Comments (6)
It's not obviously clear that the key will be the target
and value will be the holdings
. Apart from being similar in terms of dealing with weak objects, WeakMap and FinalizationGroup seem pretty orthogonal in their use cases. It seems better to have separate API for different use cases. Your particular use case would be better solved with a FinalizationGroup rather than a WeakMap.
from proposal-weakrefs.
WeakSet
/WeakMap
provide ephemerons, not weak references - they cannot be followed. A finalisation callback would be one thing, the more important thing would be to make the collections iterable. And in many cases, you need only a single weak reference, not a collection of them, so this approach misses objective.
from proposal-weakrefs.
Real use case, I have a library that returns WASM objects with native memory that needs to be reclaimed, it offers a dispose() method on such objects to do so, but the library user might forget to call it (therefore produce a memory leak)
library side
const wasmObjects = new WeakSet([], obj => obj.dispose());
function gimmeAWasmObject() {
const wasmObject = createWasmObjectWithDisposer();
wasmObjects.add(wasmObject);
return wasmObject;
}
user side
const obj = gimmeAWasmObject();
obj = undefined; // no worries, the callback in the WeakSet will be called and dispose it
from proposal-weakrefs.
The finalization callback can't be given the object itself. That would allow the finalizer to either revive the dead object or create memory unsafety, neither of which are permissible.
Broader point: wasm finalization is definitely something that this proposal intends to support :)
from proposal-weakrefs.
What about making it only available for WeakMap and being the value (rather than the key, which is the dead object) the one that is sent to the callback?
const wasmObjects = new WeakMap({}, valueWhichIsTheDisposer => valueWhichIsTheDisposer());
function gimmeAWasmObject() {
const [wasmObject, disposer] = createWasmObjectWithDisposer();
wasmObjects.set(wasmObject, disposer);
return wasmObject;
}
If value keeps the object alive then the callback will never be called.
If the value doesn't keep the object alive (as it should be) then the callback will be called.
from proposal-weakrefs.
Let's add an explanation in the README about why this would not provide a solution. PRs welcome.
from proposal-weakrefs.
Related Issues (20)
- README feedback from @jorendorff HOT 1
- HostCleanupFinalizationGroup needs to pick a VM decided max iteration count HOT 30
- Should the fg copy the empty cells before calling cleanup callback? HOT 4
- Add API summary to README.md HOT 2
- Use of 'Job' in KeepDuringJob is misleading HOT 4
- Problem with definition of liveness HOT 12
- Rename FinalizationGroup to FinalizationRegistry (or other name?) HOT 5
- Document FinalizationGroup independent lifetime
- Soft check for WeakRef with reclaimed referent? HOT 15
- makeWeakCached passes key for unregister token; keys are often primitives HOT 1
- Document expectations of WeakRef behavior in practice HOT 3
- Documentation should encourage people to use cleanupSome only when appropriate HOT 2
- cleanupSome on main thread questions HOT 18
- Guarantee finalizers being called soonish. HOT 3
- Is this proposal stable enough for other specs to make use of weak refs? HOT 8
- The WeakRef object can also cause memory leak, why not make the reference self null? HOT 6
- WeakRef.prototype.deref() is misnamed HOT 17
- Iterable WeakMap implementation in README is incorrect?
- Q: Why not to add `getKeys() : array` instead? HOT 5
- Will heldValue be GC, after cleanupCallback executed? HOT 1
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from proposal-weakrefs.