std::condition_variable_any::wait
template< class Lock > void wait( Lock& lock ); | (1) | (since C++11) |
|---|---|---|
template< class Lock, class Predicate > void wait( Lock& lock, Predicate pred ); | (2) | (since C++11) |
wait导致当前线程阻塞，直到通知条件变量或出现虚假唤醒为止，还可以选择循环直到满足某个谓词。
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()被处决了。它也可能是伪造的。不管原因是什么，lock重新获得和wait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
二次
while (!pred()) {
wait(lock);
}二次
这种过载可能被用来忽略虚假的唤醒，而等待特定的条件成为现实。请注意，在输入此方法之前lock必须获得，之后wait(lock)退出也会被重新获取，即lock可以用作警卫pred()进入。
If these functions fail to meet the postconditions (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 |
|---|---|---|
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
%280%29
例外
1%29
May throw std::system_error, may also propagate exceptions thrown by lock.lock() or lock.unlock(). | (until C++14) |
|---|---|
Does not throw. | (since C++14) |
2%29与%281%29相同，但也可能传播由pred
注记
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 <condition_variable>
#include <thread>
#include <chrono>
std::condition_variable_any cv;
std::mutex cv_m; // This mutex is used for three purposes:
// 1) to synchronize accesses to i
// 2) to synchronize accesses to std::cerr
// 3) for the condition variable cv
int i = 0;
void waits()
{
std::unique_lock<std::mutex> lk(cv_m);
std::cerr << "Waiting... \n";
cv.wait(lk, []{return i == 1;});
std::cerr << "...finished waiting. i == 1\n";
}
void signals()
{
std::this_thread::sleep_for(std::chrono::seconds(1));
{
std::lock_guard<std::mutex> lk(cv_m);
std::cerr << "Notifying...\n";
}
cv.notify_all();
std::this_thread::sleep_for(std::chrono::seconds(1));
{
std::lock_guard<std::mutex> lk(cv_m);
i = 1;
std::cerr << "Notifying again...\n";
}
cv.notify_all();
}
int main()
{
std::thread t1(waits), t2(waits), t3(waits), t4(signals);
t1.join();
t2.join();
t3.join();
t4.join();
}二次
可能的产出：
二次
Waiting...
Waiting...
Waiting...
Notifying...
Notifying again...
...finished waiting. i == 1
...finished waiting. i == 1
...finished waiting. i == 1二次
另见
wait_for | blocks the current thread until the condition variable is woken up or after the specified timeout duration (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) |
c CND文件[医]等待
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