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

[Jonathan Halliday (JIRA)]

make memory leak tests more robust
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                 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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