Yeah, you're really in trouble if a thread dies while holding a lock,
because it's illegal (throws an exception) to call
ReentrantLock#unlock if you're not the owning thread. So I'm not sure
how you could possibly "clean up" in that case, but I don't see a way
to do that automatically, either.
~~ Robert.
That'd actually be a useful stunt for something I'm working on, too.
On Sun, Jun 12, 2011 at 7:13 AM, Charles Oliver Nutter
<head...@headius.com> wrote:
> I'm trying to reimplement JRuby's version of Ruby's Mutex class, a
> non-reentrant locking mechanism. One of the properties of a Mutex is
> that when the thread holding its lock dies, the lock is released:
>
> ~/projects/jruby ➔ ruby -rthread -e "m = Mutex.new; Thread.new {
> m.lock; p m.locked? }.join; p m.locked?"
> true
> false
>
> Previously our implementation simply maintained a volatile reference
> to the thread owning the lock, considering it unlocked if the thread
> was no longer alive. However that implementation did not use any
> JVM-level monitor state, so it was not possible for Hotspot to detect
> deadlocks between two threads trying to mutually acquire the same
> locks in different order. A modified version that uses ReentrantLock
> does show up in Hotspot's deadlock detection, but does not appear to
> release locks on thread death:
>
> ~/projects/jruby ➔ jruby -rthread -e "m = Mutex.new; Thread.new {
> m.lock; p m.locked? }.join; p m.locked?"
> true
> true
>
> Am I forced to use my own locking mechanism to get on-death lock
> releasing, or is there some mechanism in java.util.* I've overlooked?
>
> - Charlie
>
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