1bbf75017c
According to the promise specification, promises are not cancellable by default. Once a promise is created, it will either resolve or reject, and it doesn't provide a built-in mechanism to cancel it. There may be situations where a promise is provided, and it either resolves after the pipe has been destroyed or never resolves at all. If the promise never resolves — potentially due to factors beyond our control, such as third-party libraries — this can lead to a memory leak. When we use `async.then(updateLatestValue)`, the engine captures a reference to the `updateLatestValue` function. This allows the promise to invoke that function when it resolves. In this case, the promise directly captures a reference to the `updateLatestValue` function. If the promise resolves later, it retains a reference to the original `updateLatestValue`, meaning that even if the context where `updateLatestValue` was defined has been destroyed, the function reference remains in memory. This can lead to memory leaks if `updateLatestValue` is no longer needed or if it holds onto resources that should be released. When we do `async.then(v => ...)` the promise captures a reference to the lambda function (the arrow function). When we assign `updateLatestValue = null` within the context of an `unsubscribe` function, we're changing the reference of `updateLatestValue` in the current scope to `null`. The lambda will no longer have access to it after the assignment, effectively preventing any further calls to the original function and allowing it to be garbage collected. If Chrome is built with additional flags and run with `--allow-natives-syntax --track-retaining-path`, we could use `%DebugTrackRetainingPath` to see the distance from the root for `updateLatestValue` if it's passed directly to async.then, e.g.: ```js %DebugTrackRetainingPath(updateLatestValue); // Distance from root 4: 0x123456789abc <JSPromise (sfi = 0x1fbb02e2d7f1)> ``` PR Close #58041 |
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