3 ms·

The main benefit of using the Web Assembly GC is not improved performance within the language, but rather having a single GC that handles both native DOM object

The main benefit of using the Web Assembly GC is not improved performance within the language, but rather having a single GC that handles both native DOM objects and language objects. Having two GCs interoperate is a big pain, and it's very difficult to pull off without leaks or performance problems. This is especially true for DOM objects, which have no user-visible finalizers. (The closest thing is WeakMaps, but I don't believe these are enough to implement proper cross-language GC, because you can't query whether an potentially-dead object is actually dead.) Web Assembly GC is not a performance optimization; it's necessary for correctness.

sseth 9y ago
In Chrome today, as an example, the C++ based DOM and V8 (Javascript ) objects are using different GCs. Obviously it is a pain point, but the situation of having different GCs for DOM and language objects is not new with Web Assembly.
- slimsag 9y ago
  It's also worth mentioning WASM has no GC today.
  - pjmlp 9y ago
    My amd64 and ARM CPUs also don't have it. On languages where the algorithm is an implementation detail, one can make use of reference counting with a cycle collector, which are just a few hundred lines. Implementing one is pretty simple, making it perform well is another matter.
    - hajile 9y ago
      Unlike your real processor though, you can't directly access memory or ensure its absolute location. You can make an advanced GC that is slow or a basic one that is not.
  - Sawamara 9y ago
    Which is good. You can always implement GC inside it, but personally, for performance-intensive computing, I do not want GC inside WASM unless eplicitly enabled.
- pcwalton 9y ago
  I mean, as of Oilpan the V8 garbage collector marks C++ objects by calling trace hooks, as I understand things. That isn't an option for Web Assembly, which doesn't have access to the V8 garbage collector in that way (except via the wasm GC proposal; in fact, that's fundamentally what the wasm GC proposal is).

sseth 9y ago

In Chrome today, as an example, the C++ based DOM and V8 (Javascript ) objects are using different GCs. Obviously it is a pain point, but the situation of having different GCs for DOM and language objects is not new with Web Assembly.

slimsag 9y ago
It's also worth mentioning WASM has no GC today.
- pjmlp 9y ago
  My amd64 and ARM CPUs also don't have it. On languages where the algorithm is an implementation detail, one can make use of reference counting with a cycle collector, which are just a few hundred lines. Implementing one is pretty simple, making it perform well is another matter.
  - hajile 9y ago
    Unlike your real processor though, you can't directly access memory or ensure its absolute location. You can make an advanced GC that is slow or a basic one that is not.
- Sawamara 9y ago
  Which is good. You can always implement GC inside it, but personally, for performance-intensive computing, I do not want GC inside WASM unless eplicitly enabled.
pcwalton 9y ago
I mean, as of Oilpan the V8 garbage collector marks C++ objects by calling trace hooks, as I understand things. That isn't an option for Web Assembly, which doesn't have access to the V8 garbage collector in that way (except via the wasm GC proposal; in fact, that's fundamentally what the wasm GC proposal is).