internal: adds utility for refcounting and cleanup by eshitachandwani · Pull Request #9189 · grpc/grpc-go

eshitachandwani · 2026-06-18T07:37:29Z

This PR adds the utility for refcounting objects and cleanups when the references go to zero.

For now it will be used for channel retention in A93 :Ext proc.

#ext-proc-a93

RELEASE NOTES: None

codecov · 2026-06-18T07:41:01Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.25%. Comparing base (5c7f936) to head (ff1f329).
⚠️ Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9189      +/-   ##
==========================================
+ Coverage   83.09%   83.25%   +0.16%     
==========================================
  Files         419      421       +2     
  Lines       33858    34050     +192     
==========================================
+ Hits        28134    28350     +216     
+ Misses       4291     4269      -22     
+ Partials     1433     1431       -2

Files with missing lines	Coverage Δ
internal/grpcsync/refcounted.go	`100.00% <100.00%> (ø)`

... and 39 files with indirect coverage changes

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mbissa · 2026-06-22T05:37:27Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a new generic RefCounted utility in internal/grpcsync/refcounted.go to manage resource lifecycles via atomic reference counting, accompanied by comprehensive unit tests. The review feedback focuses on enhancing safety and robustness by suggesting defensive programming checks: panicking if Increment is called on a dead resource, panicking if Decrement drops the reference count below zero, and validating that the onZero callback is not nil during initialization.

gemini-code-assist · 2026-06-22T05:38:44Z

+func NewRefCounted[V any](val V, onZero func()) *RefCounted[V] {
+	rc := &RefCounted[V]{
+		val:    val,
+		onZero: onZero,
+	}
+	rc.refCount.Store(1)
+	return rc
+}


To prevent hard-to-debug runtime panics later during asynchronous decrements, it is highly recommended to validate that the onZero callback is not nil when creating a new RefCounted instance. This ensures that any configuration errors are caught synchronously at the creation site.

func NewRefCounted[V any](val V, onZero func()) *RefCounted[V] { if onZero == nil { panic("grpcsync: onZero callback cannot be nil") } rc := &RefCounted[V]{ val: val, onZero: onZero, } rc.refCount.Store(1) return rc }

Makes sense. Added

easwars · 2026-07-08T05:26:11Z

+// drops to zero.
+func NewRefCounted[V any](val V, onZero func()) (*RefCounted[V], error) {
+	if onZero == nil {
+		return nil, fmt.Errorf("onZero callback cannot be nil")


Nit: prefix error with package name

easwars · 2026-07-08T05:27:18Z

+	"sync/atomic"
+)
+
+// RefCounted manages the lifecycle of a resource using atomic reference


Nit: Does the term "resource" apply here? This should be a generic utility that can be used to share any value among multiple users and ensure that the value is kept alive until there is at least one user.

I'm not aware if 'resource' has another specific meaning that I am missing , but I felt it was helpful here to distinguish it from a regular 'value'. Since Go's GC handles standard values automatically, 'resource' helps signal that this item needs explicit lifecycle management and teardown (via the onZero callback). What do you think?

easwars · 2026-07-08T05:28:45Z

+// NewRefCounted creates a new RefCounted instance wrapping the given value. The
+// provided onZero callback is executed exactly once when the reference count
+// drops to zero.
+func NewRefCounted[V any](val V, onZero func()) (*RefCounted[V], error) {


Nit: Should this docstring carry any recommendation about the type of V that makes sense here. For example, if someone stores something by value instead of by reference, it probably doesn't make much sense, right?

Right! CHanged. Let me know if it is better ?

easwars · 2026-07-08T05:29:21Z

+// drops to zero.
+func NewRefCounted[V any](val V, onZero func()) (*RefCounted[V], error) {
+	if onZero == nil {
+		return nil, fmt.Errorf("onZero callback cannot be nil")


Nit: this should also be specified in the docstring.

easwars · 2026-07-08T05:30:43Z

+// This method guarantees safe concurrent access by utilizing a CompareAndSwap
+// loop. This prevents race conditions where a concurrent decrement could drop
+// the count to zero between the read and the increment operation, which would
+// otherwise inadvertently resurrect a closed resource.


This seems like a load of implementation detail. Should this be part of the docstring or can we move it inside the method and have something more palatable to users of this package?

easwars · 2026-07-08T05:33:59Z

+}
+
+// Decrement decrements the reference count. If it drops to zero, the onZero
+// callback is executed.


Nit: Mention that the callback is executed before this method returns.

easwars · 2026-07-08T05:35:14Z

+	}
+
+	var wg sync.WaitGroup
+	wg.Add(numGoroutines)


Nit: Consider using the newly added wg.Go() instead.

easwars · 2026-07-08T05:36:07Z

+	if err == nil {
+		t.Fatalf("NewRefCounted(_, nil) succeeded, want error")
+	}
+	expectedErr := "onZero callback cannot be nil"


Nit: s/expectedErr/wantErr

Also, make it a const.

easwars · 2026-07-08T05:36:22Z

+		t.Fatalf("NewRefCounted(_, nil) succeeded, want error")
+	}
+	expectedErr := "onZero callback cannot be nil"
+	if err.Error() != expectedErr {


Combine this check with err == nil

refcounting utility

ecece78

eshitachandwani added this to the 1.83 Release milestone Jun 18, 2026

eshitachandwani added Type: Feature New features or improvements in behavior Area: xDS Includes everything xDS related, including LB policies used with xDS. labels Jun 18, 2026

eshitachandwani requested review from easwars and mbissa June 18, 2026 07:41

eshitachandwani assigned easwars and mbissa Jun 18, 2026

gemini-code-assist Bot reviewed Jun 22, 2026

View reviewed changes

add nil check for onZero callback

a55e379

easwars removed their assignment Jun 25, 2026

easwars reviewed Jul 8, 2026

View reviewed changes

easwars assigned eshitachandwani and unassigned mbissa Jul 8, 2026

update comments

ff1f329

eshitachandwani requested a review from easwars July 8, 2026 15:04

eshitachandwani assigned easwars and mbissa and unassigned eshitachandwani Jul 8, 2026

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eshitachandwani commented Jun 18, 2026

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codecov Bot commented Jun 18, 2026 •

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