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20b4336cdb
A client may bind itself to a session lease to signal its continued in participation with the cluster.
107 lines
3.0 KiB
Go
107 lines
3.0 KiB
Go
// Copyright 2016 CoreOS, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package concurrency
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import (
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"sync"
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"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
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v3 "github.com/coreos/etcd/clientv3"
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"github.com/coreos/etcd/lease"
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)
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// only keep one ephemeral lease per client
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var clientSessions clientSessionMgr = clientSessionMgr{sessions: make(map[*v3.Client]*Session)}
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const sessionTTL = 60
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type clientSessionMgr struct {
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sessions map[*v3.Client]*Session
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mu sync.Mutex
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}
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// Session represents a lease kept alive for the lifetime of a client.
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// Fault-tolerant applications may use sessions to reason about liveness.
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type Session struct {
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client *v3.Client
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id lease.LeaseID
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cancel context.CancelFunc
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donec <-chan struct{}
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}
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// NewSession gets the leased session for a client.
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func NewSession(client *v3.Client) (*Session, error) {
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clientSessions.mu.Lock()
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defer clientSessions.mu.Unlock()
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if s, ok := clientSessions.sessions[client]; ok {
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return s, nil
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}
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lc := v3.NewLease(client)
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resp, err := lc.Create(context.TODO(), sessionTTL)
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if err != nil {
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return nil, err
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}
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id := lease.LeaseID(resp.ID)
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ctx, cancel := context.WithCancel(context.Background())
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keepAlive, err := lc.KeepAlive(ctx, id)
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if err != nil || keepAlive == nil {
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return nil, err
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}
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donec := make(chan struct{})
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s := &Session{client: client, id: id, cancel: cancel, donec: donec}
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clientSessions.sessions[client] = s
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// keep the lease alive until client error or cancelled context
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go func() {
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defer func() {
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clientSessions.mu.Lock()
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delete(clientSessions.sessions, client)
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clientSessions.mu.Unlock()
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lc.Close()
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close(donec)
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}()
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for range keepAlive {
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// eat messages until keep alive channel closes
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}
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}()
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return s, nil
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}
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// Lease is the lease ID for keys bound to the session.
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func (s *Session) Lease() lease.LeaseID { return s.id }
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// Done returns a channel that closes when the lease is orphaned, expires, or
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// is otherwise no longer being refreshed.
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func (s *Session) Done() <-chan struct{} { return s.donec }
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// Orphan ends the refresh for the session lease. This is useful
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// in case the state of the client connection is indeterminate (revoke
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// would fail) or when transferring lease ownership.
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func (s *Session) Orphan() {
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s.cancel()
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<-s.donec
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}
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// Close orphans the session and revokes the session lease.
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func (s *Session) Close() error {
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s.Orphan()
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_, err := v3.NewLease(s.client).Revoke(context.TODO(), s.id)
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return err
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}
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