Module: MasterLock

Defined in:
lib/master_lock.rb,
lib/master_lock/version.rb,
lib/master_lock/registry.rb,
lib/master_lock/redis_lock.rb,
lib/master_lock/redis_scripts.rb

Overview

MasterLock is a system for interprocess locking. Resources can be locked by a string identifier such that only one thread may have the lock at a time. Lock state and owners are stored on a Redis server shared by all processes. Locks are held until either the block of synchronized code completes or the thread that obtained the lock is killed. To prevent the locks from being held indefinitely in the event that the process dies without releasing them, the locks have an expiration time in Redis. While the thread owning the lock is alive, a separate thread will extend the lifetime of the locks so that they do not expire even when the code in the critical section takes a long time to execute.

Defined Under Namespace

Modules: RedisScripts Classes: Config, LockNotAcquiredError, NotStartedError, RedisLock, Registry, UnconfiguredError

Constant Summary collapse

DEFAULT_ACQUIRE_TIMEOUT = 
5
DEFAULT_EXTEND_INTERVAL = 
15
DEFAULT_KEY_PREFIX = 
"masterlock".freeze
DEFAULT_SLEEP_TIME = 
5
DEFAULT_TTL = 
60
VERSION = 
"0.10.0"

Class Method Summary collapse

Class Method Details

.config ⇒ Config

Returns MasterLock configuration settings.

Returns:

  • (Config) —

    MasterLock configuration settings



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# File 'lib/master_lock.rb', line 120

def config
  if !defined?(@config)
    @config = Config.new
    @config.acquire_timeout = DEFAULT_ACQUIRE_TIMEOUT
    @config.extend_interval = DEFAULT_EXTEND_INTERVAL
    @config.hostname = Socket.gethostname
    @config.logger = Logger.new(STDOUT)
    @config.logger.progname = name
    @config.key_prefix = DEFAULT_KEY_PREFIX
    @config.sleep_time = DEFAULT_SLEEP_TIME
    @config.ttl = DEFAULT_TTL
  end
  @config
end

.configure {|Config| ... } ⇒ Object

Configure MasterLock using block syntax. Simply yields #config to the block.

Yields:

  • (Config) —

    the configuration



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# File 'lib/master_lock.rb', line 139

def configure
  yield config
end

.logger ⇒ Logger

Get the configured logger.

Returns:

  • (Logger) 


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# File 'lib/master_lock.rb', line 115

def logger
  config.logger
end

.start ⇒ Object

Starts the background thread to manage and extend currently held locks. The thread remains alive for the lifetime of the process. This must be called before any locks may be acquired.



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# File 'lib/master_lock.rb', line 102

def start
  @registry = Registry.new
  Thread.new do
    loop do
      @registry.extend_locks
      sleep(config.sleep_time)
    end
  end
end

.synchronize(key, options = {}) ⇒ Object

Obtain a mutex around a critical section of code. Only one thread on any machine can execute the given block at a time. Returns the result of the block.

Parameters:

  • key (String) —

    the unique identifier for the locked resource

  • options (Hash) (defaults to: {}) —

    a customizable set of options

Options Hash (options):

  • :ttl (Fixnum) — default: 60 —

    the length of time in seconds before the lock expires

  • :acquire_timeout (Fixnum) — default: 5 —

    the length of time to wait to acquire the lock before timing out

  • :extend_interval (Fixnum) — default: 15 —

    the amount of time in seconds that may pass before extending the lock

  • :if (Boolean) —

    if this option is falsey, the block will be executed without obtaining the lock

  • :unless (Boolean) —

    if this option is truthy, the block will be executed without obtaining the lock

Raises:



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# File 'lib/master_lock.rb', line 58

def synchronize(key, options = {})
  check_configured
  raise NotStartedError unless @registry

  ttl = options[:ttl] || config.ttl
  acquire_timeout = options[:acquire_timeout] || config.acquire_timeout
  extend_interval = options[:extend_interval] || config.extend_interval

  raise ArgumentError, "extend_interval cannot be negative" if extend_interval < 0
  raise ArgumentError, "ttl must be greater extend_interval" if ttl <= extend_interval

  if (options.include?(:if) && !options[:if]) ||
      (options.include?(:unless) && options[:unless])
    return yield
  end

  lock = RedisLock.new(
    redis: config.redis,
    key: key,
    ttl: ttl,
    owner: generate_owner
  )
  if !lock.acquire(timeout: acquire_timeout)
    raise LockNotAcquiredError, key
  end

  registration =
    @registry.register(lock, extend_interval)
  logger.debug("Acquired lock #{key}")
  begin
    yield
  ensure
    @registry.unregister(registration)
    if lock.release
      logger.debug("Released lock #{key}")
    else
      logger.warn("Failed to release lock #{key}")
    end
  end
end