Golang Context.Err方法代码示例

// GetBlocks returns a channel where the caller may receive blocks that
// correspond to the provided |keys|. Returns an error if BitSwap is unable to
// begin this request within the deadline enforced by the context.
//
// NB: Your request remains open until the context expires. To conserve
// resources, provide a context with a reasonably short deadline (ie. not one
// that lasts throughout the lifetime of the server)
func (bs *Bitswap) GetBlocks(ctx context.Context, keys []key.Key) (<-chan *blocks.Block, error) {
	select {
	case <-bs.process.Closing():
		return nil, errors.New("bitswap is closed")
	default:
	}
	promise := bs.notifications.Subscribe(ctx, keys...)

	for _, k := range keys {
		log.Event(ctx, "Bitswap.GetBlockRequest.Start", &k)
	}

	bs.wm.WantBlocks(keys)

	req := &blockRequest{
		keys: keys,
		ctx:  ctx,
	}
	select {
	case bs.findKeys <- req:
		return promise, nil
	case <-ctx.Done():
		return nil, ctx.Err()
	}
}

func readMsgCtx(ctx context.Context, r msgio.Reader, p proto.Message) ([]byte, error) {
	var msg []byte

	// read in a goroutine so we can exit when our context is cancelled.
	done := make(chan error)
	go func() {
		var err error
		msg, err = r.ReadMsg()
		select {
		case done <- err:
		case <-ctx.Done():
		}
	}()

	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case e := <-done:
		if e != nil {
			return nil, e
		}
	}

	return msg, proto.Unmarshal(msg, p)
}

// gatedDialAttempt is an attempt to dial a node. It is gated by the swarm's
// dial synchronization systems: dialsync and dialbackoff.
func (s *Swarm) gatedDialAttempt(ctx context.Context, p peer.ID) (*Conn, error) {
	var logdial = lgbl.Dial("swarm", s.LocalPeer(), p, nil, nil)
	defer log.EventBegin(ctx, "swarmDialAttemptSync", logdial).Done()

	// check if we already have an open connection first
	conn := s.bestConnectionToPeer(p)
	if conn != nil {
		return conn, nil
	}

	// check if there's an ongoing dial to this peer
	if ok, wait := s.dsync.Lock(p); ok {
		// ok, we have been charged to dial! let's do it.
		// if it succeeds, dial will add the conn to the swarm itself.

		defer log.EventBegin(ctx, "swarmDialAttemptStart", logdial).Done()
		ctxT, cancel := context.WithTimeout(ctx, s.dialT)
		conn, err := s.dial(ctxT, p)
		cancel()
		s.dsync.Unlock(p)
		log.Debugf("dial end %s", conn)
		if err != nil {
			log.Event(ctx, "swarmDialBackoffAdd", logdial)
			s.backf.AddBackoff(p) // let others know to backoff

			// ok, we failed. try again. (if loop is done, our error is output)
			return nil, fmt.Errorf("dial attempt failed: %s", err)
		}
		log.Event(ctx, "swarmDialBackoffClear", logdial)
		s.backf.Clear(p) // okay, no longer need to backoff
		return conn, nil

	} else {
		// we did not dial. we must wait for someone else to dial.

		// check whether we should backoff first...
		if s.backf.Backoff(p) {
			log.Event(ctx, "swarmDialBackoff", logdial)
			return nil, ErrDialBackoff
		}

		defer log.EventBegin(ctx, "swarmDialWait", logdial).Done()
		select {
		case <-wait: // wait for that other dial to finish.

			// see if it worked, OR we got an incoming dial in the meantime...
			conn := s.bestConnectionToPeer(p)
			if conn != nil {
				return conn, nil
			}
			return nil, ErrDialFailed
		case <-ctx.Done(): // or we may have to bail...
			return nil, ctx.Err()
		}
	}
}

// Fsync flushes the content in the file to disk, but does not
// update the dag tree internally
func (fi *File) Fsync(ctx context.Context, req *fuse.FsyncRequest) error {
	errs := make(chan error, 1)
	go func() {
		errs <- fi.fi.Sync()
	}()
	select {
	case err := <-errs:
		return err
	case <-ctx.Done():
		return ctx.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 EnumerateChildrenAsync(ctx context.Context, ds DAGService, root *Node, set key.KeySet) error {
	toprocess := make(chan []key.Key, 8)
	nodes := make(chan *Node, 8)
	errs := make(chan error, 1)

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

	go fetchNodes(ctx, ds, toprocess, nodes, errs)

	nodes <- root
	live := 1

	for {
		select {
		case nd, ok := <-nodes:
			if !ok {
				return nil
			}
			// a node has been fetched
			live--

			var keys []key.Key
			for _, lnk := range nd.Links {
				k := key.Key(lnk.Hash)
				if !set.Has(k) {
					set.Add(k)
					live++
					keys = append(keys, k)
				}
			}

			if live == 0 {
				return nil
			}

			if len(keys) > 0 {
				select {
				case toprocess <- keys:
				case <-ctx.Done():
					return ctx.Err()
				}
			}
		case err := <-errs:
			return err
		case <-ctx.Done():
			return ctx.Err()
		}
	}
}

func (np *nodePromise) Get(ctx context.Context) (*Node, error) {
	if np.cache != nil {
		return np.cache, nil
	}

	select {
	case blk := <-np.recv:
		np.cache = blk
	case <-np.ctx.Done():
		return nil, np.ctx.Err()
	case <-ctx.Done():
		return nil, ctx.Err()
	}
	return np.cache, nil
}

func ContextDo(ctx context.Context, f func() error) error {

	ch := make(chan error)

	go func() {
		select {
		case <-ctx.Done():
		case ch <- f():
		}
	}()
	select {
	case <-ctx.Done():
		return ctx.Err()
	case val := <-ch:
		return val
	}
	return nil
}

// resolveOnce implements resolver.
// TXT records for a given domain name should contain a b58
// encoded multihash.
func (r *DNSResolver) resolveOnce(ctx context.Context, name string) (path.Path, error) {
	segments := strings.SplitN(name, "/", 2)
	domain := segments[0]

	if !isd.IsDomain(domain) {
		return "", errors.New("not a valid domain name")
	}
	log.Infof("DNSResolver resolving %s", domain)

	rootChan := make(chan lookupRes, 1)
	go workDomain(r, domain, rootChan)

	subChan := make(chan lookupRes, 1)
	go workDomain(r, "_dnslink."+domain, subChan)

	var subRes lookupRes
	select {
	case subRes = <-subChan:
	case <-ctx.Done():
		return "", ctx.Err()
	}

	var p path.Path
	if subRes.error == nil {
		p = subRes.path
	} else {
		var rootRes lookupRes
		select {
		case rootRes = <-rootChan:
		case <-ctx.Done():
			return "", ctx.Err()
		}
		if rootRes.error == nil {
			p = rootRes.path
		} else {
			return "", ErrResolveFailed
		}
	}
	if len(segments) > 1 {
		return path.FromSegments("", strings.TrimRight(p.String(), "/"), segments[1])
	} else {
		return p, nil
	}
}

// HasBlock announces the existance of a block to this bitswap service. The
// service will potentially notify its peers.
func (bs *Bitswap) HasBlock(ctx context.Context, blk *blocks.Block) error {
	select {
	case <-bs.process.Closing():
		return errors.New("bitswap is closed")
	default:
	}

	if err := bs.blockstore.Put(blk); err != nil {
		return err
	}

	bs.notifications.Publish(blk)
	select {
	case bs.newBlocks <- blk:
		// send block off to be reprovided
	case <-ctx.Done():
		return ctx.Err()
	}
	return nil
}

func GarbageCollect(n *core.IpfsNode, ctx context.Context) error {
	ctx, cancel := context.WithCancel(ctx)
	defer cancel() // in case error occurs during operation
	rmed, err := gc.GC(ctx, n.Blockstore, n.Pinning)
	if err != nil {
		return err
	}

	for {
		select {
		case _, ok := <-rmed:
			if !ok {
				return nil
			}
		case <-ctx.Done():
			return ctx.Err()
		}
	}

}

func (fi *File) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.ReadResponse) error {
	_, err := fi.fi.Seek(req.Offset, os.SEEK_SET)
	if err != nil {
		return err
	}

	fisize, err := fi.fi.Size()
	if err != nil {
		return err
	}

	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}

	readsize := min(req.Size, int(fisize-req.Offset))
	n, err := fi.fi.CtxReadFull(ctx, resp.Data[:readsize])
	resp.Data = resp.Data[:n]
	return err
}

// GetBlock attempts to retrieve a particular block from peers within the
// deadline enforced by the context.
func (bs *Bitswap) GetBlock(parent context.Context, k key.Key) (*blocks.Block, error) {

	// Any async work initiated by this function must end when this function
	// returns. To ensure this, derive a new context. Note that it is okay to
	// listen on parent in this scope, but NOT okay to pass |parent| to
	// functions called by this one. Otherwise those functions won't return
	// when this context's cancel func is executed. This is difficult to
	// enforce. May this comment keep you safe.

	ctx, cancelFunc := context.WithCancel(parent)

	ctx = logging.ContextWithLoggable(ctx, logging.Uuid("GetBlockRequest"))
	log.Event(ctx, "Bitswap.GetBlockRequest.Start", &k)
	defer log.Event(ctx, "Bitswap.GetBlockRequest.End", &k)

	defer func() {
		cancelFunc()
	}()

	promise, err := bs.GetBlocks(ctx, []key.Key{k})
	if err != nil {
		return nil, err
	}

	select {
	case block, ok := <-promise:
		if !ok {
			select {
			case <-ctx.Done():
				return nil, ctx.Err()
			default:
				return nil, errors.New("promise channel was closed")
			}
		}
		return block, nil
	case <-parent.Done():
		return nil, parent.Err()
	}
}

// writeMsgCtx is used by the
func writeMsgCtx(ctx context.Context, w msgio.Writer, msg proto.Message) ([]byte, error) {
	enc, err := proto.Marshal(msg)
	if err != nil {
		return nil, err
	}

	// write in a goroutine so we can exit when our context is cancelled.
	done := make(chan error)
	go func(m []byte) {
		err := w.WriteMsg(m)
		select {
		case done <- err:
		case <-ctx.Done():
		}
	}(enc)

	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	case e := <-done:
		return enc, e
	}
}

func (c *Client) FindProvidersAsync(ctx context.Context, k key.Key, max int) <-chan peer.PeerInfo {
	ctx = logging.ContextWithLoggable(ctx, logging.Uuid("findProviders"))
	defer log.EventBegin(ctx, "findProviders", &k).Done()
	ch := make(chan peer.PeerInfo)
	go func() {
		defer close(ch)
		request := pb.NewMessage(pb.Message_GET_PROVIDERS, string(k), 0)
		response, err := c.proxy.SendRequest(ctx, request)
		if err != nil {
			log.Debug(err)
			return
		}
		for _, p := range pb.PBPeersToPeerInfos(response.GetProviderPeers()) {
			select {
			case <-ctx.Done():
				log.Debug(ctx.Err())
				return
			case ch <- p:
			}
		}
	}()
	return ch
}