7.5.2 RLock Objects
A reentrant lock is a synchronization primitive that may be acquired multiple times by the
same thread. Internally, it uses the concepts of ``owning thread'' and ``recursion level'' in
addition to the locked/unlocked state used by primitive locks. In the locked state, some
thread owns the lock; in the unlocked state, no thread owns it.
To lock the lock, a thread calls its acquire() method; this returns
once the thread owns the lock. To unlock the lock, a thread calls its release()
method. acquire()/release() call pairs may be
nested; only the final release() (the release()
of the outermost pair) resets the lock to unlocked and allows another thread blocked in acquire() to proceed.
-
- Acquire a lock, blocking or non-blocking.
When invoked without arguments: if this thread already owns the lock, increment the
recursion level by one, and return immediately. Otherwise, if another thread owns the
lock, block until the lock is unlocked. Once the lock is unlocked (not owned by any
thread), then grab ownership, set the recursion level to one, and return. If more than one
thread is blocked waiting until the lock is unlocked, only one at a time will be able to
grab ownership of the lock. There is no return value in this case.
When invoked with the blocking argument set to true, do the same thing as
when called without arguments, and return true.
When invoked with the blocking argument set to false, do not block. If a
call without an argument would block, return false immediately; otherwise, do the same
thing as when called without arguments, and return true.
-
- Release a lock, decrementing the recursion level. If after the decrement it is zero,
reset the lock to unlocked (not owned by any thread), and if any other threads are blocked
waiting for the lock to become unlocked, allow exactly one of them to proceed. If after
the decrement the recursion level is still nonzero, the lock remains locked and owned by
the calling thread.
Only call this method when the calling thread owns the lock. Do not call this method
when the lock is unlocked.
There is no return value.
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