go-distributed-lock

README

go-distributed-lock

Extremely simple redis-backed distributed lock / counter

Release history

2019-06-13: Initial v0.0.1 release with a counter backed by redis or in-mem.

Building and testing

Use the supplied Makefile to build and test this library.

> make all
go fmt ./...
go build ./...
go test ./...
ok  	github.com/inteleon/go-distributed-lock/counter	(cached)
?   	github.com/inteleon/go-distributed-lock/mock_redis	[no test files]

Using this library

In your application where you want to use this library. Edit your go.mod, add:

require (
    ... other dependencies ...
    github.com/inteleon/go-distributed-lock v0.0.1
)

Usage in code

Counter

The counter comes in two flavors, in-memory (for testing and local development) and redis (for usage in integration tests, staging, prod etc where there's a Redis available).

Both uses an int64 as store for the counter, with the semantic that a counter > 0 is "locked", while a nil or counter <= 0 is "not locked".

The primary use case is when we have some asynchronous processing such as consuming a finite number of messages from a queue, where the enqueuer knows how many messages that was enqueued but won't know when all the enqueued message have been processed.

The number of messages is Set(num) on a counter. Each consumer then can decrease this counter using Decr() once an item has been processed. When the counter reaches 0, we know that the entire "batch" has been completed.

Initialization of Redis counter

// Create an instance of a RediCounter with 30 minute expiry.
counter, err := counter.NewRedisCounter("my-counter", "redis:6379", "some-password", 1800)

// Check for errors. Stop the application if there is a problem.
if err != nil {
    logrus.Fatalf(err.Error())
}

// Sets the created instance as a application specific singleton
lock.SetSingleton(counter)

Sample usage (in-memory counter)

counter := NewInMemoryCounter("my-key", time.Now().Add(3*time.Second))
counter.Set(1337)
fmt.Printf("Is locked: %v\n", counter.IsLocked()) // true
counter.Decr()
fmt.Printf("Value: %v\n", counter.Get()) // 136
for ;counter.Get() > 0; {
    counter.Decr()
}
fmt.Printf("Is locked: %v\n", counter.IsLocked()) // false

Should output

Is locked: true
Value: 136
Is locked: false

Mocking this library

The project provides a mock for its interface using gomock.

Gomock and its mockgen tool can be installed using the following commands:

go get github.com/golang/mock/gomock
go install github.com/golang/mock/mockgen

To re-generate the mock, run:

make mock