package swarm import ( "context" "sync" "github.com/libp2p/go-libp2p/core/network" "github.com/libp2p/go-libp2p/core/peer" ) // dialWorkerFunc is used by dialSync to spawn a new dial worker type dialWorkerFunc func(peer.ID, <-chan dialRequest) // newDialSync constructs a new dialSync func newDialSync(worker dialWorkerFunc) *dialSync { return &dialSync{ dials: make(map[peer.ID]*activeDial), dialWorker: worker, } } // dialSync is a dial synchronization helper that ensures that at most one dial // to any given peer is active at any given time. type dialSync struct { mutex sync.Mutex dials map[peer.ID]*activeDial dialWorker dialWorkerFunc } type activeDial struct { refCnt int ctx context.Context cancel func() reqch chan dialRequest } func (ad *activeDial) close() { ad.cancel() close(ad.reqch) } func (ad *activeDial) dial(ctx context.Context) (*Conn, error) { dialCtx := ad.ctx if forceDirect, reason := network.GetForceDirectDial(ctx); forceDirect { dialCtx = network.WithForceDirectDial(dialCtx, reason) } if simConnect, isClient, reason := network.GetSimultaneousConnect(ctx); simConnect { dialCtx = network.WithSimultaneousConnect(dialCtx, isClient, reason) } resch := make(chan dialResponse, 1) select { case ad.reqch <- dialRequest{ctx: dialCtx, resch: resch}: case <-ctx.Done(): return nil, ctx.Err() } select { case res := <-resch: return res.conn, res.err case <-ctx.Done(): return nil, ctx.Err() } } func (ds *dialSync) getActiveDial(p peer.ID) (*activeDial, error) { ds.mutex.Lock() defer ds.mutex.Unlock() actd, ok := ds.dials[p] if !ok { // This code intentionally uses the background context. Otherwise, if the first call // to Dial is canceled, subsequent dial calls will also be canceled. ctx, cancel := context.WithCancel(context.Background()) actd = &activeDial{ ctx: ctx, cancel: cancel, reqch: make(chan dialRequest), } go ds.dialWorker(p, actd.reqch) ds.dials[p] = actd } // increase ref count before dropping mutex actd.refCnt++ return actd, nil } // Dial initiates a dial to the given peer if there are none in progress // then waits for the dial to that peer to complete. func (ds *dialSync) Dial(ctx context.Context, p peer.ID) (*Conn, error) { ad, err := ds.getActiveDial(p) if err != nil { return nil, err } defer func() { ds.mutex.Lock() defer ds.mutex.Unlock() ad.refCnt-- if ad.refCnt == 0 { ad.close() delete(ds.dials, p) } }() return ad.dial(ctx) }