Make number of available threads isolate-dependent and expose it to ResourceConstraints.

Make number of available threads isolate-dependent and expose it to ResourceConstraints.

R=svenpanne@chromium.org
BUG=v8:2991
LOG=Y

Committed: https://code.google.com/p/v8/source/detail?r=17866

[Sven Panne, 2013-11-18 14:40:06]

LGTM with nits

https://codereview.chromium.org/68203029/diff/1/include/v8.h
File include/v8.h (right):

https://codereview.chromium.org/68203029/diff/1/include/v8.h#newcode3825
include/v8.h:3825: int max_available_threads() { return max_available_threads_;
}
const

Furthermore, the semantics and the typing are slightly confusing: What the
getter returns is actually a Maybe<int>, but even then it is not clear what e.g.
1 means: Does it mean no concurrency at all or 1 additional thread apart from
the main JavaScript thread? I guess it's the former, but this is a bit unclear.
Either add a comment or choose a better name.

The "Maybe" part holds for all the other fields of this POD, too, but it's
already baked into our current API. :-( I propose to leave everything as it is
and get the typing right when the constraints become part of the Isolate's
constructor arguments.

https://codereview.chromium.org/68203029/diff/1/src/heap.cc
File src/heap.cc (right):

https://codereview.chromium.org/68203029/diff/1/src/heap.cc#newcode6587
src/heap.cc:6587: sweeping_complete &=
old_pointer_space()->AdvanceSweeper(step_size);
Evil! But this has been here before... :-]

https://codereview.chromium.org/68203029/diff/1/src/optimizing-compiler-threa...
File src/optimizing-compiler-thread.cc (right):

https://codereview.chromium.org/68203029/diff/1/src/optimizing-compiler-threa...
src/optimizing-compiler-thread.cc:374: if
(!isolate->concurrent_recompilation_enabled()) return false;
return ... && ...;

[Yang, 2013-11-19 11:53:02]

Committed patchset #2 manually as r17866 (presubmit successful).