runtime, internal/synctest, sync: associate WaitGroups with bubbles

Add support to internal/synctest for managing associations between
arbitrary pointers and synctest bubbles. (Implemented internally to
the runtime package by attaching a special to the pointer.)

Associate WaitGroups with bubbles.
Since WaitGroups don't have a constructor,
perform the association when Add is called.
All Add calls must be made from within the same bubble,
or outside any bubble.

When a bubbled goroutine calls WaitGroup.Wait,
the wait is durably blocking iff the WaitGroup is associated
with the current bubble.

Change-Id: I77e2701e734ac2fa2b32b28d5b0c853b7b2825c9
Reviewed-on: https://go-review.googlesource.com/c/go/+/676656
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Damien Neil <dneil@google.com>

1 files changed, 14 insertions, 12 deletions

diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 94ab87f6db..cd40586bc2 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -1096,6 +1096,7 @@ const (
 	waitReasonSynctestChanReceive                     // "chan receive (synctest)"
 	waitReasonSynctestChanSend                        // "chan send (synctest)"
 	waitReasonSynctestSelect                          // "select (synctest)"
+	waitReasonSynctestWaitGroupWait                   // "sync.WaitGroup.Wait (synctest)"
 	waitReasonCleanupWait                             // "cleanup wait"
 )
 
@@ -1145,6 +1146,7 @@ var waitReasonStrings = [...]string{
 	waitReasonSynctestChanReceive:   "chan receive (synctest)",
 	waitReasonSynctestChanSend:      "chan send (synctest)",
 	waitReasonSynctestSelect:        "select (synctest)",
+	waitReasonSynctestWaitGroupWait: "sync.WaitGroup.Wait (synctest)",
 	waitReasonCleanupWait:           "cleanup wait",
 }
 
@@ -1190,18 +1192,18 @@ func (w waitReason) isIdleInSynctest() bool {
 
 // isIdleInSynctest indicates that a goroutine is considered idle by synctest.Wait.
 var isIdleInSynctest = [len(waitReasonStrings)]bool{
-	waitReasonChanReceiveNilChan:  true,
-	waitReasonChanSendNilChan:     true,
-	waitReasonSelectNoCases:       true,
-	waitReasonSleep:               true,
-	waitReasonSyncCondWait:        true,
-	waitReasonSyncWaitGroupWait:   true,
-	waitReasonCoroutine:           true,
-	waitReasonSynctestRun:         true,
-	waitReasonSynctestWait:        true,
-	waitReasonSynctestChanReceive: true,
-	waitReasonSynctestChanSend:    true,
-	waitReasonSynctestSelect:      true,
+	waitReasonChanReceiveNilChan:    true,
+	waitReasonChanSendNilChan:       true,
+	waitReasonSelectNoCases:         true,
+	waitReasonSleep:                 true,
+	waitReasonSyncCondWait:          true,
+	waitReasonSynctestWaitGroupWait: true,
+	waitReasonCoroutine:             true,
+	waitReasonSynctestRun:           true,
+	waitReasonSynctestWait:          true,
+	waitReasonSynctestChanReceive:   true,
+	waitReasonSynctestChanSend:      true,
+	waitReasonSynctestSelect:        true,
 }
 
 var (