FIX: Memory leak in Animated API by managing parent-child references

[rodriguescarson]

Summary:
This pull request addresses a memory leak issue in React Native's Animated API by ensuring proper cleanup of parent-child relationships between AnimatedNode instances. The existing implementation did not manage bidirectional references effectively, leading to potential memory retention and performance degradation.

The fix introduces public methods (addChild and removeChild) to provide a consistent API for managing child nodes and modifies the internal methods to maintain a bidirectional relationship between parent and child nodes. This ensures proper cleanup of references, allowing garbage collection to function as intended.

Changelog:
[GENERAL][FIXED] - Resolved memory leak in Animated API by managing parent-child references between AnimatedNode instances.

Test Plan:
Verified that child nodes are correctly added and removed using the new public methods addChild and removeChild.
Confirmed that parent nodes are properly added to and removed from the _parents array of child nodes.
Ran the existing Animated API tests to ensure no regressions in functionality.
Monitored memory usage in Chrome DevTools to verify that parent-child relationships are correctly cleared, preventing memory leaks.
Tested the changes in a sample React Native project with complex animations to ensure stability and performance.
This description provides a clear motivation, solution summary, and test validation steps for reviewers and maintainers.

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[rodriguescarson]

Yes I have done this

[c-miles]

Yarn build was failing because child doesn't always implement addParent or removeParent.

I had to add checks (typeof child.addParent === 'function' and typeof child.removeParent === 'function') to avoid calling nonexistent methods.

I’m not necessarily recommending to adopt this; I just wanted to share what I had to do locally to test the rest of these changes.

(See attached screenshot of the terminal output.)

[c-miles]

I’m still seeing a memory leak as we keep adding the same child to _children multiple times. Here's an example where there's 334 children in the array while only 2 is expected.

I resolved this locally by adding an !this._children.includes(child) check just like you're doing in addParent below

Here's my original issue on react-native-web for reference, where I implemented just that change to resolve it: RN-web issue

I was able to achieve the same result by tweaking the changes to your updated __addChild method, which resolves the issue

  __addChild(child: AnimatedNode): void {
    if (!this._children.includes(child)) {
      if (this._children.length === 0) {
        this.__attach()
      }
  
      this._children.push(child)
  
      if (typeof child.addParent === 'function') {
        child.addParent(this)
      }
  
      if (this.__isNative) {
        child.__makeNative(this.__getPlatformConfig())
        connectAnimatedNodes(this.__getNativeTag(), child.__getNativeTag())
      }
    }
  }

[rodriguescarson]

Hey, got busy, can someone contribute to this pr and close. I think the reveiwers have done a fantasic job, can take some help from there. @c-miles @mojodna @jsierles