RFR(XXS): 8007147: Trace event ExecuteVMOperation may get dangling pointer

[Staffan Larsen]

I don't like this solution since we are swallowing information that could potentially be interesting (that a VMOperation happened). I think it's fine to say that in the case of non-blocking VMOperations, the caller thread will be undefined or set to 0. We could add that information to the event field description in traceevents.xml so that it is documented.

/Staffan


On 19 feb 2013, at 10:47, Markus Grönlund <markus.gronlund at oracle.com> wrote:

> Hi David,
> 
> Thanks for taking a look.
> 
> The original idea was to use thread id 0 as a signal for "Unknown Thread" or "no thread" if you like - however, there is nothing actually enforcing this; it was more of an implicit assumption (and to be honest, the only OS which I know for sure will never give a tid of 0 is Windows). I have tried to find information if a 0 will ever be given out by pthreads and mach_t, but I mostly find info on "process relative opaque id"...so it could be likely that a 0 is used as a valid tid here (probably unlikely but still...)
> 
> Also, I see that the tracing output just happily gives out tid == 0 if I write it in as suggested in webrev01...I am not entirely happy with this. If we view 0 as "Unknown Thread", this should maybe be treated differently.
> 
> I don't know yet what Id I will be able to use here to signal the fact that thread is unknown (in a platform agnostic way) - but I will try to come up with something.
> 
> In the interim, we should just avoid committing the event for non-concurrent VM operations event altogether (I have mostly seen these as EnableBiasLocking and Thread.Stop's).
> 
> The updated webrev02 gives a suggestion on only committing the tracing event for non-concurrent vm ops:
> 
> http://cr.openjdk.java.net/~mgronlun/8007147/webrev02/
> 
> (follow up work will also need rework the event fields).
> 
> Thanks
> Markus
> 
> 
> 
> -----Original Message-----
> From: David Holmes 
> Sent: den 18 februari 2013 05:06
> To: Markus Grönlund
> Cc: serviceability-dev at openjdk.java.net; hotspot-runtime-dev at openjdk.java.net
> Subject: Re: RFR(XXS): 8007147: Trace event ExecuteVMOperation may get dangling pointer
> 
> Hi Markus,
> 
> So is zero as a thread id defined to mean "no thread" ?
> 
> David
> 
> On 13/02/2013 12:03 AM, Markus Grönlund wrote:
>> Greetings,
>> 
>> Kindly asking for reviews and a putback sponsorship for the following
>> change:
>> 
>> Bugid: http://bugs.sun.com/view_bug.do?bug_id=8007147
>> 
>> Webrev: http://cr.openjdk.java.net/~mgronlun/8007147/webrev01/
>> 
>> Please also note this is for hs24.
>> 
>> Thanks to David Holmes for pointing out this problem.
>> 
>> Thanks
>> 
>> Markus
>>