Suspending the JVM for a limited amount of time

Question

How can I suspend the execution of a JVM for a configurable amount of time, similar to want happens on a full, serial, Garbage Collection? I want to test some edge cases but it's difficult to create the exact pauses I need with manually generating garbage + System.gc().

I'm trying to 'freeze' all the threads in the application, to simulate a situation where an application becomes unresponsive, and then resumes execution. The application is part of a cluster, and I'm trying to debug some leave / join / re-join problems.

Not sure what you are trying to do. Would a simple sleep() work ? — Romain Hippeau, Apr 20 '10 at 13:25
you ended up answering your own question? :) any chance you ever came across the info on how to suspect the JVM itself from within? I'm in need of that solution right now. :) — , Jul 31 '10 at 02:52

Vadzim · Answer 1 · 2019-02-11T15:59:32.977

4

JVM suspend can be done from command line with jdb:

jdb -attach 8787
Initializing jdb ...
> suspend
All threads suspended.
> resume
All threads resumed.
> exit

But this requires it to be started with -Xdebug ...

There is also universal way to suspend and resume any process on Linux/Unix:

kill -SIGSTOP PID
kill -SIGCONT PID

See also How to suspend/resume a process in Windows?

edited Feb 11 '19 at 15:59

answered Dec 26 '12 at 18:59

Vadzim

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Guillaume · Answer 2 · 2010-04-20T14:27:16.890

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When debugging from Eclipse you can supsend all threads, I guess other debuggers allow to do that too. So you'd need to start your server with JVM debug options and remote connect to it.

In my case (running JBoss) I modify the startup script by adding this line:

set JAVA_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n %JAVA_OPTS%

Then in Eclipse, Run -> Debug Configurations -> Remove Java Application -> New

Normally you just need to provide the hostname and the port.

edited Apr 20 '10 at 14:27

answered Apr 20 '10 at 14:01

Guillaume

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Thanks, I was considering that. Do you happen to know how I can do that without Eclipse? – Robert Munteanu Apr 20 '10 at 14:18

Robert Munteanu · Accepted Answer · 2010-04-26T13:19:36.233

2

Use a Virtual Machine and suspend its execution outright.

edited Apr 26 '10 at 13:19

answered Apr 20 '10 at 12:19

Robert Munteanu

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score 1 · Answer 4 · answered Apr 20 '10 at 13:52

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I think you probably want something that is less invasive, but one approach is to have a controlling thread obtain a lock and then have all the other threads also try to obtain that lock. Then have the controlling thread sleep for the time you need before giving it up. A slightly less clumsy version of this would be to use a semaphore with one permit per thread and then have the controlling thread obtain them all, before having all the other threads try to acquire a permit.

As I said that's pretty invasive you'd have to hack that into your code for each thread.

Another approach would be to run your code under a debugger and manually suspend each thread.

answered Apr 20 '10 at 13:52

Dean Povey

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Thanks for you answer. I was looking for something which locks all threads, including some which are controlled by third party code. – Robert Munteanu Apr 20 '10 at 14:23
A slightly more involved approach might be to use the JPDA api to write your own debugger which enumerates the threads and suspends them. – Dean Povey Apr 20 '10 at 14:53
Sounds interesting. I did not find anything related to this in jdb. Do you have any pointers on how that can be done? – Robert Munteanu Apr 20 '10 at 15:05

Suspending the JVM for a limited amount of time

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