redislock

README

redislock

Forked from redislock

Seperate waitTimeout and lockTTL to build a pessimistic lock

Documentation

Overview

Example

// Connect to redis.
client := redis.NewClient(&redis.Options{
	Network: "tcp",
	Addr:    "127.0.0.1:6379",
})
defer client.Close()

// Create a new lock client.
locker := redislock.New(client)

ctx := context.Background()

// Try to obtain lock.
lock, err := locker.Obtain(ctx, "my-key", 100*time.Millisecond, 100*time.Millisecond, nil)
if err == redislock.ErrNotObtained {
	fmt.Println("Could not obtain lock!")
} else if err != nil {
	log.Fatalln(err)
}

// Don't forget to defer Release.
defer lock.Release(ctx)
fmt.Println("I have a lock!")

// Sleep and check the remaining TTL.
time.Sleep(50 * time.Millisecond)
if ttl, err := lock.TTL(ctx); err != nil {
	log.Fatalln(err)
} else if ttl > 0 {
	fmt.Println("Yay, I still have my lock!")
}

// Extend my lock.
if err := lock.Refresh(ctx, 100*time.Millisecond, nil); err != nil {
	log.Fatalln(err)
}

// Sleep a little longer, then check.
time.Sleep(100 * time.Millisecond)
if ttl, err := lock.TTL(ctx); err != nil {
	log.Fatalln(err)
} else if ttl == 0 {
	fmt.Println("Now, my lock has expired!")
}

Output:

I have a lock!
Yay, I still have my lock!
Now, my lock has expired!

Index

• Variables
• type Client
  • func New(client RedisClient) *Client
  • func (c *Client) Obtain(ctx context.Context, key string, waitTimeout, lockTTL time.Duration, ...) (*Lock, error)
• type Lock
  • func Obtain(ctx context.Context, client RedisClient, key string, ...) (*Lock, error)
  • func (l *Lock) Key() string
  • func (l *Lock) Metadata() string
  • func (l *Lock) Refresh(ctx context.Context, ttl time.Duration, opt *Options) error
  • func (l *Lock) Release(ctx context.Context) error
  • func (l *Lock) TTL(ctx context.Context) (time.Duration, error)
  • func (l *Lock) Token() string
• type Options
• type RedisClient
• type RetryStrategy
  • func ExponentialBackoff(min, max time.Duration) RetryStrategy
  • func LimitRetry(s RetryStrategy, max int) RetryStrategy
  • func LinearBackoff(backoff time.Duration) RetryStrategy
  • func NoRetry() RetryStrategy

Examples

• Package
• Client.Obtain (CustomDeadline)
• Client.Obtain (Retry)

Variables

var (
	// ErrNotObtained is returned when a lock cannot be obtained.
	ErrNotObtained = errors.New("redislock: not obtained")

	// ErrLockNotHeld is returned when trying to release an inactive lock.
	ErrLockNotHeld = errors.New("redislock: lock not held")
)

Types

type Client

type Client struct {
	// contains filtered or unexported fields
}

Client wraps a redis client.

func New

func New(client RedisClient) *Client

New creates a new Client instance with a custom namespace.

func (*Client) Obtain

func (c *Client) Obtain(ctx context.Context, key string, waitTimeout, lockTTL time.Duration, opt *Options) (*Lock, error)

Obtain tries to obtain a new lock using a key with the given TTL. May return ErrNotObtained if not successful.

Example (CustomDeadline)

client := redis.NewClient(&redis.Options{Network: "tcp", Addr: "127.0.0.1:6379"})
defer client.Close()

locker := redislock.New(client)

// Retry every 500ms, for up-to a minute
backoff := redislock.LinearBackoff(500 * time.Millisecond)
ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(time.Minute))
defer cancel()

// Obtain lock with retry + custom deadline
lock, err := locker.Obtain(ctx, "my-key", time.Second, time.Second, &redislock.Options{
	RetryStrategy: backoff,
})
if err == redislock.ErrNotObtained {
	fmt.Println("Could not obtain lock!")
} else if err != nil {
	log.Fatalln(err)
}
defer lock.Release(context.Background())

fmt.Println("I have a lock!")

Example (Retry)

client := redis.NewClient(&redis.Options{Network: "tcp", Addr: "127.0.0.1:6379"})
defer client.Close()

locker := redislock.New(client)

ctx := context.Background()

// Retry every 100ms, for up-to 3x
backoff := redislock.LimitRetry(redislock.LinearBackoff(100*time.Millisecond), 3)

// Obtain lock with retry
lock, err := locker.Obtain(ctx, "my-key", time.Second, time.Second, &redislock.Options{
	RetryStrategy: backoff,
})
if err == redislock.ErrNotObtained {
	fmt.Println("Could not obtain lock!")
} else if err != nil {
	log.Fatalln(err)
}
defer lock.Release(ctx)

fmt.Println("I have a lock!")

type Lock

type Lock struct {
	// contains filtered or unexported fields
}

Lock represents an obtained, distributed lock.

func Obtain

func Obtain(ctx context.Context, client RedisClient, key string, waitTimeout, lockTTL time.Duration, opt *Options) (*Lock, error)

Obtain is a short-cut for New(...).Obtain(...).

func (*Lock) Key

func (l *Lock) Key() string

Key returns the redis key used by the lock.

func (*Lock) Metadata

func (l *Lock) Metadata() string

Metadata returns the metadata of the lock.

func (*Lock) Refresh

func (l *Lock) Refresh(ctx context.Context, ttl time.Duration, opt *Options) error

Refresh extends the lock with a new TTL. May return ErrNotObtained if refresh is unsuccessful.

func (*Lock) Release

func (l *Lock) Release(ctx context.Context) error

Release manually releases the lock. May return ErrLockNotHeld.

func (*Lock) TTL

func (l *Lock) TTL(ctx context.Context) (time.Duration, error)

TTL returns the remaining time-to-live. Returns 0 if the lock has expired.

func (*Lock) Token

func (l *Lock) Token() string

Token returns the token value set by the lock.

type Options

type Options struct {
	// RetryStrategy allows to customise the lock retry strategy.
	// Default: do not retry
	RetryStrategy RetryStrategy

	// Metadata string is appended to the lock token.
	Metadata string
}

Options describe the options for the lock

type RedisClient

type RedisClient interface {
	SetNX(ctx context.Context, key string, value interface{}, expiration time.Duration) *redis.BoolCmd
	Eval(ctx context.Context, script string, keys []string, args ...interface{}) *redis.Cmd
	EvalSha(ctx context.Context, sha1 string, keys []string, args ...interface{}) *redis.Cmd
	ScriptExists(ctx context.Context, scripts ...string) *redis.BoolSliceCmd
	ScriptLoad(ctx context.Context, script string) *redis.StringCmd
}

RedisClient is a minimal client interface.

type RetryStrategy

type RetryStrategy interface {
	// NextBackoff returns the next backoff duration.
	NextBackoff() time.Duration
}

RetryStrategy allows to customise the lock retry strategy.

func ExponentialBackoff

func ExponentialBackoff(min, max time.Duration) RetryStrategy

ExponentialBackoff strategy is an optimization strategy with a retry time of 2**n milliseconds (n means number of times). You can set a minimum and maximum value, the recommended minimum value is not less than 16ms.

func LimitRetry

func LimitRetry(s RetryStrategy, max int) RetryStrategy

LimitRetry limits the number of retries to max attempts.

func LinearBackoff

func LinearBackoff(backoff time.Duration) RetryStrategy

LinearBackoff allows retries regularly with customized intervals

func NoRetry

func NoRetry() RetryStrategy

NoRetry acquire the lock only once.