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https://github.com/sonots/redis_getlock
Distributed locking using redis, which ensures releasing orphaned lock shortly
https://github.com/sonots/redis_getlock
Last synced: 3 months ago
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Distributed locking using redis, which ensures releasing orphaned lock shortly
- Host: GitHub
- URL: https://github.com/sonots/redis_getlock
- Owner: sonots
- License: mit
- Created: 2016-08-27T17:52:47.000Z (over 8 years ago)
- Default Branch: master
- Last Pushed: 2018-05-08T17:08:10.000Z (over 6 years ago)
- Last Synced: 2024-09-17T17:21:43.913Z (4 months ago)
- Language: Ruby
- Size: 17.6 KB
- Stars: 6
- Watchers: 1
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE.txt
- Code of conduct: CODE_OF_CONDUCT.md
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README
# RedisGetlock
Distributed locking using redis. Unlike other implementations available, this gem ensures releasing orphaned lock shortly.
# How It Works
This gem basically works as [http://redis.io/commands/set](http://redis.io/commands/set) describes for redis >= 2.6.12, and [http://redis.io/commands/setnx](http://redis.io/commands/setnx) describes for redis < 2.6.12.
Simple ruby codes which [http://redis.io/commands/set](http://redis.io/commands/set) describes are as follows:
```ruby
loop do
break if redis.set(key, 'anystring', {nx: true, ex: expire})
sleep 1
end
puts 'get lock'
begin
# do a job
ensure
redis.del(key) # unlock
end
```
The problem here is the value of `expire`.
The expiration time `expire` is necessary so that a lock will eventually be released even if a process is crashed or killed by SIGKILL before deleting the key.
However, how long should we set if we are uncertain how long a job takes?
This gem takes a following approach to resolve this problem.
1. Expiration time is set to `2` (default) seconds
2. Extend the lock in each `1` (default) second interval invoking another thread
This way ensures to release orphaned lock in 2 seconds. We are released from caring of the value of `expire`!!
Simple ruby codes to explain how this gem works are as follows:
```ruby
loop do
break if redis.set(key, 'anystring', {nx: true, ex: 2})
sleep 1
end
puts 'get lock'
thr = Thread.new do
loop do
redis.expire(key, 2)
sleep 1
end
end
begin
# do a job
ensure
thr.terminate
redis.del(key) # unlock
end
```
## Installation
Add this line to your application's Gemfile:
```ruby
gem 'redis_getlock'
```
And then execute:
$ bundle
Or install it yourself as:
$ gem install redis_getlock
## Usage
Similarly with ruby standard library [mutex](https://ruby-doc.org/core-2.2.0/Mutex.html), following methods are available:
* lock
* Attempts to grab the lock and waits if it isn’t available. Returns true if successfully acquired a lock
* locked?
* Returns true if this lock is currently held by some (including myself).
* synchronize {}
* Obtains a lock, runs the block, and releases the lock when the block completes. Raises `RedisGetlock::LockError` error when failed to acquire a lock.
* unlock
* Releases the lock. Returns true if successfully released a lock
* self_locked?
* Returns true if this lock is currently held by myself.
* try_lock
* Attempts to grab the lock and returns immediately without waits. Returns true if successfully acquired a lock
Options of `RedisGetlock.new` are:
* redis
* Provide a redis instance
* key
* Key name for a distributed lock
* timeout
* The timeout of trying to get the lock. A negative value means infinite timeout (default: -1)
* logger
* Provide a logger for RedisGetlock (for debug)
* expire
* The expiration seconds of the lock. The default is `2` second. Users usually do not need to care of this because the expiration is automatically extended in a invoked thread.
* interval
* Interval to extend lock expiration. Must be `expire > interval`. The default is `1` second.
### Example
```ruby
require 'redis'
require 'redis_getlock'
redis = Redis.new # Redis.new(options)
mutex = RedisGetlock.new(redis: redis, key: 'lock_key')
mutex.lock
begin
puts 'get lock'
ensure
mutex.unlock
end
mutex.synchronize do
puts 'get lock'
end
```
## Contributing
Bug reports and pull requests are welcome on GitHub at https://github.com/sonots/redis_getlock. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant](http://contributor-covenant.org) code of conduct.
## License
The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).
## ChangeLog
[CHANGELOG.md](./CHANGELOG.md)