Released mysql_getlock gem to provide distributed locking using mysql get_lock().
Unlike distributed locking using redis, this ensures releasing orphaned lock.
How It Works
This gem uses MySQL get_lock().
Simple ruby codes which describes how it works are as follows:
mysql.query(%Q[select get_lock('db_name.key', -1)])
puts 'get lock'
begin
# do a job
ensure
mysql.query(%Q[select release_lock('db_name.key')])
endMySQL get_lock() has a characteristic that the lock is implicitly released when your session terminates (either normally or abnormally).
NOTICE
Note that
- Before 5.7.5, only a single simultaneous lock can be acquired in a session, and
GET_LOCK()releases any existing lock. This gem raisesMysqlGetlock::Erroron such situation. - The key name is global in a mysql instance. It is advised to use database-specific or application-specific lock names such as
db_name.strorapp_name.environment.str
Installation
Add this line to your application's Gemfile:
gem 'mysql_getlock'And then execute:
$ bundle
Or install it yourself as:
$ gem install mysql_getlock
Usage
Similarly with ruby standard library mutex, following methods are available:
- lock
- Attempts to grab the lock and waits if it isn’t available.
- locked?
- Returns true if this lock is currently held by some.
- synchronize {}
- Obtains a lock, runs the block, and releases the lock when the block completes.
- unlock
- Releases the lock.
Options of MysqlGetlock.new are:
- mysql2
- Provide a mysql2 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 MysqlGetlock (for debug)
Example
require 'mysql2'
require 'mysql_getlock'
mysql2 = Mysql2::Client.new # Mysql2::Client.new(options)
mutex = MysqlGetlock.new(mysql2: mysql2, key: 'db_name.lock_key')
mutex.lock
begin
puts 'get lock'
ensure
mutex.unlock
end
mutex.synchronize do
puts 'get lock'
end
