On Jan 25, 2011, at 11:00 AM, Tom Rodriguez wrote:
On Jan 25, 2011, at 8:49 AM, Keith McGuigan wrote:
Hello,
This code modifies the way that JVMTI compiled-method-load events
are posted. Previously, they were posted directly from the
compiler thread, which could cause issues if the JVMTI event
handling code made calls to RedefineClasses, since the compiler
thread is unable to load classes if that is required. This
solution is to defer the posting of the events to the Service
thread (formerly: LowMemoryDetector
thread) which is a Java thread and is able to load classes.
The posting appears to be asynchronous which I don't think will
work. The method could be unloaded or invalidated and freed before
the event has been posted. It has to be done synchronously I think.
I have a vague memory of someone saying that there were restrictions
on what a JVMTI client was allowed to do in response to a
CompiledMethodLoad but I can't find any evidence of that. So is
that just a bogus memory or is there some restriction like this?
It's been a while now, but there are restrictions as to what a JVMTI
event handler can do, and I'm pretty sure redefining
classes may be on that limitation list, but I'm not seeing it
explicitly spelled out.
I see this:
http://download.oracle.com/javase/1.5.0/docs/guide/jvmti/jvmti.html#EventSection
It says "and the JVM TI implementation does not queue events in any
way".
And these compiled-method-load events can also be generated from this:
http://download.oracle.com/javase/1.5.0/docs/guide/jvmti/jvmti.html#GenerateEvents
And it mentions some issues with JNI.
Sorry, it's been so long, my serviceability brain cells have not been
maintained very well. :^(
-kto
tom
The "Service thread" now handles both low-memory detection and
JVMTI deferred event posting. I left the door open for other
types of events to be deferred and posted via this mechanism in
case we find other situations where posting events from a non-Java
thread causes problems.
webrev: http://cr.openjdk.java.net/~kamg/6766644/webrev.01/
--
- Keith
