std::condition_variable_any::wait_for
From cppreference.com
< cpp | thread | condition variable any
template< class Lock, class Rep, class Period >
std::cv_status wait_for( Lock& lock, |
(1) | (since C++11) |
template< class Lock, class Rep, class Period, class Predicate >
bool wait_for( Lock& lock, |
(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 relative timeout rel_time
expires. It may also be unblocked spuriously. When unblocked, regardless of the reason, lock
is reacquired and wait_for()
exits. If this function exits via exception, lock
is also reacquired.
2) Equivalent to
while (!pred()) { if (wait_for(lock, rel_time) == std::cv_status::timeout) { return pred(); } } return true;
This overload may be used to ignore spurious awakenings.
A steady clock is used to measure the duration. This function may block for longer than timeout_duration
due to scheduling or resource contention delays.
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.
Contents |
[edit] Parameters
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:
|
[edit] Return value
1) std::cv_status::timeout if the relative timeout specified by
rel_time
expired, std::cv_status::no_timeout overwise.
2) false if the predicate
pred
still evaluates to false after the rel_time
timeout expired, otherwise true.[edit] Exceptions
May throw std::system_error, may also propagate exceptions thrown by lock.lock() or lock.unlock().
[edit] 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); if(cv.wait_for(lk, 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
[edit] See also
blocks the current thread until the condition variable is woken up (public member function) |
|
blocks the current thread until the condition variable is woken up or until specified time point has been reached (public member function) |