Make dart:ffi Pointer an extension type over int

[alexmarkov]

Currently Pointer from dart:ffi is a heap object. It takes 3 words of memory (object header, address value and type arguments). Accessing pointer involves an extra indirection - we need to read an address value from the Pointer object before address value can be used to access pointed memory or do address arithmetic.

If large number of Pointer objects are used to point to small structs, the overhead of Pointer can be comparable to the amount of useful memory being addressed, which makes Pointer pretty much useless for building off-heap data structures.

With extension types, it is possible to make Pointer a zero-cost abstraction over address value (represented as int) and avoid these overheads: we would not need a heap object at all (unless int is boxed), Pointer would take only 1 word on 64-bit systems and it would not need an extra indirection when accessing address.

/cc @dcharkes @mraleph

[dcharkes]

👍

Duplicate of:

• [vm/ffi] Unbox Pointer #50777

See the comments there about 32-bit pointers. Let's discuss on that issue.