Thanks for your input on this one. I think I am hearing that we can proceed with assigning a 0 (zero) as the thread id to indicate the thread information is unknown for a non-blocking operation. Risk being of course to have a false "hit" if a 0 is assigned by some OS as a thread id, and even worse if 0 is also re-used across threads. This should be considered low risk. In addition, the occasional wrong info in the caller thread field might not warrant avoiding presenting info about non-blocking operations.
Resolving this would incorporate a lot of investigation which must be dealt with outside the scope of this bug. By adding additional comments about this fact (thread 0 being used to indicate "thread unknown" for non-blocking ops) I think we can proceed with a modified version of the first webrev01, but with additional comments added. Updated webrev can be found here: http://cr.openjdk.java.net/~mgronlun/8007147/webrev03/ Thanks again Markus -----Original Message----- From: David Holmes Sent: den 20 februari 2013 03:38 To: Dean Long Cc: Staffan Larsen; Markus Grönlund; [email protected]; [email protected] Subject: Re: RFR(XXS): 8007147: Trace event ExecuteVMOperation may get dangling pointer On 20/02/2013 5:30 AM, Dean Long wrote: > On 2/19/2013 11:00 AM, Staffan Larsen wrote: >> >> On 19 feb 2013, at 19:56, Dean Long <[email protected] >> <mailto:[email protected]>> wrote: >> >>> When the VM_Operation is created, we could take a snapshot of the >>> thread_id of the caller, then use that later. >> >> One problem with that is if the thread_id gets reused for a new >> thread quickly after the old thread terminates. This is perhps >> ulikely, but could happen. >> >>> Or we could block the creating thread from fully exiting until the >>> VM op executes. >> >> That would introduce a lot more synchronization and state to keep >> track of. >> > I think we could do it with a reference count on the thread, a wait in > thread exit, and a notify in the VM thread. > We have a similar dangling pointer problem with JVMTI (7154963), and a > reference count should solve that problem as well. I think that proposal needs a lot more investigation, certainly it is well out of scope for this bug. There are potential dangling thread pointers all over the JVM interfaces. David ----- > > dl > >> /Staffan >> >
