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List:       openjdk-serviceability-dev
Subject:    RFR: 8293006: sun/tools/jhsdb/JStackStressTest.java fails with "UnalignedAddressException: 8baadbabe
From:       Chris Plummer <cjplummer () openjdk ! org>
Date:       2022-08-30 23:37:05
Message-ID: 30MiZ6W_yFw0pgh8t8LUcoeUPllcUgjlUmzIE7-UJhU=.46a806ca-006e-43be-b1db-76277242f2b9 () github ! com
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The root cause of this CR is that we are trying to access the java heap during the \
middle of a GC. This particular test is prone to that happening since it runs jstack \
4 times on the debuggee as it starts up (the debuggee is jshell, so it does a lot of \
initialization on startup).

SA needs to deal with potentially bad references to java objects. These might come \
from VM structs (such as the JavaThread reference to its java Thread instance), or a \
java object reference from a field of another java objects. There's always the \
possibility that these can be invalid. We work around this in most of our testing by \
getting the debuggee into a steady state so no GC can be in progress.

For the most part SA is pretty good about dealing with these bad object refernces, \
and fails gracefully with an exception, but otherwise continues to run. However, this \
test exposed some holes that resulted in (1) way to many exception stack traces and \
(2) exiting the SA tool rather than trying to continue.

The main fix is in JavaThread.printThreadInfo() where we now do a better job of \
dealing with exceptions if any of the java objects references are not valid. Even \
without access to the Thread instance, we can still produce a stack trace, but it \
will be missing things like the thread name and priority. This is a lot better than \
just giving up with the first exception.

The other changes are for the most part just improvements in the error output, and \
getting rid of the printStackTrace() that was cluttering up the output.

-------------

Commit messages:
 - When dumping the stack, be more cautious with references to java objects that \
might not be valid due to a GC in progress.

Changes: https://git.openjdk.org/jdk/pull/10088/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10088&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293006
  Stats: 77 lines in 5 files changed: 38 ins; 0 del; 39 mod
  Patch: https://git.openjdk.org/jdk/pull/10088.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10088/head:pull/10088

PR: https://git.openjdk.org/jdk/pull/10088


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