C++ named requirements: Lockable
The Lockable requirements extends the BasicLockable requirements to include attempted locking.
L to be Lockable, it must meet the above condition as well as the following:
|m.try_lock()||Attempts to acquire the lock for the current execution agent (thread, process, task) without blocking. If an exception is thrown, no lock is obtained.||true if the lock was acquired, false otherwise|