Background Emailer instead of just CRON

includes/class-wc-background-emailer.php

@@ -0,0 +1,79 @@
+<?php
+/**
+ * Background Emailer
+ *
+ * Uses https://github.com/A5hleyRich/wp-background-processing to handle emails
+ * in the background.
+ *
+ * @class    WC_Background_Emailer
+ * @version  3.0.0
+ * @package  WooCommerce/Classes
+ * @category Class
+ * @author   WooThemes
+ */
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+if ( ! class_exists( 'WP_Async_Request', false ) ) {
+	include_once( dirname( __FILE__ ) . '/libraries/wp-async-request.php' );
+}
+
+if ( ! class_exists( 'WP_Background_Process', false ) ) {
+	include_once( dirname( __FILE__ ) . '/libraries/wp-background-process.php' );
+}
+
+/**
+ * WC_Background_Emailer Class.
+ */
+class WC_Background_Emailer extends WP_Background_Process {
+
+	/**
+	 * @var string
+	 */
+	protected $action = 'wc_emailer';
+
+	/**
+	 * Initiate new background process
+	 */
+	public function __construct() {
+		parent::__construct();
+		add_action( 'shutdown', array( $this, 'dispatch_queue' ) );
+	}
+
+	/**
+	 * Schedule fallback event.
+	 */
+	protected function schedule_event() {
+		if ( ! wp_next_scheduled( $this->cron_hook_identifier ) ) {
+			wp_schedule_event( time() + 10, $this->cron_interval_identifier, $this->cron_hook_identifier );
+		}
+	}
+
+	/**
+	 * Task
+	 *
+	 * Override this method to perform any actions required on each
+	 * queue item. Return the modified item for further processing
+	 * in the next pass through. Or, return false to remove the
+	 * item from the queue.
+	 *
+	 * @param string $callback Update callback function
+	 * @return mixed
+	 */
+	protected function task( $callback ) {
+		if ( isset( $callback['filter'], $callback['args'] ) ) {
+			WC_Emails::send_queued_transactional_email( $callback['filter'], $callback['args'] );
+		}
+		return false;
+	}
+
+	/**
+	 * Save and run queue.
+	 */
+	public function dispatch_queue() {
+		if ( ! empty( $this->data ) ) {
+			$this->save()->dispatch();
+		}
+	}
+}

includes/class-wc-emails.php

@@ -23,6 +23,11 @@ class WC_Emails {
 	/** @var WC_Emails The single instance of the class */
 	protected static $_instance = null;
 
+	/**
+	 * Background emailer class.
+	 */
+	protected static $background_emailer;
+
 	/**
 	 * Main WC_Emails Instance.
 	 *
@@ -83,21 +88,26 @@ class WC_Emails {
 			'woocommerce_created_customer',
 		) );
 
-		foreach ( $email_actions as $action ) {
-			add_action( $action, array( __CLASS__, 'queue_transactional_email' ), 10, 10 );
+		if ( apply_filters( 'woocommerce_defer_transactional_emails', true ) ) {
+			self::$background_emailer = new WC_Background_Emailer();
+
+			foreach ( $email_actions as $action ) {
+				add_action( $action, array( __CLASS__, 'queue_transactional_email' ), 10, 10 );
+			}
+		} else {
+			foreach ( $email_actions as $action ) {
+				add_action( $action, array( __CLASS__, 'send_transactional_email' ), 10, 10 );
+			}
 		}
 	}
 
 	/**
-	 * Queue transactional email via cron so it's not sent in current request.
+	 * Queue transactional email so it's not sent in current request.
 	 */
 	public static function queue_transactional_email() {
-		$filter = current_filter();
-		$args   = func_get_args();
-
-		wp_schedule_single_event( time() + 5, 'woocommerce_send_queued_transactional_email', array(
-			'filter' => $filter,
-			'args'   => $args,
+		self::$background_emailer->push_to_queue( array(
+			'filter' => current_filter(),
+			'args'   => func_get_args(),
 		) );
 	}
 

woocommerce.php

@@ -181,7 +181,6 @@ final class WooCommerce {
 		add_action( 'init', array( $this, 'init' ), 0 );
 		add_action( 'init', array( 'WC_Shortcodes', 'init' ) );
 		add_action( 'init', array( 'WC_Emails', 'init_transactional_emails' ) );
-		add_action( 'woocommerce_send_queued_transactional_email', array( 'WC_Emails', 'send_queued_transactional_email' ), 10, 2 );
 		add_action( 'init', array( $this, 'wpdb_table_fix' ), 0 );
 		add_action( 'switch_blog', array( $this, 'wpdb_table_fix' ), 0 );
 	}
@@ -319,6 +318,7 @@ final class WooCommerce {
 		include_once( WC_ABSPATH . 'includes/class-wc-https.php' ); // https Helper
 		include_once( WC_ABSPATH . 'includes/class-wc-deprecated-action-hooks.php' );
 		include_once( WC_ABSPATH . 'includes/class-wc-deprecated-filter-hooks.php' );
+		include_once( WC_ABSPATH . 'includes/class-wc-background-emailer.php' );
 
 		/**
 		 * Data stores - used to store and retrieve CRUD object data from the database.