Class: Oni::Daemon

Inherits:
Object
  • Object
show all
Includes:
Configurable
Defined in:
lib/oni/daemon.rb

Overview

The Daemon class takes care of retrieving work to be processed, scheduling it and dispatching it to a mapper and worker. In essence a Daemon instance can be seen as a controller when compared with typical MVC frameworks.

This daemon starts a number of threads (5 by default) that will each perform work on their own using the corresponding mapper and worker class.

Direct Known Subclasses

Oni::Daemons::SQS

Constant Summary collapse

DEFAULT_THREAD_AMOUNT =

The default amount of threads to start.

Returns:

  • (Fixnum) 
5

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Configurable

included, #option, #require_option!

Constructor Details

#initialize ⇒ Daemon

Creates a new instance of the class and calls #after_initialize if it is defined.



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# File 'lib/oni/daemon.rb', line 29

def initialize
  @workers = []

  after_initialize if respond_to?(:after_initialize)
end

Instance Attribute Details

#workers ⇒ Array<Thread> (readonly)

Returns:

  • (Array<Thread>) 


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# File 'lib/oni/daemon.rb', line 13

class Daemon
  include Configurable

  attr_reader :workers

  ##
  # The default amount of threads to start.
  #
  # @return [Fixnum]
  #
  DEFAULT_THREAD_AMOUNT = 5

  ##
  # Creates a new instance of the class and calls `#after_initialize` if it
  # is defined.
  #
  def initialize
    @workers = []

    after_initialize if respond_to?(:after_initialize)
  end

  ##
  # Starts the daemon and waits for all threads to finish execution. This
  # method is blocking since it will wait for all threads to finish.
  #
  # If the current class has a `before_start` method defined it's called
  # before starting the daemon.
  #
  def start
    before_start if respond_to?(:before_start)

    # If we don't have any threads run in non threaded mode.
    if threads > 0
      threads.times do
        workers << spawn_thread
      end

      workers.each(&:join)
    else
      run_thread
    end
  rescue => error
    error(error)
  end

  ##
  # Terminates all the threads and clears up the list. Note that calling this
  # method acts much like sending a SIGKILL signal to a process: threads will
  # be shut down *immediately*.
  #
  def stop
    workers.each(&:kill)
    workers.clear
  end

  ##
  # Returns the amount of threads to use.
  #
  # @return [Fixnum]
  #
  def threads
    return option(:threads, DEFAULT_THREAD_AMOUNT)
  end

  ##
  # Processes the given message. Upon completion the `#complete` method is
  # called and passed the resulting output.
  #
  # @param [Mixed] message
  #
  def process(message)
    output  = nil
    timings = Benchmark.measure do
      output = run_worker(message)
    end

    complete(message, output, timings)
  end

  ##
  # Maps the input, runs the worker and then maps the output into something
  # that the daemon can understand.
  #
  # @param [Mixed] message
  # @return [Mixed]
  #
  def run_worker(message)
    mapper = create_mapper
    input  = mapper.map_input(message)
    worker = option(:worker).new(*input)
    output = worker.process

    return mapper.map_output(output)
  end

  ##
  # Receives a message, by default this method raises an error.
  #
  # @raise [NotImplementedError]
  #
  def receive
    raise NotImplementedError, 'You must manually implement #receive'
  end

  ##
  # Called when a job has been completed, by default this method is a noop.
  # This method is passed 3 arguments:
  #
  # 1. The raw input message.
  # 2. The output of the worker (remapped by the mapper).
  # 3. A Benchmark::Tms instance that contains the timings for processing the
  #    message.
  #
  # @param [Mixed] message The raw input message (e.g. an AWS SQS message)
  # @param [Mixed] output The output of the worker.
  # @param [Benchmark::Tms] timings
  #
  def complete(message, output, timings)
  end

  ##
  # Called whenever an error is raised in the daemon, mapper or worker. By
  # default this method just re-raises the error.
  #
  # Note that this callback method is called from a thread in which the
  # exception occured, not from the main thread.
  #
  # @param [StandardError] error
  #
  def error(error)
    raise error
  end

  ##
  # Creates a new mapper and passes it a set of arguments as defined in
  # {Oni::Daemon#mapper_arguments}.
  #
  # @return [Oni::Mapper]
  #
  def create_mapper
    unless option(:mapper)
      raise ArgumentError, 'No mapper has been set in the `:mapper` option'
    end

    return option(:mapper).new
  end

  ##
  # Spawns a new thread that waits for daemon input.
  #
  # @return [Thread]
  #
  def spawn_thread
    thread = Thread.new { run_thread }

    thread.abort_on_exception = true

    return thread
  end

  ##
  # The main code to execute in individual threads.
  #
  # If an error occurs in the receive method or processing a job the error
  # handler is executed and the process is retried. It's the responsibility
  # of the `error` method to determine if the process should fail only once
  # (and fail hard) or if it should continue running.
  #
  def run_thread
    receive { |message| process(message) }
  rescue => error
    error(error)

    retry
  end
end

Instance Method Details

#complete(message, output, timings) ⇒ Object

Called when a job has been completed, by default this method is a noop. This method is passed 3 arguments:

  1. The raw input message.
  2. The output of the worker (remapped by the mapper).
  3. A Benchmark::Tms instance that contains the timings for processing the message.

Parameters:

  • message (Mixed) —

    The raw input message (e.g. an AWS SQS message)

  • output (Mixed) —

    The output of the worker.

  • timings (Benchmark::Tms) 


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# File 'lib/oni/daemon.rb', line 131

def complete(message, output, timings)
end

#create_mapper ⇒ Oni::Mapper

Creates a new mapper and passes it a set of arguments as defined in #mapper_arguments.

Returns:



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# File 'lib/oni/daemon.rb', line 153

def create_mapper
  unless option(:mapper)
    raise ArgumentError, 'No mapper has been set in the `:mapper` option'
  end

  return option(:mapper).new
end

#error(error) ⇒ Object

Called whenever an error is raised in the daemon, mapper or worker. By default this method just re-raises the error.

Note that this callback method is called from a thread in which the exception occured, not from the main thread.

Parameters:

  • error (StandardError) 


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# File 'lib/oni/daemon.rb', line 143

def error(error)
  raise error
end

#process(message) ⇒ Object

Processes the given message. Upon completion the #complete method is called and passed the resulting output.

Parameters:

  • message (Mixed) 


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# File 'lib/oni/daemon.rb', line 84

def process(message)
  output  = nil
  timings = Benchmark.measure do
    output = run_worker(message)
  end

  complete(message, output, timings)
end

#receive ⇒ Object

Receives a message, by default this method raises an error.

Raises:

  • (NotImplementedError) 


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# File 'lib/oni/daemon.rb', line 114

def receive
  raise NotImplementedError, 'You must manually implement #receive'
end

#run_thread ⇒ Object

The main code to execute in individual threads.

If an error occurs in the receive method or processing a job the error handler is executed and the process is retried. It's the responsibility of the error method to determine if the process should fail only once (and fail hard) or if it should continue running.



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# File 'lib/oni/daemon.rb', line 182

def run_thread
  receive { |message| process(message) }
rescue => error
  error(error)

  retry
end

#run_worker(message) ⇒ Mixed

Maps the input, runs the worker and then maps the output into something that the daemon can understand.

Parameters:

  • message (Mixed)

Returns:

  • (Mixed) 


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# File 'lib/oni/daemon.rb', line 100

def run_worker(message)
  mapper = create_mapper
  input  = mapper.map_input(message)
  worker = option(:worker).new(*input)
  output = worker.process

  return mapper.map_output(output)
end

#spawn_thread ⇒ Thread

Spawns a new thread that waits for daemon input.

Returns:

  • (Thread) 


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# File 'lib/oni/daemon.rb', line 166

def spawn_thread
  thread = Thread.new { run_thread }

  thread.abort_on_exception = true

  return thread
end

#start ⇒ Object

Starts the daemon and waits for all threads to finish execution. This method is blocking since it will wait for all threads to finish.

If the current class has a before_start method defined it's called before starting the daemon.



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# File 'lib/oni/daemon.rb', line 42

def start
  before_start if respond_to?(:before_start)

  # If we don't have any threads run in non threaded mode.
  if threads > 0
    threads.times do
      workers << spawn_thread
    end

    workers.each(&:join)
  else
    run_thread
  end
rescue => error
  error(error)
end

#stop ⇒ Object

Terminates all the threads and clears up the list. Note that calling this method acts much like sending a SIGKILL signal to a process: threads will be shut down immediately.



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# File 'lib/oni/daemon.rb', line 64

def stop
  workers.each(&:kill)
  workers.clear
end

#threads ⇒ Fixnum

Returns the amount of threads to use.

Returns:

  • (Fixnum) 


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# File 'lib/oni/daemon.rb', line 74

def threads
  return option(:threads, DEFAULT_THREAD_AMOUNT)
end