Integrated: 8324066: "clhsdb jstack" should not by default scan for j.u.c locks because it can be very slow

[Chris Plummer]

On Thu, 18 Jan 2024 02:17:56 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> I noticed that "clhsdb jstack" seemed to hang when I attached to process with a somewhat large heap. It had taken over 10 minutes when I finally decided to have a look at the SA process (using bin/jstack), which came up with the following in the stack:
> 
> 
> at sun.jvm.hotspot.oops.ObjectHeap.iterateObjectsOfKlass([jdk.hotspot.agent at 23-internal](jdk.hotspot.agent at 23-internal)/ObjectHeap.java:117)
> at sun.jvm.hotspot.runtime.ConcurrentLocksPrinter.fillLocks([jdk.hotspot.agent at 23-internal](jdk.hotspot.agent at 23-internal)/ConcurrentLocksPrinter.java:70)
> at sun.jvm.hotspot.runtime.ConcurrentLocksPrinter.<init>([jdk.hotspot.agent at 23-internal](jdk.hotspot.agent at 23-internal)/ConcurrentLocksPrinter.java:36)
> at sun.jvm.hotspot.tools.StackTrace.run([jdk.hotspot.agent at 23-internal](jdk.hotspot.agent at 23-internal)/StackTrace.java:71)
> 
> 
> This code is meant to print information about j.u.c. locks. It it works by searching the entire java heap for instances of AbstractOwnableSynchronizer. This is a very expensive operation because it means not only does SA need to read in the entire java heap, but it needs to create a Klass mirror for every heap object so it can determine its type.
> 
> Our testing doesn't seem to run into this slowness problem because "clhsdb jstack" only iterates over the heap if AbstractOwnableSynchronizer has been loaded, which it won't be if no j.u.c. locks have been created. This seems to be the case wherever we use "clhsdb jstack" in testing. We do have some tests that likely result in j.u.c locks, but they all use "jhsdb jstack", which doesn't have this issue (it requires use of the --locks argument to enable printing of j.u.c locks).
> 
> This issue was already called out in [JDK-8262098](https://bugs.openjdk.org/browse/JDK-8262098). For this CR I am proposing that "clhsdb jstack" not include j.u.c lock scanning by default, and add the -l argument to enable it. This will make it similar to bin/jstack, which also has a -l argument, and to "clhsdb jstack", which has a --locks argument (which maps internally to the Jstack.java -l argument).
> 
> The same changes are also being made to "clhsdb pstack".
> 
> Tested with all tier1, tier2, and tier5 svc tests.

This pull request has now been integrated.

Changeset: 192349ee
Author:    Chris Plummer <cjplummer at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/192349eee4b6d50f16d44969eb882875c67d651d
Stats:     228 lines in 10 files changed: 204 ins; 1 del; 23 mod

8324066: "clhsdb jstack" should not by default scan for j.u.c locks because it can be very slow

Reviewed-by: kevinw, amenkov

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PR: https://git.openjdk.org/jdk/pull/17479