Module: Stud::Buffer

Defined in:
lib/stud/buffer.rb

Overview

Implements a generic framework for accepting events which are later flushed in batches. Flushing occurs whenever :max_items or :max_interval (seconds) has been reached.

Including class must implement flush, which will be called with all accumulated items either when the output buffer fills (:max_items) or when a fixed amount of time (:max_interval) passes.

batch_receive and flush

General receive/flush can be implemented in one of two ways.

batch_receive(event) / flush(events)

flush will receive an array of events which were passed to buffer_receive.

batch_receive('one')
batch_receive('two')

will cause a flush invocation like

flush(['one', 'two'])

batch_receive(event, group) / flush(events, group)

flush() will receive an array of events, plus a grouping key.

batch_receive('one',   :server => 'a')
batch_receive('two',   :server => 'b')
batch_receive('three', :server => 'a')
batch_receive('four',  :server => 'b')

will result in the following flush calls

flush(['one', 'three'], {:server => 'a'})
flush(['two', 'four'],  {:server => 'b'})

Grouping keys can be anything which are valid Hash keys. (They don’t have to be hashes themselves.) Strings or Fixnums work fine. Use anything which you’d like to receive in your flush method to help enable different handling for various groups of events.

on_flush_error

Including class may implement on_flush_error, which will be called with an Exception instance whenever buffer_flush encounters an error.

  • buffer_flush will automatically re-try failed flushes, so on_flush_error should not try to implement retry behavior.

  • Exceptions occurring within on_flush_error are not handled by buffer_flush.

on_full_buffer_receive

Including class may implement on_full_buffer_receive, which will be called whenever buffer_receive is called while the buffer is full.

on_full_buffer_receive will receive a Hash like {:pending => 30, :outgoing => 20} which describes the internal state of the module at the moment.

final flush

Including class should call buffer_flush(:final => true) during a teardown/shutdown routine (after the last call to buffer_receive) to ensure that all accumulated messages are flushed.

Author:

Instance Method Summary collapse

Instance Method Details

#buffer_flush(options = {}) ⇒ Fixnum

Try to flush events.

Returns immediately if flushing is not necessary/possible at the moment:

  • :max_items have not been accumulated

  • :max_interval seconds have not elapased since the last flush

  • another flush is in progress

buffer_flush(:force => true) will cause a flush to occur even if :max_items or :max_interval have not been reached. A forced flush will still return immediately (without flushing) if another flush is currently in progress.

buffer_flush(:final => true) is identical to buffer_flush(:force => true), except that if another flush is already in progress, buffer_flush(:final => true) will block/wait for the other flush to finish before proceeding.

Parameters:

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

    Optional. May be {:force => true} or {:final => true}.

Returns:

  • (Fixnum) —

    The number of items successfully passed to flush.



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# File 'lib/stud/buffer.rb', line 180

def buffer_flush(options={})
  force = options[:force] || options[:final]
  final = options[:final]

  # final flush will wait for lock, so we are sure to flush out all buffered events
  if options[:final]
    @buffer_state[:flush_mutex].lock
  elsif ! @buffer_state[:flush_mutex].try_lock # failed to get lock, another flush already in progress
    return 0
  end

  items_flushed = 0

  begin
    time_since_last_flush = (Time.now - @buffer_state[:last_flush])

    return 0 if @buffer_state[:pending_count] == 0
    return 0 if (!force) &&
       (@buffer_state[:pending_count] < @buffer_config[:max_items]) &&
       (time_since_last_flush < @buffer_config[:max_interval])

    @buffer_state[:pending_mutex].synchronize do
      @buffer_state[:outgoing_items] = @buffer_state[:pending_items]
      @buffer_state[:outgoing_count] = @buffer_state[:pending_count]
      buffer_clear_pending
    end

    @buffer_config[:logger].debug("Flushing output",
      :outgoing_count => @buffer_state[:outgoing_count],
      :time_since_last_flush => time_since_last_flush,
      :outgoing_events => @buffer_state[:outgoing_items],
      :batch_timeout => @buffer_config[:max_interval],
      :force => force,
      :final => final
    ) if @buffer_config[:logger]

    @buffer_state[:outgoing_items].each do |group, events|
      begin
        if group.nil?
          flush(events,final)
        else
          flush(events, group, final)
        end

        @buffer_state[:outgoing_items].delete(group)
        events_size = events.size
        @buffer_state[:outgoing_count] -= events_size
        items_flushed += events_size

      rescue => e

        @buffer_config[:logger].warn("Failed to flush outgoing items",
          :outgoing_count => @buffer_state[:outgoing_count],
          :exception => e,
          :backtrace => e.backtrace
        ) if @buffer_config[:logger]

        if @buffer_config[:has_on_flush_error]
          on_flush_error e
        end

        sleep 1
        retry
      end
      @buffer_state[:last_flush] = Time.now
    end

  ensure
    @buffer_state[:flush_mutex].unlock
  end

  return items_flushed
end

#buffer_full? ⇒ bool

Determine if :max_items has been reached.

buffer_receive calls will block while buffer_full? == true.

Returns:

  • (bool) —

    Is the buffer full?



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# File 'lib/stud/buffer.rb', line 126

def buffer_full?
  @buffer_state[:pending_count] + @buffer_state[:outgoing_count] >= @buffer_config[:max_items]
end

#buffer_initialize(options = {}) ⇒ Object

Initialize the buffer.

Call directly from your constructor if you wish to set some non-default options. Otherwise buffer_initialize will be called automatically during the first buffer_receive call.

Options:

  • :max_items, Max number of items to buffer before flushing. Default 50.

  • :max_interval, Max number of seconds to wait between flushes. Default 5.

  • :logger, A logger to write log messages to. No default. Optional.

Parameters:

  • options (Hash) (defaults to: {}) 


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# File 'lib/stud/buffer.rb', line 80

def buffer_initialize(options={})
  if ! self.class.method_defined?(:flush)
    raise ArgumentError, "Any class including Stud::Buffer must define a flush() method."
  end

  @buffer_config = {
    :max_items => options[:max_items] || 50,
    :max_interval => options[:max_interval] || 5,
    :logger => options[:logger] || nil,
    :has_on_flush_error => self.class.method_defined?(:on_flush_error),
    :has_on_full_buffer_receive => self.class.method_defined?(:on_full_buffer_receive)
  }
  @buffer_state = {
    # items accepted from including class
    :pending_items => {},
    :pending_count => 0,

    # guard access to pending_items & pending_count
    :pending_mutex => Mutex.new,

    # items which are currently being flushed
    :outgoing_items => {},
    :outgoing_count => 0,

    # ensure only 1 flush is operating at once
    :flush_mutex => Mutex.new,

    # data for timed flushes
    :last_flush => Time.now,
    :timer => Thread.new do
      loop do
        sleep(@buffer_config[:max_interval])
        buffer_flush(:force => true)
      end
    end
  }

  # events we've accumulated
  buffer_clear_pending
end

#buffer_receive(event, group = nil) ⇒ Object

Save an event for later delivery

Events are grouped by the (optional) group parameter you provide. Groups of events, plus the group name, are later passed to flush.

This call will block if :max_items has been reached.

Parameters:

  • event —

    An item to buffer for flushing later.

  • group (defaults to: nil) —

    Optional grouping key. All events with the same key will be passed to flush together, along with the grouping key itself.

See Also:



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# File 'lib/stud/buffer.rb', line 142

def buffer_receive(event, group=nil)
  buffer_initialize if ! @buffer_state

  # block if we've accumulated too many events
  while buffer_full? do
    on_full_buffer_receive(
      :pending => @buffer_state[:pending_count],
      :outgoing => @buffer_state[:outgoing_count]
    ) if @buffer_config[:has_on_full_buffer_receive]
    sleep 0.1
  end

  @buffer_state[:pending_mutex].synchronize do
    @buffer_state[:pending_items][group] << event
    @buffer_state[:pending_count] += 1
  end

  buffer_flush
end