Avoid redundant GCs and waits when near OOM

This should improve behavior if we are nearly out of memory, and
multiple threads detect this at roughly the same time. This seems
to be common if system server uses too much memory for some reason.

1) When calling WaitForGcToComplete without holding gc_complete_lock_
only wait for the current GC to complete. Do not wait until no GC
is running. This avoids repeated waits when an allocation could
actually succeed.

2) If we tried to run a GC, but another thread got in before us,
check if we can allocate anyway, rather than treating this as failure
and forcing a GC.

3) After we tried to run a last ditch "emergency" GC, also try to
allocate again if another thread intervened, rather than insisting
on doing our own. We still weakly insist on doing our own before
throwing OOME, since we don't know if the other intervening GC
cleared soft references, etc.

Moved a logging call out of WaitForGcToComplete, since it belongs
in the caller.

Better documented a couple of almost-incorrect WaitForGcToComplete()
calls.

Bug: 353333767
Test: testrunner.py --host -b --all-gc --all-debuggable
Change-Id: Ie6d8789a4ca94978029f4ddee1a8fc62ea2a0e80

0 files changed, 0 insertions, 0 deletions