add semaphore to control push/delta concurrency

This avoids stream storms that can clog the transient scope when we have a largish number of peers.

Author: vyzo

p2p/protocol/identify/id.go

@@ -43,6 +43,8 @@ const LibP2PVersion = "ipfs/0.1.0"
 
 const ServiceName = "libp2p.identify"
 
+const maxPushConcurrency = 32
+
 // StreamReadTimeout is the read timeout on all incoming Identify family streams.
 var StreamReadTimeout = 60 * time.Second
 
@@ -129,6 +131,10 @@ type idService struct {
 
 	addPeerHandlerCh chan addPeerHandlerReq
 	rmPeerHandlerCh  chan rmPeerHandlerReq
+
+	// pushSemaphore limits the push/delta concurrency to avoid storms
+	// that clog the transient scope.
+	pushSemaphore chan struct{}
 }
 
 // NewIDService constructs a new *idService and activates it by
@@ -154,6 +160,8 @@ func NewIDService(h host.Host, opts ...Option) (*idService, error) {
 
 		addPeerHandlerCh: make(chan addPeerHandlerReq),
 		rmPeerHandlerCh:  make(chan rmPeerHandlerReq),
+
+		pushSemaphore: make(chan struct{}, maxPushConcurrency),
 	}
 	s.ctx, s.ctxCancel = context.WithCancel(context.Background())
 

p2p/protocol/identify/peer_loop.go

@@ -179,6 +179,11 @@ func (ph *peerHandler) openStream(ctx context.Context, protos []string) (network
 		return nil, errProtocolNotSupported
 	}
 
+	ph.ids.pushSemaphore <- struct{}{}
+	defer func() {
+		<-ph.ids.pushSemaphore
+	}()
+
 	// negotiate a stream without opening a new connection as we "should" already have a connection.
 	ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
 	defer cancel()