RFR: 8231289: Disentangle JvmtiRawMonitor from ObjectMonitor and clean it up
david.holmes at oracle.com
Fri Oct 4 23:15:28 UTC 2019
Thanks for the second look.
On 5/10/2019 1:51 am, Daniel D. Daugherty wrote:
> On 10/3/19 11:58 PM, David Holmes wrote:
>> Okay, to allow for me to make forward progress here I've decided to
>> follow the "principle of least brokenness" ;-)
>> Recap: Because of JVMTI event callbacks it is possible for a thread to
>> set its current pending monitor as a JvmtiRawMonitor when it was
>> already set for an ObjectMonitor. This is broken in at least two ways:
>> - when the raw monitor use completes the pending monitor is set to
>> NULL, not restored to the ObjectMonitor
>> - whilst the raw monitor is seen as the pending monitor the
>> ObjectMonitor is not considered by the deadlock detection logic
>> Ignoring what I'm currently doing with jvmtiRawMonitor, I do not know
>> how to fix the above brokenness and it is out of scope for what I am
>> trying to do.
>> So what I propose is to make things no more broken than they are now,
>> and actually improve things a little:
>> - the pending JvmtiRawMonitor is given preference over the
>> ObjectMonitor in the deadlock detection code (this emulates current
>> situation of the raw monitor overwriting the pending ObjectMonitor)
>> - we no longer lose the fact we were also pending on an ObjectMonitor
>> - the stack printing code in the deadlock detector prints information
>> about both the raw monitor and the ObjectMonitor
>> Updated webrev:
> L399: // waiting on both a raw monitor and ObjectMonitor at the
> same time. It
> s/waiting on/waiting to lock/
> L981: const char* owner_desc = ",\n which is held by";
> L994: st->print_cr(",\n which has now been released");
> L1008: owner_desc = "\n in JNI, which is held by";
> Not your bug for L981 or L1008, but those '\n' aren't portable
> I think a 'st->cr()' is needed instead.
\n within a string literal should be perfectly portable. It's a symbolic
representation of a "newline". If it eventually get written to somewhere
that cares (like a file) it will be converted into appropriate CR or
CRLF characters for the platform.
> Of course, I don't understand why the newline is there anyway,
> but without seeing an example output its hard to say.
Yes I assume it looks pretty if you see it written out.
> Thumbs up. Don't need to see another webrev...
>> The only change is threadService.cpp
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