net: synchronize instead of sleeping in TestDialParallelSpuriousConnection

The arbitrary sleep in this test is empirically not always long enough
on slower builders. However, we know the exact number of connections
that should be dialed: we can wait on that number in the dial hook
instead.

Fixes #34495

Change-Id: I538244ceb75a80271a724304b993309482bd5b41
Reviewed-on: https://go-review.googlesource.com/c/go/+/375694
Trust: Bryan Mills <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: Bryan C. Mills

src/net/dial_test.go

@@ -429,22 +429,23 @@ func TestDialParallelSpuriousConnection(t *testing.T) {
 		readDeadline = time.Now().Add(5 * time.Second)
 	}
 
-	var wg sync.WaitGroup
-	wg.Add(2)
+	var closed sync.WaitGroup
+	closed.Add(2)
 	handler := func(dss *dualStackServer, ln Listener) {
 		// Accept one connection per address.
 		c, err := ln.Accept()
 		if err != nil {
 			t.Fatal(err)
 		}
+
 		// The client should close itself, without sending data.
 		c.SetReadDeadline(readDeadline)
 		var b [1]byte
 		if _, err := c.Read(b[:]); err != io.EOF {
 			t.Errorf("got %v; want %v", err, io.EOF)
 		}
 		c.Close()
-		wg.Done()
+		closed.Done()
 	}
 	dss, err := newDualStackServer()
 	if err != nil {
@@ -457,12 +458,16 @@ func TestDialParallelSpuriousConnection(t *testing.T) {
 
 	const fallbackDelay = 100 * time.Millisecond
 
+	var dialing sync.WaitGroup
+	dialing.Add(2)
 	origTestHookDialTCP := testHookDialTCP
 	defer func() { testHookDialTCP = origTestHookDialTCP }()
 	testHookDialTCP = func(ctx context.Context, net string, laddr, raddr *TCPAddr) (*TCPConn, error) {
-		// Sleep long enough for Happy Eyeballs to kick in, and inhibit cancellation.
+		// Wait until Happy Eyeballs kicks in and both connections are dialing,
+		// and inhibit cancellation.
 		// This forces dialParallel to juggle two successful connections.
-		time.Sleep(fallbackDelay * 2)
+		dialing.Done()
+		dialing.Wait()
 
 		// Now ignore the provided context (which will be canceled) and use a
 		// different one to make sure this completes with a valid connection,
@@ -496,7 +501,7 @@ func TestDialParallelSpuriousConnection(t *testing.T) {
 	c.Close()
 
 	// The server should've seen both connections.
-	wg.Wait()
+	closed.Wait()
 }
 
 func TestDialerPartialDeadline(t *testing.T) {