# NAME MooX::Role::Pluggable - A plugin pipeline for your Moo-based class # SYNOPSIS # A simple pluggable dispatcher: package MyDispatcher; use MooX::Role::Pluggable::Constants; use Moo; 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](https://metacpan.org/pod/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"](#_pluggable_process)). The logic and behavior is based almost entirely on [Object::Pluggable](https://metacpan.org/pod/Object::Pluggable) (see ["AUTHOR"](#author)). Some methods are the same; implementation & some interface differ. Dispatch is significantly faster -- see ["Performance"](#performance). If you're using [POE](https://metacpan.org/pod/POE), also see [MooX::Role::POE::Emitter](https://metacpan.org/pod/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 can be named arbitrarily. Their respective prefix is # prepended when dispatching events of that type. # Here are the defaults: 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"](#_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 trailing `_` is automatically appended to event type prefixes when events are dispatched via ["\_pluggable\_process"](#_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 is a valid value for `reg_prefix`/`event_prefix`. ### \_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, $event, @args) = @_; # Dispatch out, perhaps. } `_pluggable_event` is called for internal notifications, such as plugin load/unload and error reporting (see ["Internal Events"](#internal-events)) -- it can be overriden in your consuming class to do something useful with the dispatched event and any arguments passed. The `$event` given will be prefixed with the configured **event\_prefix**. (It's not strictly necessary to implement a `_pluggable_event` handler; errors will also `warn`.) ## Registration A plugin is any blessed object that is registered with your Pluggable object via ["plugin\_add"](#plugin_add); during registration, plugins usually subscribe to some events via ["subscribe"](#subscribe). See ["plugin\_add"](#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 typically called from within the plugin's registration handler (see ["plugin\_register"](#plugin_register)): # In a plugin: sub plugin_register { my ($self, $core) = @_; $core->subscribe( $self, PROCESS => qw/ my_event another_event / ); $core->subscribe( $self, NOTIFY => 'all' ); EAT_NONE } Subscribe to **all** to receive all events -- but note that subscribing many plugins to 'all' events is less performant during calls to ["\_pluggable\_process"](#_pluggable_process) than many subscriptions to specific events. ### unsubscribe **Unsubscribe a plugin from subscribed events.** Carries the same arguments as ["subscribe"](#subscribe). The plugin is still loaded and registered until ["plugin\_del"](#plugin_del) is called, even if there are no current event subscriptions. ### plugin\_register **Defined in your plugin(s) and called at load time.** (Note that 'plugin\_' is just a default register method prefix; it can be changed prior to loading plugins. See ["\_pluggable\_init"](#_pluggable_init) for details.) The `plugin_register` method is called on a loaded plugin when it is added to the pipeline; it is passed the plugin object (`$self`), the Pluggable object, and any arguments given to ["plugin\_add"](#plugin_add) (or similar registration methods). Normally one might call a ["subscribe"](#subscribe) from here to start receiving events after load-time: # In a plugin: sub plugin_register { my ($self, $core, @args) = @_; $core->subscribe( $self, 'NOTIFY', @events ); EAT_NONE } ### plugin\_unregister **Defined in your plugin(s) and called at load time.** (Note that 'plugin\_' is just a default register method prefix; it can be changed prior to loading plugins. See ["\_pluggable\_init"](#_pluggable_init) for details.) The unregister counterpart to ["plugin\_register"](#plugin_register), called when the plugin object is removed from the pipeline (via ["plugin\_del"](#plugin_del) or ["\_pluggable\_destroy"](#_pluggable_destroy)). # In a plugin: sub plugin_unregister { my ($self, $core) = @_; EAT_NONE } Carries the same arguments as ["plugin\_register"](#plugin_register). ## Dispatch ### \_pluggable\_process # In your consumer's dispatch method: 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"](#_pluggable_init)), the prefix is stripped prior to dispatch (to be replaced with a type prefix matching the specified `$type`). Arguments should be passed as a reference to an array. During dispatch, references to the provided arguments are passed to relevant plugin subroutines following the automatically-prepended plugin and Pluggable consumer objects (respectively); this allows for argument modification as an event is passed along the plugin pipeline: my @args = qw/baz bar/; $self->_pluggable_process( NOTIFY => foo => \@args ); # In a plugin: sub N_foo { # Remove automatically-provided plugin and consumer objects from @_ my ($self, $core) = splice @_, 0, 2; # Dereference expected scalars my $bar = ${ $_[0] }; my $num = ${ $_[1] }; # Increment actual second argument before pipeline dispatch continues ++${ $_[1] }; EAT_NONE } #### Dispatch Process Your Pluggable consuming class typically provides syntax sugar to dispatch different types or "classes" of events: sub process { # Dispatch to 'PROCESS'-type events my ($self, $event, @args) = @_; my $eat = $self->_pluggable_process( PROCESS => $event, \@args ); # ... possibly take further action based on $eat return value, see below } sub notify { # Dispatch to 'NOTIFY'-type events my ($self, $event, @args) = @_; my $eat = $self->_pluggable_process( NOTIFY => $event, \@args ); # ... } Event types and matching prefixes can be arbitrarily named to provide event dispatch flexibility. For example, the dispatch process for `$event` 'foo' of `$type` 'NOTIFY' performs the following actions: $self->_pluggable_process( NOTIFY => foo => \@args ); # - 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() # (When using _default, the method we were attempting to call is prepended # to arguments.) # # - If the event was not eaten by the Pluggable consumer (see below), call # $plugin->N_foo() for subscribed plugins sequentially until event is eaten # or no relevant plugins remain. "Eaten" means a handler returned an EAT\_\* constant from [MooX::Role::Pluggable::Constants](https://metacpan.org/pod/MooX::Role::Pluggable::Constants) indicating that the event's lifetime should terminate. **If our consuming class provides a method or '\_default' that returns:** EAT_ALL: skip plugin pipeline, return EAT_ALL EAT_CLIENT: continue to plugin pipeline return EAT_ALL if plugin returns EAT_PLUGIN later EAT_PLUGIN: skip plugin pipeline entirely return EAT_NONE unless EAT_CLIENT was seen previously EAT_NONE: continue to plugin pipeline **If one of our plugins in the pipeline returns:** EAT_ALL: skip further plugins, return EAT_ALL EAT_CLIENT: continue to next plugin, set pending EAT_ALL (EAT_ALL will be returned when plugin processing finishes) EAT_PLUGIN: return EAT_ALL if previous sub returned EAT_CLIENT else return EAT_NONE EAT_NONE: continue to next plugin This functionality (derived from [Object::Pluggable](https://metacpan.org/pod/Object::Pluggable)) provides fine-grained control over event lifetime. Higher-level layers (see [MooX::Role::POE::Emitter](https://metacpan.org/pod/MooX::Role::POE::Emitter) for an example) can check for an `EAT_ALL` return value from ["\_pluggable\_process"](#_pluggable_process) to determine whether to continue operating on a particular event (re-dispatch elsewhere, for example). Plugins can use `EAT_CLIENT` to indicate that an event should be eaten after plugin processing is complete, `EAT_PLUGIN` to stop plugin processing, and `EAT_ALL` to indicate that the event should not be dispatched further. ## Plugin Management Methods These plugin pipeline management methods will set `$@`, warn via [Carp](https://metacpan.org/pod/Carp), and return an empty list on error (unless otherwise noted). See ["plugin\_error"](#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_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 the list of loaded plugin aliases. As of version `1.002`, the list is ordered to match actual plugin dispatch order. In prior versions, the list is unordered. ### 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 call ["plugin\_add"](#plugin_add) rather than using 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"](#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"](#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"](#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"](#_pluggable_event) prefixed with our pluggable event prefix; see ["\_pluggable\_init"](#_pluggable_init). ### plugin\_error Issued via ["\_pluggable\_event"](#_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"](#_pluggable_event) when a new plugin is registered. Arguments are the new plugin alias and object, respectively. ### plugin\_removed Issued via ["\_pluggable\_event"](#_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](https://metacpan.org/pod/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](https://metacpan.org/pod/Benchmark) runs. 30000 ["\_pluggable\_process"](#_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 [https://github.com/avenj/moox-role-pluggable](https://github.com/avenj/moox-role-pluggable)) # AUTHOR Jon Portnoy Written from the ground up, but conceptually derived entirely from [Object::Pluggable](https://metacpan.org/pod/Object::Pluggable) (c) Chris Williams, Apocalypse, Hinrik Orn Sigurosson and Jeff Pinyan. Licensed under the same terms as Perl 5; please see the license that came with your Perl distribution for details.