BP Reply By Email - IMAP Object Cache extension. Replaces the default filesystem IMAP locking system in RBE with a persistent object cache.

_bp_rbe_imap_object_cache.php

<?php
/*
Plugin Name: BP Reply By Email - IMAP Object Cache extension
Description: Replaces the default filesystem IMAP locking system in RBE with a persistent object cache.
Author: r-a-y
Author URI: http://profiles.wordpress.org/r-a-y
License: GPLv2 or later
*/

/*
 * Bail if we're not using a persistent object cache.
 *
 * This plugin has only been tested with Memcached and the WP PECL Memcached
 * Object cache plugin:
 * https://github.com/tollmanz/wordpress-pecl-memcached-object-cache
 *
 * It might work with other object cache plugins, but will need testing and
 * possible modification.
 *
 * ---
 *
 * By default, RBE's IMAP checking uses the filesystem to place a file in the
 * uploads folder to determine whether or not we are connected to the IMAP
 * inbox. This technique works well on a single server set up, however if your
 * site is on a load balancer, this filesystem check will not be as reliable.
 *
 * To counteract this and if your site is using an object cache like Memcached
 * or Redis, deactivate RBE first, then activate this plugin and reactivate
 * RBE.
 *
 * Be aware of the general nature of object caching. If your site generates a
 * ton of cache items, it is possible that you will hit your cache limit. As
 * such, our IMAP markers *could* get evicted, meaning we will have no
 * reliable way of determining if the IMAP connection exists or how long the
 * current connection is. If you regularly hit your cache memory limit,
 * consider increasing it before enabling this option.
 */
if ( false === wp_using_ext_object_cache() ) {
	return;
}

/**
 * Registers RBE with WordPress' global cachegroups.
 */
function _bp_rbe_register_global_cachegroup() {
	wp_cache_add_global_groups( 'bp_rbe' );
}
add_action( 'bp_loaded', '_bp_rbe_register_global_cachegroup' );

/** PLUGGABLES ***********************************************************/

function bp_rbe_is_connected( $args = array() ) {
	$timestamp = wp_cache_get( 'connected', 'bp_rbe', true );

	// Check if we're connected
	if ( ! empty( $timestamp ) && time() <= ( $timestamp + bp_rbe_get_execution_time() + 15 ) ) {
		return true;
	}

	return false;
}

function bp_rbe_is_connecting( $args = array() ) {
	$timestamp = wp_cache_get( 'lock', 'bp_rbe', true );

	// check if we're already attempting to connect
	if ( ! empty( $timestamp ) && time() <= $timestamp + WP_CRON_LOCK_TIMEOUT ) {
		return true;
	}

	return false;
}

function bp_rbe_stop_imap() {
	wp_cache_set( 'stop', 1, 'bp_rbe' );
	ray_log( 'rbe stop value: ' . wp_cache_get( 'stop', 'bp_rbe' ) );

	remove_action( 'shutdown', 'bp_rbe_spawn_inbox_check' );
}

function bp_rbe_should_stop() {
	$stop = wp_cache_get( 'stop', 'bp_rbe', true );

	if ( false !== $stop ) {
		//ray_log( 'should stop value: ' . var_export( $stop, true ) );

		$test = wp_cache_delete( 'stop', 'bp_rbe' );
		//ray_log( 'should stop cache delete: ' . var_export( $test, true ) );
		return true;
	}

	return false;
}

function bp_rbe_add_imap_lock() {
	wp_cache_set( 'lock', time(), 'bp_rbe' );
}

function bp_rbe_remove_imap_lock() {
	wp_cache_delete( 'lock', 'bp_rbe' );
}

function bp_rbe_add_imap_connection_marker() {
	wp_cache_set( 'connected', time(), 'bp_rbe' );
}

function bp_rbe_remove_imap_connection_marker() {
	$connected = wp_cache_get( 'connected', 'bp_rbe', true );

	//ray_log( 'connected value: ' . var_export( $connected, true ) );

	if ( false !== $connected ) {
		$test = wp_cache_delete( 'connected', 'bp_rbe' );
		//ray_log( 'connected cache delete: ' . var_export( $test, true ) );
	}
}