Golang context.WithCancel函數代碼示例

func (bs *Bitswap) connectToProviders(ctx context.Context, entries []wantlist.Entry) {

	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	// Get providers for all entries in wantlist (could take a while)
	wg := sync.WaitGroup{}
	for _, e := range entries {
		wg.Add(1)
		go func(k key.Key) {
			defer wg.Done()

			child, cancel := context.WithTimeout(ctx, providerRequestTimeout)
			defer cancel()
			providers := bs.network.FindProvidersAsync(child, k, maxProvidersPerRequest)
			for prov := range providers {
				go func(p peer.ID) {
					bs.network.ConnectTo(ctx, p)
				}(prov)
			}
		}(e.Key)
	}

	wg.Wait() // make sure all our children do finish.
}

// newKeyRoot creates a new KeyRoot for the given key, and starts up a republisher routine
// for it
func (fs *Filesystem) newKeyRoot(parent context.Context, k ci.PrivKey) (*KeyRoot, error) {
	hash, err := k.GetPublic().Hash()
	if err != nil {
		return nil, err
	}

	name := "/ipns/" + key.Key(hash).String()

	root := new(KeyRoot)
	root.key = k
	root.fs = fs
	root.name = name

	ctx, cancel := context.WithCancel(parent)
	defer cancel()

	pointsTo, err := fs.nsys.Resolve(ctx, name)
	if err != nil {
		err = namesys.InitializeKeyspace(ctx, fs.dserv, fs.nsys, fs.pins, k)
		if err != nil {
			return nil, err
		}

		pointsTo, err = fs.nsys.Resolve(ctx, name)
		if err != nil {
			return nil, err
		}
	}

	mnode, err := fs.resolver.ResolvePath(ctx, pointsTo)
	if err != nil {
		log.Errorf("Failed to retrieve value '%s' for ipns entry: %s\n", pointsTo, err)
		return nil, err
	}

	root.node = mnode

	root.repub = NewRepublisher(root, time.Millisecond*300, time.Second*3)
	go root.repub.Run(parent)

	pbn, err := ft.FromBytes(mnode.Data)
	if err != nil {
		log.Error("IPNS pointer was not unixfs node")
		return nil, err
	}

	switch pbn.GetType() {
	case ft.TDirectory:
		root.val = NewDirectory(ctx, pointsTo.String(), mnode, root, fs)
	case ft.TFile, ft.TMetadata, ft.TRaw:
		fi, err := NewFile(pointsTo.String(), mnode, root, fs)
		if err != nil {
			return nil, err
		}
		root.val = fi
	default:
		panic("unrecognized! (NYI)")
	}
	return root, nil
}

func (rp *Republisher) republishEntries(p goprocess.Process) error {
	ctx, cancel := context.WithCancel(gpctx.OnClosingContext(p))
	defer cancel()

	for id, _ := range rp.entries {
		log.Debugf("republishing ipns entry for %s", id)
		priv := rp.ps.PrivKey(id)

		// Look for it locally only
		_, ipnskey := namesys.IpnsKeysForID(id)
		p, seq, err := rp.getLastVal(ipnskey)
		if err != nil {
			if err == errNoEntry {
				continue
			}
			return err
		}

		// update record with same sequence number
		eol := time.Now().Add(rp.RecordLifetime)
		err = namesys.PutRecordToRouting(ctx, priv, p, seq, eol, rp.r, id)
		if err != nil {
			return err
		}
	}

	return nil
}

func Pin(n *core.IpfsNode, ctx context.Context, paths []string, recursive bool) ([]key.Key, error) {
	dagnodes := make([]*merkledag.Node, 0)
	for _, fpath := range paths {
		dagnode, err := core.Resolve(ctx, n, path.Path(fpath))
		if err != nil {
			return nil, fmt.Errorf("pin: %s", err)
		}
		dagnodes = append(dagnodes, dagnode)
	}

	var out []key.Key
	for _, dagnode := range dagnodes {
		k, err := dagnode.Key()
		if err != nil {
			return nil, err
		}

		ctx, cancel := context.WithCancel(ctx)
		defer cancel()
		err = n.Pinning.Pin(ctx, dagnode, recursive)
		if err != nil {
			return nil, fmt.Errorf("pin: %s", err)
		}
		out = append(out, k)
	}

	err := n.Pinning.Flush()
	if err != nil {
		return nil, err
	}

	return out, nil
}

func Unpin(n *core.IpfsNode, ctx context.Context, paths []string, recursive bool) ([]key.Key, error) {

	dagnodes := make([]*merkledag.Node, 0)
	for _, fpath := range paths {
		dagnode, err := core.Resolve(ctx, n, path.Path(fpath))
		if err != nil {
			return nil, err
		}
		dagnodes = append(dagnodes, dagnode)
	}

	var unpinned []key.Key
	for _, dagnode := range dagnodes {
		k, _ := dagnode.Key()

		ctx, cancel := context.WithCancel(ctx)
		defer cancel()
		err := n.Pinning.Unpin(ctx, k, recursive)
		if err != nil {
			return nil, err
		}
		unpinned = append(unpinned, k)
	}

	err := n.Pinning.Flush()
	if err != nil {
		return nil, err
	}
	return unpinned, nil
}

func (dm *DagModifier) readPrep() error {
	err := dm.Sync()
	if err != nil {
		return err
	}

	if dm.read == nil {
		ctx, cancel := context.WithCancel(dm.ctx)
		dr, err := uio.NewDagReader(ctx, dm.curNode, dm.dagserv)
		if err != nil {
			return err
		}

		i, err := dr.Seek(int64(dm.curWrOff), os.SEEK_SET)
		if err != nil {
			return err
		}

		if i != int64(dm.curWrOff) {
			return ErrSeekFail
		}

		dm.readCancel = cancel
		dm.read = dr
	}

	return nil
}

func (bs *Bitswap) rebroadcastWorker(parent context.Context) {
	ctx, cancel := context.WithCancel(parent)
	defer cancel()

	broadcastSignal := time.NewTicker(rebroadcastDelay.Get())
	defer broadcastSignal.Stop()

	tick := time.NewTicker(10 * time.Second)
	defer tick.Stop()

	for {
		log.Event(ctx, "Bitswap.Rebroadcast.idle")
		select {
		case <-tick.C:
			n := bs.wm.wl.Len()
			if n > 0 {
				log.Debug(n, "keys in bitswap wantlist")
			}
		case <-broadcastSignal.C: // resend unfulfilled wantlist keys
			log.Event(ctx, "Bitswap.Rebroadcast.active")
			entries := bs.wm.wl.Entries()
			if len(entries) > 0 {
				bs.connectToProviders(ctx, entries)
			}
		case <-parent.Done():
			return
		}
	}
}

// WithDeadlineFraction returns a Context with a fraction of the
// original context's timeout. This is useful in sequential pipelines
// of work, where one might try options and fall back to others
// depending on the time available, or failure to respond. For example:
//
//  // getPicture returns a picture from our encrypted database
//  // we have a pipeline of multiple steps. we need to:
//  // - get the data from a database
//  // - decrypt it
//  // - apply many transforms
//  //
//  // we **know** that each step takes increasingly more time.
//  // The transforms are much more expensive than decryption, and
//  // decryption is more expensive than the database lookup.
//  // If our database takes too long (i.e. >0.2 of available time),
//  // there's no use in continuing.
//  func getPicture(ctx context.Context, key string) ([]byte, error) {
//    // fractional timeout contexts to the rescue!
//
//    // try the database with 0.2 of remaining time.
//    ctx1, _ := ctxext.WithDeadlineFraction(ctx, 0.2)
//    val, err := db.Get(ctx1, key)
//    if err != nil {
//      return nil, err
//    }
//
//    // try decryption with 0.3 of remaining time.
//    ctx2, _ := ctxext.WithDeadlineFraction(ctx, 0.3)
//    if val, err = decryptor.Decrypt(ctx2, val); err != nil {
//      return nil, err
//    }
//
//    // try transforms with all remaining time. hopefully it's enough!
//    return transformer.Transform(ctx, val)
//  }
//
//
func WithDeadlineFraction(ctx context.Context, fraction float64) (
	context.Context, context.CancelFunc) {

	d, found := ctx.Deadline()
	if !found { // no deadline
		return context.WithCancel(ctx)
	}

	left := d.Sub(time.Now())
	if left < 0 { // already passed...
		return context.WithCancel(ctx)
	}

	left = time.Duration(float64(left) * fraction)
	return context.WithTimeout(ctx, left)
}

// WithProcessClosing returns a context.Context derived from ctx that
// is cancelled as p is Closing (after: <-p.Closing()). It is simply:
//
//   func WithProcessClosing(ctx context.Context, p goprocess.Process) context.Context {
//     ctx, cancel := context.WithCancel(ctx)
//     go func() {
//       <-p.Closing()
//       cancel()
//     }()
//     return ctx
//   }
//
func WithProcessClosing(ctx context.Context, p goprocess.Process) context.Context {
	ctx, cancel := context.WithCancel(ctx)
	go func() {
		<-p.Closing()
		cancel()
	}()
	return ctx
}

func addNode(n *core.IpfsNode, node *merkledag.Node) error {
	if err := n.DAG.AddRecursive(node); err != nil { // add the file to the graph + local storage
		return err
	}
	ctx, cancel := context.WithCancel(n.Context())
	defer cancel()
	err := n.Pinning.Pin(ctx, node, true) // ensure we keep it
	return err
}

// Run runs the query at hand. pass in a list of peers to use first.
func (q *dhtQuery) Run(ctx context.Context, peers []peer.ID) (*dhtQueryResult, error) {
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	default:
	}

	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	runner := newQueryRunner(q)
	return runner.Run(ctx, peers)
}

func NewDataFileReader(ctx context.Context, n *mdag.Node, pb *ftpb.Data, serv mdag.DAGService) *DagReader {
	fctx, cancel := context.WithCancel(ctx)
	promises := serv.GetDAG(fctx, n)
	return &DagReader{
		node:     n,
		serv:     serv,
		buf:      NewRSNCFromBytes(pb.GetData()),
		promises: promises,
		ctx:      fctx,
		cancel:   cancel,
		pbdata:   pb,
	}
}

func get(path, outFile string) error {
	start := time.Now()
	ctx, cancel := context.WithCancel(context.Background())
	node, err := core.NewNode(ctx, &core.BuildCfg{
		Online: true,
	})
	if err != nil {
		return fmt.Errorf("ipfs NewNode() failed: %s", err)
	}

	err = node.Bootstrap(core.DefaultBootstrapConfig)
	if err != nil {
		return fmt.Errorf("node Bootstrap() failed: %s", err)
	}

	fmt.Fprintf(os.Stderr, "IPFS Node bootstrapping (took %v)\n", time.Since(start))

	// Cancel the ipfs node context if the process gets interrupted or killed.
	go func() {
		interrupts := make(chan os.Signal, 1)
		signal.Notify(interrupts, os.Interrupt, os.Kill)
		<-interrupts
		cancel()
	}()

	reader, length, err := cat(node.Context(), node, path)
	if err != nil {
		return fmt.Errorf("cat failed: %s", err)
	}

	file, err := os.Create(outFile)
	if err != nil {
		return fmt.Errorf("Creating output file %q failed: %s", outFile, err)
	}

	bar := pb.New(int(length)).SetUnits(pb.U_BYTES)
	bar.Output = os.Stderr
	bar.ShowSpeed = false
	bar.Start()
	writer := io.MultiWriter(file, bar)

	if _, err := io.Copy(writer, reader); err != nil {
		return fmt.Errorf("copy failed: %s", err)
	}

	bar.Finish()

	fmt.Fprintf(os.Stderr, "Wrote %q to %q (%s) (took %v)\n", path, outFile,
		humanize.Bytes(length), time.Since(start))
	return nil
}

// PutValue adds value corresponding to given Key.
// This is the top level "Store" operation of the DHT
func (dht *IpfsDHT) PutValue(ctx context.Context, key key.Key, value []byte) error {
	log.Debugf("PutValue %s", key)
	sk, err := dht.getOwnPrivateKey()
	if err != nil {
		return err
	}

	sign, err := dht.Validator.IsSigned(key)
	if err != nil {
		return err
	}

	rec, err := record.MakePutRecord(sk, key, value, sign)
	if err != nil {
		log.Debug("Creation of record failed!")
		return err
	}

	err = dht.putLocal(key, rec)
	if err != nil {
		return err
	}

	pchan, err := dht.GetClosestPeers(ctx, key)
	if err != nil {
		return err
	}

	wg := sync.WaitGroup{}
	for p := range pchan {
		wg.Add(1)
		go func(p peer.ID) {
			ctx, cancel := context.WithCancel(ctx)
			defer cancel()
			defer wg.Done()
			notif.PublishQueryEvent(ctx, &notif.QueryEvent{
				Type: notif.Value,
				ID:   p,
			})

			err := dht.putValueToPeer(ctx, p, key, rec)
			if err != nil {
				log.Debugf("failed putting value to peer: %s", err)
			}
		}(p)
	}
	wg.Wait()
	return nil
}

func GarbageCollect(n *core.IpfsNode, ctx context.Context) error {
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel() // in case error occurs during operation
	keychan, err := n.Blockstore.AllKeysChan(ctx)
	if err != nil {
		return err
	}
	for k := range keychan { // rely on AllKeysChan to close chan
		if !n.Pinning.IsPinned(k) {
			err := n.Blockstore.DeleteBlock(k)
			if err != nil {
				return err
			}
		}
	}
	return nil
}