etcd-io__etcd/clientv3/concurrency/example_mutex_test.go

// Copyright 2017 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_test

import (
	"context"
	"fmt"
	"log"

	"go.etcd.io/etcd/clientv3"
	"go.etcd.io/etcd/clientv3/concurrency"
)

func ExampleMutex_TryLock() {
	cli, err := clientv3.New(clientv3.Config{Endpoints: endpoints})
	if err != nil {
		log.Fatal(err)
	}
	defer cli.Close()

	// create two separate sessions for lock competition
	s1, err := concurrency.NewSession(cli)
	if err != nil {
		log.Fatal(err)
	}
	defer s1.Close()
	m1 := concurrency.NewMutex(s1, "/my-lock")

	s2, err := concurrency.NewSession(cli)
	if err != nil {
		log.Fatal(err)
	}
	defer s2.Close()
	m2 := concurrency.NewMutex(s2, "/my-lock")

	// acquire lock for s1
	if err = m1.Lock(context.TODO()); err != nil {
		log.Fatal(err)
	}
	fmt.Println("acquired lock for s1")

	if err = m2.TryLock(context.TODO()); err == nil {
		log.Fatal("should not acquire lock")
	}
	if err == concurrency.ErrLocked {
		fmt.Println("cannot acquire lock for s2, as already locked in another session")
	}

	if err = m1.Unlock(context.TODO()); err != nil {
		log.Fatal(err)
	}
	fmt.Println("released lock for s1")
	if err = m2.TryLock(context.TODO()); err != nil {
		log.Fatal(err)
	}
	fmt.Println("acquired lock for s2")

	// Output:
	// acquired lock for s1
	// cannot acquire lock for s2, as already locked in another session
	// released lock for s1
	// acquired lock for s2
}

func ExampleMutex_Lock() {
	cli, err := clientv3.New(clientv3.Config{Endpoints: endpoints})
	if err != nil {
		log.Fatal(err)
	}
	defer cli.Close()

	// create two separate sessions for lock competition
	s1, err := concurrency.NewSession(cli)
	if err != nil {
		log.Fatal(err)
	}
	defer s1.Close()
	m1 := concurrency.NewMutex(s1, "/my-lock/")

	s2, err := concurrency.NewSession(cli)
	if err != nil {
		log.Fatal(err)
	}
	defer s2.Close()
	m2 := concurrency.NewMutex(s2, "/my-lock/")

	// acquire lock for s1
	if err := m1.Lock(context.TODO()); err != nil {
		log.Fatal(err)
	}
	fmt.Println("acquired lock for s1")

	m2Locked := make(chan struct{})
	go func() {
		defer close(m2Locked)
		// wait until s1 is locks /my-lock/
		if err := m2.Lock(context.TODO()); err != nil {
			log.Fatal(err)
		}
	}()

	if err := m1.Unlock(context.TODO()); err != nil {
		log.Fatal(err)
	}
	fmt.Println("released lock for s1")

	<-m2Locked
	fmt.Println("acquired lock for s2")

	// Output:
	// acquired lock for s1
	// released lock for s1
	// acquired lock for s2
}