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Unblocking on a shared monitor
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Unblocking on a shared monitor
by Cássio M. M. Pereira
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Let's assume I have three threads trying to get the monitor of a
shared object. Thread-1 gets the exclusive access to a synchronized code block, while Thread-2 and Thread-3 remain blocked. What is the priority of unblocking the two threads when Thread-1 releases the lock ? Assume Thread-2 asked for the lock a moment before Thread-3. Is FIFO guaranteed? I couldn't find this in the Java language specification, but I've been told there's no order guarantee. Thank you, Cássio. -- Cássio M. M. Pereira _______________________________________________ tc-users mailing list tc-users@... http://lists.terracotta.org/mailman/listinfo/tc-users |
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Re: Unblocking on a shared monitor
by Orion Letizi
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You're right. There's no order guarantee.
--Orion On Apr 6, 2008, at 8:24 PM, Cássio M. M. Pereira wrote: > Let's assume I have three threads trying to get the monitor of a > shared object. Thread-1 gets the exclusive access to a synchronized > code block, while Thread-2 and Thread-3 remain blocked. What is the > priority of unblocking the two threads when Thread-1 releases the lock > ? > > Assume Thread-2 asked for the lock a moment before Thread-3. Is FIFO > guaranteed? > > I couldn't find this in the Java language specification, but I've been > told there's no order guarantee. > > Thank you, > Cássio. > > -- > Cássio M. M. Pereira > _______________________________________________ > tc-users mailing list > tc-users@... > http://lists.terracotta.org/mailman/listinfo/tc-users _______________________________________________ tc-users mailing list tc-users@... http://lists.terracotta.org/mailman/listinfo/tc-users |
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Re: Unblocking on a shared monitor
by Cássio M. M. Pereira
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Ok, so how can we avoid starvation?
If more threads start blocking on the monitor, how can we be sure that Thread-2 will eventually grab the lock? Thanks, Cássio On Mon, Apr 7, 2008 at 12:59 AM, Orion Letizi <orion@...> wrote: > You're right. There's no order guarantee. > > --Orion > > > > On Apr 6, 2008, at 8:24 PM, Cássio M. M. Pereira wrote: > > Let's assume I have three threads trying to get the monitor of a > > shared object. Thread-1 gets the exclusive access to a synchronized > > code block, while Thread-2 and Thread-3 remain blocked. What is the > > priority of unblocking the two threads when Thread-1 releases the lock > > ? > > > > Assume Thread-2 asked for the lock a moment before Thread-3. Is FIFO > > guaranteed? > > > > I couldn't find this in the Java language specification, but I've been > > told there's no order guarantee. > > > > Thank you, > > Cássio. > > > > -- > > Cássio M. M. Pereira > > _______________________________________________ > > tc-users mailing list > > tc-users@... > > http://lists.terracotta.org/mailman/listinfo/tc-users > > _______________________________________________ > tc-users mailing list > tc-users@... > http://lists.terracotta.org/mailman/listinfo/tc-users > -- Cássio M. M. Pereira _______________________________________________ tc-users mailing list tc-users@... http://lists.terracotta.org/mailman/listinfo/tc-users |
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Re: Unblocking on a shared monitor
by Orion Letizi
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Here' s an interesting section of a book called "Java Threads" by
Scott Oaks and Henry Wong on lock fairness that might shed some light: http://books.google.com/books?id=gekyqm8epMkC&pg=PA65&lpg=PA65&dq=java+lock+fairness&source=web&ots=0AVfLA4sup&sig=LeGaSaRXrqPszn2Oub3dFteLRq8&hl=en#PPA65,M1 --Orion On Apr 7, 2008, at 4:32 AM, Cássio M. M. Pereira wrote: > Ok, so how can we avoid starvation? > > If more threads start blocking on the monitor, how can we be sure that > Thread-2 will eventually grab the lock? > > Thanks, > Cássio > > On Mon, Apr 7, 2008 at 12:59 AM, Orion Letizi <orion@...> > wrote: >> You're right. There's no order guarantee. >> >> --Orion >> >> >> >> On Apr 6, 2008, at 8:24 PM, Cássio M. M. Pereira wrote: >>> Let's assume I have three threads trying to get the monitor of a >>> shared object. Thread-1 gets the exclusive access to a synchronized >>> code block, while Thread-2 and Thread-3 remain blocked. What is the >>> priority of unblocking the two threads when Thread-1 releases the >>> lock >>> ? >>> >>> Assume Thread-2 asked for the lock a moment before Thread-3. Is FIFO >>> guaranteed? >>> >>> I couldn't find this in the Java language specification, but I've >>> been >>> told there's no order guarantee. >>> >>> Thank you, >>> Cássio. >>> >>> -- >>> Cássio M. M. Pereira >>> _______________________________________________ >>> tc-users mailing list >>> tc-users@... >>> http://lists.terracotta.org/mailman/listinfo/tc-users >> >> _______________________________________________ >> tc-users mailing list >> tc-users@... >> http://lists.terracotta.org/mailman/listinfo/tc-users >> > > > > -- > Cássio M. M. Pereira > _______________________________________________ > tc-users mailing list > tc-users@... > http://lists.terracotta.org/mailman/listinfo/tc-users _______________________________________________ tc-users mailing list tc-users@... http://lists.terracotta.org/mailman/listinfo/tc-users |
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Re: Unblocking on a shared monitor
by Taylor Gautier-2
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Interestingly enough, Terracotta 2.5.x and lower is pretty much
extremely fair. In 2.6 we have added some unfairness, because it
improves overall throughput. I don't think you'll get starvation even
in 2.6.
Orion Letizi wrote: Here' s an interesting section of a book called "Java Threads" by Scott Oaks and Henry Wong on lock fairness that might shed some light: http://books.google.com/books?id=gekyqm8epMkC&pg=PA65&lpg=PA65&dq=java+lock+fairness&source=web&ots=0AVfLA4sup&sig=LeGaSaRXrqPszn2Oub3dFteLRq8&hl=en#PPA65,M1 --Orion On Apr 7, 2008, at 4:32 AM, Cássio M. M. Pereira wrote:Ok, so how can we avoid starvation? If more threads start blocking on the monitor, how can we be sure that Thread-2 will eventually grab the lock? Thanks, Cássio On Mon, Apr 7, 2008 at 12:59 AM, Orion Letizi orion@... wrote: _______________________________________________ tc-users mailing list tc-users@... http://lists.terracotta.org/mailman/listinfo/tc-users |
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Re: Unblocking on a shared monitor
by Tim Eck
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Another bit of fun with java locks with regards to notifies
http://www.cs.kent.ac.uk/projects/ofa/java-threads/0.html wot, no chickens? > -----Original Message----- > From: tc-users-bounces@... [mailto:tc-users- > bounces@...] On Behalf Of Cássio M. M. Pereira > Sent: Monday, April 07, 2008 4:33 AM > To: tc-users@... > Subject: Re: [tc-users] Unblocking on a shared monitor > > Ok, so how can we avoid starvation? > > If more threads start blocking on the monitor, how can we be sure that > Thread-2 will eventually grab the lock? > > Thanks, > Cássio > > On Mon, Apr 7, 2008 at 12:59 AM, Orion Letizi <orion@...> > wrote: > > You're right. There's no order guarantee. > > > > --Orion > > > > > > > > On Apr 6, 2008, at 8:24 PM, Cássio M. M. Pereira wrote: > > > Let's assume I have three threads trying to get the monitor of a > > > shared object. Thread-1 gets the exclusive access to a synchronized > > > code block, while Thread-2 and Thread-3 remain blocked. What is the > > > priority of unblocking the two threads when Thread-1 releases the > lock > > > ? > > > > > > Assume Thread-2 asked for the lock a moment before Thread-3. Is > > > guaranteed? > > > > > > I couldn't find this in the Java language specification, but I've > been > > > told there's no order guarantee. > > > > > > Thank you, > > > Cássio. > > > > > > -- > > > Cássio M. M. Pereira > > > _______________________________________________ > > > tc-users mailing list > > > tc-users@... > > > http://lists.terracotta.org/mailman/listinfo/tc-users > > > > _______________________________________________ > > tc-users mailing list > > tc-users@... > > http://lists.terracotta.org/mailman/listinfo/tc-users > > > > > > -- > Cássio M. M. Pereira > _______________________________________________ > tc-users mailing list > tc-users@... > http://lists.terracotta.org/mailman/listinfo/tc-users _______________________________________________ tc-users mailing list tc-users@... http://lists.terracotta.org/mailman/listinfo/tc-users |
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