This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of New status.

2819. Unspecified Return type: elements

Section: 33.2.5 [thread.req.lockable], 33.6.4 [thread.mutex.requirements] Status: New Submitter: Agustín K-ballo Bergé Opened: 2016-11-12 Last modified: 2020-05-12

Priority: 3

View all issues with New status.

Discussion:

The current draft contains 14 occurrences of a Return type: clause. That clause is not covered by 16.3.2.4 [structure.specifications] p3. This was reported as editorial request #266.

[Issues Telecon 16-Dec-2016]

Priority 3; Jonathan to provide wording.

[12-May-2020, Jonathan provides wording to correct the 13 occurences.]

Proposed resolution:

This wording is relative to N4681.

1. Modify 33.2.5.3 [thread.req.lockable.req] as indicated:

   -1- A type L meets the Cpp17Lockable requirements if it meets the Cpp17BasicLockable requirements and the following expressions are well-formed, have type bool, and have the specified semantics (m denotes a value of type L).

   m.try_lock()

   -2- Effects: [...]

   -3- Return type: bool.

   -4- Returns: true if the lock was acquired, false otherwise.

2. Modify 33.2.5.4 [thread.req.lockable.timed] as indicated:

   -1- A type L meets the Cpp17TimedLockable requirements if it meets the Cpp17BasicLockable requirements and the following expressions are well-formed, have type bool, and have the specified semantics (m denotes a value of type L, rel_time denotes a value of an instantiation of duration (29.5 [time.duration]), and abs_time denotes a value of an instantiation of time_point (29.6 [time.point])).

   m.try_lock_for(rel_time)

   -2- Effects: [...]

   -3- Return type: bool.

   -4- Returns: true if the lock was acquired, false otherwise.

   m.try_lock_until(abs_time)

   -2- Effects: [...]

   -3- Return type: bool.

   -4- Returns: true if the lock was acquired, false otherwise.

3. Modify 33.6.4.2 [thread.mutex.requirements.mutex] as indicated:

   -6- The expression m.lock() is well-formed, has type void, and has the following semantics:

   -7- Preconditions: [...]

   -8- Effects: [...]

   -9- Postconditions: [...]

   -10- Return type: void.

   -11- Synchronization: [...]

   -12- Throws: [...]

   -13- Error conditions: [...]

   -14- The expression m.try_lock() is well-formed, has type bool, and has the following semantics:

   -15- Preconditions: [...]

   -16- Effects: [...]

   -17- Return type: bool.

   -18- Returns: true if ownership of the mutex was obtained for the calling thread, otherwise false.

   -19- Synchronization: [...]

   -20- Throws: Nothing.

   -21- The expression m.unlock() is well-formed, has type void, and has the following semantics:

   -22- Preconditions: [...]

   -23- Effects: [...]

   -24- Return type: void.

   -25- Synchronization: [...]

   -26- Throws: Nothing.

4. Modify 33.6.4.3 [thread.timedmutex.requirements] as indicated:

   -1- The timed mutex types are the standard library types [...]

   -2- The timed mutex types meet the Cpp17TimedLockable requirements (33.2.5.4 [thread.req.lockable.timed]).

   -3- The expression m.try_lock_for(rel_time) is well-formed, has type bool, and has the following semantics:

   -4- Preconditions: [...]

   -5- Effects: [...]

   -6- Return type: bool.

   -7- Returns: true if the shared lock was acquired, false otherwise.

   -8- Synchronization: [...]

   -9- Throws: [...]

   -10- The expression m.try_lock_until(abs_time) is well-formed, has type bool, and has the following semantics:

   -11- Preconditions: [...]

   -12- Effects: [...]

   -13- Return type: bool.

   -14- Returns: true if ownership was obtained, otherwise false.

   -15- Synchronization: [...]

   -16- Throws: [...]

5. Modify 33.6.4.4 [thread.sharedmutex.requirements] as indicated:

   -1- The standard library types shared_mutex and shared_timed_mutex are shared mutex types. [...]

   -2- In addition to the exclusive lock ownership mode [...]

   -3- The expression m.lock_shared() is well-formed, has type void, and has the following semantics:

   -4- Preconditions: [...]

   -5- Effects: [...]

   -6- Postconditions: [...]

   -7- Return type: void.

   -8- Synchronization: [...]

   -9- Throws: [...]

   -10- Error conditions: [...]

   -11- The expression m.unlock_shared() is well-formed, has type void, and has the following semantics:

   -12- Preconditions: [...]

   -13- Effects: [...]

   -14- Return type: void.

   -15- Synchronization: [...]

   -16- Throws: [...]

   -17- The expression m.try_lock_shared() is well-formed, has type bool, and has the following semantics:

   -18- Preconditions: [...]

   -19- Effects: [...]

   -20- Return type: bool.

   -21- Returns: true if the shared ownership lock was acquired, false otherwise.

   -22- Synchronization: [...]

   -23- Throws: [...]

6. Modify 33.6.4.5 [thread.sharedtimedmutex.requirements] as indicated:

   -1- The standard library type shared_timed_mutex is a shared timed mutex type. [...]

   -2- The expression m.try_lock_shared_for(rel_time) is well-formed, has type bool, and has the following semantics:

   -3- Preconditions: [...]

   -4- Effects: [...]

   -5- Return type: bool.

   -6- Returns: true if the shared lock was acquired, false otherwise.

   -7- Synchronization: [...]

   -8- Throws: [...]

   -9- The expression m.try_lock_shared_until(abs_time) is well-formed, has type bool, and has the following semantics:

   -10- Preconditions: [...]

   -11- Effects: [...]

   -12- Return type: bool.

   -13- Returns: true if the shared lock was acquired, false otherwise.

   -14- Synchronization: [...]

   -15- Throws: [...]