runtime/race: test that close synchronizes with read

Add a test to ensure that the race detector sees that closing a
channel synchronizes with a read from that channel.
This test case failed when CL 181543 was in the tree.
CL 181543 was reverted in CL 216158; this adds a test to make
sure that we don't re-introduce the problem at a later date.

For #32529
For #36714

Change-Id: I5a40f744c67c3f8191d6ad822710c180880a7375
Reviewed-on: https://go-review.googlesource.com/c/go/+/216099
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

diff --git a/src/runtime/race/testdata/chan_test.go b/src/runtime/race/testdata/chan_test.go
index 60e55ed66a4b0542864d0fc6df65447791336348..3e57b8221c7d253dad7162ca8a7a17cb8660dad2 100644 (file)
--- a/src/runtime/race/testdata/chan_test.go
+++ b/src/runtime/race/testdata/chan_test.go
@@ -737,3 +737,29 @@ func TestNoRaceBlockedSelectSendSync(t *testing.T) {
        case <-make(chan int):
        }
 }
+
+// Test that close synchronizes with a read from the empty closed channel.
+// See https://golang.org/issue/36714.
+func TestNoRaceCloseHappensBeforeRead(t *testing.T) {
+       for i := 0; i < 100; i++ {
+               var loc int
+               var write = make(chan struct{})
+               var read = make(chan struct{})
+
+               go func() {
+                       select {
+                       case <-write:
+                               _ = loc
+                       default:
+                       }
+                       close(read)
+               }()
+
+               go func() {
+                       loc = 1
+                       close(write)
+               }()
+
+               <-read
+       }
+}