leaks when using primitives; fixable with WeakRef

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难度
5/5
预计耗时
一周以上
新手友好度
35/100
Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
停滞
技术栈
javascript
领域
data

调研方向

首先定位 Tuple 和 UniversalWeakMap 的实现，然后跟踪 Tuple(primitive) 如何创建并保留父节点。将当前的强引用与提议的 WeakRef、FinalizationRegistry 和全局 WeakMap 方案进行比较；完成标准是：垃圾回收后，元组及其映射不再保留内存，包括各种由基本类型值组成的元组。

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描述

The description claims "no leaks", but if you do Tuple(primitive), that creates a UniversalWeakMap which can never be garbage collected. If you're creating a lot of tuples with a lot of different primitives, that can be a problem.

Now that we have WeakRef and FinalizationRegistry, I'm pretty sure it's possible to do better, so that there's actually no leaks: that is, no matter how many tuples you create and how you create them, once they've all been GC'd you're guaranteed that no additional memory is held.

The necessary changes are:

  1. When set(key, value) is called on a UniversalWeakMap, store a WeakRef to value instead of storing value directly, and register value in a FinalizationRegistry so that when it is collected key is cleared from the map.
  2. Use a global WeakMap to store a map from each created tuple to all of its parent nodes.

Then the only strong references to UniversalWeakMap objects (except the root) are from the tuples stored in those maps. Once all the tuples stored in a given UniversalWeakMap are GC'd, it can be GC'd as well.

The only caveat with this approach is if the user uses a tuple as a key in a weak collection. In that case the tuple can still get collected even if it was only holding primitives, which might be surprising. But that's unavoidable if avoiding leaks.

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JavaScript
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38
派生
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