testing: panic in AllocsPerRun if parallel tests are running

If other tests are running, AllocsPerRun's result will be inherently flaky.
Saw this with CL 630136 and #70327.

Proposed in #70464.

Fixes #70464.

Change-Id: I190afdf26bc31299f6e5e8665b4fb420ffd554ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/630137
Auto-Submit: Russ Cox <rsc@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/src/testing/testing.go b/src/testing/testing.go
index aefcb84fc8..8b0915a0ef 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -424,6 +424,11 @@ import (
 
 var initRan bool
 
+var (
+	parallelStart atomic.Int64 // number of parallel tests started
+	parallelStop  atomic.Int64 // number of parallel tests stopped
+)
+
 // Init registers testing flags. These flags are automatically registered by
 // the "go test" command before running test functions, so Init is only needed
 // when calling functions such as Benchmark without using "go test".
@@ -1536,7 +1541,6 @@ func (t *T) Parallel() {
 	if t.denyParallel {
 		panic(parallelConflict)
 	}
-	t.isParallel = true
 	if t.parent.barrier == nil {
 		// T.Parallel has no effect when fuzzing.
 		// Multiple processes may run in parallel, but only one input can run at a
@@ -1544,6 +1548,8 @@ func (t *T) Parallel() {
 		return
 	}
 
+	t.isParallel = true
+
 	// We don't want to include the time we spend waiting for serial tests
 	// in the test duration. Record the elapsed time thus far and reset the
 	// timer afterwards.
@@ -1572,6 +1578,7 @@ func (t *T) Parallel() {
 	t.signal <- true   // Release calling test.
 	<-t.parent.barrier // Wait for the parent test to complete.
 	t.tstate.waitParallel()
+	parallelStart.Add(1)
 
 	if t.chatty != nil {
 		t.chatty.Updatef(t.name, "=== CONT  %s\n", t.name)
@@ -1707,6 +1714,9 @@ func tRunner(t *T, fn func(t *T)) {
 				panic(err)
 			}
 			running.Delete(t.name)
+			if t.isParallel {
+				parallelStop.Add(1)
+			}
 			t.signal <- signal
 		}()