RFR (XS): 8027756: assert(!hr->isHumongous()) failed: code root in humongous region? (P2-JDK8!)

Thomas Schatzl thomas.schatzl at oracle.com
Tue Nov 5 13:46:37 UTC 2013

Hi all,

  can I get quick reviews for the following small changes?

The patchset fixes wrong assertions that assume that references to
humongous/large objects cannot be embedded into the code stream. They

This is not true, and in the failing (existing) test case just that

The fix is to just change all these wrong assertions to check whether
the region we want to add the code root to is a humongous continuation:
that really should not occur as they do not contain an object header.

Note that there is a similar assertions with the same conditions in e.g.
MigrateCodeRootsHeapRegionClosure::doHeapRegion() - however this one
checks a different situation: there should be no migration of code roots
because (currently) large objects can never move.

The original reasons for adding this assertion, and why this assertion
only triggers just now (the code has been in for a few months) are
unknown. I will try to find out what change (possibly in the compiler)
triggered this.

The changeset also adds a new test in addition to the original one that
particularly targets most reasons why the assertion failed before:
 - when adding a new code root to a humongous region
 - when removing a new code root to a humongous region
 - during verification (does anybody know why
G1VerifyHeapRegionCodeRoots is false by default?)
 - strong code roots root marking (in anticipation of class unloading
during concurrent marking)



jprt, manual invocation of the failing test (verifying that without the
change the assertion triggers, and does not with the patch), new test


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