我正在尝试在前worker_thread
的工作开始后立即启动新线程,但可能结束或不结束。我用时间延迟替换了开始和结束的工作。我的代码是:
#include <iostream>
#include <string>
#include <mutex>
#include <condition_variable>
#include <future>
#include <atomic>
#include <chrono>
#include <thread>
std::mutex m;
std::condition_variable cv;
bool started = false;
void worker_thread()
{
std::unique_lock<std::mutex> lk(m);
static std::atomic<int> count(1);
std::this_thread::sleep_for(std::chrono::milliseconds{(count % 5) * 100});
std::cerr << "Start Worker thread: " << count << "n";
started = true;
lk.unlock();
cv.notify_one();
std::this_thread::sleep_for(std::chrono::milliseconds{3000});
std::cerr << "Exit Worker thread: " << count << "n";
++count;
}
int main()
{
while(1) {
std::async(std::launch::async, worker_thread);
std::unique_lock<std::mutex> lk(m);
cv.wait(lk, []{return started;});
started = false;
}
}
输出如下所示:
Start Worker thread: 1
Exit Worker thread: 1
Start Worker thread: 2
Exit Worker thread: 2
Start Worker thread: 3
Exit Worker thread: 3
Start Worker thread: 4
Exit Worker thread: 4
Start Worker thread: 5
Exit Worker thread: 5
这不是我想要的行为。我想要的是(不完全是(这样的东西:
Start Worker thread: 1
Start Worker thread: 2
Start Worker thread: 3
Start Worker thread: 4
Exit Worker thread: 1
Exit Worker thread: 3
Exit Worker thread: 4
Exit Worker thread: 2
Start Worker thread: 5
Exit Worker thread: 5
目前,下一个线程仅在上一个线程中的工作完成时启动。但是我想在上一个线程中启动工作后立即启动下一个线程,而不是等待它结束,只等待启动。
std::async
返回函数执行的std::future
保持结果。在你的情况下,它是一个临时的物体,被立即摧毁。std::future
的文档说:
这些操作不会阻止共享状态变为就绪状态,但如果满足以下所有条件,则可能会阻止:
✔ 共享状态是通过调用 std::async 创建的
✔ 共享状态尚未就绪
✔ 这是对共享状态的最后一次引用
所有这些都是正确的,因此该future
的销毁将阻止,直到工作线程函数完成执行。
您可以创建分离的线程来避免此问题:
std::thread(worker_thread).detach();