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mutex.go
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mutex.go
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package redsync
import (
"context"
"crypto/rand"
"encoding/base64"
"time"
"github.com/hashicorp/go-multierror"
"github.com/wpmedia/redsync/v4/redis"
)
// 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
quorum int
genValueFunc func() (string, error)
value string
until time.Time
pools []redis.Pool
}
// 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 {
return m.LockContext(nil)
}
// 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) LockContext(ctx context.Context) error {
value, err := m.genValueFunc()
if err != nil {
return err
}
for i := 0; i < m.tries; i++ {
if i != 0 {
time.Sleep(m.delayFunc(i))
}
start := time.Now()
n, err := m.actOnPoolsAsync(func(pool redis.Pool) (bool, error) {
return m.acquire(ctx, pool, value)
})
if n == 0 && err != nil {
return err
}
now := time.Now()
until := now.Add(m.expiry - now.Sub(start) - time.Duration(int64(float64(m.expiry)*m.factor)))
if n >= m.quorum && now.Before(until) {
m.value = value
m.until = until
return nil
}
_, _ = m.actOnPoolsAsync(func(pool redis.Pool) (bool, error) {
return m.release(ctx, pool, value)
})
}
return ErrFailed
}
// Unlock unlocks m and returns the status of unlock.
func (m *Mutex) Unlock() (bool, error) {
return m.UnlockContext(nil)
}
// Unlock unlocks m and returns the status of unlock.
func (m *Mutex) UnlockContext(ctx context.Context) (bool, error) {
n, err := m.actOnPoolsAsync(func(pool redis.Pool) (bool, error) {
return m.release(ctx, pool, m.value)
})
if n < m.quorum {
return false, err
}
return true, nil
}
// Extend resets the mutex's expiry and returns the status of expiry extension.
func (m *Mutex) Extend() (bool, error) {
return m.ExtendContext(nil)
}
// Extend resets the mutex's expiry and returns the status of expiry extension.
func (m *Mutex) ExtendContext(ctx context.Context) (bool, error) {
n, err := m.actOnPoolsAsync(func(pool redis.Pool) (bool, error) {
return m.touch(ctx, pool, m.value, int(m.expiry/time.Millisecond))
})
if n < m.quorum {
return false, err
}
return true, nil
}
func (m *Mutex) Valid() (bool, error) {
return m.ValidContext(nil)
}
func (m *Mutex) ValidContext(ctx context.Context) (bool, error) {
n, err := m.actOnPoolsAsync(func(pool redis.Pool) (bool, error) {
return m.valid(ctx, pool)
})
return n >= m.quorum, err
}
func (m *Mutex) valid(ctx context.Context, pool redis.Pool) (bool, error) {
conn, err := pool.Get(ctx)
if err != nil {
return false, err
}
defer conn.Close()
reply, err := conn.Get(m.name)
if err != nil {
return false, err
}
return m.value == reply, nil
}
func genValue() (string, error) {
b := make([]byte, 16)
_, err := rand.Read(b)
if err != nil {
return "", err
}
return base64.StdEncoding.EncodeToString(b), nil
}
func (m *Mutex) acquire(ctx context.Context, pool redis.Pool, value string) (bool, error) {
conn, err := pool.Get(ctx)
if err != nil {
return false, err
}
defer conn.Close()
reply, err := conn.SetNX(m.name, value, m.expiry)
if err != nil {
return false, err
}
return reply, nil
}
var deleteScript = redis.NewScript(1, `
if redis.call("GET", KEYS[1]) == ARGV[1] then
return redis.call("DEL", KEYS[1])
else
return 0
end
`)
func (m *Mutex) release(ctx context.Context, pool redis.Pool, value string) (bool, error) {
conn, err := pool.Get(ctx)
if err != nil {
return false, err
}
defer conn.Close()
status, err := conn.Eval(deleteScript, m.name, value)
if err != nil {
return false, err
}
return status != 0, nil
}
var touchScript = redis.NewScript(1, `
if redis.call("GET", KEYS[1]) == ARGV[1] then
return redis.call("PEXPIRE", KEYS[1], ARGV[2])
else
return 0
end
`)
func (m *Mutex) touch(ctx context.Context, pool redis.Pool, value string, expiry int) (bool, error) {
conn, err := pool.Get(ctx)
if err != nil {
return false, err
}
defer conn.Close()
status, err := conn.Eval(touchScript, m.name, value, expiry)
if err != nil {
return false, err
}
return status != "ERR", nil
}
func (m *Mutex) actOnPoolsAsync(actFn func(redis.Pool) (bool, error)) (int, error) {
type result struct {
Status bool
Err error
}
ch := make(chan result)
for _, pool := range m.pools {
go func(pool redis.Pool) {
r := result{}
r.Status, r.Err = actFn(pool)
ch <- r
}(pool)
}
n := 0
var err error
for range m.pools {
r := <-ch
if r.Status {
n++
} else if r.Err != nil {
err = multierror.Append(err, r.Err)
}
}
return n, err
}