行运行,但是函数的每个调用都会按顺序发生,如。为什么?并行函数调用与异步
template<typename T>
void say(int n, T t) {
cout << " say: " << n << std::flush;
for(int i=0; i<10; ++i) {
cout << " " << t << std::flush;
std::this_thread::sleep_for(std::chrono::milliseconds(1000));
} cout << " end " << std::flush << endl;
}
template<typename F, typename... Ts>
inline auto reallyAsync(F&& f, Ts&&... params){
return std::async(
std::launch::async,
std::forward<F>(f),
std::forward<Ts>(params)...);
}
int main() {
float x = 100;
for(int i=0; i<3; ++i) {
auto f = reallyAsync(&say<decltype(x)>, i, x*(i+1)) ;
}
}
output:
say: 0 100 100 100 100 100 100 100 100 100 100 end
say: 1 200 200 200 200 200 200 200 200 200 200 end
say: 2 300 300 300 300 300 300 300 300 300 300 end