I agree with David's opinion here. Please do not make this change.
Dan
On 7/23/19 7:08 AM, David Holmes wrote:
On 23/07/2019 6:16 pm, Yasumasa Suenaga wrote:
Sorry, the format is broken... I re-sent the email:
There are not documented the relation between -XX:*OnOutOfMemoryError
and ResourceExhausted,
but JVMTI spec says ResourceExhausted is sent when VM resource are
exhausted.
https://docs.oracle.com/en/java/javase/12/docs/specs/jvmti.html#ResourceExhausted
The JVMTI spec can't say anything about -XX:*OnOutOfMemoryError as
they are a hotspot implementation detail. If you use the -XX flag you
get whatever the hotspot implementation does. That may override normal
specified behaviour. For example, if you use
-XX:+ExitOnOutOfMemoryError you can't then complain that the VM never
executes a catch block for OutOfMemoryError because it exited first!
It's the same for the event processing - we're exiting before we reach
that code.
As you said, we should not do other things when OutOfMemoryError is
occurred.
But I think it should be compliant when we will use Java related code
in the event handler.
If we do with C/C++ only (e.g. call printf()), I think we can do that.
But we don't know what the handler will do. Nor do we know why the -XX
flag was used, or even what it may do in some cases.
If all codes should not be run when OutOfMemoryError is occurred,
ResourceExhausted should be obsoleted, or we need to add the note for
JVMTI document.
There is no logical argument there for obsoleting the
ResourceExhausted event.
I understand you want the event to be posted before the flag is
processed, but somebody else may want it exactly as it is - e.g.
dumping the heap before their event handler does some cleanup/recovery
work.
And as I said the JVM TI spec knows nothing of this XX flag so cannot
say anything about it.
David
-----
Thanks,
Yasumasa
On 2019/07/23 16:43, David Holmes wrote:
Hi Yasumasa,
On 23/07/2019 5:24 pm, Yasumasa Suenaga wrote:
Hi all,
I tried to use JVMTI agent which hooks ResourceExhausted event and
-XX:ExitOnOutOfMemoryError together.
The process was exited when OutOfMemoryError was occurred, but
ResourceExhausted event was not fired.
I checked HotSpot implementation, -XX:*OutOfMemoryError is
processed before JVMTI event processing.
http://hg.openjdk.java.net/jdk/jdk/file/d999a1a11485/src/hotspot/share/gc/shared/memAllocator.cpp#l125
IMHO ResourceExhausted should be called before -XX:*OutOfMemoryError.
If it is a bug, I will file it to JBS and fix it.
I don't think it is a bug. First, there's no specification for how
these two things interact - -XX:*OnOutOfMemoryError is just a VM
specific debugging/diagnostic hook. Second, if we're out of memory
then we don't want to be doing other things which may need to also
acquire memory. Third, no matter which way you code this someone may
in some case want it the other way - and it's not worth coding to
allow such flexibility IMO.
Just my $2. :)
Cheers,
David
Thanks,
Yasumasa
