c++ - 重置线程的休眠时间

Question

假设有这样一个线程

void mythread()
{
  int res;
  while(1) {
    {
       boost::lock_guard<boost::mutex> lock(mylock);
       res = do_my_stuff();
    }
    boost::this_thread::sleep(boost::posix_time::seconds(5));
  }
}

并且线程当前正在休眠。如果线程外发生某些事情，我希望能够增加 sleep 时间。

最好的方法是什么？

Answer 1

使用condition_variable表明截止日期的变化

这有利于支持超时缩短的场景:

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#include <thread>
#include <chrono>
#include <iostream>
#include <condition_variable>

namespace demo
{
    namespace chrono = std::chrono;

    using our_clock = chrono::system_clock;

    struct Worker
    {
        mutable std::mutex _mx;

        // shared, protected by _mx:
        our_clock::time_point _deadline; 
        mutable std::condition_variable _cv;

        Worker(our_clock::time_point deadline) : _deadline(deadline) {}

        void operator()() const {
            std::unique_lock<std::mutex> lk(_mx);
            _cv.wait_until(lk, _deadline, [this] 
                    { 
                        std::cout << "worker: Signaled\n";
                        auto now = our_clock::now();
                        if (now >= _deadline)
                            return true;
                        std::cout << "worker: Still waiting " << chrono::duration_cast<chrono::milliseconds>(_deadline - now).count() << "ms...\n"; 
                        return false;
                    });
            std::cout << "worker: Done\n";
        }
    };
}

int main()
{
    using namespace demo;

    Worker worker(our_clock::now() + chrono::seconds(2));
    auto th = std::thread(std::cref(worker));

    // after 2 seconds, update the timepoint
    std::this_thread::sleep_for(chrono::seconds(1));

    {
        std::lock_guard<std::mutex> lk(worker._mx);
        std::cout << "Updating shared delay value..." << "\n";

        worker._deadline = our_clock::now() + chrono::seconds(1);
        worker._cv.notify_all();
    }

    th.join();
}

C++11 标准库(无信号)

这是一种仅在截止日期前不使用同步的标准库方法。

我更喜欢使用 atomic time_point deadline 值本身，但这不受支持。下一个最好的事情是 shared_ptr<time_point> (使用 std::atomic_load/atomic_store )但是我的编译器库还没有实现它( grrr )。

因此，我从一开始就分享“偏移量”:

#include <thread>
#include <chrono>
#include <iostream>
#include <atomic>

namespace demo
{
    namespace chrono = std::chrono;

    using our_clock = chrono::system_clock;
    using shared_delay = std::atomic<our_clock::duration>;

    void worker(our_clock::time_point const start, shared_delay const& delay)
    {
        for (our_clock::time_point deadline; our_clock::now() < (deadline = start + delay.load());)
        {
            std::cout << "worker: Sleeping for " << chrono::duration_cast<chrono::milliseconds>(deadline - our_clock::now()).count() << "ms...\n";
            std::this_thread::sleep_until(deadline);
        }

        std::cout << "worker: Done\n";
    }
}

int main()
{
    using namespace demo;

    shared_delay delay(chrono::seconds(2));
    auto th = std::thread(worker, our_clock::now(), std::cref(delay));

    // after 2 seconds, update the timepoint
    std::this_thread::sleep_for(chrono::seconds(1));
    std::cout << "Updating shared delay value..." << "\n";
    delay.store(chrono::seconds(3));

    th.join();
}

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