[Opensim-dev] Lockless Lists?

[Hurliman, John]

LockTime already provides the second feature. The first could be implemented by replacing Monitor.Enter() calls with Monitor.TryEnter(200) and printing out an error if that returns false. Easier to modify the bytecode with a program than replace all of the locks in the source code.

My post on LockTime is up now at http://software.intel.com/en-us/blogs/2008/12/02/timing-locks-in-c/

John

> -----Original Message-----
> From: opensim-dev-bounces at lists.berlios.de [mailto:opensim-dev- 
> bounces at lists.berlios.de] On Behalf Of Tedd Hansen
> Sent: Monday, December 01, 2008 9:38 AM
> To: opensim-dev at lists.berlios.de; homer.horwitz at gmail.com
> Subject: Re: [Opensim-dev] Lockless Lists?
> 
> Hi
> 
> You could create your own implementation of lock and mutex commands,
> and do all solution wide replacement of all their usages.
> Then use these custom implementations to identify deadlock situations.
> Using these you could also time how long each lock lasts, and print
> some debug containing "StackFrame.GetFrame().GetMethod().Name" when
> lock exceeds a certain time span.
> Should give a fairly good picture of trouble spots. :)
> 
> - Tedd
> 
> -----Original Message----- From: opensim-dev-bounces at lists.berlios.de
> [mailto:opensim-dev-bounces at lists.berlios.de] On Behalf Of Hurliman,
> John Sent: 26. november 2008 02:19 To: opensim-dev at lists.berlios.de;
> homer.horwitz at gmail.com Subject: Re: [Opensim-dev] Lockless Lists?
> 
> 
> 
> -----Original Message----- From: opensim-dev-bounces at lists.berlios.de
> [mailto:opensim-dev-bounces at lists.berlios.de] On Behalf Of Christopher
> Yeoh Sent: Tuesday, November 25, 2008 3:26 PM To:
> homer.horwitz at gmail.com; opensim-dev at lists.berlios.de Subject: Re:
> [Opensim-dev] Lockless Lists?
> 
> On Mon, 24 Nov 2008 20:43:09 +0100
> "Homer Horwitz" <homerhorwitz at googlemail.com> wrote:
>> 
>> So, I'm not sure if we really should do that move. If at all, I'm
>> for a very slow move to lock-free versions from a rather stable
>> software base (which we currently don't have in trunk), so errors
>> that are introduced during that move are more easily identifiable,
>> with much testing in-between. Even then, I'm absolutely sure we will
>> get a lot of Heisenbugs in the process, which will take us weeks to find.
>> 
> 
> Perhaps what is really needed here is some performance benchmarks
> which highlight existing problems? So for individual changes to
> lockless versions we better see what improvements we'd get on both
> small and large SMP machines and whether its worth the increase in complexity.
> 
> I did some debugging of a deadlock a couple of weeks ago and found it
> already pretty complicated. Any suggestions on how other people approach
> these problems with OpenSim? I sprinkled lots of console messages around
> as mdb doesn't seem to work for me, but in retrospect it would have been
> really handy to have been able to just turn on a lock debugging flag and
> have debug output when locks are taken and released.
> 
> Regards,
> 
> Chris
> 
> 
> 
> One idea I've tossed around is using Mono.Cecil to inject some code
> for profiling locks. Since
> 
> lock (lockObject)
> {
>         ...
> }
> 
> Gets expanded out by the compiler to:
> 
> Monitor.Enter(lockObject);
> try
> {
>         ...
> }
> finally
> {
>         Monitor.Exit(lockObject);
> }
> 
> It shouldn't be too difficult to follow up any Monitor.Enter() calls
> by storing current ticks, and do a check in the finally if current
> ticks - stored ticks > lock_warn_const. Then we could scan any binary
> for long- held locks.
> 
> John _______________________________________________ Opensim-dev mailing
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