fix: mutationobserver memory leak - use weakmap for bookkeeping #1423
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Use a WeakMap to store all nodes watched by an observer. On disconnect(), clean up references to the observer on all the nodes. Limitation: If MutationObservers are not disconnected, this could lead to memory leak of nodes.
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caridy
reviewed
Jul 20, 2019
| // maintain a list of all nodes observed by this observer | ||
| if (observerToNodesMap.has(this)) { | ||
| const observedNodes = observerToNodesMap.get(this)!; | ||
| if (observedNodes.indexOf(target) === -1) { |
caridy
reviewed
Jul 20, 2019
| if (observerToNodesMap.has(this)) { | ||
| const observedNodes = observerToNodesMap.get(this)!; | ||
| if (observedNodes.indexOf(target) === -1) { | ||
| observedNodes.push(target); |
caridy
reviewed
Jul 20, 2019
| observedNodes.push(target); | ||
| } | ||
| } else { | ||
| observerToNodesMap.set(this, [target]); |
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set from lang, although we are not doing that today... we should probably start doing it at some point.
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Its a polyfilled feature in IE11, wasn't sure if was okay to cache these. Let me know.
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yes, it should be ok. they all run before everything else.
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lets open a seprate issue for this in general.
nolanlawson
requested changes
Jul 20, 2019
| if (observerToNodesMap.has(this)) { | ||
| const observedNodes = observerToNodesMap.get(this)!; | ||
| if (observedNodes.indexOf(target) === -1) { | ||
| observedNodes.push(target); |
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Should these be ArrayIndexOf.call() and ArrayPush.call?
nolanlawson
reviewed
Jul 20, 2019
|
|
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| // maintain a list of all nodes observed by this observer | ||
| if (observerToNodesMap.has(this)) { | ||
| const observedNodes = observerToNodesMap.get(this)!; |
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Is there a reason we use ArrayPush.call() but not WeakMapHas.call()? I.e. we cache the Array prototype functions but not the WeakMap ones?
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Benchmark resultsBase commit: lwc-engine-benchmark
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caridy
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Jul 22, 2019
ravijayaramappa
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Jul 22, 2019
* fix: mutationobserver memory leak - use weakmap for bookkeeping Use a WeakMap to store all nodes watched by an observer. On disconnect(), clean up references to the observer on all the nodes. Limitation: If MutationObservers are not disconnected, this could lead to memory leak of nodes. * fix: comments fixes * fix: address PR comments
@ravijayaramappa Is this the case? I thought that if the MutationObserver (the key) has no more references, then both the key and the value (the array of nodes) should be removed from the WeakMap? |
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@nolanlawson Each observed node has a hard reference to the mutation observer[the |
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… (#1426) * fix: mutationobserver memory leak - use weakmap for bookkeeping Use a WeakMap to store all nodes watched by an observer. On disconnect(), clean up references to the observer on all the nodes. Limitation: If MutationObservers are not disconnected, this could lead to memory leak of nodes. * fix: comments fixes * fix: address PR comments
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Details
Use a WeakMap to store all nodes watched by an observer. On disconnect(), clean up references to the observer on all the nodes.
Limitation: If MutationObservers are not disconnected, this could lead to memory leak of nodes.
Does this PR introduce breaking changes?
No, it does not introduce breaking changes.If yes, please describe the impact and migration path for existing applications.
The PR fulfills these requirements: