我正在尝试在之前的工作完成后立即启动新线程worker_thread
has started,但也许结束了,也可能没有结束。我已经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;
}
}
输出看起来像这样:
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,仅当上一个线程中的工作完成时才会启动下一个线程。但我想在上一个线程中开始工作后立即启动下一个线程,而不是等待它结束,只等待开始。
std::async
返回一个std::future
保存函数执行的结果。就您而言,它是一个临时对象,会立即被销毁。的文档std::future
says:
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 http://en.cppreference.com/w/cpp/thread/future/%7Efuture:
✔ 共享状态是通过调用 std::async 创建的
✔ 共享状态尚未就绪
✔ 这是最后一次引用共享状态
所有这些都是真的,所以破坏它future
将阻塞直到工作函数完成执行。
您可以创建分离线程来避免此问题:
std::thread(worker_thread).detach();
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