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multithreadingreentrantlock

Why do we need a lock to be reentrant?

I understand (somewhat) the features of the jdk 5 ReentrantLock here

But why we would want a 're-entrant' lock? i.e if a Thread already has the lock on an Object, why would it need to acquire it again?

Solution

  • Consider this theoretical example: You are using a lock to protect some back-end data while updating some items in a list box in your GUI. You loop through and modify the items. While doing so, the list box fires an event (perhaps a Selection Changed event or something) for which you have a handler registered. This handler also locks the same lock in order to process the new item. If the lock is not recursive, this thread would deadlock on the second attempt to acquire the lock.