事件:'locks.request.miss'
🌐 Event: 'locks.request.miss'
当 ifAvailable 为 true 且锁不可立即获取时发出,并且请求回调被调用时传入 null 而不是 Lock 对象。
🌐 Emitted when ifAvailable is true and the lock is not immediately available,
and the request callback is invoked with null instead of a Lock object.