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Diffstat (limited to 'lib/puppet/util/queue.rb')
| -rw-r--r-- | lib/puppet/util/queue.rb | 102 |
1 files changed, 102 insertions, 0 deletions
diff --git a/lib/puppet/util/queue.rb b/lib/puppet/util/queue.rb new file mode 100644 index 000000000..3724bab92 --- /dev/null +++ b/lib/puppet/util/queue.rb @@ -0,0 +1,102 @@ + +require 'puppet/indirector' +require 'puppet/util/instance_loader' + +# Implements a message queue client type plugin registry for use by the indirector facility. +# Client modules for speaking a particular protocol (e.g. Stomp::Client for Stomp message +# brokers, Memcached for Starling and Sparrow, etc.) register themselves with this module. +# +# Client classes are expected to live under the Puppet::Util::Queue namespace and corresponding +# directory; the attempted use of a client via its typename (see below) will cause Puppet::Util::Queue +# to attempt to load the corresponding plugin if it is not yet loaded. The client class registers itself +# with Puppet::Util::Queue and should use the same type name as the autloader expects for the plugin file. +# class Puppet::Util::Queue::SpecialMagicalClient < Messaging::SpecialMagic +# ... +# Puppet::Util::Queue.register_queue_type_class(self) +# end +# +# This module reduces the rightmost segment of the class name into a pretty symbol that will +# serve as the queuing client's name. Which means that the "SpecialMagicalClient" above will +# be named <em>:special_magical_client</em> within the registry. +# +# Another class/module may mix-in this module, and may then make use of the registered clients. +# class Queue::Fue +# # mix it in at the class object level rather than instance level +# extend ::Puppet::Util::Queue +# +# # specify the default client type to use. +# self.queue_type_default = :special_magical_type +# end +# +# Queue::Fue instances can get a message queue client through the registry through the mixed-in method +# +client+, which will return a class-wide singleton client instance, determined by +client_class+. +# +# The client plugins are expected to implement an interface similar to that of Stomp::Client: +# * <tt>new()</tt> should return a connected, ready-to-go client instance. Note that no arguments are passed in. +# * <tt>send_message(queue, message)</tt> should send the _message_ to the specified _queue_. +# * <tt>subscribe(queue)</tt> _block_ subscribes to _queue_ and executes _block_ upon receiving a message. +# * _queue_ names are simple names independent of the message broker or client library. No "/queue/" prefixes like in Stomp::Client. +module Puppet::Util::Queue + extend Puppet::Util::InstanceLoader + attr_accessor :queue_type_default + instance_load :queue_clients, 'puppet/util/queue' + + # Adds a new class/queue-type pair to the registry. The _type_ argument is optional; if not provided, + # _type_ defaults to a lowercased, underscored symbol programmatically derived from the rightmost + # namespace of <em>klass.name</em>. + # + # # register with default name +:you+ + # register_queue_type(Foo::You) + # + # # register with explicit queue type name +:myself+ + # register_queue_type(Foo::Me, :myself) + # + # If the type is already registered, an exception is thrown. No checking is performed of _klass_, + # however; a given class could be registered any number of times, as long as the _type_ differs with + # each registration. + def self.register_queue_type(klass, type = nil) + type ||= queue_type_from_class(klass) + raise Puppet::Error, "Queue type %s is already registered" % type.to_s if instance_hash(:queue_clients).include?(type) + instance_hash(:queue_clients)[type] = klass + end + + # Given a queue type symbol, returns the associated +Class+ object. If the queue type is unknown + # (meaning it hasn't been registered with this module), an exception is thrown. + def self.queue_type_to_class(type) + c = loaded_instance :queue_clients, type + raise Puppet::Error, "Queue type %s is unknown." % type unless c + c + end + + # Given a class object _klass_, returns the programmatic default queue type name symbol for _klass_. + # The algorithm is as shown in earlier examples; the last namespace segment of _klass.name_ is taken + # and converted from mixed case to underscore-separated lowercase, and interned. + # queue_type_from_class(Foo) -> :foo + # queue_type_from_class(Foo::Too) -> :too + # queue_type_from_class(Foo::ForYouTwo) -> :for_you_too + # + # The implicit assumption here, consistent with Puppet's approach to plugins in general, + # is that all your client modules live in the same namespace, such that reduction to + # a flat namespace of symbols is reasonably safe. + def self.queue_type_from_class(klass) + # convert last segment of classname from studly caps to lower case with underscores, and symbolize + klass.name.split('::').pop.sub(/^[A-Z]/) {|c| c.downcase}.gsub(/[A-Z]/) {|c| '_' + c.downcase }.intern + end + + # The class object for the client to be used, determined by queue configuration + # settings and known queue client types. + # Looked to the <tt>:queue_client</tt> configuration entry in the running application for + # the default queue type to use, and fails over to +queue_type_default+ if the configuration + # information is not present. + def client_class + Puppet::Util::Queue.queue_type_to_class(Puppet[:queue_client] || queue_type_default) + # Puppet::Util::Queue.queue_type_to_class(Puppet[:queue_client] || :stomp) + end + + # Returns (instantiating as necessary) the singleton queue client instance, according to the + # client_class. No arguments go to the client class constructor, meaning its up to the client class + # to know how to determine its queue message source (presumably through Puppet configuration data). + def client + @client ||= client_class.new + end +end |