Chromium - Notification Service

Overview

Notification Service provides notification delivery mechanism from producer to observer in the same thread. This class is created and used in browser process’s sub threads.

Refer to src/content/browser/browser_process_sub_thread.cc

Components

a. NotificationService

It handles notification delivery and manages observer list.

This service provides method that can add or remove notification for observer.

Also, Notify method is provided for notification provider.

To get the NotificationService object, content::NotificationService::current() is used.

It could be used in that thread only. It means calling content::NotifcationService::current()

returns different object in UI thread and IO thread.

b. Notification Observer:

This component is responsible for registration its preferred notification type to

NotificationService.

For receiving notification, Observer must implement NotificationObserver class.

c. Notification Provider:

It is a notification producer. This component sends notification to NotificationService.

How To Register Notification to NotificationService

a. Add Notification

For registration, NotificationRegistrar class is used instead of using NotificationService

directly. It is a helper class for registering notification and ensures that all registered

notifications are unregistered when the class is destroyed.

Refer to src/content/public/browser/notification_registrar.h

b. Implement Notification Handler

For implementing handler, Observer should implement NotificationObserver class as a base

class. It has only one function, observe(). When registered notification is occured,

NotificationService calls this function.

Refer to src/content/public/browser/notification_observer.h

How to Notify to NotificationService

NotificationService provides Notify() for synchronous notify mechanism. Notification provider should deliver notification type, source that originates this notification and details that contains additional information to NotificationService via Notify().

Refer to src/content/browser/notification_service_impl.cc