Extension Manager:Bootstrapped Extensions: Difference between revisions

__NOTOC__Bootstrapped add-ons exist as a means of restricting what is available to an add-on in order to allow it to be started up and shutdown without restarting the application.

Current XPI add-ons cannot be removed from memory without restarting the application. This is because the features that we give them (XPCOM components, chrome registration and overlays etc.) cannot be removed in a managed fashion. Adding an add-on without a restart could possibly be implemented however that really only solves a small part of the problem as updates etc. would still require restarts.

 

The approach taken here is to simplify what it means to be an add-on. Instead of registering XPCOM components and chrome in bootstrapped add-ons we do nothing except execute a bootstrap script that the add-on provides, telling it to startup. The add-on can do whatever it likes at that point however it must undo anything it has done when we call the bootstrap script to tell it to shutdown.

A key feature of bootstrapped add-ons is that they must be able to be started and shutdown on demand by the platform. When told to startup it is up to the add-on's bootstrap code to do anything necessary to inject UI and behaviour into the application. When told to shutdown it is required that the add-on remove anything it has added and removing all references to its objects. Some examples of when startup and shutdown happen:

* When first installed (if the add-on is compatible and enabled) the platform will tell the add-on to start up.

* When uninstalled (if the add-on is currently enabled) the platform will tell the add-on to shutdown.

* When enabled or disabled while the application is running the platform will tell the add-on to startup or shutdown as appropriate.

* When the application is started the platform will tell any enabled add-ons to startup.

* When the user quits the application the platform will tell any enabled add-ons to shutdown.

Bootstrapped add-ons must provide a bootstrap.js file which defines main entry functions as defined below. When the platform needs to call a function the script will be executed in a privileged sandbox which is cached until the add-on is shutdown.

Whenever an add-on needs to be started the platform will call a function named <code>startup</code> in the bootstrap script. It will be passed the following arguments:

The add-on must at this point do anything necessary to make its functionality available, the platform will not execute any other part of the add-on.

Whenever an add-on needs to be shutdown the platform will call a function named <code>shutdown</code> in the bootstrap script. It will be passed the following arguments: