[jbossts-issues] [JBoss JIRA] Commented: (JBTM-555) make memory leak tests more robust

[Romain PELISSE (JIRA)]

    [ https://jira.jboss.org/jira/browse/JBTM-555?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12467595#action_12467595 ] 

Romain PELISSE commented on JBTM-555:
-------------------------------------

yes, you 're right... Well, if I got the time, I'll take a look at OpenJDK source code for you, they are bound to have some kind of mechanism to test the GC efficiency, with any luck it'll be reusable for JBossTS.

> make memory leak tests more robust
> ----------------------------------
>
>                 Key: JBTM-555
>                 URL: https://jira.jboss.org/jira/browse/JBTM-555
>             Project: JBoss Transaction Manager
>          Issue Type: Task
>      Security Level: Public(Everyone can see) 
>          Components: Testing, Transaction Core
>    Affects Versions: 4.6.1
>            Reporter: Jonathan Halliday
>            Assignee: Jonathan Halliday
>             Fix For: future
>
>
> Some tests in the txcore group attempt to detect memory leaks by
> setup
> System.gc()
> take memory reading
> doTransactionStuff
> System.gc()
> take another memory reading
> This is unreliable, as System.gc() is only advisory to the runtime. There is no way to FORCE gc from within the jvm. This causes the tests to be somewhat unreliable.
> Dirty tricks to work around this include running the tests with a small heap (-Xmx5m). With less free space to work with, the gc tries harder. On a default size heap it mostly ignores System.gc().  Unfortunately the test framework does not make it easy to set -Xmx on a per test / test group basis.
> Similar effect could perhaps be achieved by allocating all except a small portion of the available heap from within the vm using eg. new byte[].
> There is also the jvmti ForceGarbageCollection method, but that would require us to have a chunk of C code on each test platform, which is a pain.

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