From fcece3e32e54daea7ae940ad7eece0df23b60564 Mon Sep 17 00:00:00 2001
From: Juan Batiz-Benet <juan@benet.ai>
Date: Mon, 12 Jan 2015 22:14:23 -0800
Subject: [PATCH] p2p/net/swarm: dial once at a time

---
 p2p/net/swarm/simul_test.go | 43 +++++++++++++++++++++++++++++++++++++
 p2p/net/swarm/swarm.go      | 15 +++++++++----
 p2p/net/swarm/swarm_dial.go | 39 ++++++++++++++++++++++++++++-----
 3 files changed, 88 insertions(+), 9 deletions(-)

diff --git a/p2p/net/swarm/simul_test.go b/p2p/net/swarm/simul_test.go
index c87df91c3..9382cb645 100644
--- a/p2p/net/swarm/simul_test.go
+++ b/p2p/net/swarm/simul_test.go
@@ -11,6 +11,49 @@ import (
 	ma "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multiaddr"
 )
 
+func TestSimultDials(t *testing.T) {
+	// t.Skip("skipping for another test")
+
+	ctx := context.Background()
+	swarms := makeSwarms(ctx, t, 2)
+
+	// connect everyone
+	{
+		var wg sync.WaitGroup
+		connect := func(s *Swarm, dst peer.ID, addr ma.Multiaddr) {
+			// copy for other peer
+			log.Debugf("TestSimultOpen: connecting: %s --> %s (%s)", s.local, dst, addr)
+			s.peers.AddAddress(dst, addr)
+			if _, err := s.Dial(ctx, dst); err != nil {
+				t.Fatal("error swarm dialing to peer", err)
+			}
+			wg.Done()
+		}
+
+		log.Info("Connecting swarms simultaneously.")
+		for i := 0; i < 10; i++ { // connect 10x for each.
+			wg.Add(2)
+			go connect(swarms[0], swarms[1].local, swarms[1].ListenAddresses()[0])
+			go connect(swarms[1], swarms[0].local, swarms[0].ListenAddresses()[0])
+		}
+		wg.Wait()
+	}
+
+	// should still just have 1, at most 2 connections :)
+	c01l := len(swarms[0].ConnectionsToPeer(swarms[1].local))
+	if c01l > 2 {
+		t.Error("0->1 has", c01l)
+	}
+	c10l := len(swarms[1].ConnectionsToPeer(swarms[0].local))
+	if c10l > 2 {
+		t.Error("1->0 has", c10l)
+	}
+
+	for _, s := range swarms {
+		s.Close()
+	}
+}
+
 func TestSimultOpen(t *testing.T) {
 	// t.Skip("skipping for another test")
 
diff --git a/p2p/net/swarm/swarm.go b/p2p/net/swarm/swarm.go
index 8080fcde9..42511752a 100644
--- a/p2p/net/swarm/swarm.go
+++ b/p2p/net/swarm/swarm.go
@@ -4,6 +4,7 @@ package swarm
 
 import (
 	"fmt"
+	"sync"
 
 	inet "github.com/jbenet/go-ipfs/p2p/net"
 	addrutil "github.com/jbenet/go-ipfs/p2p/net/swarm/addr"
@@ -33,6 +34,11 @@ type Swarm struct {
 	peers peer.Peerstore
 	connh ConnHandler
 
+	// dialing is a channel for the current peers being dialed.
+	// this way, we dont kick off N dials simultaneously.
+	dialing   map[peer.ID]chan struct{}
+	dialingmu sync.Mutex
+
 	cg ctxgroup.ContextGroup
 }
 
@@ -49,10 +55,11 @@ func NewSwarm(ctx context.Context, listenAddrs []ma.Multiaddr,
 	}
 
 	s := &Swarm{
-		swarm: ps.NewSwarm(PSTransport),
-		local: local,
-		peers: peers,
-		cg:    ctxgroup.WithContext(ctx),
+		swarm:   ps.NewSwarm(PSTransport),
+		local:   local,
+		peers:   peers,
+		cg:      ctxgroup.WithContext(ctx),
+		dialing: map[peer.ID]chan struct{}{},
 	}
 
 	// configure Swarm
diff --git a/p2p/net/swarm/swarm_dial.go b/p2p/net/swarm/swarm_dial.go
index 96581009e..dc2e94e01 100644
--- a/p2p/net/swarm/swarm_dial.go
+++ b/p2p/net/swarm/swarm_dial.go
@@ -25,12 +25,41 @@ func (s *Swarm) Dial(ctx context.Context, p peer.ID) (*Conn, error) {
 		return nil, errors.New("Attempted connection to self!")
 	}
 
-	// check if we already have an open connection first
-	cs := s.ConnectionsToPeer(p)
-	for _, c := range cs {
-		if c != nil { // dump out the first one we find
-			return c, nil
+	for {
+		// check if we already have an open connection first
+		cs := s.ConnectionsToPeer(p)
+		for _, c := range cs {
+			if c != nil { // dump out the first one we find
+				return c, nil
+			}
 		}
+
+		// check if there's an ongoing dial to this peer
+		s.dialingmu.Lock()
+		dialDone, found := s.dialing[p]
+		if !found { // if not, set one up.
+			dialDone = make(chan struct{})
+			s.dialing[p] = dialDone
+		}
+		s.dialingmu.Unlock()
+
+		if found {
+			select {
+			case <-dialDone: // wait for that dial to finish.
+				continue // and see if it worked (loop). it may not have.
+			case <-ctx.Done():
+				return nil, ctx.Err()
+			}
+		}
+
+		// else, we're the ones dialing for others.
+		defer func() {
+			s.dialingmu.Lock()
+			delete(s.dialing, p)
+			close(dialDone)
+			s.dialingmu.Unlock()
+		}()
+		break
 	}
 
 	sk := s.peers.PrivKey(s.local)