$priority argument should be declared as float, because function expects float value in range between 0 and 1.
Otherwise you get "Unable to set event priority" error.
(PECL event >= 1.2.6-beta)
Event::setPriority — Set event priority
$priority
): boolSet event priority.
priority
The event priority.
成功时返回 true， 或者在失败时返回 false。