Class: DaemonRunner::Session

Inherits:
Object
  • Object
show all
Includes:
Logger
Defined in:
lib/daemon_runner/session.rb

Overview

Manage distributed locks with Consul

Defined Under Namespace

Classes: CreateSessionError, SessionError

Class Attribute Summary collapse

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Logger

#logger, #logger_name

Constructor Details

#initialize(name, **options) ⇒ Session

Returns a new instance of Session.

Parameters:

  • name (String) —

    Session name

  • options (Hash) —

    a customizable set of options

Options Hash (**options):

  • ttl (Fixnum) — default: 15 —

    Session TTL in seconds

  • delay (Fixnum) — default: 15 —

    Session release dealy in seconds

  • behavior (String) — default: release —

    Session release behavior



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# File 'lib/daemon_runner/session.rb', line 62

def initialize(name, **options)
  logger.info('Initializing a Consul session')

  @name = name
  @ttl = options.fetch(:ttl, 15)
  @delay = options.fetch(:delay, 15)
  @behavior = options.fetch(:behavior, 'release')

  init
end

Class Attribute Details

.session ⇒ Object (readonly)

Returns the value of attribute session.



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# File 'lib/daemon_runner/session.rb', line 14

def session
  @session
end

Instance Attribute Details

#behavior ⇒ Object (readonly)

Behavior when a session is invalidated, can be set to either release or delete



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# File 'lib/daemon_runner/session.rb', line 56

def behavior
  @behavior
end

#delay ⇒ Object (readonly)

Period, in seconds, that a session’s locks will be



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# File 'lib/daemon_runner/session.rb', line 53

def delay
  @delay
end

#id ⇒ Object (readonly)

Consul session ID



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# File 'lib/daemon_runner/session.rb', line 44

def id
  @id
end

#name ⇒ Object (readonly)

Session name



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# File 'lib/daemon_runner/session.rb', line 47

def name
  @name
end

#ttl ⇒ Object (readonly)

Period, in seconds, after which session expires



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# File 'lib/daemon_runner/session.rb', line 50

def ttl
  @ttl
end

Class Method Details

.lock(path) ⇒ Boolean

Acquire a lock with the current session, or initialize a new session

Parameters:

  • path (String) —

    A path in the Consul key-value space to lock

  • lock_session (Session) —

    The Session instance to lock the lock to

Returns:

  • (Boolean) —

    ‘true` if the lock was acquired



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# File 'lib/daemon_runner/session.rb', line 29

def lock(path)
  Diplomat::Lock.wait_to_acquire(path, session.id)
end

.release(path) ⇒ Object

Release a lock held by the current session

Parameters:

  • path (String) —

    A path in the Consul key-value space to release

  • lock_session (Session) —

    The Session instance that the lock was acquired with



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# File 'lib/daemon_runner/session.rb', line 38

def release(path)
  Diplomat::Lock.release(path, session.id)
end

.start(name, **options) ⇒ Object

Raises:



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# File 'lib/daemon_runner/session.rb', line 16

def start(name, **options)
  @session = Session.new(name, options).renew!
  raise CreateSessionError, 'Failed to create session' if @session == false
  @session.verify_session
  @session
end

Instance Method Details

#destroy! ⇒ Object

Stop the renew thread and destroy the session



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# File 'lib/daemon_runner/session.rb', line 110

def destroy!
  @renew.kill if renew?
  Diplomat::Session.destroy(id)
end

#renew! ⇒ Object

Create a thread to periodically renew the lock session



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# File 'lib/daemon_runner/session.rb', line 82

def renew!
  return if renew?

  @renew = Thread.new do
    ## Wakeup every TTL/2 seconds and renew the session
    loop do
      sleep ttl / 2

      begin
        logger.debug(" - Renewing Consul session #{id}")
        Diplomat::Session.renew(id)

      rescue Faraday::ResourceNotFound
        logger.warn("Consul session #{id} has expired!")

        init
      rescue StandardError => e
        ## Keep the thread from exiting
        logger.error(e)
      end
    end
  end

  self
end

#renew? ⇒ Boolean

Check if there is an active renew thread

Returns:

  • (Boolean) —

    ‘true` if the thread is alive



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# File 'lib/daemon_runner/session.rb', line 76

def renew?
  @renew.is_a?(Thread) && @renew.alive?
end

#verify_session(wait_time = 2) ⇒ Object

Verify wheather the session exists after a period of time



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# File 'lib/daemon_runner/session.rb', line 116

def verify_session(wait_time = 2)
  logger.info(" - Wait until Consul session #{id} exists")
  wait_time.times do
    exists = session_exist?
    raise CreateSessionError, 'Error creating session' unless exists
    sleep 1
  end
  logger.info(" - Found Consul session #{id}")
rescue CreateSessionError
  init
end