std::condition_variable::wait - cppreference.com (original) (raw)

wait causes the current thread to block until the condition variable is notified 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. It may also be unblocked spuriously.

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

1. Equivalent to

while (!pred())
wait(lock);.

This overload may be used to ignore spurious awakenings while waiting for a specific condition to become true.

Right after wait returns, lock.owns_lock() is true, and lock.mutex() is locked by the calling thread. If these postconditions cannot be satisfied[1], calls std::terminate.

If any of the following conditions is satisfied, the behavior is undefined:

• lock.owns_lock() is false.
• lock.mutex() is not locked by the calling thread.
• If some other threads are also waiting on *this, lock.mutex() is different from the mutex unlocked by the waiting functions (wait, wait_for and wait_until) called on *this by those threads.

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

Contents

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

[edit] Parameters

[edit] Exceptions

1. Throws nothing.

2. Any exception thrown by pred.

[edit] Notes

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 or after the specified timeout duration (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] | | |

[edit] External links