[thread.req.lockable] (original) (raw)
32 Thread support library [thread]
32.2 Requirements [thread.req]
32.2.5 Requirements for Cpp17Lockable types [thread.req.lockable]
32.2.5.1 In general [thread.req.lockable.general]
An execution agent is an entity such as a thread that may perform work in parallel with other execution agents.
[Note 1:
Implementations or users can introduce other kinds of agents such as processes or thread-pool tasks.
— _end note_]
The calling agent is determined by context, e.g., the calling thread that contains the call, and so on.
[Note 2:
Some lockable objects are “agent oblivious” in that they work for any execution agent model because they do not determine or store the agent's ID (e.g., an ordinary spin lock).
— _end note_]
The Cpp17BasicLockable requirements, the Cpp17Lockable requirements, and the Cpp17TimedLockable requirements list the requirements imposed by these library types in order to acquire or release ownership of a lock by a given execution agent.
[Note 3:
The nature of any lock ownership and any synchronization it entails are not part of these requirements.
— _end note_]
32.2.5.2 Cpp17BasicLockable requirements [thread.req.lockable.basic]
A type L meets the Cpp17BasicLockable requirements if the following expressions are well-formed and have the specified semantics (m denotes a value of type L).
Effects: Blocks until a lock can be acquired for the current execution agent.
If an exception is thrown then a lock shall not have been acquired for the current execution agent.
Preconditions: The current execution agent holds a lock on m.
Effects: Releases a lock on m held by the current execution agent.
32.2.5.3 Cpp17Lockable requirements [thread.req.lockable.req]
A type L meets the Cpp17Lockable requirements if it meets the _Cpp17BasicLockable_requirements and the following expressions are well-formed and have the specified semantics (m denotes a value of type L).
Effects: Attempts to acquire a lock for the current execution agent without blocking.
If an exception is thrown then a lock shall not have been acquired for the current execution agent.
Returns: true if the lock was acquired, otherwise false.
32.2.5.4 Cpp17TimedLockable requirements [thread.req.lockable.timed]
A type L meets the Cpp17TimedLockable requirements if it meets the _Cpp17Lockable_requirements and the following expressions are well-formed and have the specified semantics (m denotes a value of type L, rel_time denotes a value of an instantiation of duration, and abs_time denotes a value of an instantiation of time_point).
Effects: Attempts to acquire a lock for the current execution agent within the relative timeout ([thread.req.timing]) specified by rel_time.
The function will not return within the timeout specified by rel_time unless it has obtained a lock on mfor the current execution agent.
If an exception is thrown then a lock has not been acquired for the current execution agent.
Returns: true if the lock was acquired, otherwise false.
m.try_lock_until(abs_time)
Effects: Attempts to acquire a lock for the current execution agent before the absolute timeout ([thread.req.timing]) specified by abs_time.
The function will not return before the timeout specified by abs_time unless it has obtained a lock on m for the current execution agent.
If an exception is thrown then a lock has not been acquired for the current execution agent.
Returns: true if the lock was acquired, otherwise false.