diff --git a/wp-cron.php b/wp-cron.php
index efd66c68b6..f7b3fa16b3 100644
--- a/wp-cron.php
+++ b/wp-cron.php
@@ -23,31 +23,41 @@ require_once('./wp-load.php');
 if ( $_GET['check'] != wp_hash('187425') )
 	exit;
 
-if ( get_option('doing_cron') > time() )
-	exit;
-
-update_option('doing_cron', time() + 30);
+$local_time = time();
 
 $crons = _get_cron_array();
-$keys = array_keys($crons);
-if (!is_array($crons) || $keys[0] > time())
-	return;
+$keys = array_keys( $crons );
+
+if (!is_array($crons) || $keys[0] > $local_time) {
+	update_option('doing_cron', 0);
+	return;
+}
+
+foreach ($crons as $timestamp  => $cronhooks) {
+
+	if ( $timestamp > $local_time )
+		break;
 
-foreach ($crons as $timestamp => $cronhooks) {
-	if ($timestamp > time()) break;
 	foreach ($cronhooks as $hook => $keys) {
-		foreach ($keys as $key => $args) {
-			$schedule = $args['schedule'];
+
+		foreach ($keys as $k => $v) {
+
+			$schedule = $v['schedule'];
+
 			if ($schedule != false) {
-				$new_args = array($timestamp, $schedule, $hook, $args['args']);
+				$new_args = array($timestamp, $schedule, $hook, $v['args']);
 				call_user_func_array('wp_reschedule_event', $new_args);
 			}
-			wp_unschedule_event($timestamp, $hook, $args['args']);
- 			do_action_ref_array($hook, $args['args']);
+
+			wp_unschedule_event($timestamp, $hook, $v['args']);
+
+ 			do_action_ref_array($hook, $v['args']);
 		}
 	}
 }
 
 update_option('doing_cron', 0);
 
-?>
\ No newline at end of file
+die();
+
+?>
diff --git a/wp-includes/cron.php b/wp-includes/cron.php
index 50a95fde55..cdd11ea172 100644
--- a/wp-includes/cron.php
+++ b/wp-includes/cron.php
@@ -152,17 +152,47 @@ function wp_next_scheduled( $hook, $args = array() ) {
  *
  * @return null Cron could not be spawned, because it is not needed to run.
  */
-function spawn_cron() {
-	$crons = _get_cron_array();
+function spawn_cron( $local_time ) {
+	global $current_blog;
 
+	/*
+	 * do not even start the cron if local server timer has drifted
+	 * such as due to power failure, or misconfiguration
+	 */
+	$timer_accurate = check_server_timer( $local_time );
+	if ( !$timer_accurate )
+		return;
+
+	//sanity check
+	$crons = _get_cron_array();
 	if ( !is_array($crons) )
 		return;
 
 	$keys = array_keys( $crons );
-	if ( array_shift( $keys ) > time() )
+	$timestamp =  $keys[0];
+	if ( $timestamp > $local_time )
 		return;
 
 	$cron_url = get_option( 'siteurl' ) . '/wp-cron.php?check=' . wp_hash('187425');
+	/*
+	* multiple processes on multiple web servers can run this code concurrently
+	* try to make this as atomic as possible by setting doing_cron switch
+	*/
+	$flag = get_option('doing_cron');
+
+	// clean up potential invalid value resulted from various system chaos
+	if ( $flag != 0 ) {
+	 	if ( $flag > $local_time + 10*60 || $flag < $local_time - 10*60 ) {
+	 		update_option('doing_cron', 0);
+	 		$flag = 0;
+	 	}
+	}
+
+	 //don't run if another process is currently running it
+	if ( $flag > $local_time )
+		return;
+
+	update_option( 'doing_cron', $local_time + 30 );
 
 	wp_remote_post($cron_url, array('timeout' => 0.01, 'blocking' => false));
 }
@@ -175,6 +205,7 @@ function spawn_cron() {
  * @return null When doesn't need to run Cron.
  */
 function wp_cron() {
+
 	// Prevent infinite loops caused by lack of wp-cron.php
 	if ( strpos($_SERVER['REQUEST_URI'], '/wp-cron.php') !== false )
 		return;
@@ -188,13 +219,14 @@ function wp_cron() {
 	if ( isset($keys[0]) && $keys[0] > time() )
 		return;
 
+	$local_time = time();
 	$schedules = wp_get_schedules();
 	foreach ( $crons as $timestamp => $cronhooks ) {
-		if ( $timestamp > time() ) break;
+		if ( $timestamp > $local_time ) break;
 		foreach ( (array) $cronhooks as $hook => $args ) {
 			if ( isset($schedules[$hook]['callback']) && !call_user_func( $schedules[$hook]['callback'] ) )
 				continue;
-			spawn_cron();
+			spawn_cron( $local_time );
 			break 2;
 		}
 	}
@@ -327,4 +359,9 @@ function _upgrade_cron_array($cron) {
 	return $new_cron;
 }
 
+// stub for checking server timer accuracy, using outside standard time sources
+function check_server_timer( $local_time ) {
+	return true;
+}
+
 ?>