std::condition_variable_any::wait_until - cppreference.com (original) (raw)

wait_until causes the current thread to block until the condition variable is notified, the given duration has been elapsed, or a spurious wakeup occurs. pred can be optionally provided to detect spurious wakeup.

1. Atomically calls lock.unlock() and blocks on *this.

The thread will be unblocked when notify_all() or notify_one() is executed, or abs_time is reached. It may also be unblocked spuriously.

When unblocked, calls lock.lock() (possibly blocking on the lock), then returns.

2,3) Waiting for a specific condition to become true, can be used to ignore spurious awakenings.

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

2. Registers *this for the duration of this call, to be notified if a stop request is made on stoken's associated stop-state; it is then equivalent to while (!stoken.stop_requested())
   {
   if (pred())
   return true;
   if (wait_until(lock, abs_time) == std::cv_status::timeout)
   return pred();
   }
   return pred();.

Right after wait_until returns, lock is locked by the calling thread. If this postcondition cannot be satisfied[1], calls std::terminate.

1. ↑ This can happen if the re-locking of the mutex throws an exception.

Contents

• 1 Parameters
• 2 Return value
• 3 Exceptions
• 4 Notes
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Parameters

[edit] Return value

2,3) The latest result of pred() before returning to the caller.

[edit] Exceptions

1. Timeout-related exceptions.

2,3) Timeout-related exceptions, and any exception thrown by pred.

[edit] Notes

The standard recommends that the clock tied to abs_time be used to measure time; that clock is not required to be a monotonic clock. There are no guarantees regarding the behavior of this function if the clock is adjusted discontinuously, but the existing implementations convert abs_time from Clock to std::chrono::system_clock and delegate to POSIX pthread_cond_timedwait so that the wait honors adjustments to the system clock, but not to the user-provided Clock. In any case, the function also may wait for longer than until after abs_time has been reached due to scheduling or resource contention delays.

Even if the clock in use is std::chrono::steady_clock or another monotonic clock, a system clock adjustment may induce a spurious wakeup.

The effects of notify_one()/notify_all() and each of the three atomic parts of wait()/wait_for()/wait_until() (unlock+wait, wakeup, and lock) take place in a single total order that can be viewed as modification order of an atomic variable: the order is specific to this individual condition variable. This makes it impossible for notify_one() to, for example, be delayed and unblock a thread that started waiting just after the call to notify_one() was made.

[edit] Example

Possible output:

Waiting... Waiting... Waiting... Notifying... Notifying again... ...finished waiting. i == 1 ...finished waiting. i == 1 ...finished waiting. i == 1

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

| | blocks the current thread until the condition variable is awakened (public member function) [edit] | | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | blocks the current thread until the condition variable is awakened or until specified time point has been reached (public member function) [edit] |