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Schedule next action before current one is mark completed/failed. #830

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@vedanshujain vedanshujain commented Jun 20, 2022

This prevents race conditions that may happen if we are trying to schedule the same action, and the check as_has_scheduled_action runs after the action is marked complete but before the next one is scheduled.

Fixes #698

This prevents race condition that may happen if we are trying to schedule same action, and the check `as_has_scheduled_action` runs after action is marked complete but before next one is scheduled.
Comment on lines +67 to +71
$this->maybe_schedule_next_instance( $action, $action_id );
$this->store->mark_complete( $action_id );
} catch ( Exception $e ) {
if ( $valid_action ) {
$this->maybe_schedule_next_instance( $action, $action_id );
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Annotated this block with comments at the end of each line:

	$this->maybe_schedule_next_instance( $action, $action_id );          # 1. Next instance is scheduled
	$this->store->mark_complete( $action_id );                           # 2. Exception can be thrown by this method
} catch ( Exception $e ) {                                               # 3. Execution enters the catch block
	if ( $valid_action ) {                                               # 4. Action still 'valid'
		$this->maybe_schedule_next_instance( $action, $action_id );      # 5. We schedule another instance

↑ This chain of events seems unlikely, but still technically possible and could result in a duplicate.

$this->store->mark_complete( $action_id );
} catch ( Exception $e ) {
if ( $valid_action ) {
$this->maybe_schedule_next_instance( $action, $action_id );
$this->store->mark_failure( $action_id );
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Thinking of PR #806, it may be better to wait until the action has been marked as a failure before we call ::maybe_schedule_next_instance() (though, if this is merged first we can also update that other PR accordingly).

* @param ActionScheduler_Action $action Action object.
* @param int $action_id Action ID.
*/
private function maybe_schedule_next_instance( $action, $action_id ) {
if ( isset( $action ) && is_a( $action, 'ActionScheduler_Action' ) && $action->get_schedule()->is_recurring() ) {
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Does testing if $action is set still make sense, now this is in its own method?

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Scheduling just one recurring action makes more than one
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