PubSub

PubSub provides an API for publishing messages and subscribing to published messages. Additionally, it provides a cascading structure for messages allowing modules to extend PubSub in creative ways.

You publish a message by calling pubsub_publish('your.message', $any, $args, $you, $want). Messages are expanded and sent to all subscribers. For example:

Calling the following method:

pubsub_publish('foo.bar.baz', $arg1, $arg2);

Will execute the following hooks:

hook_pubsub('foo.bar.baz', $arg1, $arg2);

hook_pubsub_foo('bar.baz', $arg1, $arg2);

hook_pubsub_foo_bar('baz', $arg1, $arg2);

Examples

Publishing and subscribing to messages.

/**
 * Implementation of hook_nodeapi().
 */
function mymodule_nodeapi(&$node, $op, $a3 = NULL, $a4 = NULL) {
  switch ($op) {
    case 'update':
      pubsub_publish('node.update', $node);
  }
}

/**
 * Implementation of hook_pubsub().
 */
function mymodule_pubsub($message, $node) {
  switch ($message) {
    case 'node.update':
      /* Do something awesome with $node */
      break;
  }
}

/**
 * Implementation of hook_pubsub_MESSAGE().
 */
function mymodule_pubsub_node($message, $node) {
  switch ($message) {
    case 'update':
      /* Do something awesome with $node */
      break;
  }
}

Sub Modules

Out of the box, PubSub comes with 2 sub modules: PubSub Cron and PubSub JavaScript.

PubSub Cron

PubSub Cron re-publishes all messages of the pattern cron.* when Drupal's cron runs. This can be very useful as a sort of message queue, allowing you to offload expensive operations to cron.

Example

/**
 * Implementation of hook_init().
 */
function mymodule_init() {
  // Publish a message to PubSub Cron.
  pubsub_publish('cron.mymodule.init', 1, 2, 3, 4);
}

/**
 * Implementation of hook_pubsub_MESSAGE().
 *
 * This hook will be called when Drupal's cron runs.
 */
function mymodule_pubsub_mymodule($message, $arg1, $arg2, $arg3, $arg4) {
  switch ($message) {
    case 'init':
      /* Do something awesome */
      break;
  }
}

PubSub JavaScript

PubSub JavaScript re-publishes all messages of the pattern js.* to JavaScript, executing subscribers in Drupal.behaviors.

Example

/**
 * Implementation of hook_init().
 */
function mymodule_init() {
  // Publish a message to PubSub JavaScript
  pubsub_publish('js.mymodule.init', 1, 2, 3, 4);
}

In JavaScript:

/**
 * Subscribe to the js.mymodule.init message.
 */
Drupal.pubsub.subscribe('mymodule.init', function(one, two, three, four) {
  /* Do something awesome */
});