net/http: deflake TestCancelRequestWhenSharingConnection

The test sleeps for 1 millisecond to give the cancellation a moment
to take effect. This is flaky because the request can finish before
the cancellation of the context is seen. It's easy to verify by adding

    time.Sleep(2*time.Millisecond)

after https://github.com/golang/go/blob/0a6c4c87404ecb018faf002919e5d5db04c69ee2/src/net/http/transport.go#L2619.
With this modification, the test fails about 5 times out of 10 runs.

The fix is easy. We just need to block the handler of the second
request until this request is cancelled. I have verify that the
updated test can uncover the issue fixed by CL 257818.

Fixes #55226.

Change-Id: I81575beef1a920a2ffaa5c6a5ca70a4008bd5f94
GitHub-Last-Rev: 99cb1c2eaed7839394adbb6bbcd4950cd4bfb6f3
GitHub-Pull-Request: golang/go#56500
Reviewed-on: https://go-review.googlesource.com/c/go/+/446676
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

diff --git a/src/net/http/transport_test.go b/src/net/http/transport_test.go
index cd31141e52d9220a33417dcd856f944d4239310c..a581845516090190c47e3873c15e7e64eadb19bb 100644 (file)
--- a/src/net/http/transport_test.go
+++ b/src/net/http/transport_test.go
@@ -6530,6 +6530,9 @@ func testCancelRequestWhenSharingConnection(t *testing.T, mode testMode) {
                if !errors.Is(err, context.Canceled) {
                        t.Errorf("request 2: got err %v, want Canceled", err)
                }
+
+               // Unblock the first request.
+               close(idlec)
        }()
 
        // Wait for the second request to arrive at the server, and then cancel
@@ -6537,9 +6540,7 @@ func testCancelRequestWhenSharingConnection(t *testing.T, mode testMode) {
        r2c := <-reqc
        cancel()
 
-       // Give the cancellation a moment to take effect, and then unblock the first request.
-       time.Sleep(1 * time.Millisecond)
-       close(idlec)
+       <-idlec
 
        close(r2c)
        wg.Wait()