* in-memory and support nested locking calls (using reference counting).
* At least LOCK_UW and LOCK_EX must be implemented. LOCK_SH can be a no-op.
* Locks should either be non-blocking or have low wait timeouts.
* in-memory and support nested locking calls (using reference counting).
* At least LOCK_UW and LOCK_EX must be implemented. LOCK_SH can be a no-op.
* Locks should either be non-blocking or have low wait timeouts.