Chris, David
Yes. This can be after crash with core file, but some time no core file
generated (also if the error could not repeat, we will never got information
again), so dumping target process is also a choice. To avoid more confusion,
this step was launched at the very last moment, just before raise abort to
exit. At this moment, if client process could not attach to the target process
it will exit right away.
Answers to David:
Note that the SA is only present in a full JDK, not a JRE (full or compact
profile).
Yes, in code, if no sa-jdi.jar found, skip fork.
- What mechanism will the SA try to use to query the VM?
After successfully attached to target process, SA will read via proc APIs and
vmStructs (named TYPEDB) to iterate memory of system dictionary read (only)
from target process to dump class information.
- What if the state of the crashed VM stops the SA from being able to attach
properly (ie both processes hang)?
That should be an attaching API problem. We haven't watched such case
happened so far.
- What if it the SA also crashes, will it launch a third VM then a fourth etc?
Definitely don't want to see this happened in a chain. The solution may use a
property such as sun.jvm.hotspot.DumpLoadedClasses.dumpingInProcess=true to
pass into SA process, at launching call, check if the property set, if set, do
not fork. When SA process died, it will generate core file first, note the
target process still waiting for its exit, so when target exit, the core file
(if both use default core as name) will be override by target. The SA process
will only leave a hs_err_pid*.log file. (? read such property in handler is
possible?)
Also what is the nature of this dump? How big is it? Where will it go?
The jars includes *app.jar and *boot.jar, the later usually can be ignored
(rt.jar etc system jars) unless it's rewritten by JVMTI agent. The app.jar will
contain all classes by customer, so we can do whatever we can to the jar.
Thanks
Yumin
On 8/12/2013 5:51 AM, Christian Tornqvist wrote:
Hi Yumin,
The idea is to do as little as possible in the VM error handler, since we've
crashed for some reason we don't know what state the process is in and we have
to be extremely careful in when we're gathering the information. This seems
like a step that is risky for all of the reasons David mentioned below.
It's also information that can easily be extracted post-mortem from the
core/mdmp using the method you described for OSX, so gathering this at the time
of a crash seems like an unnecessary risk.
Thanks,
Christian
-----Original Message-----
From: hotspot-compiler-dev-boun...@openjdk.java.net
[mailto:hotspot-compiler-dev-boun...@openjdk.java.net] On Behalf Of David Holmes
Sent: Monday, August 12, 2013 1:56 AM
To: Yumin Qi
Cc: hotspot compiler; hotspot-runtime-...@openjdk.java.net
Subject: Re: RFR: 8020962: dump loaded java classes when vm crash
Hi Yumin,
Note that the SA is only present in a full JDK, not a JRE (full or compact
profile).
I have quite a few concerns with this:
We already do a lot of things that are not valid to be done from a signal
handling context but this really takes that to an extreme. Doing fork-exec from
a signal handler seems like a recipe for disaster (Note the existing onError
facility is typically used for synchronous failures.)
The idea of launching a second VM to try and query a VM that has crashed also
seems somewhat problematic:
- What mechanism will the SA try to use to query the VM?
- What if the state of the crashed VM stops the SA from being able to attach
properly (ie both processes hang)?
- What if it the SA also crashes, will it launch a third VM then a fourth etc?
Also what is the nature of this dump? How big is it? Where will it go?
Thanks,
David
On 12/08/2013 9:36 AM, Yumin Qi wrote:
Hi, all
I would like to have your review for
http://cr.openjdk.java.net/~minqi/8020962/webrev0/
<http://cr.openjdk.java.net/%7Eminqi/8020962/webrev0/>
Description: When JVM crashed, we also want to check the application
class files especially we got core file from customers. The aftermath
analysis will benefit from all loaded java classes available. In this
change, spawn another process running SA to do the job when JVM
crashes, this way also avoid further messing up with the error report
which already in signal handler.
Note: The test has done with following two bugs worked around:
8022655: ClassDump ignored jarStream setting (This will be fixed
and integrated by Kevin Walls soon)
8011888: sa.js: TypeError: [object JSAdapter] has no such function
"__has__" (Not know when it will be integrated)
That is, without those two fixed, the jars of loaded classes will
not be successfully dumped.
Also, on MacOS it requires security access permission to attach to
another process, so omit doing so. To get loaded jar file s, with core
file available (on all platforms), one can (only after this
change) do
$JAVA_HOME/bin/java [-d64] -cp $JAVA_HOME/lib/sa-jdi.jar
sun.jvm.hotspot.DumpLoadedClasses $JAVA_HOME/bin/java corefile
Thanks
Yumin
