Class MQ
In: lib/mq.rb
lib/mq/exchange.rb
lib/mq/header.rb
lib/mq/logger.rb
lib/mq/queue.rb
lib/mq/rpc.rb
Parent: Object

The top-level class for building AMQP clients. This class contains several convenience methods for working with queues and exchanges. Many calls delegate/forward to subclasses, but this is the preferred API. The subclass API is subject to change while this high-level API will likely remain unchanged as the library evolves. All code examples will be written using the MQ API.

Below is a somewhat complex example that demonstrates several capabilities of the library. The example starts a clock using a fanout exchange which is used for 1 to many communications. Each consumer generates a queue to receive messages and do some operation (in this case, print the time). One consumer prints messages every second while the second consumer prints messages every 2 seconds. After 5 seconds has elapsed, the 1 second consumer is deleted.

Of interest is the relationship of EventMachine to the process. All MQ operations must occur within the context of an EM.run block. We start EventMachine in its own thread with an empty block; all subsequent calls to the MQ API add their blocks to the EM.run block. This demonstrates how the library could be used to build up and tear down communications outside the context of an EventMachine block and/or integrate the library with other synchronous operations. See the EventMachine documentation for more information.

  require 'rubygems'
  require 'mq'

  thr = Thread.new { EM.run }

  # turns on extreme logging
  #AMQP.logging = true

  def log *args
    p args
  end

  def publisher
    clock = MQ.fanout('clock')
    EM.add_periodic_timer(1) do
      puts

      log :publishing, time = Time.now
      clock.publish(Marshal.dump(time))
    end
  end

  def one_second_consumer
    MQ.queue('every second').bind(MQ.fanout('clock')).subscribe do |time|
      log 'every second', :received, Marshal.load(time)
    end
  end

  def two_second_consumer
    MQ.queue('every 2 seconds').bind('clock').subscribe do |time|
      time = Marshal.load(time)
      log 'every 2 seconds', :received, time if time.sec % 2 == 0
    end
  end

  def delete_one_second
    EM.add_timer(5) do
      # delete the 'every second' queue
      log 'Deleting [every second] queue'
      MQ.queue('every second').delete
    end
  end

  publisher
  one_second_consumer
  two_second_consumer
  delete_one_second
  thr.join

 __END__

 [:publishing, Tue Jan 06 22:46:14 -0600 2009]
 ["every second", :received, Tue Jan 06 22:46:14 -0600 2009]
 ["every 2 seconds", :received, Tue Jan 06 22:46:14 -0600 2009]

 [:publishing, Tue Jan 06 22:46:16 -0600 2009]
 ["every second", :received, Tue Jan 06 22:46:16 -0600 2009]
 ["every 2 seconds", :received, Tue Jan 06 22:46:16 -0600 2009]

 [:publishing, Tue Jan 06 22:46:17 -0600 2009]
 ["every second", :received, Tue Jan 06 22:46:17 -0600 2009]

 [:publishing, Tue Jan 06 22:46:18 -0600 2009]
 ["every second", :received, Tue Jan 06 22:46:18 -0600 2009]
 ["every 2 seconds", :received, Tue Jan 06 22:46:18 -0600 2009]
 ["Deleting [every second] queue"]

 [:publishing, Tue Jan 06 22:46:19 -0600 2009]

 [:publishing, Tue Jan 06 22:46:20 -0600 2009]
 ["every 2 seconds", :received, Tue Jan 06 22:46:20 -0600 2009]

Methods

close   consumers   default   direct   error   exchanges   fanout   get_queue   headers   id   method_missing   new   prefetch   process_frame   queue   queues   recover   reset   rpc   rpcs   send   topic  

Included Modules

AMQP EM::Deferrable

Classes and Modules

Class MQ::Error
Class MQ::Exchange
Class MQ::Header
Class MQ::Logger
Class MQ::Queue
Class MQ::RPC

External Aliases

connection -> conn

Attributes

channel  [R] 
connection  [R] 
connection  [R] 
logging  [RW] 

Public Class methods

Define a message and callback block to be executed on all errors.

unique identifier

Allows for calls to all MQ instance methods. This implicitly calls MQ.new so that a new channel is allocated for subsequent operations.

Returns a new channel. A channel is a bidirectional virtual connection between the client and the AMQP server. Elsewhere in the library the channel is referred to in parameter lists as mq.

Optionally takes the result from calling AMQP::connect.

Rarely called directly by client code. This is implicitly called by most instance methods. See method_missing.

 EM.run do
   channel = MQ.new
 end

 EM.run do
   channel = MQ.new AMQP::connect
 end

Public Instance methods

Queue objects keyed on their consumer tags.

Not typically called by client code.

Defines, intializes and returns an Exchange to act as an ingress point for all published messages.

Direct

A direct exchange is useful for 1:1 communication between a publisher and subscriber. Messages are routed to the queue with a binding that shares the same name as the exchange. Alternately, the messages are routed to the bound queue that shares the same name as the routing key used for defining the exchange. This exchange type does not honor the +:key+ option when defining a new instance with a name. It will honor the +:key+ option if the exchange name is the empty string. Allocating this exchange without a name or with the empty string will use the internal ‘amq.direct’ exchange.

Any published message, regardless of its persistence setting, is thrown away by the exchange when there are no queues bound to it.

 # exchange is named 'foo'
 exchange = MQ.direct('foo')

 # or, the exchange can use the default name (amq.direct) and perform
 # routing comparisons using the :key
 exchange = MQ.direct("", :key => 'foo')
 exchange.publish('some data') # will be delivered to queue bound to 'foo'

 queue = MQ.queue('foo')
 # can receive data since the queue name and the exchange key match exactly
 queue.pop { |data| puts "received data [#{data}]" }

Options

  • :passive => true | false (default false)

If set, the server will not create the exchange if it does not already exist. The client can use this to check whether an exchange exists without modifying the server state.

  • :durable => true | false (default false)

If set when creating a new exchange, the exchange will be marked as durable. Durable exchanges remain active when a server restarts. Non-durable exchanges (transient exchanges) are purged if/when a server restarts.

A transient exchange (the default) is stored in memory-only. The exchange and all bindings will be lost on a server restart. It makes no sense to publish a persistent message to a transient exchange.

Durable exchanges and their bindings are recreated upon a server restart. Any published messages not routed to a bound queue are lost.

  • :auto_delete => true | false (default false)

If set, the exchange is deleted when all queues have finished using it. The server waits for a short period of time before determining the exchange is unused to give time to the client code to bind a queue to it.

If the exchange has been previously declared, this option is ignored on subsequent declarations.

  • :internal => true | false (default false)

If set, the exchange may not be used directly by publishers, but only when bound to other exchanges. Internal exchanges are used to construct wiring that is not visible to applications.

  • :nowait => true | false (default true)

If set, the server will not respond to the method. The client should not wait for a reply method. If the server could not complete the method it will raise a channel or connection exception.

Exceptions

Doing any of these activities are illegal and will raise MQ:Error.

  • redeclare an already-declared exchange to a different type
  • :passive => true and the exchange does not exist (NOT_FOUND)

Returns a hash of all the exchange proxy objects.

Not typically called by client code.

Defines, intializes and returns an Exchange to act as an ingress point for all published messages.

Fanout

A fanout exchange is useful for 1:N communication where one publisher feeds multiple subscribers. Like direct exchanges, messages published to a fanout exchange are delivered to queues whose name matches the exchange name (or are bound to that exchange name). Each queue gets its own copy of the message.

Any published message, regardless of its persistence setting, is thrown away by the exchange when there are no queues bound to it.

Like the direct exchange type, this exchange type does not honor the +:key+ option when defining a new instance with a name. It will honor the +:key+ option if the exchange name is the empty string. Allocating this exchange without a name or with the empty string will use the internal ‘amq.fanout’ exchange.

 EM.run do
   clock = MQ.fanout('clock')
   EM.add_periodic_timer(1) do
     puts "\npublishing #{time = Time.now}"
     clock.publish(Marshal.dump(time))
   end

   amq = MQ.queue('every second')
   amq.bind(MQ.fanout('clock')).subscribe do |time|
     puts "every second received #{Marshal.load(time)}"
   end

   # note the string passed to #bind
   MQ.queue('every 5 seconds').bind('clock').subscribe do |time|
     time = Marshal.load(time)
     puts "every 5 seconds received #{time}" if time.strftime('%S').to_i%5 == 0
   end
 end

Options

  • :passive => true | false (default false)

If set, the server will not create the exchange if it does not already exist. The client can use this to check whether an exchange exists without modifying the server state.

  • :durable => true | false (default false)

If set when creating a new exchange, the exchange will be marked as durable. Durable exchanges remain active when a server restarts. Non-durable exchanges (transient exchanges) are purged if/when a server restarts.

A transient exchange (the default) is stored in memory-only. The exchange and all bindings will be lost on a server restart. It makes no sense to publish a persistent message to a transient exchange.

Durable exchanges and their bindings are recreated upon a server restart. Any published messages not routed to a bound queue are lost.

  • :auto_delete => true | false (default false)

If set, the exchange is deleted when all queues have finished using it. The server waits for a short period of time before determining the exchange is unused to give time to the client code to bind a queue to it.

If the exchange has been previously declared, this option is ignored on subsequent declarations.

  • :internal => true | false (default false)

If set, the exchange may not be used directly by publishers, but only when bound to other exchanges. Internal exchanges are used to construct wiring that is not visible to applications.

  • :nowait => true | false (default true)

If set, the server will not respond to the method. The client should not wait for a reply method. If the server could not complete the method it will raise a channel or connection exception.

Exceptions

Doing any of these activities are illegal and will raise MQ:Error.

  • redeclare an already-declared exchange to a different type
  • :passive => true and the exchange does not exist (NOT_FOUND)

Defines, intializes and returns an Exchange to act as an ingress point for all published messages.

Headers

A headers exchange allows for messages to be published to an exchange

Any published message, regardless of its persistence setting, is thrown away by the exchange when there are no queues bound to it.

As part of the AMQP standard, each server should predeclare a headers exchange called ‘amq.match’ (this is not required by the standard). Allocating this exchange without a name or with the empty string will use the internal ‘amq.match’ exchange.

TODO: The classic example is …

When publishing data to the exchange, bound queues subscribing to the exchange indicate which data interests them by passing arguments for matching against the headers in published messages. The form of the matching can be controlled by the ‘x-match’ argument, which may be ‘any’ or ‘all’. If unspecified (in RabbitMQ at least), it defaults to "all".

A value of ‘all’ for ‘x-match’ implies that all values must match (i.e. it does an AND of the headers ), while a value of ‘any’ implies that at least one should match (ie. it does an OR).

TODO: document behavior when either the binding or the message is missing

      a header present in the other

TODO: insert example

Options

  • :passive => true | false (default false)

If set, the server will not create the exchange if it does not already exist. The client can use this to check whether an exchange exists without modifying the server state.

  • :durable => true | false (default false)

If set when creating a new exchange, the exchange will be marked as durable. Durable exchanges remain active when a server restarts. Non-durable exchanges (transient exchanges) are purged if/when a server restarts.

A transient exchange (the default) is stored in memory-only. The exchange and all bindings will be lost on a server restart. It makes no sense to publish a persistent message to a transient exchange.

Durable exchanges and their bindings are recreated upon a server restart. Any published messages not routed to a bound queue are lost.

  • :auto_delete => true | false (default false)

If set, the exchange is deleted when all queues have finished using it. The server waits for a short period of time before determining the exchange is unused to give time to the client code to bind a queue to it.

If the exchange has been previously declared, this option is ignored on subsequent declarations.

  • :internal => true | false (default false)

If set, the exchange may not be used directly by publishers, but only when bound to other exchanges. Internal exchanges are used to construct wiring that is not visible to applications.

  • :nowait => true | false (default true)

If set, the server will not respond to the method. The client should not wait for a reply method. If the server could not complete the method it will raise a channel or connection exception.

Exceptions

Doing any of these activities are illegal and will raise MQ:Error.

  • redeclare an already-declared exchange to a different type
  • :passive => true and the exchange does not exist (NOT_FOUND)
  • using a value other than "any" or "all" for "x-match"

May raise a MQ::Error exception when the frame payload contains a Protocol::Channel::Close object.

This usually occurs when a client attempts to perform an illegal operation. A short, and incomplete, list of potential illegal operations follows:

  • publish a message to a deleted exchange (NOT_FOUND)
  • declare an exchange using the reserved ‘amq.’ naming structure (ACCESS_REFUSED)

Queues store and forward messages. Queues can be configured in the server or created at runtime. Queues must be attached to at least one exchange in order to receive messages from publishers.

Like an Exchange, queue names starting with ‘amq.’ are reserved for internal use. Attempts to create queue names in violation of this reservation will raise MQ:Error (ACCESS_REFUSED).

It is not supported to create a queue without a name; some string (even the empty string) must be passed in the name parameter.

Options

  • :passive => true | false (default false)

If set, the server will not create the exchange if it does not already exist. The client can use this to check whether an exchange exists without modifying the server state.

  • :durable => true | false (default false)

If set when creating a new queue, the queue will be marked as durable. Durable queues remain active when a server restarts. Non-durable queues (transient queues) are purged if/when a server restarts. Note that durable queues do not necessarily hold persistent messages, although it does not make sense to send persistent messages to a transient queue (though it is allowed).

Again, note the durability property on a queue has no influence on the persistence of published messages. A durable queue containing transient messages will flush those messages on a restart.

If the queue has already been declared, any redeclaration will ignore this setting. A queue may only be declared durable the first time when it is created.

  • :exclusive => true | false (default false)

Exclusive queues may only be consumed from by the current connection. Setting the ‘exclusive’ flag always implies ‘auto-delete’. Only a single consumer is allowed to remove messages from this queue.

The default is a shared queue. Multiple clients may consume messages from this queue.

Attempting to redeclare an already-declared queue as :exclusive => true will raise MQ:Error.

  • :auto_delete = true | false (default false)

If set, the queue is deleted when all consumers have finished using it. Last consumer can be cancelled either explicitly or because its channel is closed. If there was no consumer ever on the queue, it won‘t be deleted.

The server waits for a short period of time before determining the queue is unused to give time to the client code to bind an exchange to it.

If the queue has been previously declared, this option is ignored on subsequent declarations.

Any remaining messages in the queue will be purged when the queue is deleted regardless of the message‘s persistence setting.

  • :nowait => true | false (default true)

If set, the server will not respond to the method. The client should not wait for a reply method. If the server could not complete the method it will raise a channel or connection exception.

Returns a hash of all the queue proxy objects.

Not typically called by client code.

Asks the broker to redeliver all unacknowledged messages on this channel.

If this parameter is false, the message will be redelivered to the original recipient. If this flag is true, the server will attempt to requeue the message, potentially then delivering it to an alternative subscriber.

Takes a channel, queue and optional object.

The optional object may be a class name, module name or object instance. When given a class or module name, the object is instantiated during this setup. The passed queue is automatically subscribed to so it passes all messages (and their arguments) to the object.

Marshalling and unmarshalling the objects is handled internally. This marshalling is subject to the same restrictions as defined in the Marshal standard library. See that documentation for further reference.

When the optional object is not passed, the returned rpc reference is used to send messages and arguments to the queue. See method_missing which does all of the heavy lifting with the proxy. Some client elsewhere must call this method with the optional block so that there is a valid destination. Failure to do so will just enqueue marshalled messages that are never consumed.

 EM.run do
   server = MQ.rpc('hash table node', Hash)

   client = MQ.rpc('hash table node')
   client[:now] = Time.now
   client[:one] = 1

   client.values do |res|
     p 'client', :values => res
   end

   client.keys do |res|
     p 'client', :keys => res
     EM.stop_event_loop
   end
 end

Returns a hash of all rpc proxy objects.

Not typically called by client code.

Defines, intializes and returns an Exchange to act as an ingress point for all published messages.

Topic

A topic exchange allows for messages to be published to an exchange tagged with a specific routing key. The Exchange uses the routing key to determine which queues to deliver the message. Wildcard matching is allowed. The topic must be declared using dot notation to separate each subtopic.

This is the only exchange type to honor the key hash key for all cases.

Any published message, regardless of its persistence setting, is thrown away by the exchange when there are no queues bound to it.

As part of the AMQP standard, each server should predeclare a topic exchange called ‘amq.topic’ (this is not required by the standard). Allocating this exchange without a name or with the empty string will use the internal ‘amq.topic’ exchange.

The classic example is delivering market data. When publishing market data for stocks, we may subdivide the stream based on 2 characteristics: nation code and trading symbol. The topic tree for Apple Computer would look like:

 'stock.us.aapl'

For a foreign stock, it may look like:

 'stock.de.dax'

When publishing data to the exchange, bound queues subscribing to the exchange indicate which data interests them by passing a routing key for matching against the published routing key.

 EM.run do
   exch = MQ.topic("stocks")
   keys = ['stock.us.aapl', 'stock.de.dax']

   EM.add_periodic_timer(1) do # every second
     puts
     exch.publish(10+rand(10), :routing_key => keys[rand(2)])
   end

   # match against one dot-separated item
   MQ.queue('us stocks').bind(exch, :key => 'stock.us.*').subscribe do |price|
     puts "us stock price [#{price}]"
   end

   # match against multiple dot-separated items
   MQ.queue('all stocks').bind(exch, :key => 'stock.#').subscribe do |price|
     puts "all stocks: price [#{price}]"
   end

   # require exact match
   MQ.queue('only dax').bind(exch, :key => 'stock.de.dax').subscribe do |price|
     puts "dax price [#{price}]"
   end
 end

For matching, the ’*’ (asterisk) wildcard matches against one dot-separated item only. The ’#’ wildcard (hash or pound symbol) matches against 0 or more dot-separated items. If none of these symbols are used, the exchange performs a comparison looking for an exact match.

Options

  • :passive => true | false (default false)

If set, the server will not create the exchange if it does not already exist. The client can use this to check whether an exchange exists without modifying the server state.

  • :durable => true | false (default false)

If set when creating a new exchange, the exchange will be marked as durable. Durable exchanges remain active when a server restarts. Non-durable exchanges (transient exchanges) are purged if/when a server restarts.

A transient exchange (the default) is stored in memory-only. The exchange and all bindings will be lost on a server restart. It makes no sense to publish a persistent message to a transient exchange.

Durable exchanges and their bindings are recreated upon a server restart. Any published messages not routed to a bound queue are lost.

  • :auto_delete => true | false (default false)

If set, the exchange is deleted when all queues have finished using it. The server waits for a short period of time before determining the exchange is unused to give time to the client code to bind a queue to it.

If the exchange has been previously declared, this option is ignored on subsequent declarations.

  • :internal => true | false (default false)

If set, the exchange may not be used directly by publishers, but only when bound to other exchanges. Internal exchanges are used to construct wiring that is not visible to applications.

  • :nowait => true | false (default true)

If set, the server will not respond to the method. The client should not wait for a reply method. If the server could not complete the method it will raise a channel or connection exception.

Exceptions

Doing any of these activities are illegal and will raise MQ:Error.

  • redeclare an already-declared exchange to a different type
  • :passive => true and the exchange does not exist (NOT_FOUND)

[Validate]