Backdrop is a simple library that does one thing: allows you to run one-off tasks in the background.

function my_awesome_function( $id ) {
	// Download initial data to my site. Might take a long time!
	$data = wp_remote_get( 'http://example.com/' . $id );

	if ( is_wp_error( $data ) ) {
		return $data;
	}

	update_option( 'initial_data', $data );
}

add_action( 'init', function () {
	if ( ! get_option( 'initial_data' ) ) {
		$task = new \HM\Backdrop\Task( 'my_awesome_function', get_current_user_id() );
		$task->schedule();
	}
} );

Creating a new task sets up all of the internal data for your task. Pass in your callback followed by your arguments to the function, and Backdrop will call it in a background process.

• $callback: Callback method you want to use. Can be any callable type (including object methods and static methods) except for anonymous functions. Closures cannot be serialized, so they cannot be used for Backdrop callbacks. This is an internal PHP limitation.
• $...: Any other arguments you'd like to pass to your callback, as variable arguments. e.g. new Task( 'a', 'b', 'c', 'd' ) maps to a( 'b', 'c', 'd' )

None (constructor).

Schedules your task to run. Typically runs after your page has been rendered, in a separate process.

Backdrop de-duplicates tasks based on the arguments passed in. For example, you can do new Task( 'myfunc', 1 ) on every request, and only one will be run. After this has been run, the next call will schedule again.

To avoid this, you should pass in unique identifiers as needed. Everything that makes your task unique should be passed in and used by your function, as global state may change.

None.

Either true, or a WP_Error on failure. The error object will indicate the type of error; typically this is a hm_backdrop_scheduled if the task is already scheduled to run or is currently running.

Checks whether your task is scheduled to run.

None.

Boolean indicating whether your task is scheduled to run, or is already running.

Cancels a previously scheduled task.

Note that if the task is already running, this will not cancel execution; it simply removes it from the tasks scheduled to run.

None.

Either true, or a WP_Error on failure. The error object will indicate the type of error; typically this is a hm_backdrop_not_scheduled if the task hasn't been scheduled.

Backdrop is compatible with PHP 5.2 and upwards.

Use the HM_Backdrop_Task class (and HM_Backdrop_Server).

Important note: If subclassing HM_Backdrop_Server with 5.2 compatibility, you must reimplement the spawn method, as PHP 5.2 does not include late static bindings. This is automatically handled for 5.3+.

Here's a minimal implementation that you can use:

class MyBackdrop_Server extends HM_Backdrop_Server {
	public static function spawn() {
		return self::spawn_run( __CLASS__ );
	}
}

Use the HM\Backdrop\Task class (and HM\Backdrop\Server). You can also import the classes with the use keyword; for example, use HM\Backdrop\Task will allow you to create tasks with new Task.

Backdrop is licensed under the GPL version 2.

Copyright 2014 Human Made Limited