std::condition_variable_any::wait_for
template< class Lock, class Rep, class Period > std::cv_status wait_for( Lock& lock, const std::chrono::duration<Rep, Period>& rel_time); | (1) | (since C++11) |
|---|---|---|
template< class Lock, class Rep, class Period, class Predicate > bool wait_for( Lock& lock, const std::chrono::duration<Rep, Period>& rel_time, Predicate pred); | (2) | (since C++11) |
1%29原子释放lock，阻止当前正在执行的线程，并将其添加到等待执行的线程列表中。*this.线程将在notify_all()或notify_one()执行，或者在相对超时时执行。rel_time过期了。它也可能是伪造的。不管原因是什么，lock重新获得和wait_for()出口。如果此函数通过异常退出，lock也被重新获得。%28直到C++14%29
2%29相当于return wait_until(lock, std::chrono::steady_clock::now() + rel_time, std::move(pred));这种过载可能被用来忽略虚假的唤醒。
用一个稳定的时钟来测量持续时间。此函数的阻塞时间可能超过timeout_duration由于调度或资源争用延迟。
If these functions fail to meet the postcondition (lock is locked by the calling thread), std::terminate is called. For example, this could happen if relocking the mutex throws an exception, | (since C++14) |
|---|
参数
lock | - | an object of type Lock that meets the BasicLockable requirements, which must be locked by the current thread |
|---|---|---|
rel_time | - | an object of type std::chrono::duration representing the maximum time to spend waiting |
pred | - | predicate which returns ?false if the waiting should be continued. The signature of the predicate function should be equivalent to the following: bool pred();? |
返回值
1%29std::cv_status::timeout指定的相对超时rel_time过期了，std::cv_status::no_timeout否则。
2%29false如果谓词pred仍然评估为false在...之后rel_time超时过期，否则为true...
例外
1%29
May throw std::system_error, may also propagate exceptions thrown by lock.lock() or lock.unlock(). | (until C++14) |
|---|---|
Any exception thrown by clock, time_point, or duration during the execution (clocks, time points, and durations provided by the standard library never throw). | (since C++14) |
2%29与%281%29相同，但也可能传播由pred
注记
即使在锁定下通知，重载%281%29也不能保证在由于超时而返回时关联谓词的状态。
对…的影响notify_one()/notify_all()三个原子部分wait()/wait_for()/wait_until()%28解锁+等待、唤醒和锁定%29按一个总顺序进行，可视为修改顺序原子变量的顺序是特定于这个单独的条件的。[医]变量。这使得不可能notify_one()，例如，延迟并取消阻塞在调用之后才开始等待的线程。notify_one()被制造出来了。
例
二次
#include <iostream>
#include <atomic>
#include <condition_variable>
#include <thread>
#include <chrono>
using namespace std::chrono_literals;
std::condition_variable_any cv;
std::mutex cv_m;
int i;
void waits(int idx)
{
std::unique_lock<std::mutex> lk(cv_m);
if(cv.wait_for(lk, idx*100ms, []{return i == 1;}))
std::cerr << "Thread " << idx << " finished waiting. i == " << i << '\n';
else
std::cerr << "Thread " << idx << " timed out. i == " << i << '\n';
}
void signals()
{
std::this_thread::sleep_for(120ms);
std::cerr << "Notifying...\n";
cv.notify_all();
std::this_thread::sleep_for(100ms);
{
std::lock_guard<std::mutex> lk(cv_m);
i = 1;
}
std::cerr << "Notifying again...\n";
cv.notify_all();
}
int main()
{
std::thread t1(waits, 1), t2(waits, 2), t3(waits, 3), t4(signals);
t1.join(); t2.join(), t3.join(), t4.join();
}二次
产出：
二次
Thread 1 timed out. i == 0
Notifying...
Thread 2 timed out. i == 0
Notifying again...
Thread 3 finished waiting. i == 1二次
另见
wait | blocks the current thread until the condition variable is woken up (public member function) |
|---|---|
wait_until | blocks the current thread until the condition variable is woken up or until specified time point has been reached (public member function) |
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