Create read only handles for empty_array and sentinel objects

Create read only handles for empty_array and sentinel objects
(trying out a basic framework and will extend it to others once this
works).
Committed: https://code.google.com/p/dart/source/detail?r=16416

[Ivan Posva, 2012-12-20 23:43:52]

LGTM with mostly comments about comments.

-Ivan

https://codereview.chromium.org/11648006/diff/7005/vm/dart.cc
File vm/dart.cc (right):

https://codereview.chromium.org/11648006/diff/7005/vm/dart.cc#newcode58
vm/dart.cc:58: // (e.g: symbols, null object, empty array etc.
Maybe explain why this is wrapped in an object in itself and not just a static
VMHandles?

https://codereview.chromium.org/11648006/diff/7005/vm/object.cc
File vm/object.cc (right):

https://codereview.chromium.org/11648006/diff/7005/vm/object.cc#newcode1260
vm/object.cc:1260: Dart::IsReadOnlyHandle(reinterpret_cast<uword>(this)));
Could we have a IsReadOnlyHandle similar to IsZoneHandle on object instead?

Also I find it a bit strange to have a method called IsNotXYZ.

https://codereview.chromium.org/11648006/diff/7005/vm/object.cc#newcode7071
vm/object.cc:7071: new Comments(Array::ZoneHandle(Array::New(count *
kNumberOfEntries)));
Should probably be a regular scoped handle.

https://codereview.chromium.org/11648006/diff/7005/vm/object.h
File vm/object.h (right):

https://codereview.chromium.org/11648006/diff/7005/vm/object.h#newcode449
vm/object.h:449: // The static values below are read only handle pointers for
singleton
read-only

[siva, 2012-12-21 02:28:06]

https://codereview.chromium.org/11648006/diff/7005/vm/dart.cc
File vm/dart.cc (right):

https://codereview.chromium.org/11648006/diff/7005/vm/dart.cc#newcode58
vm/dart.cc:58: // (e.g: symbols, null object, empty array etc.
On 2012/12/20 23:43:52, Ivan Posva wrote:
> Maybe explain why this is wrapped in an object in itself and not just a static
> VMHandles?

Done.

https://codereview.chromium.org/11648006/diff/7005/vm/object.cc
File vm/object.cc (right):

https://codereview.chromium.org/11648006/diff/7005/vm/object.cc#newcode1260
vm/object.cc:1260: Dart::IsReadOnlyHandle(reinterpret_cast<uword>(this)));
Added IsReadOnlyHandle method to Object.

Regarding IsNotTemporaryScopedHandle(): Srdjan was not
in favour of changing all the places where we have
ASSERt(IsZoneHandle()) to also be 
ASSERT(IsZoneHandle() || IsReadOnlyHandle());
Maybe I should talk with him regarding this and replace
IsNotTemporaryScopedHandle to something more meaningful.

On 2012/12/20 23:43:52, Ivan Posva wrote:
> Could we have a IsReadOnlyHandle similar to IsZoneHandle on object instead?
> 
> Also I find it a bit strange to have a method called IsNotXYZ.

https://codereview.chromium.org/11648006/diff/7005/vm/object.cc#newcode7071
vm/object.cc:7071: new Comments(Array::ZoneHandle(Array::New(count *
kNumberOfEntries)));
On 2012/12/20 23:43:52, Ivan Posva wrote:
> Should probably be a regular scoped handle.

Done.

https://codereview.chromium.org/11648006/diff/7005/vm/object.h
File vm/object.h (right):

https://codereview.chromium.org/11648006/diff/7005/vm/object.h#newcode449
vm/object.h:449: // The static values below are read only handle pointers for
singleton
On 2012/12/20 23:43:52, Ivan Posva wrote:
> read-only

Done.

[Ivan Posva, 2012-12-21 07:33:41]

https://codereview.chromium.org/11648006/diff/7005/vm/object.cc
File vm/object.cc (right):

https://codereview.chromium.org/11648006/diff/7005/vm/object.cc#newcode1260
vm/object.cc:1260: Dart::IsReadOnlyHandle(reinterpret_cast<uword>(this)));
On 2012/12/21 02:28:06, siva wrote:
> Added IsReadOnlyHandle method to Object.
> 
> Regarding IsNotTemporaryScopedHandle(): Srdjan was not
> in favour of changing all the places where we have
> ASSERt(IsZoneHandle()) to also be 
> ASSERT(IsZoneHandle() || IsReadOnlyHandle());
> Maybe I should talk with him regarding this and replace
> IsNotTemporaryScopedHandle to something more meaningful.
> 
> On 2012/12/20 23:43:52, Ivan Posva wrote:
> > Could we have a IsReadOnlyHandle similar to IsZoneHandle on object instead?
> > 
> > Also I find it a bit strange to have a method called IsNotXYZ.
> 

I find the name confusing on two fronts:
- The Not in IsNotXYZ. We try to avoid that in general.
- What is a non-temporary scoped handle? Or are all scoped handles temporary,
then either the scoped or the temporary are redundant.

Personally I would favor IsScopedHandle or something less mind-twisting.