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Showing content from https://cplusplus.github.io/LWG/issue1497 below:

lock() postcondition can not be generally achieved

void wait(unique_lock<mutex>& lock);

9 Requires: lock .owns_lock() is true and lock.mutex() is locked by the calling thread, and either

• no other thread is waiting on this condition_variable object or
• lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently waiting (via wait or timed_wait) threads.

11 Postcondition: lock .owns_lock() is true and lock.mutex() is locked by the calling thread.

template <class Predicate>
void wait(unique_lock<mutex>& lock, Predicate pred);

?? Requires: lock.owns_lock() is true and lock.mutex() is locked by the calling thread, and either

• no other thread is waiting on this condition_variable object or
• lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently waiting (via wait or timed_wait) threads.

14 Effects:

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

?? Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling thread.

?? Throws: std::system_error when an exception is required (30.2.2).

?? Error conditions:

• equivalent error condition from lock.lock() or lock.unlock().

template <class Clock, class Duration>
cv_status wait_until(unique_lock<mutex>& lock,
  const chrono::time_point<Clock, Duration>& abs_time);

15 Requires: lock .owns_lock() is true and lock.mutex() is locked by the calling thread, and either

• no other thread is waiting on this condition_variable object or
• lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently waiting (via wait, wait_for, or wait_until) threads.

[..]

17 Postcondition: lock .owns_lock() is true and lock.mutex() is locked by the calling thread.

20 Error conditions:

• operation_not_permitted — if the thread does not own the lock.
• equivalent error condition from lock.lock() or lock.unlock().

template <class Rep, class Period>
cv_status wait_for(unique_lock<mutex>& lock,
  const chrono::duration<Rep, Period>& rel_time);

21 Requires: lock .owns_lock() is true and lock.mutex() is locked by the calling thread, and either

• no other thread is waiting on this condition_variable object or
• lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently waiting (via wait, wait_for, or wait_until) threads.

[..]

24 Postcondition: lock .owns_lock() is true and lock.mutex() is locked by the calling thread.

26 Error conditions:

• operation_not_permitted — if the thread does not own the lock.
• equivalent error condition from lock.lock() or lock.unlock().

template <class Clock, class Duration, class Predicate>
bool wait_until(unique_lock<mutex>& lock,
  const chrono::time_point<Clock, Duration>& abs_time,
    Predicate pred);

?? Requires: lock.owns_lock() is true and lock.mutex() is locked by the calling thread, and either

• no other thread is waiting on this condition_variable object or
• lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently waiting (via wait or timed_wait) threads.

27 Effects:

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

28 Returns: pred()

?? Postcondition: lock.owns_lock() is true and lock.mutex() is locked by the calling thread.

29 [ Note: The returned value indicates whether the predicate evaluates to true regardless of whether the timeout was triggered. — end note ]

?? Throws: std::system_error when an exception is required (30.2.2).

?? Error conditions:

• equivalent error condition from lock.lock() or lock.unlock().

template <class Rep, class Period, class Predicate>
bool wait_for(unique_lock<mutex>& lock,
  const chrono::duration<Rep, Period>& rel_time,
    Predicate pred);

30 Requires: lock .owns_lock() is true and lock.mutex() is locked by the calling thread, and either

• no other thread is waiting on this condition_variable object or
• lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently waiting (via wait, wait_for, or wait_until) threads.

[..]

33 Postcondition: lock .owns_lock() is true and lock.mutex() is locked by the calling thread.

[..]

37 Error conditions:

• operation_not_permitted — if the thread does not own the lock.
• equivalent error condition from lock.lock() or lock.unlock().

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