Instrumentation

MVC::Keayl::Notifications is a pub/sub bus modeled on ActiveSupport::Notifications. The framework instruments the points it controls, subscribers receive each event's payload, and a request id ties a request's events together.

Subscribing

State is process-wide, so subscribe once at boot. A subscriber is a callback that receives the event's payload hash.

MVC::Keayl::Notifications.subscribe('dispatch.keayl', -> %payload {
  say "{%payload<controller>}#{%payload<action>} took {%payload<duration>}s";
});

subscribe returns an id for unsubscribe. has-subscribers($event) reports whether anyone is listening, and reset clears every subscription (useful between tests).

Emitting events

notify($event, %payload) fires an instantaneous event. instrument($event, %payload, &block) runs the block, times it, and notifies subscribers with duration (seconds) merged into the payload, returning the block's result. When the block throws, subscribers still see the event with the exception in exception, and the error is rethrown.

Both short-circuit when nothing is subscribed to the event, so instrumentation left in place costs a hash lookup when no one is listening.

Framework events

Event	Emitted around	Payload keys
dispatch.keayl	a controller action	controller, action, method, path, request-id, duration
render.keayl	a template / partial render	kind, name, duration

kind is one of template, inline, partial, or object.

Database events

ORM::ActiveRecord publishes sql.active_record on its own notifications bus. Bridge it onto the framework bus so DB queries arrive alongside dispatch and render events:

use ORM::ActiveRecord::Instrumentation::Notifications;

MVC::Keayl::Notifications.bridge(Notifications);

bridge($source, $event = 'sql.active_record') subscribes to the source bus and re-emits each event onto the framework bus, so one subscriber sees the whole request.

Request ids

MVC::Keayl::Middleware::RequestId gives every request an id, wired into the application by default. It reuses a valid incoming X-Request-Id header (word characters and hyphens, up to 255), generates one otherwise, exposes it as the $*KEAYL-REQUEST-ID dynamic variable for the rest of the request, and sets the X-Request-Id response header for propagation. The logger prefixes its line with the id, and dispatch.keayl carries it in request-id.

my $middleware = MVC::Keayl::Middleware::RequestId.new(
  header    => 'X-Request-Id',
  generator => &my-id-generator,
);