NAME MooX::Role::Pluggable - Add a plugin pipeline to your cows SYNOPSIS # A simple pluggable dispatcher: package MyDispatcher; use Moo; use MooX::Role::Pluggable::Constants; with 'MooX::Role::Pluggable'; sub BUILD { my ($self) = @_; # (optionally) Configure our plugin pipeline $self->_pluggable_init( reg_prefix => 'Plug_', ev_prefix => 'Event_', types => { NOTIFY => 'N', PROCESS => 'P', }, ); } around '_pluggable_event' => sub { # This override redirects internal events (errors, etc) to ->process() my ($orig, $self) = splice @_, 0, 2; $self->process( @_ ) }; sub process { my ($self, $event, @args) = @_; # Dispatch to 'P_' prefixed "PROCESS" type handlers. # # _pluggable_process will automatically strip a leading 'ev_prefix' # (see the call to _pluggable_init above); that lets us easily # dispatch errors to our P_plugin_error handler below without worrying # about our ev_prefix ourselves: my $retval = $self->_pluggable_process( PROCESS => $event, \@args ); unless ($retval == EAT_ALL) { # The pipeline allowed the event to continue. # A dispatcher might re-dispatch elsewhere, etc. } } sub shutdown { my ($self) = @_; # Unregister all of our plugins. $self->_pluggable_destroy; } sub P_plugin_error { # Since we re-dispatched errors in our _pluggable_event handler, # we could handle exceptions here and then eat them, perhaps: my ($self, undef) = splice @_, 0, 2; # Arguments are references: my $plug_err = ${ $_[0] }; my $plug_obj = ${ $_[1] }; my $error_src = ${ $_[2] }; # ... EAT_ALL } # A Plugin object. package MyPlugin; use MooX::Role::Pluggable::Constants; sub new { bless {}, shift } sub Plug_register { my ($self, $core) = @_; # Subscribe to events: $core->subscribe( $self, 'PROCESS', 'my_event', 'another_event' ); # Log that we're here, do some initialization, etc ... return EAT_NONE } sub Plug_unregister { my ($self, $core) = @_; # Called when this plugin is unregistered # ... do some cleanup, etc ... return EAT_NONE } sub P_my_event { # Handle a dispatched "PROCESS"-type event: my ($self, $core) = splice @_, 0, 2; # Arguments are references and can be modified: my $arg = ${ $_[0] }; # ... do some work ... # Return an EAT constant to control event lifetime # EAT_NONE allows this event to continue through the pipeline return EAT_NONE } # An external package that interacts with our dispatcher; # this is just a quick and dirty example to show external # plugin manipulation: package MyController; use Moo; has 'dispatcher' => ( is => 'rw', default => sub { MyDispatcher->new() }, ); sub BUILD { my ($self) = @_; $self->dispatcher->plugin_add( 'MyPlugin', MyPlugin->new() ); } sub do_stuff { my $self = shift; $self->dispatcher->process( 'my_event', @_ ) } DESCRIPTION A Moo::Role for turning instances of your class into pluggable objects. Consumers of this role gain a plugin pipeline and methods to manipulate it, as well as a flexible dispatch system (see "_pluggable_process"). The logic and behavior is based almost entirely on Object::Pluggable (see "AUTHOR"). Some methods are the same; implementation & interface differ and you will still want to read thoroughly if coming from Object::Pluggable. Dispatch is significantly faster -- see "Performance". It may be worth noting that this is nothing at all like the Moose counterpart MooseX::Role::Pluggable. If the names confuse ... well, I lacked for better ideas. ;-) If you're using POE, also see MooX::Role::POE::Emitter, which consumes this role. Initialization _pluggable_init $self->_pluggable_init( # Prefix for registration events. # Defaults to 'plugin_' ('plugin_register' / 'plugin_unregister') reg_prefix => 'plugin_', # Prefix for dispatched internal events # (add, del, error, register, unregister ...) # Defaults to 'plugin_ev_' event_prefix => 'plugin_ev_', # Map type names to prefixes. # Event types are arbitrary. # Prefix is prepended when dispathing events of a particular type. # Defaults to: { NOTIFY => 'N', PROCESS => 'P' } types => { NOTIFY => 'N', PROCESS => 'P', }, ); A consumer can call _pluggable_init to set up pipeline-related options appropriately; this should be done prior to loading plugins or dispatching to "_pluggable_process". If it is not called, the defaults (as shown above) are used. types => can be either an ARRAY of event types (which will be used as prefixes): types => [ qw/ IncomingEvent OutgoingEvent / ], ... or a HASH mapping an event type to a prefix: types => { Incoming => 'I', Outgoing => 'O', }, A '_' is automatically appended to event type prefixes when events are dispatched via "_pluggable_process"; thus, an event destined for our 'Incoming' type shown above will be dispatched to appropriate "I_" handlers: # Dispatched to 'I_foo' method in plugins registered for Incoming 'foo': $self->_pluggable_process( Incoming => 'foo', 'bar', 'baz' ); "reg_prefix"/"event_prefix" are not automatically munged in any way. An empty string "reg_prefix"/"event_prefix" is valid. _pluggable_destroy $self->_pluggable_destroy; Shuts down the plugin pipeline, unregistering/unloading all known plugins. _pluggable_event # In our consumer sub _pluggable_event { my ($self, $event, @args) = @_; # Dispatch out, perhaps. } "_pluggable_event" is called for internal notifications, such as plugin load/unload and error reporting (see "Internal events"). It should be overriden in your consuming class to do something useful with the dispatched event (and any other arguments passed in). The $event passed will be prefixed with the configured event_prefix. Also see "Internal events". Registration A plugin is any blessed object that is registered with your Pluggable object via "plugin_add"; during registration, plugins usually subscribe to some events via "subscribe". See "plugin_add" regarding loading plugins. subscribe Subscribe a plugin to some pluggable events. $self->subscribe( $plugin_obj, $type, @events ); Registers a plugin object to receive @events of type $type. This is frequently called from within the plugin's registration handler (see "plugin_register"): # In a plugin: sub plugin_register { my ($self, $core) = @_; $core->subscribe( $self, PROCESS => qw/ my_event another_event / ); $core->subscribe( $self, NOTIFY => 'all' ); EAT_NONE } Subscribe to all to receive all events. (It may be worth noting that subscribing a lot of plugins to 'all' events will cause a performance hit in "_pluggable_process" dispatch versus subscribing to specific events.) unsubscribe Unsubscribe a plugin from subscribed events. The unregister counterpart to "subscribe"; stops delivering specified events to a plugin. The plugin is still loaded and registered until "plugin_del" is called. Carries the same arguments as "subscribe". plugin_register Defined in your plugin(s) and called at load time. (Note that 'plugin_' is just a default register method prefix; it can be changed prior to loading plugins. See "_pluggable_init" for details.) The "plugin_register" method is called on a loaded plugin when it is added to the pipeline; it is passed the plugin object ($self), the Pluggable object, and any arguments given to "plugin_add" (or similar registration methods). Normally one might call a "subscribe" from here to start receiving events after load-time: sub plugin_register { my ($self, $core, @args) = @_; $core->subscribe( $self, 'NOTIFY', @events ); EAT_NONE } plugin_unregister Defined in your plugin(s) and called at load time. (Note that 'plugin_' is just a default register method prefix; it can be changed prior to loading plugins. See "_pluggable_init" for details.) The unregister counterpart to "plugin_register", called when the object is removed from the pipeline (via "plugin_del" or "_pluggable_destroy"). sub plugin_unregister { my ($self, $core) = @_; EAT_NONE } Carries the same arguments. Dispatch _pluggable_process my $eat = $self->_pluggable_process( $type, $event, \@args ); return 1 if $eat == EAT_ALL; The "_pluggable_process" method handles dispatching. If $event is prefixed with our event prefix (see "_pluggable_init"), the prefix is stripped prior to dispatch (to be replaced with a type prefix matching the specified $type). Arguments should be passed in as an ARRAY. During dispatch, references to the arguments are passed to subs following automatically-prepended objects belonging to the plugin and the pluggable caller, respectively: my @args = qw/baz bar/; $self->_pluggable_process( 'NOTIFY', 'foo', \@args ); # In a plugin: sub N_foo { my ($self, $core) = splice @_, 0, 2; # Dereferenced expected scalars: my $baz = ${ $_[0] }; my $bar = ${ $_[1] }; } This allows for argument modification as an event is passed along the pipeline. Dispatch process for $event 'foo' of $type 'NOTIFY': - Prepend the known prefix for the specified type, and '_' 'foo' -> 'N_foo' - Attempt to dispatch to $self->N_foo() - If no such method, attempt to dispatch to $self->_default() (The method we were attempting to call is prepended to arguments) - If the event was not eaten (see below), dispatch to plugins "Eaten" means a handler returned a EAT_* constant from MooX::Role::Pluggable::Constants indicating that the event's lifetime should terminate. Specifically: If our consuming class provides a method or '_default' that returns: EAT_ALL: skip plugin pipeline, return EAT_ALL EAT_CLIENT: continue to plugin pipeline return EAT_ALL if plugin returns EAT_PLUGIN later EAT_PLUGIN: skip plugin pipeline entirely return EAT_NONE unless EAT_CLIENT was seen previously EAT_NONE: continue to plugin pipeline If one of our plugins in the pipeline returns: EAT_ALL: skip further plugins, return EAT_ALL EAT_CLIENT: continue to next plugin, set pending EAT_ALL (EAT_ALL will be returned when plugin processing finishes) EAT_PLUGIN: return EAT_ALL if previous sub returned EAT_CLIENT else return EAT_NONE EAT_NONE: continue to next plugin This functionality (derived from Object::Pluggable) provides fine-grained control over event lifetime. Higher layers can check for an "EAT_ALL" return value from _pluggable_process to determine whether to continue operating on a particular event (re-dispatch elsewhere, for example). Plugins can use 'EAT_CLIENT' to indicate that an event should be eaten after plugin processing is complete, 'EAT_PLUGIN' to stop plugin processing, and 'EAT_ALL' to indicate that the event should not be dispatched further. Plugin Management Methods Plugin pipeline manipulation methods will set $@, "carp()", and return empty list on error (unless otherwise noted). See "plugin_error" regarding errors raised during plugin registration and dispatch. plugin_add $self->plugin_add( $alias, $plugin_obj, @args ); Add a plugin object to the pipeline. Returns the same values as "plugin_pipe_push". plugin_del $self->plugin_del( $alias_or_plugin_obj, @args ); Remove a plugin from the pipeline. Takes either a plugin alias or object. Returns the removed plugin object. plugin_get my $plug_obj = $self->plugin_get( $alias ); my ($plug_obj, $plug_alias) = $self->plugin_get( $alias_or_plugin_obj ); In scalar context, returns the plugin object belonging to the specified alias. In list context, returns the object and alias, respectively. plugin_alias_list my @loaded = $self->plugin_alias_list; Returns a list of loaded plugin aliases. plugin_replace $self->plugin_replace( old => $alias_or_plugin_obj, alias => $new_alias, plugin => $new_plugin_obj, # Optional: register_args => [ ], unregister_args => [ ], ); Replace an existing plugin object with a new one. Returns the old (removed) plugin object. Pipeline methods plugin_pipe_push $self->plugin_pipe_push( $alias, $plugin_obj, @args ); Add a plugin to the end of the pipeline. (Typically one would use "plugin_add" rather than calling this method directly.) plugin_pipe_pop my $plug = $self->plugin_pipe_pop( @unregister_args ); Pop the last plugin off the pipeline, passing any specified arguments to "plugin_unregister". In scalar context, returns the plugin object that was removed. In list context, returns the plugin object and alias, respectively. plugin_pipe_unshift $self->plugin_pipe_unshift( $alias, $plugin_obj, @args ); Add a plugin to the beginning of the pipeline. Returns the total number of loaded plugins (or an empty list on failure). plugin_pipe_shift $self->plugin_pipe_shift( @unregister_args ); Shift the first plugin off the pipeline, passing any specified args to "plugin_unregister". In scalar context, returns the plugin object that was removed. In list context, returns the plugin object and alias, respectively. plugin_pipe_get_index my $idx = $self->plugin_pipe_get_index( $alias_or_plugin_obj ); if ($idx < 0) { # Plugin doesn't exist } Returns the position of the specified plugin in the pipeline. Returns -1 if the plugin does not exist. plugin_pipe_insert_after $self->plugin_pipe_insert_after( after => $alias_or_plugin_obj, alias => $new_alias, plugin => $new_plugin_obj, # Optional: register_args => [ ], ); Add a plugin to the pipeline after the specified previously-existing alias or plugin object. Returns boolean true on success. plugin_pipe_insert_before $self->plugin_pipe_insert_before( before => $alias_or_plugin_obj, alias => $new_alias, plugin => $new_plugin_obj, # Optional: register_args => [ ], ); Similar to "plugin_pipe_insert_after", but insert before the specified previously-existing plugin, not after. plugin_pipe_bump_up $self->plugin_pipe_bump_up( $alias_or_plugin_obj, $count ); Move the specified plugin 'up' $count positions in the pipeline. Returns -1 if the plugin cannot be bumped up any farther. plugin_pipe_bump_down $self->plugin_pipe_bump_down( $alias_or_plugin_obj, $count ); Move the specified plugin 'down' $count positions in the pipeline. Returns -1 if the plugin cannot be bumped down any farther. Internal events These events are dispatched to "_pluggable_event" prefixed with our pluggable event prefix; see "_pluggable_init". plugin_error Issued via "_pluggable_event" when an error occurs. The arguments are, respectively: the error string, the offending object, and a string describing the offending object ('self' or 'plugin' with name appended). plugin_added Issued via "_pluggable_event" when a new plugin is registered. Arguments are the new plugin alias and object, respectively. plugin_removed Issued via "_pluggable_event" when a plugin is unregistered. Arguments are the old plugin alias and object, respectively. Performance My motivation for writing this role was two-fold; I wanted Object::Pluggable behavior but without screwing up my class inheritance, and I needed a little bit more juice out of the pipeline dispatch process for a fast-paced daemon. Dispatcher performance has been profiled and micro-optimized, but I'm most certainly open to further ideas ;-) Some Benchmark runs. 30000 "_pluggable_process" calls with 20 loaded plugins dispatching one argument to one handler that does nothing except return EAT_NONE: Rate object-pluggable moox-role-pluggable object-pluggable 6173/s -- -38% moox-role-pluggable 9967/s 61% Rate object-pluggable moox-role-pluggable object-pluggable 6224/s -- -38% moox-role-pluggable 10000/s 61% -- Rate object-pluggable moox-role-pluggable object-pluggable 6383/s -- -35% moox-role-pluggable 9868/s 55% (Benchmark script is available in the "bench/" directory of the upstream repository; see ) AUTHOR Jon Portnoy Written from the ground up, but conceptually based entirely on Object::Pluggable by BINGOS, HINRIK, APOCAL, japhy et al.