forked from go-redsync/redsync
/
mutex.go
144 lines (114 loc) · 2.96 KB
/
mutex.go
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package redsync
import (
"crypto/rand"
"encoding/base64"
"github.com/go-redis/redis"
"strings"
"sync"
"time"
)
// A DelayFunc is used to decide the amount of time to wait between retries.
type DelayFunc func(tries int) time.Duration
// A Mutex is a distributed mutual exclusion lock.
type Mutex struct {
name string
expiry time.Duration
tries int
delayFunc DelayFunc
factor float64
value string
until time.Time
nodem sync.Mutex
redisClient *redis.Client
}
// Lock locks m. In case it returns an error on failure, you may retry to acquire the lock by calling this method again.
func (m *Mutex) Lock() error {
m.nodem.Lock()
defer m.nodem.Unlock()
value, err := m.genValue()
if err != nil {
return err
}
for i := 0; i < m.tries; i++ {
if i != 0 {
time.Sleep(m.delayFunc(i))
}
start := time.Now()
acquireSuccess := m.acquire(value)
until := time.Now().Add(m.expiry - time.Now().Sub(start) - time.Duration(int64(float64(m.expiry)*m.factor)) + 2*time.Millisecond)
if acquireSuccess && time.Now().Before(until) {
m.value = value
m.until = until
return nil
}
m.release(value)
}
return ErrFailed
}
// Unlock unlocks m and returns the status of unlock.
func (m *Mutex) Unlock() bool {
m.nodem.Lock()
defer m.nodem.Unlock()
return m.release(m.value)
}
// Extend resets the mutex's expiry and returns the status of expiry extension.
func (m *Mutex) Extend() bool {
m.nodem.Lock()
defer m.nodem.Unlock()
return m.touch(m.value, int(m.expiry/time.Millisecond))
}
func (m *Mutex) Acquire() bool {
m.nodem.Lock()
defer m.nodem.Unlock()
value, err := m.genValue()
if err != nil {
return false
}
return m.acquire(value)
}
func (m *Mutex) genValue() (string, error) {
b := make([]byte, 32)
_, err := rand.Read(b)
if err != nil {
return "", err
}
return base64.StdEncoding.EncodeToString(b), nil
}
func (m *Mutex) acquire(value string) bool {
reply, err := m.redisClient.SetNX(m.name, value, m.expiry).Result()
if err != nil {
return false
} else {
return reply
}
}
var deleteScript = redis.NewScript(`
if redis.call("GET", KEYS[1]) == ARGV[1] then
return redis.call("DEL", KEYS[1])
else
return 0
end
`)
func (m *Mutex) release(value string) bool {
status, err := m.evalScript(deleteScript, m.name, value)
return err == nil && status != 0
}
var touchScript = redis.NewScript(`
if redis.call("GET", KEYS[1]) == ARGV[1] then
return redis.call("SET", KEYS[1], ARGV[1], "XX", "PX", ARGV[2])
else
return "ERR"
end
`)
func (m *Mutex) touch(value string, expiry int) bool {
status, err := m.evalScript(touchScript, m.name, value)
return err == nil && status != "ERR"
}
func (m *Mutex) evalScript(script *redis.Script, key string, args ...interface{}) (interface{}, error) {
keys := []string{m.name}
status, err := script.EvalSha(m.redisClient, keys, args...).Result()
if err != nil && strings.HasPrefix(err.Error(), "NOSCRIPT ") {
status, err = script.Eval(m.redisClient, keys, args...).Result()
}
return status, err
}