I'm committing my work on HphpArray in bite-sized pieces for easier review. This piece replaces calls to NEW with a factory method. There are many problems with operator new, starting with the fact that the allocator cannot communicate properly with the constructor.
The newly introduced factory method should return ArrayData but that causes many issues right now, so I left that step to a future diff.
I was learning from @jdelong and he said that you should use
double quotes for local includes and angle brackets for library
includes. I asked why our code was the way it was, and he said he wanted
to clean it up. I beat him to it :)
Conflicts:
hphp/runtime/base/server/admin_request_handler.cpp
hphp/runtime/vm/named_entity.h
PolicyArray splits the ArrayData implementation in two parts. ArrayShell implements the baroque ArrayData implementation in terms of a much smaller statically-bound core that concerns itself exclusively with the storage strategy for the array. This way the two aspects can be worked on separately, and different stores can be easily plugged into the given ArrayShell.
To give a better perspective, the featured SimpleArrayStore has about 340 lines all told (including solid documentation), whereas ArrayShell has some 1100 lines. The shell can be reused with other stores of unbounded sophistication. The store needs to implement only 22 primitives, some of which are trivial. Basically a new store implementation saves 1100 of difficult-to-get-right lines of code right off the bat, and only needs to focus on implementing 22 well-defined primitives.
Things to watch for when reviewing:
- Is the store API small/expressive enough? What should be added/removed?
- Are various forms of duplication present? If so, how could code be factored better?
- Any subtle change in semantics from HphpArray and friends that should be minded?
Known issues:
* Currently ArrayShell is defined as:
class ArrayShell : public ArrayData, private SimpleArrayStore { ... };
when in fact it should be:
template <class StorePolicy>
class ArrayShell : public ArrayData, private StorePolicy { ... };
Extenuating circumstances related to allocator design prevent use of templates at this point. I'll work on these in parallel with the review.
* growNoResize is almost always prefaced by a test-and-grow. This sequence should be encoded in a function.
* The growth policy is spread all over the place in a subtle form of duplication.
* The current store design makes almost no effort to be particularly efficient.
SharedMap was the last dependency on ZendArray. For its localCache,
use a TypedValue[] array indexed by SharedVariant.getIndex(), and
for escalate(mutableIteration), escalate to an HphpArray instead of
a ZendArray.
This change is mostly for FB internal organizational reasons.
Building is not effected beyond the fact that the target now
lands in hphp/hhvm/hhvm rather than src/hhvm/hhvm.
Tim Starling