"Nestegg" buffer for error reporting in native oom scenarios

[Thomas Stüfe]

Hi,,

I carry this tiny patch around since quite a while which makes error
handling more stable in native OOM situations. I usually apply it when
dealing with memory leaks, to increase the chance of useful error reports.

A number of error reporting things require memory. When we are out of
memory, those steps may fail.

A prominent example is NMT: when creating a detailed report, it allocates
memory. In OOM scenarios NMT will not work because of this, which is a pity
since this is exactly the time where having an NMT report would be super
useful.

A clean solution would be to harden everything running inside error
handling to work with pre-allocated buffers instead, or to not alloc memory
at all. But that is difficult or even impossible.

What I do instead is tp allocate memory at VM startup and to release it
back into the clib when a native OOM happens (of course, only when the
switch is set).

This is of course no guarantee that this works - code running concurrently
may gobble the memory up the moment I release it, for instance - but it
works surprisingly often, and in a number of cases helped me e.g. to get a
detailed NMT report where otherwise I would have gotten nothing.

Patch:

http://cr.openjdk.java.net/~stuefe/webrevs/nestegg/webrev.00/webrev/index.html

What do you think? Too stupid or weird? We can talk of course about the
naming :)

I am not especially proud of that hack, but as a technique, it is at least
dead simple and reasonably successful.

Thanks, Thomas