Class: MessageBus::ReliablePubSub

Inherits:
Object
  • Object
show all
Defined in:
lib/message_bus/reliable_pub_sub.rb

Defined Under Namespace

Classes: BackLogOutOfOrder, NoMoreRetries

Constant Summary collapse

UNSUB_MESSAGE = 
"$$UNSUBSCRIBE"

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(redis_config = {}, max_backlog_size = 1000) ⇒ ReliablePubSub

max_backlog_size is per multiplexed channel



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# File 'lib/message_bus/reliable_pub_sub.rb', line 42

def initialize(redis_config = {}, max_backlog_size = 1000)
  @redis_config = redis_config
  @max_backlog_size = 1000
  # we can store a ton here ...
  @max_global_backlog_size = 100000
end

Instance Attribute Details

#subscribed ⇒ Object (readonly)

Returns the value of attribute subscribed.



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# File 'lib/message_bus/reliable_pub_sub.rb', line 12

def subscribed
  @subscribed
end

Instance Method Details

#after_fork ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 63

def after_fork
  pub_redis.client.reconnect
end

#backlog(channel, last_id = nil) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 140

def backlog(channel, last_id = nil)
  redis = pub_redis
  backlog_key = backlog_key(channel)
  items = redis.zrangebyscore backlog_key, last_id.to_i + 1, "+inf"

  items.map do |i|
    MessageBus::Message.decode(i)
  end
end

#backlog_id_key(channel) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 81

def backlog_id_key(channel)
  "__mb_backlog_id_n_#{channel}"
end

#backlog_key(channel) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 77

def backlog_key(channel)
  "__mb_backlog_n_#{channel}"
end

#get_message(channel, message_id) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 168

def get_message(channel, message_id)
  redis = pub_redis
  backlog_key = backlog_key(channel)

  items = redis.zrangebyscore backlog_key, message_id, message_id
  if items && items[0]
    MessageBus::Message.decode(items[0])
  else
    nil
  end
end

#global_backlog(last_id = nil) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 150

def global_backlog(last_id = nil)
  last_id = last_id.to_i
  redis = pub_redis

  items = redis.zrangebyscore global_backlog_key, last_id.to_i + 1, "+inf"

  items.map! do |i|
    pipe = i.index "|"
    message_id = i[0..pipe].to_i
    channel = i[pipe+1..-1]
    m = get_message(channel, message_id)
    m
  end

  items.compact!
  items
end

#global_backlog_key ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 89

def global_backlog_key
  "__mb_global_backlog_n"
end

#global_id_key ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 85

def global_id_key
  "__mb_global_id_n"
end

#global_subscribe(last_id = nil, &blk) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/message_bus/reliable_pub_sub.rb', line 223

def global_subscribe(last_id=nil, &blk)
  raise ArgumentError unless block_given?
  highest_id = last_id

  clear_backlog = lambda do
    retries = 4
    begin
      highest_id = process_global_backlog(highest_id, retries > 0, &blk)
    rescue BackLogOutOfOrder => e
      highest_id = e.highest_id
      retries -= 1
      sleep(rand(50) / 1000.0)
      retry
    end
  end


  begin
    @redis_global = new_redis_connection

    if highest_id
      clear_backlog.call(&blk)
    end

    @redis_global.subscribe(redis_channel_name) do |on|
      on.subscribe do
        if highest_id
          clear_backlog.call(&blk)
        end
        @subscribed = true
      end

      on.unsubscribe do
        @subscribed = false
      end

      on.message do |c,m|
        if m == UNSUB_MESSAGE
          @redis_global.unsubscribe
          return
        end
        m = MessageBus::Message.decode m

        # we have 2 options
        #
        # 1. message came in the correct order GREAT, just deal with it
        # 2. message came in the incorrect order COMPLICATED, wait a tiny bit and clear backlog

        if highest_id.nil? || m.global_id == highest_id + 1
          highest_id = m.global_id
          yield m
        else
          clear_backlog.call(&blk)
        end
      end
    end
  rescue => error
    MessageBus.logger.warn "#{error} subscribe failed, reconnecting in 1 second. Call stack #{error.backtrace}"
    sleep 1
    retry
  end
end

#global_unsubscribe ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 215

def global_unsubscribe
  if @redis_global
    pub_redis.publish(redis_channel_name, UNSUB_MESSAGE)
    @redis_global.disconnect
    @redis_global = nil
  end
end

#last_id(channel) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 135

def last_id(channel)
  backlog_id_key = backlog_id_key(channel)
  pub_redis.get(backlog_id_key).to_i
end

#max_backlog_size=(val) ⇒ Object

per channel backlog size



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# File 'lib/message_bus/reliable_pub_sub.rb', line 55

def max_backlog_size=(val)
  @max_backlog_size = val
end

#max_global_backlog_size=(val) ⇒ Object

amount of global backlog we can spin through



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# File 'lib/message_bus/reliable_pub_sub.rb', line 50

def max_global_backlog_size=(val)
  @max_global_backlog_size = val
end

#max_publish_retries ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 29

def max_publish_retries
  @max_publish_retries ||= 10
end

#max_publish_retries=(val) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 25

def max_publish_retries=(val)
  @max_publish_retries = val
end

#max_publish_wait ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 37

def max_publish_wait
  @max_publish_wait ||= 500
end

#max_publish_wait=(ms) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 33

def max_publish_wait=(ms)
  @max_publish_wait = ms
end

#new_redis_connection ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 59

def new_redis_connection
  ::Redis.new(@redis_config)
end

#process_global_backlog(highest_id, raise_error, &blk) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 199

def process_global_backlog(highest_id, raise_error, &blk)
  global_backlog(highest_id).each do |old|
    if highest_id + 1 == old.global_id
      yield old
      highest_id = old.global_id
    else
      raise BackLogOutOfOrder.new(highest_id) if raise_error
      if old.global_id > highest_id
        yield old
        highest_id = old.global_id
      end
    end
  end
  highest_id
end

#pub_redis ⇒ Object

redis connection used for publishing messages



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# File 'lib/message_bus/reliable_pub_sub.rb', line 73

def pub_redis
  @pub_redis ||= new_redis_connection
end

#publish(channel, data) ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 100

def publish(channel, data)
  redis = pub_redis
  backlog_id_key = backlog_id_key(channel)
  backlog_key = backlog_key(channel)

  global_id = nil
  backlog_id = nil

  redis.multi do |m|
    global_id = m.incr(global_id_key)
    backlog_id = m.incr(backlog_id_key)
  end

  global_id = global_id.value
  backlog_id = backlog_id.value

  msg = MessageBus::Message.new global_id, backlog_id, channel, data
  payload = msg.encode

  redis.zadd backlog_key, backlog_id, payload
  redis.zadd global_backlog_key, global_id, backlog_id.to_s << "|" << channel

  redis.publish redis_channel_name, payload

  if backlog_id > @max_backlog_size
    redis.zremrangebyscore backlog_key, 1, backlog_id - @max_backlog_size
  end

  if global_id > @max_global_backlog_size
    redis.zremrangebyscore global_backlog_key, 1, backlog_id - @max_backlog_size
  end

  backlog_id
end

#redis_channel_name ⇒ Object 



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# File 'lib/message_bus/reliable_pub_sub.rb', line 67

def redis_channel_name
  db = @redis_config[:db] || 0
  "discourse_#{db}"
end

#reset! ⇒ Object

use with extreme care, will nuke all of the data



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# File 'lib/message_bus/reliable_pub_sub.rb', line 94

def reset!
  pub_redis.keys("__mb_*").each do |k|
    pub_redis.del k
  end
end

#subscribe(channel, last_id = nil) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/message_bus/reliable_pub_sub.rb', line 180

def subscribe(channel, last_id = nil)
  # trivial implementation for now,
  #   can cut down on connections if we only have one global subscriber
  raise ArgumentError unless block_given?

  if last_id
    # we need to translate this to a global id, at least give it a shot
    #   we are subscribing on global and global is always going to be bigger than local
    #   so worst case is a replay of a few messages
    message = get_message(channel, last_id)
    if message
      last_id = message.global_id
    end
  end
  global_subscribe(last_id) do |m|
    yield m if m.channel == channel
  end
end