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]

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An execution agent is an entity such as a thread that may perform work in parallel with other execution agents.
[ Note
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Implementations or users can introduce other kinds of agents such as processes or thread-pool tasks.
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The calling agent is determined by context, e.g., the calling thread that contains the call, and so on.
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[ Note
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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).
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The standard library templates unique_­lock ([thread.lock.unique]), shared_­lock ([thread.lock.shared]), scoped_­lock ([thread.lock.scoped]), 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 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
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The nature of any lock ownership and any synchronization it entails are not part of these requirements.
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 ]