An execution agent is an entity such as a thread that may perform work in parallel with other execution agents. [ Note: Implementations or users may 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: 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 standard library templates unique_lock ([thread.lock.unique]), lock_guard ([thread.lock.guard]), lock, try_lock ([thread.lock.algorithm]), and condition_variable_any ([thread.condition.condvarany]) all operate on user-supplied lockable objects. The BasicLockable requirements, the Lockable requirements, and the TimedLockable 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: The nature of any lock ownership and any synchronization it may entail are not part of these requirements. — end note ]