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Add forward References to the GC collection context - #13634
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Pull request overview
Extends the core/metadata garbage-collection traversal logic to support lazy, forward reference emission from externally-registered collectible resource types, complementing the existing eager/back-reference mechanism.
Changes:
- Introduces an optional
collectionWithReferencesinterface forCollectionContextto emit forward references on demand. - Caches per-resource-type
collectionWithReferencesimplementations ingcContext.refContextsduringstartGCContext. - Updates
gcContext.referencesto invokeReferences(...)for matching external resource types after handling built-in core types.
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Extend the garbage-collection framework so a collectible resource can emit forward references during graph traversal, in addition to the existing back-reference mechanism. A CollectionContext may now implement the optional collectionWithReferences interface: References(ctx context.Context, node gc.Node, fn func(gc.Node)) When the GC visits a node whose resource type was registered by an external collector, gcContext.references consults the per-type References implementation after the built-in core resource types are handled. This is the forward-reference analogue of collectionWithBackRefs. Whereas ActiveWithBackRefs must enumerate every edge up front and the gcContext holds all of them in its backRefs map for the entire collection, References is invoked on demand for a single node. A collector whose resources fan out to many other nodes can therefore emit those edges without retaining them in memory for the gc context. This commit is intentionally a no-op: no plugin registers a collector that uses collectionWithReferences yet. It is isolated here so that concurrent development efforts that depend on this interface can be proposed and reviewed upstream independently. Signed-off-by: Derek McGowan <derek@mcg.dev>
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Extend the garbage-collection framework so a collectible resource can emit forward references during graph traversal, in addition to the existing back-reference mechanism.
A CollectionContext may now implement the optional collectionWithReferences interface:
When the GC visits a node whose resource type was registered by an external collector, gcContext.references consults the per-type References implementation after the built-in core resource types are handled.
This is the forward-reference analogue of collectionWithBackRefs. Whereas ActiveWithBackRefs must enumerate every edge up front and the gcContext holds all of them in its backRefs map for the entire collection, References is invoked on demand for a single node. A collector whose resources fan out to many other nodes can therefore emit those edges without retaining them in memory for the gc context.
This commit is intentionally a no-op: no plugin registers a collector that uses collectionWithReferences yet. It is isolated here so that concurrent development efforts that depend on this interface can be proposed and reviewed upstream independently. This is useful for implementing chunked storage as a plugin, which will directly reference blobs in the content store. This is also useful for any plugin that might hold a reference to a core containerd type.