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session.go
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session.go
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// Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package concurrency
import (
"time"
v3 "github.com/coreos/etcd/clientv3"
"golang.org/x/net/context"
)
const defaultSessionTTL = 60
// Session represents a lease kept alive for the lifetime of a client.
// Fault-tolerant applications may use sessions to reason about liveness.
type Session struct {
client *v3.Client
opts *sessionOptions
id v3.LeaseID
cancel context.CancelFunc
donec <-chan struct{}
}
// NewSession gets the leased session for a client.
func NewSession(client *v3.Client, opts ...SessionOption) (*Session, error) {
ops := &sessionOptions{ttl: defaultSessionTTL, ctx: client.Ctx()}
for _, opt := range opts {
opt(ops)
}
id := ops.leaseID
if id == v3.NoLease {
resp, err := client.Grant(ops.ctx, int64(ops.ttl))
if err != nil {
return nil, err
}
id = v3.LeaseID(resp.ID)
}
ctx, cancel := context.WithCancel(ops.ctx)
keepAlive, err := client.KeepAlive(ctx, id)
if err != nil || keepAlive == nil {
return nil, err
}
donec := make(chan struct{})
s := &Session{client: client, opts: ops, id: id, cancel: cancel, donec: donec}
// keep the lease alive until client error or cancelled context
go func() {
defer close(donec)
for range keepAlive {
// eat messages until keep alive channel closes
}
}()
return s, nil
}
// Client is the etcd client that is attached to the session.
func (s *Session) Client() *v3.Client {
return s.client
}
// Lease is the lease ID for keys bound to the session.
func (s *Session) Lease() v3.LeaseID { return s.id }
// Done returns a channel that closes when the lease is orphaned, expires, or
// is otherwise no longer being refreshed.
func (s *Session) Done() <-chan struct{} { return s.donec }
// Orphan ends the refresh for the session lease. This is useful
// in case the state of the client connection is indeterminate (revoke
// would fail) or when transferring lease ownership.
func (s *Session) Orphan() {
s.cancel()
<-s.donec
}
// Close orphans the session and revokes the session lease.
func (s *Session) Close() error {
s.Orphan()
// if revoke takes longer than the ttl, lease is expired anyway
ctx, cancel := context.WithTimeout(s.opts.ctx, time.Duration(s.opts.ttl)*time.Second)
_, err := s.client.Revoke(ctx, s.id)
cancel()
return err