simulate semaphore contention, test

Signed-off-by: Tim Vaillancourt <[email protected]>

go/vt/topo/stats_conn_test.go

@@ -184,18 +184,33 @@ func (st *fakeConn) IsReadOnly() bool {
 	return st.readOnly
 }
 
+// createSemaphoreContention simulates semaphore contention on the test read semaphore.
+func createSemaphoreContention(ctx context.Context, duration time.Duration) {
+	if err := testStatsConnReadSem.Acquire(ctx, 1); err != nil {
+		panic(err)
+	}
+	defer testStatsConnReadSem.Release(1)
+	time.Sleep(duration)
+}
+
 // TestStatsConnTopoListDir emits stats on ListDir
 func TestStatsConnTopoListDir(t *testing.T) {
 	conn := &fakeConn{}
 	statsConn := NewStatsConn("global", conn, testStatsConnReadSem)
 	ctx := context.Background()
 
+	go createSemaphoreContention(ctx, 100*time.Millisecond)
 	statsConn.ListDir(ctx, "", true)
 	timingCounts := topoStatsConnTimings.Counts()["ListDir.global"]
 	if got, want := timingCounts, int64(1); got != want {
 		t.Errorf("stats were not properly recorded: got = %d, want = %d", got, want)
 	}
 
+	waitTimingsCounts := topoStatsConnReadWaitTimings.Counts()["ListDir.global"]
+	if got := waitTimingsCounts; got != 1 {
+		t.Errorf("stats were not properly recorded: got = %d, want = 1", got)
+	}
+
 	// error is zero before getting an error
 	errorCount := topoStatsConnErrors.Counts()["ListDir.global"]
 	if got, want := errorCount, int64(0); got != want {
@@ -271,12 +286,18 @@ func TestStatsConnTopoGet(t *testing.T) {
 	statsConn := NewStatsConn("global", conn, testStatsConnReadSem)
 	ctx := context.Background()
 
+	go createSemaphoreContention(ctx, time.Millisecond*100)
 	statsConn.Get(ctx, "")
 	timingCounts := topoStatsConnTimings.Counts()["Get.global"]
 	if got, want := timingCounts, int64(1); got != want {
 		t.Errorf("stats were not properly recorded: got = %d, want = %d", got, want)
 	}
 
+	waitTimingsCounts := topoStatsConnReadWaitTimings.Counts()["Get.global"]
+	if got := waitTimingsCounts; got != 1 {
+		t.Errorf("stats were not properly recorded: got = %d, want = 1", got)
+	}
+
 	// error is zero before getting an error
 	errorCount := topoStatsConnErrors.Counts()["Get.global"]
 	if got, want := errorCount, int64(0); got != want {