java PrintCompilation output: what's the meaning of "made not entrant" and "made zombie"

Question

When running a Java 1.6 (1.6.0_03-b05) app I've added the -XX:+PrintCompilation flag. On the output for some methods, in particular some of those that I know are getting called a lot, I see the text made not entrant and made zombie.

What do these mean? Best guess is that it's a decompilation step before recompiling either that method or a dependency with greater optimisation. Is that true? Why "zombie" and "entrant"?

Example, with quite a bit of time between some of these lines:

[... near the beginning]
42       jsr166y.LinkedTransferQueue::xfer (294 bytes)

[... much later]
42    made not entrant  jsr166y.LinkedTransferQueue::xfer (294 bytes)
---   n   sun.misc.Unsafe::compareAndSwapObject
170       jsr166y.LinkedTransferQueue::xfer (294 bytes)
170   made not entrant  jsr166y.LinkedTransferQueue::xfer (294 bytes)
  4%      jsr166y.LinkedTransferQueue::xfer @ 29 (294 bytes)
171       jsr166y.LinkedTransferQueue::xfer (294 bytes)

[... even later]
42    made zombie  jsr166y.LinkedTransferQueue::xfer (294 bytes)
170   made zombie  jsr166y.LinkedTransferQueue::xfer (294 bytes)
171   made not entrant  jsr166y.LinkedTransferQueue::xfer (294 bytes)
172       jsr166y.LinkedTransferQueue::xfer (294 bytes)

[... no further logs]

Addition: some brief information explaining some of the symbols in that output. Also n means native.

Answer 1

This is absolutely not an area of expertise for me, but I was interested and so did a bit of digging.

A couple of links you might find interesting: OpenJDK:nmethod.cpp, OpenJDK:nmethod.hpp.

A excerpt of nmethod.hpp:

// Make the nmethod non entrant. The nmethod will continue to be
// alive.  It is used when an uncommon trap happens.  Returns true
// if this thread changed the state of the nmethod or false if
// another thread performed the transition.
bool  make_not_entrant() { return make_not_entrant_or_zombie(not_entrant); }
//...

Just as a starting place.