sync: only check for successful PopHeads in long mode

In TestPoolDequeue it's surprisingly common for the queue to stay
nearly empty the whole time and for a racing PopTail to happen in the
window between the producer doing a PushHead and doing a PopHead. In
short mode, there are only 100 PopTail attempts. On linux/amd64, it's
not uncommon for this to fail 50% of the time. On linux/arm64, it's
not uncommon for this to fail 100% of the time, causing the test to
fail.

This CL fixes this by only checking for a successful PopTail in long
mode. Long mode makes 200,000 PopTail attempts, and has never been
observed to fail.

Fixes #31422.

Change-Id: If464d55eb94fcb0b8d78fbc441d35be9f056a290
Reviewed-on: https://go-review.googlesource.com/c/go/+/183981
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

diff --git a/src/sync/pool_test.go b/src/sync/pool_test.go
index 814c4a6812018abb288f3f52f2403bcc99ccddc1..ad98350b2bfa4e9c28306b21f5f20ae9b882b0a9 100644 (file)
--- a/src/sync/pool_test.go
+++ b/src/sync/pool_test.go
@@ -236,10 +236,12 @@ func testPoolDequeue(t *testing.T, d PoolDequeue) {
                        t.Errorf("expected have[%d] = 1, got %d", i, count)
                }
        }
-       if nPopHead == 0 {
-               // In theory it's possible in a valid schedule for
-               // popHead to never succeed, but in practice it almost
-               // always succeeds, so this is unlikely to flake.
+       // Check that at least some PopHeads succeeded. We skip this
+       // check in short mode because it's common enough that the
+       // queue will stay nearly empty all the time and a PopTail
+       // will happen during the window between every PushHead and
+       // PopHead.
+       if !testing.Short() && nPopHead == 0 {
                t.Errorf("popHead never succeeded")
        }
 }