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package main
import (
"fmt"
"sync"
"time"
"github.com/gomodule/redigo/redis"
)
type DistributedLock struct {
key string
value string
expiration time.Duration
pool *redis.Pool
mu sync.Mutex
stopChan chan struct{}
once sync.Once
}
func NewDistributedLock(pool *redis.Pool, key string, expiration time.Duration) *DistributedLock {
return &DistributedLock{
key: key,
value: fmt.Sprintf("%d", time.Now().UnixNano()),
expiration: expiration,
pool: pool,
stopChan: make(chan struct{}),
}
}
func (l *DistributedLock) Acquire() error {
l.mu.Lock()
defer l.mu.Unlock()
conn := l.pool.Get()
defer conn.Close()
// https://redis.io/docs/latest/commands/set/
// SET key value [NX | XX] [GET] [EX seconds | PX milliseconds |
// EX seconds：将键的过期时间设置为 seconds 秒。执行 SET key value EX seconds 的效果等同于执行 SETEX key seconds value。
// PX milliseconds：将键的过期时间设置为 milliseconds 毫秒。执行 SET key value PX milliseconds 的效果等同于执行 PSETEX key milliseconds value。
// NX：只在键不存在时，才对键进行设置操作。执行 SET key value NX 的效果等同于执行 SETNX key value。
// XX：只在键已经存在时，才对键进行设置操作。
reply, err := redis.String(conn.Do("SET", l.key, l.value, "NX", "PX", int(l.expiration.Milliseconds())))
if err != nil {
return err
}
if reply != "OK" {
return fmt.Errorf("failed to acquire lock")
}
go l.renewalLoop()
return nil
}
func (l *DistributedLock) renewalLoop() {
ticker := time.NewTicker(l.expiration / 2)
defer ticker.Stop()
for {
select {
case <-ticker.C:
select { // 防止退出和定时器并发时，定时器先被 select 执行导致的本该失效的锁被再次延长。
case <-l.stopChan:
return
default:
if err := l.renewal(); err != nil {
fmt.Println("Error renewing lock:", err)
}
}
case <-l.stopChan:
return
}
}
}
func (l *DistributedLock) renewal() error {
l.mu.Lock()
defer l.mu.Unlock()
conn := l.pool.Get()
defer conn.Close()
storedValue, err := redis.String(conn.Do("GET", l.key))
if err != nil {
return err
}
if storedValue == l.value {
_, err = conn.Do("SET", l.key, l.value, "XX", "PX", int(l.expiration.Milliseconds()))
if err != nil {
return err
}
}
return nil
}
func (l *DistributedLock) Release() (err error) {
l.mu.Lock()
defer l.mu.Unlock()
l.once.Do(func() {
close(l.stopChan)
conn := l.pool.Get()
defer conn.Close()
script := redis.NewScript(1, `
if redis.call("GET", KEYS[1]) == ARGV[1] then
return redis.call("DEL", KEYS[1])
else
return 0
end`)
_, err = script.Do(conn, l.key, l.value)
})
return
}
func main() {
pool := &redis.Pool{
Dial: func() (redis.Conn, error) {
return redis.Dial("tcp", "localhost:6379")
},
MaxIdle: 10,
MaxActive: 100,
IdleTimeout: 300 * time.Second,
}
defer pool.Close()
lock := NewDistributedLock(pool, "my_lock", 10*time.Second)
if err := lock.Acquire(); err != nil {
fmt.Println("Failed to acquire lock!", err)
return
}
defer func() {
if err := lock.Release(); err != nil {
fmt.Println("Failed to release lock!", err)
return
}
fmt.Println("Lock released!")
}()
fmt.Println("Lock acquired!")
time.Sleep(15 * time.Second) // 模拟长时间操作
}
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