From 68bc0d84e9dd74a02472bfff744e0650b4b1653c Mon Sep 17 00:00:00 2001 From: Damien Neil Date: Thu, 15 May 2025 11:03:15 -0700 Subject: encoding/json: avoid supurious synctest deadlock detection Use a sync.OnceValue rather than a sync.WaitGroup to coordinate access to encoderCache entries. The OnceValue better expresses the intent of the code (we want to initialize the cache entry only once). However, the motivation for this change is to avoid testing/synctest incorrectly reporting a deadlock when multiple bubbles call Marshal at the same time. Goroutines blocked on WaitGroup.Wait are "durably blocked", causing confusion when a goroutine in one bubble Waits for a goroutine in a different bubble. Goroutines blocked on OnceValue are not durably blocked, avoiding the problem. Fixes #73733 For #67434 Change-Id: I81cddda80af67cf5c280fd4327620bc37e7a6fe6 Reviewed-on: https://go-review.googlesource.com/c/go/+/673335 Auto-Submit: Damien Neil Reviewed-by: Michael Pratt LUCI-TryBot-Result: Go LUCI --- src/encoding/json/v2_encode_test.go | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'src/encoding/json/v2_encode_test.go') diff --git a/src/encoding/json/v2_encode_test.go b/src/encoding/json/v2_encode_test.go index 16e8d01218..11c5218649 100644 --- a/src/encoding/json/v2_encode_test.go +++ b/src/encoding/json/v2_encode_test.go @@ -16,7 +16,9 @@ import ( "regexp" "runtime/debug" "strconv" + "sync" "testing" + "testing/synctest" "time" ) @@ -1408,3 +1410,21 @@ func TestIssue63379(t *testing.T) { } } } + +// Issue #73733: encoding/json used a WaitGroup to coordinate access to cache entries. +// Since WaitGroup.Wait is durably blocking, this caused apparent deadlocks when +// multiple bubbles called json.Marshal at the same time. +func TestSynctestMarshal(t *testing.T) { + var wg sync.WaitGroup + for range 5 { + wg.Go(func() { + synctest.Test(t, func(t *testing.T) { + _, err := Marshal([]string{}) + if err != nil { + t.Errorf("Marshal: %v", err) + } + }) + }) + } + wg.Wait() +} -- cgit v1.3