Memory Leaks in Angular CDK Scrolling Module Potentially core/signals references

[aderito7]

Which @angular/* package(s) are the source of the bug?

core

Is this a regression?

Yes

Description

A similar bug to this has been logged here: angular/angular#65265

When creating instances of objects into memory that are used by the virtual scroller they are not cleared from memory when being replaced. I have also verified the issue persists when making use of a production build

Please provide a link to a minimal reproduction of the bug

https://stackblitz.com/edit/virtual-scroll-memory-test-angular

Please provide the exception or error you saw

Generating a user leads up to old User references still being held in memory when checking the Heap Snapshot. Destroying the virtual scroller helps ("Hide") button

Please provide the environment you discovered this bug in (run ng version)

Angular CLI       : 21.0.3
Angular           : 21.0.4
Node.js           : 24.11.1
Package Manager   : npm 11.3.0
Operating System  : win32 x64

┌───────────────────────────┬───────────────────┬───────────────────┐
│ Package                   │ Installed Version │ Requested Version │
├───────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build            │ 21.0.3            │ ^21.0.3           │
│ @angular/cdk              │ 21.0.3            │ ^21.0.3           │
│ @angular/cli              │ 21.0.3            │ ^21.0.3           │
│ @angular/common           │ 21.0.4            │ ^21.0.4           │
│ @angular/compiler         │ 21.0.4            │ ^21.0.4           │
│ @angular/compiler-cli     │ 21.0.4            │ ^21.0.4           │
│ @angular/core             │ 21.0.4            │ ^21.0.4           │
│ @angular/forms            │ 21.0.4            │ ^21.0.4           │
│ @angular/platform-browser │ 21.0.4            │ ^21.0.4           │
│ @angular/router           │ 21.0.4            │ ^21.0.4           │
│ rxjs                      │ 7.8.2             │ ~7.8.0            │
│ typescript                │ 5.9.3             │ ~5.9.2            │
└───────────────────────────┴───────────────────┴───────────────────┘

Anything else?

[crisbeto]

At most I can see it retaining 2x User objects so I'm not sure it's a leak. Also from my observations it's always the currently-active user and the previous value which is likely used by change detection to determine if the value changes.

[aderito7]

@crisbeto , if the Change Detection holds on to the object for some purpose we would expect it to behave the same when not using the Angular CDK. This is not the case, however. As well, destroying the cdk-virtual-scroll-viewport frees up the memory. This is a simple example, however the real-world application is working with objects in the 10s of thousands and is causing serious issue when these objects are retained without good use for our application, i.e. a complete fresh reload of objects is the premise with no use of anything from before

[crisbeto]

Can you show a case where this problematic? The virtual scroller does its own diffing of the list so it's possible that it's holding onto references there, but I'm not sure if we can do much about it if we need to know whether the value actually changed.

[aderito7]

Thanks, it is making sense to keep a few for some diffing. I can confirm the whole set is not kept as the list gets larger and scrolling essentially resets it