close return channel when we're done

Benchmark results:

```
BenchmarkSwitchBroadcast-2         30000             71275 ns/op
--- BENCH: BenchmarkSwitchBroadcast-2
        switch_test.go:339: success: 1, failure: 0
        switch_test.go:339: success: 100, failure: 0
        switch_test.go:339: success: 10000, failure: 0
        switch_test.go:339: success: 30000, failure: 0
```

p2p/conn/secret_connection_test.go

@@ -4,7 +4,7 @@ import (
 	"io"
 	"testing"
 
-	"github.com/tendermint/go-crypto"
+	crypto "github.com/tendermint/go-crypto"
 	cmn "github.com/tendermint/tmlibs/common"
 )
 

p2p/switch.go

@@ -5,6 +5,7 @@ import (
 	"math"
 	"math/rand"
 	"net"
+	"sync"
 	"time"
 
 	"github.com/pkg/errors"
@@ -200,20 +201,28 @@ func (sw *Switch) OnStop() {
 //---------------------------------------------------------------------
 // Peers
 
-// Broadcast runs a go routine for each attempted send, which will block
-// trying to send for defaultSendTimeoutSeconds. Returns a channel
-// which receives success values for each attempted send (false if times out).
+// Broadcast runs a go routine for each attempted send, which will block trying
+// to send for defaultSendTimeoutSeconds. Returns a channel which receives
+// success values for each attempted send (false if times out). Channel will be
+// closed once msg send to all peers.
+//
 // NOTE: Broadcast uses goroutines, so order of broadcast may not be preserved.
-// TODO: Something more intelligent.
 func (sw *Switch) Broadcast(chID byte, msg interface{}) chan bool {
 	successChan := make(chan bool, len(sw.peers.List()))
 	sw.Logger.Debug("Broadcast", "channel", chID, "msg", msg)
+	var wg sync.WaitGroup
 	for _, peer := range sw.peers.List() {
+		wg.Add(1)
 		go func(peer Peer) {
+			defer wg.Done()
 			success := peer.Send(chID, msg)
 			successChan <- success
 		}(peer)
 	}
+	go func() {
+		wg.Wait()
+		close(successChan)
+	}()
 	return successChan
 }
 

p2p/switch_test.go

@@ -300,10 +300,8 @@ func TestSwitchFullConnectivity(t *testing.T) {
 	}
 }
 
-func BenchmarkSwitches(b *testing.B) {
-	b.StopTimer()
-
-	s1, s2 := MakeSwitchPair(b, func(i int, sw *Switch) *Switch {
+func BenchmarkSwitchBroadcast(b *testing.B) {
+	s1, s2 := makeSwitchPair(b, func(i int, sw *Switch) *Switch {
 		// Make bar reactors of bar channels each
 		sw.AddReactor("foo", NewTestReactor([]*conn.ChannelDescriptor{
 			{ID: byte(0x00), Priority: 10},
@@ -320,7 +318,8 @@ func BenchmarkSwitches(b *testing.B) {
 
 	// Allow time for goroutines to boot up
 	time.Sleep(1 * time.Second)
-	b.StartTimer()
+
+	b.ResetTimer()
 
 	numSuccess, numFailure := 0, 0
 
@@ -338,7 +337,4 @@ func BenchmarkSwitches(b *testing.B) {
 	}
 
 	b.Logf("success: %v, failure: %v", numSuccess, numFailure)
-
-	// Allow everything to flush before stopping switches & closing connections.
-	b.StopTimer()
 }