Class: AMQP::Queue

Inherits:
Object
  • Object
show all
Extended by:
ProtocolMethodHandlers
Includes:
Entity, ServerNamedEntity
Defined in:
lib/amqp/queue.rb

Overview

Note:

Please make sure you read http://rubyamqp.info/articles/durability/ that covers exchanges durability vs. messages persistence.

What are AMQP queues?

Queues store and forward messages to consumers. They are similar to mailboxes in SMTP. Messages flow from producing applications to exchanges that route them to queues and finally queues deliver them to consumer applications (or consumer applications fetch messages as needed).

Note that unlike some other messaging protocols/systems, messages are not delivered directly to queues. They are delivered to exchanges that route messages to queues using rules knows as bindings.

Concept of bindings

Binding is an association between a queue and an exchange. Queues must be bound to at least one exchange in order to receive messages from publishers. Learn more about bindings in Exchange class documentation.

Key methods

Key methods of Queue class are

Queue names. Server-named queues. Predefined queues.

Every queue has a name that identifies it. Queue names often contain several segments separated by a dot (.), similarly to how URI path segments are separated by a slash (/), although it may be almost any string, with some limitations (see below). Applications may pick queue names or ask broker to generate a name for them. To do so, pass empty string as queue name argument.

Here is an example:

If you want to declare a queue with a particular name, for example, “images.resize”, pass it to Queue class constructor:

Queue names starting with ‘amq.’ are reserved for internal use by the broker. Attempts to declare queue with a name that violates this rule will result in AMQP::IncompatibleOptionsError to be thrown (when queue is re-declared on the same channel object) or channel-level exception (when originally queue was declared on one channel and re-declaration with different attributes happens on another channel). Learn more in Queues guide and Error Handling guide.

Queue life-cycles. When use of server-named queues is optimal and when it isn’t.

To quote AMQP 0.9.1 spec, there are two common message queue life-cycles:

  • Durable message queues that are shared by many consumers and have an independent existence: i.e. they will continue to exist and collect messages whether or not there are consumers to receive them.
  • Temporary message queues that are private to one consumer and are tied to that consumer. When the consumer disconnects, the message queue is deleted.

There are some variations on these, such as shared message queues that are deleted when the last of many consumers disconnects.

One example of durable message queues is well-known services like event collectors (event loggers). They are usually up whether there are services to log anything or not. Other applications know what queues they use and can rely on those queues being around all the time, survive broker restarts and in general be available should an application in the network need to use them. In this case, explicitly named durable queues are optimal and coupling it creates between applications is not an issue. Another scenario of a well-known long-lived service is distributed metadata/directory/locking server like Apache Zookeeper, Google’s Chubby or DNS. Services like this benefit from using well-known, not generated queue names, and so do other applications that use them.

Different scenario is in “a cloud settings” when some kind of workers/instances may come online and go down basically any time and other applications cannot rely on them being available. Using well-known queue names in this case is possible but server-generated, short-lived queues that are bound to topic or fanout exchanges to receive relevant messages is a better idea.

Imagine a service that processes an endless stream of events (Twitter is one example). When traffic goes up, development operations may spin up additional applications instances in the cloud to handle the load. Those new instances want to subscribe to receive messages to process but the rest of the system doesn’t know anything about them, rely on them being online or try to address them directly: they process events from a shared stream and are not different from their peers. In a case like this, there is no reason for message consumers to not use queue names generated by the broker.

In general, use of explicitly named or server-named queues depends on messaging pattern your application needs. Enterprise Integration Patters discusses many messaging patterns in depth. RabbitMQ FAQ also has a section on use cases.

Queue durability and persistence of messages.

Learn more in our http://rubyamqp.info/articles/durability/.

Message ordering

RabbitMQ FAQ explains ordering of messages in AMQP queues

Error handling

When channel-level error occurs, queues associated with that channel are reset: internal state and callbacks are cleared. Recommended strategy is to open a new channel and re-declare all the entities you need. Learn more in Error Handling guide.

See Also:

Constant Summary

Constant Summary

Constants included from Openable

Openable::VALUES

Instance Attribute Summary (collapse)

Attributes included from Entity

#callbacks

Declaration (collapse)

Binding (collapse)

Consuming messages (collapse)

Working With Messages (collapse)

Acknowledging & Rejecting Messages (collapse)

Error Handling & Recovery (collapse)

Instance Method Summary (collapse)

Methods included from ProtocolMethodHandlers

handle, handlers

Methods included from Callbacks

#clear_callbacks, #define_callback, #exec_callback, #exec_callback_once, #exec_callback_once_yielding_self, #exec_callback_yielding_self, #has_callback?, #prepend_callback, #redefine_callback

Methods included from Openable

#closed!, #closed?, #closing!, #closing?, #opened!, #opened?, #opening!, #opening?

Constructor Details

- (Queue) initialize(channel, name = AMQ::Protocol::EMPTY_STRING, opts = {}) {|queue, declare_ok| ... }

Returns a new instance of Queue

Parameters:

  • opts (Hash) (defaults to: {})

    a customizable set of options

Options Hash (opts):

  • :passive (Boolean) — default: false

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

  • :durable (Boolean) — 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).

  • :exclusive (Boolean) — 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.

  • :auto_delete (Boolean) — 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.

  • :nowait (Boolean) — 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.

  • :arguments (Hash) — default: nil

    A hash of optional arguments with the declaration. Some brokers implement AMQP extensions using x-prefixed declaration arguments. For example, RabbitMQ recognizes x-message-ttl declaration arguments that defines TTL of messages in the queue.

Yields:

  • (queue, declare_ok)

    Yields successfully declared queue instance and AMQP method (queue.declare-ok) instance. The latter is optional.

Yield Parameters:

  • queue (Queue)

    Queue that is successfully declared and is ready to be used.

  • declare_ok (AMQ::Protocol::Queue::DeclareOk)

    AMQP queue.declare-ok) instance.

Raises:

  • (ArgumentError)


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# File 'lib/amqp/queue.rb', line 201

def initialize(channel, name = AMQ::Protocol::EMPTY_STRING, opts = {}, &block)
  raise ArgumentError.new("queue name must not be nil; if you want broker to generate queue name for you, pass an empty string") if name.nil?

  @channel  = channel
  @name     = name unless name.empty?
  @server_named = name.empty?
  @opts         = self.class.add_default_options(name, opts, block)

  raise ArgumentError.new("server-named queues (name = '') declaration with :nowait => true makes no sense. If you are not sure what that means, simply drop :nowait => true from opts.") if @server_named && @opts[:nowait]

  # a deferrable that we use to delay operations until this queue is actually declared.
  # one reason for this is to support a case when a server-named queue is immediately bound.
  # it's crazy, but 0.7.x supports it, so... MK.
  @declaration_deferrable = AMQP::Deferrable.new

  super(channel.connection)

  @name         = name
  # this has to stay true even after queue.declare-ok arrives. MK.
  @server_named = @name.empty?
  if @server_named
    self.on_connection_interruption do
      # server-named queue need to get new names after recovery. MK.
      @name = AMQ::Protocol::EMPTY_STRING
    end
  end

  @channel      = channel

  # primarily for autorecovery. MK.
  @bindings  = Array.new

  @consumers = Hash.new

  shim = Proc.new do |q, declare_ok|
    case block.arity
    when 1 then block.call(q)
    else
      block.call(q, declare_ok)
    end
  end

  @channel.once_open do
    if @opts[:nowait]
      @declaration_deferrable.succeed
      block.call(self) if block
    end

    if block
      self.queue_declare(@opts[:passive], @opts[:durable], @opts[:exclusive], @opts[:auto_delete], @opts[:nowait], @opts[:arguments], &shim)
    else
      # we cannot pass :nowait as true here, AMQP::Queue will (rightfully) raise an exception because
      # it has no idea about crazy edge cases we are trying to support for sake of backwards compatibility. MK.
      self.queue_declare(@opts[:passive], @opts[:durable], @opts[:exclusive], @opts[:auto_delete], false, @opts[:arguments])
    end
  end
end

Instance Attribute Details

- (Hash) arguments (readonly)

Returns Additional arguments given on queue declaration. Typically used by AMQP extensions.

Returns:

  • (Hash)

    Additional arguments given on queue declaration. Typically used by AMQP extensions.



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# File 'lib/amqp/queue.rb', line 155

def arguments
  @arguments
end

- (Array<Hash>) bindings (readonly)

Returns:

  • (Array<Hash>)


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# File 'lib/amqp/queue.rb', line 158

def bindings
  @bindings
end

- (AMQP::Channel) channel (readonly)

Channel this queue belongs to.

Returns:



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# File 'lib/amqp/queue.rb', line 146

def channel
  @channel
end

- (Array<Hash>) consumers (readonly)

Returns All consumers on this queue.

Returns:

  • (Array<Hash>)

    All consumers on this queue.



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# File 'lib/amqp/queue.rb', line 149

def consumers
  @consumers
end

- (AMQP::Consumer) default_consumer (readonly)

Note:

Default consumer is the one registered with the convenience #subscribe method. It has no special properties of any kind.

Returns Default consumer associated with this queue (if any), or nil

Returns:

  • (AMQP::Consumer)

    Default consumer associated with this queue (if any), or nil

See Also:



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# File 'lib/amqp/queue.rb', line 152

def default_consumer
  @default_consumer
end

- (Object) name (readonly)

Name of this queue



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# File 'lib/amqp/queue.rb', line 140

def name
  @name
end

- (Object) opts

Options this queue object was instantiated with



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# File 'lib/amqp/queue.rb', line 142

def opts
  @opts
end

Instance Method Details

- (Queue) acknowledge(delivery_tag)

Acknowledge a delivery tag.



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# File 'lib/amqp/queue.rb', line 1168

def acknowledge(delivery_tag)
  @channel.acknowledge(delivery_tag)

  self
end

- (Boolean) auto_delete?

Returns true if this queue was declared as automatically deleted (deleted as soon as last consumer unbinds).

Returns:

  • (Boolean)

    true if this queue was declared as automatically deleted (deleted as soon as last consumer unbinds).



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# File 'lib/amqp/queue.rb', line 286

def auto_delete?
  @auto_delete
end

- (Object) auto_recover

Called by associated connection object when AMQP connection has been re-established (for example, after a network failure).



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# File 'lib/amqp/queue.rb', line 1202

def auto_recover
  self.exec_callback_yielding_self(:before_recovery)

  if self.server_named?
    old_name = @name.dup
    @name    = AMQ::Protocol::EMPTY_STRING

    @channel.queues.delete(old_name)
  end

  self.redeclare do
    self.rebind

    @consumers.each { |tag, consumer| consumer.auto_recover }

    self.exec_callback_yielding_self(:after_recovery)
  end
end

- (Queue) basic_consume(no_ack = false, exclusive = false, nowait = false, no_local = false, arguments = nil, &block)

Returns self

Returns:

Raises:

  • (RuntimeError)

See Also:



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# File 'lib/amqp/queue.rb', line 1083

def basic_consume(no_ack = false, exclusive = false, nowait = false, no_local = false, arguments = nil, &block)
  raise RuntimeError.new("This queue already has default consumer. Please instantiate AMQP::Consumer directly to register additional consumers.") if @default_consumer

  nowait            = true unless block
  @default_consumer = self.class.consumer_class.new(@channel, self, generate_consumer_tag(@name), exclusive, no_ack, arguments, no_local, &block)
  @default_consumer.consume(nowait, &block)

  self
end

- (Object) before_recovery(&block)

Defines a callback that will be executed after TCP connection is recovered after a network failure but before AMQP connection is re-opened. Only one callback can be defined (the one defined last replaces previously added ones).



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# File 'lib/amqp/queue.rb', line 1235

def before_recovery(&block)
  self.redefine_callback(:before_recovery, &block)
end

- (Queue) bind(exchange, opts = {}) { ... }

This method binds a queue to an exchange. Until a queue is bound it will not receive any messages. In a classic messaging model, store-and-forward queues are bound to a dest exchange and subscription queues are bound to a dest_wild exchange.

A valid exchange name (or reference) must be passed as the first parameter. Note that if your producer application knows consumer queue name and wants to deliver a message there, direct exchange may be sufficient (in other words, if your code declares an exchange with the same name as a queue and binds it to that queue, consider using the default exchange and routing key on publishing).

Examples:

Binding a queue to exchange using AMQP::Exchange instance


ch       = AMQP::Channel.new(connection)
exchange = ch.direct('backlog.events')
queue    = ch.queue('', :exclusive => true)
queue.bind(exchange)

Binding a queue to exchange using exchange name


ch       = AMQP::Channel.new(connection)
queue    = ch.queue('', :exclusive => true)
queue.bind('backlog.events')

Parameters:

  • Exchange (Exchange)

    to bind to. May also be a string or any object that responds to #name.

  • opts (Hash) (defaults to: {})

    a customizable set of options

Options Hash (opts):

  • :routing_key (String)

    Specifies the routing key for the binding. The routing key is used for routing messages depending on the exchange configuration. Not all exchanges use a routing key! Refer to the specific exchange documentation. If the routing key is empty and the queue name is empty, the routing key will be the current queue for the channel, which is the last declared queue.

  • :arguments (Hash) — default: nil

    A hash of optional arguments with the declaration. Headers exchange type uses these metadata attributes for routing matching. In addition, brokers may implement AMQP extensions using x-prefixed declaration arguments.

  • :nowait (Boolean) — 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.

Yields:

  • [] Since queue.bind-ok carries no attributes, no parameters are yielded to the block.

Returns:

See Also:



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# File 'lib/amqp/queue.rb', line 346

def bind(exchange, opts = {}, &block)
  @channel.once_open do
    self.once_name_is_available do
      queue_bind(exchange, (opts[:key] || opts[:routing_key] || AMQ::Protocol::EMPTY_STRING), (opts[:nowait] || block.nil?), opts[:arguments], &block)
    end
  end

  self
end

- (Object) callback

Deprecated.

Compatibility alias for #on_declare.



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# File 'lib/amqp/queue.rb', line 888

def callback
  return nil if !subscribed?

  @default_consumer.callback
end

- (Queue) cancel(nowait = false, &block)

Unsubscribes from message delivery.



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# File 'lib/amqp/queue.rb', line 1098

def cancel(nowait = false, &block)
  raise "There is no default consumer for this queue. This usually means that you are trying to unsubscribe a queue that never was subscribed for messages in the first place." if @default_consumer.nil?

  @default_consumer.cancel(nowait, &block)

  self
end

- (String) consumer_tag

Note:

Default consumer is the one registered with the convenience #subscribe method. It has no special properties of any kind.

Returns Consumer tag of the default consumer associated with this queue (if any), or nil

Returns:

  • (String)

    Consumer tag of the default consumer associated with this queue (if any), or nil

See Also:



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# File 'lib/amqp/queue.rb', line 778

def consumer_tag
  if @default_consumer
    @default_consumer.consumer_tag
  else
    nil
  end
end

- (NilClass) delete(opts = {}) {|delete_ok| ... }

This method deletes a queue. When a queue is deleted any pending messages are sent to a dead-letter queue if this is defined in the server configuration, and all consumers on the queue are cancelled.

Parameters:

  • opts (Hash) (defaults to: {})

    a customizable set of options

Options Hash (opts):

  • :if_unused (Boolean) — default: false

    If set, the server will only delete the queue if it has no consumers. If the queue has consumers the server does does not delete it but raises a channel exception instead.

  • :if_empty (Boolean) — default: false

    If set, the server will only delete the queue if it has no messages. If the queue is not empty the server raises a channel exception.

  • :nowait (Boolean) — default: false

    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.

Yields:

  • (delete_ok)

    Yields AMQP method (queue.delete-ok) instance.

Yield Parameters:

  • delete_ok (AMQ::Protocol::Queue::DeleteOk)

    AMQP queue.delete-ok) instance. Carries number of messages that were in the queue.

Returns:

  • (NilClass)

    nil (for v0.7 compatibility)

  • (NilClass)

    nil (for v0.7 compatibility)

See Also:



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# File 'lib/amqp/queue.rb', line 414

def delete(opts = {}, &block)
  @channel.once_open do
    self.once_name_is_available do
      queue_delete(opts.fetch(:if_unused, false), opts.fetch(:if_empty, false), opts.fetch(:nowait, false), &block)
    end
  end

  # backwards compatibility
  nil
end

- (Boolean) durable?

Returns true if this queue was declared as durable (will survive broker restart).

Returns:

  • (Boolean)

    true if this queue was declared as durable (will survive broker restart).



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# File 'lib/amqp/queue.rb', line 274

def durable?
  @durable
end

- (Boolean) exclusive?

Returns true if this queue was declared as exclusive (limited to just one consumer)

Returns:

  • (Boolean)

    true if this queue was declared as exclusive (limited to just one consumer)



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# File 'lib/amqp/queue.rb', line 280

def exclusive?
  @exclusive
end

- (String) generate_consumer_tag(name)

Unique string supposed to be used as a consumer tag.

Returns:

  • (String)

    Unique string.



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# File 'lib/amqp/queue.rb', line 1275

def generate_consumer_tag(name)
  "#{name}-#{Time.now.to_i * 1000}-#{Kernel.rand(999_999_999_999)}"
end

- (Queue) get(no_ack = false, &block)

Fetches messages from the queue.



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# File 'lib/amqp/queue.rb', line 1123

def get(no_ack = false, &block)
  @connection.send_frame(AMQ::Protocol::Basic::Get.encode(@channel.id, @name, no_ack))

  # most people only want one callback per #get call. Consider the following example:
  #
  # 100.times { queue.get { ... } }
  #
  # most likely you won't expect 100 callback runs per message here. MK.
  self.redefine_callback(:get, &block)
  @channel.queues_awaiting_get_response.push(self)

  self
end

- (Object) handle_bind_ok(method)

handle_purge_ok(method)



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# File 'lib/amqp/queue.rb', line 1293

def handle_bind_ok(method)
  self.exec_callback_once(:bind, method)
end

- (Object) handle_declare_ok(method)



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# File 'lib/amqp/queue.rb', line 924

def handle_declare_ok(method)
  @name = method.queue if @name.empty?
  @channel.register_queue(self)

  self.exec_callback_once_yielding_self(:declare, method)

  @declaration_deferrable.succeed
end

- (Object) handle_delete_ok(method)



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# File 'lib/amqp/queue.rb', line 1285

def handle_delete_ok(method)
  self.exec_callback_once(:delete, method)
end

- (Object) handle_get_empty(method)

handle_get_ok(method, header, payload)



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# File 'lib/amqp/queue.rb', line 1306

def handle_get_empty(method)
  method = AMQ::Protocol::GetResponse.new(method)
  self.exec_callback(:get, method)
end

- (Object) handle_get_ok(method, header, payload)

handle_unbind_ok(method)



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# File 'lib/amqp/queue.rb', line 1301

def handle_get_ok(method, header, payload)
  method = AMQ::Protocol::GetResponse.new(method)
  self.exec_callback(:get, method, header, payload)
end

- (Object) handle_purge_ok(method)

handle_delete_ok(method)



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# File 'lib/amqp/queue.rb', line 1289

def handle_purge_ok(method)
  self.exec_callback_once(:purge, method)
end

- (Object) handle_unbind_ok(method)

handle_bind_ok(method)



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# File 'lib/amqp/queue.rb', line 1297

def handle_unbind_ok(method)
  self.exec_callback_once(:unbind, method)
end

- (Object) on_cancel(&block)



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# File 'lib/amqp/queue.rb', line 1107

def on_cancel(&block)
  @default_consumer.on_cancel(&block)
end

- (Object) on_connection_interruption(&block) Also known as: after_connection_interruption

Defines a callback that will be executed after TCP connection is interrupted (typically because of a network failure). Only one callback can be defined (the one defined last replaces previously added ones).



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# File 'lib/amqp/queue.rb', line 1225

def on_connection_interruption(&block)
  self.redefine_callback(:after_connection_interruption, &block)
end

- (Object) on_delivery(&block)



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# File 'lib/amqp/queue.rb', line 768

def on_delivery(&block)
  @default_consumer.on_delivery(&block)
end

- (Object) on_recovery(&block) Also known as: after_recovery

Defines a callback that will be executed when AMQP connection is recovered after a network failure.. Only one callback can be defined (the one defined last replaces previously added ones).



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# File 'lib/amqp/queue.rb', line 1251

def on_recovery(&block)
  self.redefine_callback(:after_recovery, &block)
end

- (Object) once_declared(&block)

Defines a callback that will be executed once queue is declared. More than one callback can be defined. if queue is already declared, given callback is executed immediately.



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# File 'lib/amqp/queue.rb', line 263

def once_declared(&block)
  @declaration_deferrable.callback do
    # guards against cases when deferred operations
    # don't complete before the channel is closed
    block.call if @channel.open?
  end
end

- (Object) once_name_is_available(&block) (protected)



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# File 'lib/amqp/queue.rb', line 1383

def once_name_is_available(&block)
  if server_named?
    self.once_declared do
      block.call
    end
  else
    block.call
  end
end

- (Qeueue) pop(opts = {}) {|headers, payload| ... }

This method provides a direct access to the messages in a queue using a synchronous dialogue that is designed for specific types of application where synchronous functionality is more important than performance.

If queue is empty, `payload` callback argument will be nil, otherwise arguments are identical to those of #subscribe callback.

Examples:

Fetching messages off AMQP queue on demand


queue.pop do |, payload|
  if payload
    puts "Fetched a message: #{payload.inspect}, content_type: #{.content_type}. Shutting down..."
  else
    puts "No messages in the queue"
  end
end

Parameters:

  • opts (Hash) (defaults to: {})

    a customizable set of options

Options Hash (opts):

  • :ack (Boolean) — default: false

    If this field is set to false the server does not expect acknowledgments for messages. That is, when a message is delivered to the client the server automatically and silently acknowledges it on behalf of the client. This functionality increases performance but at the cost of reliability. Messages can get lost if a client dies before it can deliver them to the application.

Yields:

  • (headers, payload)

    When block only takes one argument, yields payload to it. In case of two arguments, yields headers and payload.

Yield Parameters:

  • headers (AMQP::Header)

    Headers (metadata) associated with this message (for example, routing key).

  • payload (String)

    Message body (content). On Ruby 1.9, you may want to check or enforce content encoding.

Returns:

  • (Qeueue)

    Self



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# File 'lib/amqp/queue.rb', line 487

def pop(opts = {}, &block)
  if block
    # We have to maintain this multiple arities jazz
    # because older versions this gem are used in examples in at least 3
    # books published by O'Reilly :(. MK.
    shim = Proc.new { |method, headers, payload|
      case block.arity
      when 1 then
        block.call(payload)
      when 2 then
        h = Header.new(@channel, method, headers ? headers.decode_payload : nil)
        block.call(h, payload)
      else
        h = Header.new(@channel, method, headers ? headers.decode_payload : nil)
        block.call(h, payload, method.delivery_tag, method.redelivered, method.exchange, method.routing_key)
      end
    }

    @channel.once_open do
      self.once_name_is_available do
        # see AMQP::Queue#get in amq-client
        self.get(!opts.fetch(:ack, false), &shim)
      end
    end
  else
    @channel.once_open do
      self.once_name_is_available do
        self.get(!opts.fetch(:ack, false))
      end
    end
  end
end

- (Object) publish(data, opts = {})

Deprecated.
Note:

This method will be removed before 1.0 release

Don’t use this method. It is a leftover from very early days and it ruins the whole point of exchanges/queue separation.



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# File 'lib/amqp/queue.rb', line 903

def publish(data, opts = {})
  exchange.publish(data, opts.merge(:routing_key => self.name))
end

- (NilClass) purge(opts = {}) {|purge_ok| ... }

This method removes all messages from a queue which are not awaiting acknowledgment.

Parameters:

  • opts (Hash) (defaults to: {})

    a customizable set of options

Options Hash (opts):

  • :nowait (Boolean) — default: false

    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.

Yields:

  • (purge_ok)

    Yields AMQP method (queue.purge-ok) instance.

Yield Parameters:

  • purge_ok (AMQ::Protocol::Queue::PurgeOk)

    AMQP queue.purge-ok) instance. Carries number of messages that were purged.

Returns:

  • (NilClass)

    nil (for v0.7 compatibility)

See Also:



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# File 'lib/amqp/queue.rb', line 441

def purge(opts = {}, &block)
  @channel.once_open do
    self.once_declared do
      queue_purge(opts.fetch(:nowait, false), &block)
    end
  end

  # backwards compatibility
  nil
end

- (Queue) queue_bind(exchange, routing_key = AMQ::Protocol::EMPTY_STRING, nowait = false, arguments = nil, &block)

Returns self



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# File 'lib/amqp/queue.rb', line 1023

def queue_bind(exchange, routing_key = AMQ::Protocol::EMPTY_STRING, nowait = false, arguments = nil, &block)
  nowait = true unless block
  exchange_name = if exchange.respond_to?(:name)
                    exchange.name
                  else

                    exchange
                  end

  @connection.send_frame(AMQ::Protocol::Queue::Bind.encode(@channel.id, @name, exchange_name, routing_key, nowait, arguments))

  if !nowait
    self.append_callback(:bind, &block)
    @channel.queues_awaiting_bind_ok.push(self)
  end

  # store bindings for automatic recovery, but BE VERY CAREFUL to
  # not cause an infinite rebinding loop here when we recover. MK.
  binding = { :exchange => exchange_name, :routing_key => routing_key, :arguments => arguments }
  @bindings.push(binding) unless @bindings.include?(binding)

  self
end

- (Queue) queue_declare(passive = false, durable = false, exclusive = false, auto_delete = false, nowait = false, arguments = nil, &block)

Declares this queue.

Returns:

Raises:

  • (ArgumentError)

See Also:



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# File 'lib/amqp/queue.rb', line 943

def queue_declare(passive = false, durable = false, exclusive = false, auto_delete = false, nowait = false, arguments = nil, &block)
  raise ArgumentError, "declaration with nowait does not make sense for server-named queues! Either specify name other than empty string or use #declare without nowait" if nowait && self.anonymous?

  # these two are for autorecovery. MK.
  @passive      = passive
  @server_named = @name.empty?

  @durable     = durable
  @exclusive   = exclusive
  @auto_delete = auto_delete
  @arguments   = arguments

  nowait = true if !block && !@name.empty? && nowait.nil?
  @connection.send_frame(AMQ::Protocol::Queue::Declare.encode(@channel.id, @name, passive, durable, exclusive, auto_delete, nowait, arguments))

  if !nowait
    self.append_callback(:declare, &block)
    @channel.queues_awaiting_declare_ok.push(self)
  end

  self
end

- (Queue) queue_delete(if_unused = false, if_empty = false, nowait = false, &block)

Deletes this queue.

Parameters:

  • if_unused (Boolean) (defaults to: false)

    delete only if queue has no consumers (subscribers).

  • if_empty (Boolean) (defaults to: false)

    delete only if queue has no messages in it.

  • nowait (Boolean) (defaults to: false)

    Don’t wait for reply from broker.

Returns:

See Also:



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# File 'lib/amqp/queue.rb', line 1000

def queue_delete(if_unused = false, if_empty = false, nowait = false, &block)
  nowait = true unless block
  @connection.send_frame(AMQ::Protocol::Queue::Delete.encode(@channel.id, @name, if_unused, if_empty, nowait))

  if !nowait
    self.append_callback(:delete, &block)

    # TODO: delete itself from queues cache
    @channel.queues_awaiting_delete_ok.push(self)
  end

  self
end

- (Queue) queue_purge(nowait = false, &block)

Purges (removes all messagse from) the queue.



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# File 'lib/amqp/queue.rb', line 1144

def queue_purge(nowait = false, &block)
  nowait = true unless block
  @connection.send_frame(AMQ::Protocol::Queue::Purge.encode(@channel.id, @name, nowait))

  if !nowait
    self.redefine_callback(:purge, &block)
    # TODO: handle channel & connection-level exceptions
    @channel.queues_awaiting_purge_ok.push(self)
  end

  self
end

- (Queue) queue_unbind(exchange, routing_key = AMQ::Protocol::EMPTY_STRING, arguments = nil, &block)

Returns self



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# File 'lib/amqp/queue.rb', line 1052

def queue_unbind(exchange, routing_key = AMQ::Protocol::EMPTY_STRING, arguments = nil, &block)
  exchange_name = if exchange.respond_to?(:name)
                    exchange.name
                  else

                    exchange
                  end

  @connection.send_frame(AMQ::Protocol::Queue::Unbind.encode(@channel.id, @name, exchange_name, routing_key, arguments))

  self.append_callback(:unbind, &block)
  @channel.queues_awaiting_unbind_ok.push(self)


  @bindings.delete_if { |b| b[:exchange] == exchange_name }

  self
end

- (Object) redeclare(&block)

Re-declares queue with the same attributes



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# File 'lib/amqp/queue.rb', line 968

def redeclare(&block)
  nowait = true if !block && !@name.empty?

  # server-named queues get their new generated names.
  new_name = if @server_named
               AMQ::Protocol::EMPTY_STRING
             else
               @name
             end
  @connection.send_frame(AMQ::Protocol::Queue::Declare.encode(@channel.id, new_name, @passive, @durable, @exclusive, @auto_delete, false, @arguments))

  if !nowait
    self.append_callback(:declare, &block)
    @channel.queues_awaiting_declare_ok.push(self)
  end

  self
end

- (Queue) reject(delivery_tag, requeue = true)

Returns self



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# File 'lib/amqp/queue.rb', line 1179

def reject(delivery_tag, requeue = true)
  @channel.reject(delivery_tag, requeue)

  self
end

- (Object) reset

Resets queue state. Useful for error handling.



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# File 'lib/amqp/queue.rb', line 909

def reset
  initialize(@channel, @name, @opts)
end

- (Boolean) server_named?

Returns true if this queue is server-named

Returns:

  • (Boolean)

    true if this queue is server-named



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# File 'lib/amqp/queue.rb', line 292

def server_named?
  @server_named
end

- (Object) status(opts = {}) {|number_of_messages, number_of_active_consumers| ... }

Get the number of messages and active consumers (with active channel flow) on a queue.

Examples:

Getting number of messages and active consumers for a queue


AMQP::Channel.queue('name').status { |number_of_messages, number_of_active_consumers|
  puts number_of_messages
}

Yields:

  • (number_of_messages, number_of_active_consumers)

Yield Parameters:

  • number_of_messages (Fixnum)

    Number of messages in the queue

  • number_of_active_consumers (Fixnum)

    Number of active consumers for the queue. Note that consumers can suspend activity (Channel.Flow) in which case they do not appear in this count.

Raises:

  • (ArgumentError)


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# File 'lib/amqp/queue.rb', line 850

def status(opts = {}, &block)
  raise ArgumentError, "AMQP::Queue#status does not make any sense without a block" unless block

  shim = Proc.new { |q, declare_ok| block.call(declare_ok.message_count, declare_ok.consumer_count) }

  @channel.once_open do
    self.once_name_is_available do
      # we do not use self.declare here to avoid caching of @passive since that will cause unexpected side-effects during automatic
      # recovery process. MK.
      @connection.send_frame(AMQ::Protocol::Queue::Declare.encode(@channel.id, @name, true, @opts[:durable], @opts[:exclusive], @opts[:auto_delete], false, @opts[:arguments]))

      self.append_callback(:declare, &shim)
      @channel.queues_awaiting_declare_ok.push(self)
    end
  end

  self
end

- (Queue) subscribe(opts = {}) {|headers, payload| ... }

Subscribes to asynchronous message delivery.

The provided block is passed a single message each time the exchange matches a message to this queue.

Attempts to #subscribe multiple times to the same exchange will raise an Exception. If you need more than one consumer per queue, use Consumer instead. Documentation guide on queues explains this and other topics in great detail.

If the block takes 2 parameters, both the header and the body will be passed in for processing.

Examples:

Use of callback with a single argument


EventMachine.run do
  exchange = AMQP::Channel.direct("foo queue")
  EM.add_periodic_timer(1) do
    exchange.publish("random number #{rand(1000)}")
  end

  queue = AMQP::Channel.queue('foo queue')
  queue.subscribe { |body| puts "received payload [#{body}]" }
end

Use of callback with two arguments


EventMachine.run do
  connection = AMQP.connect(:host => '127.0.0.1')
  puts "Connected to AMQP broker. Running #{AMQP::VERSION} version of the gem..."

  channel  = AMQP::Channel.new(connection)
  queue    = channel.queue("amqpgem.examples.hello_world", :auto_delete => true)
  exchange = channel.direct("amq.direct")

  queue.bind(exchange)

  channel.on_error do |ch, channel_close|
    puts channel_close.reply_text
    connection.close { EventMachine.stop }
  end

  queue.subscribe do |, payload|
    puts "metadata.routing_key : #{.routing_key}"
    puts "metadata.content_type: #{.content_type}"
    puts "metadata.priority    : #{.priority}"
    puts "metadata.headers     : #{.headers.inspect}"
    puts "metadata.timestamp   : #{.timestamp.inspect}"
    puts "metadata.type        : #{.type}"
    puts "metadata.delivery_tag: #{.delivery_tag}"
    puts "metadata.redelivered : #{.redelivered}"

    puts "metadata.app_id      : #{.app_id}"
    puts "metadata.exchange    : #{.exchange}"
    puts
    puts "Received a message: #{payload}. Disconnecting..."

    connection.close {
      EventMachine.stop { exit }
    }
  end

  exchange.publish("Hello, world!",
                   :app_id      => "amqpgem.example",
                   :priority    => 8,
                   :type        => "kinda.checkin",
                   # headers table keys can be anything
                   :headers     => {
                     :coordinates => {
                       :latitude  => 59.35,
                       :longitude => 18.066667
                     },
                     :participants => 11,
                     :venue        => "Stockholm"
                   },
                   :timestamp   => Time.now.to_i)
end

Using object as consumer (message handler), take one


class Consumer

  #
  # API
  #

  def initialize(channel, queue_name = AMQ::Protocol::EMPTY_STRING)
    @queue_name = queue_name

    @channel    = channel
    # Consumer#handle_channel_exception will handle channel
    # exceptions. Keep in mind that you can only register one error handler,
    # so the last one registered "wins".
    @channel.on_error(&method(:handle_channel_exception))
  end # initialize

  def start
    @queue = @channel.queue(@queue_name, :exclusive => true)
    # #handle_message method will be handling messages routed to @queue
    @queue.subscribe(&method(:handle_message))
  end # start

  #
  # Implementation
  #

  def handle_message(, payload)
    puts "Received a message: #{payload}, content_type = #{.content_type}"
  end # handle_message(metadata, payload)

  def handle_channel_exception(channel, channel_close)
    puts "Oops... a channel-level exception: code = #{channel_close.reply_code}, message = #{channel_close.reply_text}"
  end # handle_channel_exception(channel, channel_close)
end

Using object as consumer (message handler), take two: aggregatied handler

class Consumer

  #
  # API
  #

  def handle_message(, payload)
    puts "Received a message: #{payload}, content_type = #{.content_type}"
  end # handle_message(metadata, payload)
end

class Worker

  #
  # API
  #

  def initialize(channel, queue_name = AMQ::Protocol::EMPTY_STRING, consumer = Consumer.new)
    @queue_name = queue_name

    @channel    = channel
    @channel.on_error(&method(:handle_channel_exception))

    @consumer   = consumer
  end # initialize

  def start
    @queue = @channel.queue(@queue_name, :exclusive => true)
    @queue.subscribe(&@consumer.method(:handle_message))
  end # start

  #
  # Implementation
  #

  def handle_channel_exception(channel, channel_close)
    puts "Oops... a channel-level exception: code = #{channel_close.reply_code}, message = #{channel_close.reply_text}"
  end # handle_channel_exception(channel, channel_close)
end

Unit-testing objects that are used as consumers, RSpec style


require "ostruct"
require "json"

# RSpec example
describe Consumer do
  describe "when a new message arrives" do
    subject { described_class.new }

    let(:metadata) do
      o = OpenStruct.new

      o.content_type = "application/json"
      o
    end
    let(:payload)  { JSON.encode({ :command => "reload_config" }) }

    it "does some useful work" do
      # check preconditions here if necessary

      subject.handle_message(, payload)

      # add your code expectations here
    end
  end
end

Parameters:

  • opts (Hash) (defaults to: {})

    a customizable set of options

Options Hash (opts):

  • :ack (Boolean) — default: false

    If this field is set to false the server does not expect acknowledgments for messages. That is, when a message is delivered to the client the server automatically and silently acknowledges it on behalf of the client. This functionality increases performance but at the cost of reliability. Messages can get lost if a client dies before it can deliver them to the application.

  • :nowait (Boolean) — default: false

    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.

  • :confirm (#call) — default: nil

    If set, this proc will be called when the server confirms subscription to the queue with a basic.consume-ok message. Setting this option will automatically set :nowait => false. This is required for the server to send a confirmation.

  • :exclusive (Boolean) — default: false

    Request exclusive consumer access, meaning only this consumer can access the queue. This is useful when you want a long-lived shared queue to be temporarily accessible by just one application (or thread, or process). If application exclusive consumer is part of crashes or loses network connection to the broker, channel is closed and exclusive consumer is thus cancelled.

Yields:

  • (headers, payload)

    When block only takes one argument, yields payload to it. In case of two arguments, yields headers and payload.

Yield Parameters:

  • headers (AMQP::Header)

    Headers (metadata) associated with this message (for example, routing key).

  • payload (String)

    Message body (content). On Ruby 1.9, you may want to check or enforce content encoding.

Returns:

Raises:

  • (RuntimeError)

See Also:



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# File 'lib/amqp/queue.rb', line 748

def subscribe(opts = {}, &block)
  raise RuntimeError.new("This queue already has default consumer. Please instantiate AMQP::Consumer directly to register additional consumers.") if @default_consumer

  opts[:nowait] = false if (@on_confirm_subscribe = opts[:confirm])

  @channel.once_open do
    self.once_name_is_available do
      # guards against a pathological case race condition when a channel
      # is opened and closed before delayed operations are completed.
      self.basic_consume(!opts[:ack], opts[:exclusive], (opts[:nowait] || block.nil?), opts[:no_local], nil, &opts[:confirm])

      self.on_delivery(&block)
    end
  end

  self
end

- (Boolean) subscribed?

Deprecated.

Boolean check to see if the current queue has already subscribed to messages delivery (has default consumer).

Attempts to #subscribe multiple times to the same exchange will raise an Exception. If you need more than one consumer per queue, use Consumer instead.

Returns:

  • (Boolean)

    true if there is a consumer tag associated with this Queue instance



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# File 'lib/amqp/queue.rb', line 879

def subscribed?
  @default_consumer && @default_consumer.subscribed?
end

- (Object) unbind(exchange, opts = {}) { ... }

Remove the binding between the queue and exchange. The queue will not receive any more messages until it is bound to another exchange.

Due to the asynchronous nature of the protocol, it is possible for “in flight” messages to be received after this call completes. Those messages will be serviced by the last block used in a #subscribe or #pop call.

Parameters:

  • Exchange (Exchange)

    to unbind from.

  • opts (Hash) (defaults to: {})

    a customizable set of options

Options Hash (opts):

  • :routing_key (String)

    Binding routing key

  • :arguments (Hash)

    Binding arguments

  • :nowait (Boolean) — 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.

Yields:

  • [] Since queue.unbind-ok carries no attributes, no parameters are yielded to the block.

See Also:



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# File 'lib/amqp/queue.rb', line 378

def unbind(exchange, opts = {}, &block)
  @channel.once_open do
    self.once_name_is_available do
      queue_unbind(exchange, (opts[:key] || opts[:routing_key] || AMQ::Protocol::EMPTY_STRING), opts[:arguments], &block)
    end
  end
end

- (Object) unsubscribe(opts = {}) {|cancel_ok| ... }

Removes the subscription from the queue and cancels the consumer. Once consumer is cancelled, messages will no longer be delivered to it, however, due to the asynchronous nature of the protocol, it is possible for “in flight” messages to be received after this call completes. Those messages will be serviced by the last block used in a #subscribe or #pop call.

Fetching messages with #pop is still possible even after consumer is cancelled.

Additionally, if the queue was created with autodelete set to true, the server will delete the queue after its wait period has expired unless the queue is bound to an active exchange.

The method accepts a block which will be executed when the unsubscription request is acknowledged as complete by the server.

Parameters:

  • opts (Hash) (defaults to: {})

    a customizable set of options

Options Hash (opts):

  • :nowait (Boolean) — default: true

    If set, the server will not respond to the method. The client should not wait for a reply method, the callback (if passed) will be ignored. If the server could not complete the method it will raise a channel or connection exception.

Yields:

  • (cancel_ok)

Yield Parameters:

  • cancel_ok (AMQ::Protocol::Basic::CancelOk)

    AMQP method basic.cancel-ok. You can obtain consumer tag from it.



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# File 'lib/amqp/queue.rb', line 827

def unsubscribe(opts = {}, &block)
  @channel.once_open do
    self.once_name_is_available do
      if @default_consumer
        @default_consumer.cancel(opts.fetch(:nowait, true), &block); @default_consumer = nil
      end
    end
  end
end