[concurrency-interest] difference latch and lock

Brian Goetz brian at quiotix.com
Mon Sep 4 13:09:41 EDT 2006

See JCiP 5.5.1 and 5.5.2.  Also 8.5.1 and 14.2.5 for more examples.

Peter Veentjer wrote:
> Thanks for your answer Brian. Could you give an example how a Latch
> would be used?
> On 8/31/06, Brian Goetz <brian at quiotix.com> wrote:
>> Latches and locks are different.  It is easiest to think of them in
>> terms of their state machines.  A lock goes from unlocked to locked and
>> back to unlocked with the right sequence of lock and unlock operations.
>>  A latch goes from closed to open after some sequence of state
>> transitions, and NEVER GOES BACK.  Once it transitions to the terminal
>> state, it never changes.
>> Both offer blocking behavior.  For Lock, if you try to acquire an
>> already-held lock, you block until the lock is available.  For Latch, if
>> you try to wait for the latch, you block until someone else puts the
>> latch in the terminal (open) state.
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