std::condition_variable_any::wait_until

 

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std::condition_variable_any

Member functions

condition_variable_any::condition_variable_any

condition_variable_any::~condition_variable_any

Notification

condition_variable_any::notify_one

condition_variable_any::notify_all

Waiting

condition_variable_any::wait

condition_variable_any::wait_for

condition_variable_any::wait_until

Native handle

condition_variable_any::native handle

 

template< class Clock, class Duration > std::cv_status wait_until( BasicLockable& lock,                            const std::chrono::time_point<Clock, Duration>& abs_time);	(1)	(since C++11)
template< class Clock, class Duration, class Predicate > bool wait_until( BasicLockable& lock,                  const std::chrono::time_point<Clock, Duration>& abs_time,                  Predicate pred);	(2)	(since C++11)

1) Atomically releases lock, blocks the current executing thread, and adds it to the list of threads waiting on *this. The thread will be unblocked when notify_all() or notify_one() is executed, or when the absolute time point abs_time is reached. It may also be unblocked spuriously. When unblocked, regardless of the reason, lock is reacquired and wait_until() exits. If this function exits via exception, lock is also reacquired.

2) Equivalent to

while (!pred())
    if (wait_until(lock, abs_time) == std::cv_status::timeout)
        return pred();
return true;

This overload may be used to ignore spurious awakenings.

Parameters

lock	-	an object of BasicLockable type, which must be locked by the current thread
abs_time	-	an object of type std::chrono::time_point representing the time when to stop 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(); ​

Return value

1) std::cv_status::timeout if the absolute timeout specified by abs_time was reached, std::cv_status::no_timeout overwise.

2) false if the predicate pred still evaluates to false after the abs_time timeout expired, otherwise true.

Exceptions

May throw std::system_error, may also propagate exceptions thrown by lock.lock() or lock.unlock().

Notes

Calling this function if lock.mutex() is not locked by the current thread is undefined behavior.

Calling this function if lock.mutex() is not the same mutex as the one used by all other threads that are currently waiting on the same condition variable is undefined behavior.

Example

#include <iostream>
#include <atomic>
#include <condition_variable>
#include <thread>
#include <chrono>
 
std::condition_variable_any cv;
std::mutex cv_m;
std::atomic<int> i = ATOMIC_VAR_INIT(0);
 
void waits(int idx)
{
    std::unique_lock<std::mutex> lk(cv_m);
    auto now = std::chrono::system_clock::now();
    if(cv.wait_until(lk, now + std::chrono::milliseconds(idx*100), [](){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(std::chrono::milliseconds(120));
    std::cerr << "Notifying...\n";
    cv.notify_all();
    std::this_thread::sleep_for(std::chrono::milliseconds(100));
    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();
}

Output:

Thread 1 timed out. i == 0
Notifying...
Thread 2 timed out. i == 0
Notifying again...
Thread 3 finished waiting. i == 1

See also

wait	blocks the current thread until the condition variable is woken up (public member function)
wait_for	blocks the current thread until the condition variable is woken up or after the specified timeout duration (public member function)