Memory leak in lit-labs/context

[AndrewJakubowicz]

Which package(s) are affected?

Context (@lit-labs/context)

Description

Issue captured by: https://discord.com/channels/1012791295170859069/1097902841265393716/1116635815527858237

Text from the comment:

I thought this was fixed but it's clear that context has a memory leak. This is a small repro and and in Chrome you can see how the DOM nodes grow and the garbage collector can not remove the about view because it has subscribe: true. If you use Edge to look at detached elements it's more clear that the detached elements are building up as you navigate between home and about multiple times. This is a link to a repro https://lit-context-example.vercel.app/ and this is the repository if you wish to test it without subscribe set to true. When you do, the garbage collector can remove the about view as expected. https://github.com/marcuslindblom/lit-context-example

Thank you @marcuslindblom for reporting this issue

Reproduction

Live repro: https://lit-context-example.vercel.app/

Source code repro: https://github.com/marcuslindblom/lit-context-example

Repro:

• Open https://lit-context-example.vercel.app/
• In the performance profiler select memory. Garbage collect & then profile.
• While profiling switch between Home & About page a couple times.
• Trigger a garbage collection and stop profiling.
• Notice that the number of nodes has increased & garbage collection did not clean up everything back to where we started.

This leak results in Nodes accumulating over time.

Workaround

N/A

Is this a regression?

No or unsure. This never worked, or I haven't tried before.

Affected versions

lit-labs/context latest

Browser/OS/Node environment

N/a

[AndrewJakubowicz]

The issue seems related to the callbacks map here:

lit/packages/labs/context/src/lib/value-notifier.ts

Line 23 in fc2fd4c

private callbacks: Map<ContextCallback<T>, Disposer> = new Map();

maintaining callbacks and growing after every new subscription.

Verified by adding a console.log('we are adding a callback!', this.callbacks.size); message. When switching back and forth between components in the bug reproduction, the size of the callbacks grows. Nothing disposes the callbacks.