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_WORKER_AMOUNT =

The default amount of worker to start.

Returns:

  • (Fixnum) 
1
DEFAULT_THREAD_AMOUNT =

The default amount of threads to start.

Returns:

  • (Fixnum) 
5
DEFAULT_WORKER_TIMEOUT =

The default amount of threads to start.

Returns:

  • (Fixnum) 
nil

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 43

def initialize
  @daemon_workers = Hash.new{ |h, k| h[k] = [] }

  after_initialize if respond_to?(:after_initialize)
end

Instance Attribute Details

#daemon_workers ⇒ Object (readonly)

Returns the value of attribute daemon_workers.



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# File 'lib/oni/daemon.rb', line 16

def daemon_workers
  @daemon_workers
end

#workers ⇒ Array<Thread> (readonly)

Returns:

  • (Array<Thread>) 


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

class Daemon
  include Configurable

  attr_reader :daemon_workers

  ##
  # The default amount of worker to start.
  #
  # @return [Fixnum]
  #
  DEFAULT_WORKER_AMOUNT = 1

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

  ##
  # The default amount of threads to start.
  #
  # @return [Fixnum]
  #
  DEFAULT_WORKER_TIMEOUT = nil

  ##
  # Creates a new instance of the class and calls `#after_initialize` if it
  # is defined.
  #
  def initialize
    @daemon_workers = Hash.new{ |h, k| h[k] = [] }

    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

    wthreads = if threads <= 1    then [run_thread]
               elsif workers <= 1 then standard_worker
               else wthreads = Array.new(workers){ |i| spawn_worker i } end

    after_start if respond_to? :after_start

    %i[INT TERM].each{ |sig| trap(sig){ stop } }
    wthreads.each(&:join) if workers > 1

  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
    daemon_workers.each do |pid, worker_threads|
      worker_threads.each(&:kill)
      worker_threads.clear
    end
    exit
  end

  def workers
    option :workers, DEFAULT_WORKER_AMOUNT
  end

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

  ##
  # Returns the amount of threads to use.
  #
  # @return [Fixnum]
  #
  def worker_timeout
    option :worker_timeout, DEFAULT_WORKER_TIMEOUT
  end

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

    complete(message, output)
  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 = Timeout.timeout worker_timeout do
      worker.process
    end

    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 2 arguments:
  #
  # 1. The raw input message.
  # 2. The output of the worker (remapped by the mapper).
  #
  # @param [Mixed] message The raw input message (e.g. an AWS SQS message)
  # @param [Mixed] output The output of the worker.
  #
  def complete(message, output)
  end

  ##
  # Called whenever an error is raised in the daemon, mapper or worker. By
  # default this method just re-raises the error.
  #
  # @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_worker name = nil, &block
    Thread.new do
      pid = nil
      loop do # keep restarting for OOM and other cases
        pid = fork do
          Process.setproctitle "#{$0}: worker #{name}" if name

          if block then yield else standard_worker end
        end
        Process.wait pid
      end
    ensure
      Process.kill :KILL, pid
    end
  end

  def standard_worker
    Array.new(threads) do
      spawn_thread.tap{ |t| daemon_workers[Process.pid] << t }
    end.each(&:join)
  end

  ##
  # Spawns a new thread that waits for daemon input.
  #
  # @return [Thread]
  #
  def spawn_thread
    Thread.new{ run_thread }.tap do |t|
      t.abort_on_exception = true
    end
  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 do |message|
      process message
    end
  rescue => error
    error(error)

    retry
  end

end

Instance Method Details

#complete(message, output) ⇒ Object

Called when a job has been completed, by default this method is a noop. This method is passed 2 arguments:

  1. The raw input message.
  2. The output of the worker (remapped by the mapper).

Parameters:

  • message (Mixed) —

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

  • output (Mixed) —

    The output of the worker.



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# File 'lib/oni/daemon.rb', line 156

def complete(message, output)
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 175

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.

Parameters:

  • error (StandardError) 


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# File 'lib/oni/daemon.rb', line 165

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 113

def process(message)
  output = run_worker(message)

  complete(message, output)
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 142

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 229

def run_thread
  receive do |message|
    process message
  end
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 126

def run_worker(message)
  mapper = create_mapper
  input  = mapper.map_input(message)
  worker = option(:worker).new(*input)
  output = Timeout.timeout worker_timeout do
    worker.process
  end

  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 215

def spawn_thread
  Thread.new{ run_thread }.tap do |t|
    t.abort_on_exception = true
  end
end

#spawn_worker(name = nil, &block) ⇒ Thread

Spawns a new thread that waits for daemon input.

Returns:

  • (Thread) 


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# File 'lib/oni/daemon.rb', line 188

def spawn_worker name = nil, &block
  Thread.new do
    pid = nil
    loop do # keep restarting for OOM and other cases
      pid = fork do
        Process.setproctitle "#{$0}: worker #{name}" if name

        if block then yield else standard_worker end
      end
      Process.wait pid
    end
  ensure
    Process.kill :KILL, pid
  end
end

#standard_worker ⇒ Object 



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# File 'lib/oni/daemon.rb', line 204

def standard_worker
  Array.new(threads) do
    spawn_thread.tap{ |t| daemon_workers[Process.pid] << t }
  end.each(&:join)
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 56

def start
  before_start if respond_to? :before_start

  wthreads = if threads <= 1    then [run_thread]
             elsif workers <= 1 then standard_worker
             else wthreads = Array.new(workers){ |i| spawn_worker i } end

  after_start if respond_to? :after_start

  %i[INT TERM].each{ |sig| trap(sig){ stop } }
  wthreads.each(&:join) if workers > 1

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 77

def stop
  daemon_workers.each do |pid, worker_threads|
    worker_threads.each(&:kill)
    worker_threads.clear
  end
  exit
end

#threads ⇒ Fixnum

Returns the amount of threads to use.

Returns:

  • (Fixnum) 


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# File 'lib/oni/daemon.rb', line 94

def threads
  option :threads, DEFAULT_THREAD_AMOUNT
end

#worker_timeout ⇒ Fixnum

Returns the amount of threads to use.

Returns:

  • (Fixnum) 


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# File 'lib/oni/daemon.rb', line 103

def worker_timeout
  option :worker_timeout, DEFAULT_WORKER_TIMEOUT
end