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().

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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.

Answer 1

Use a Virtual Machine and suspend its execution outright.

Answer 2

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.

Answer 3

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.

Answer 4

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. :)