APC中文叫异步过程调用（APC）是NT异步处理体系结构中的一个基础部分。Alertable IO(告警IO)提供了更有效的异步通知形式，当IO请求完成后，一旦线程进入可告警状态，回调函数将会执行，也就是一个APC的过程。线程进入告警状态时，内核将会检查线程的APC队列，如果队列中有APC，将会按FIFO方式依次执行。如果队列为空，线程将会挂起等待事件对象。以后的某个时刻，一旦APC进入队列，线程将会被唤醒执行APC。-APC called asynchronous procedure call (APC) is a basis of NT asynchronous processing system structure. Alertable IO (alarm IO) provides a more effective form of asynchronous notification, when after the completion of the I/o requests, once the thread enters the alarm status, the callback function will be executed, which is a process of APC. Thread into the alarm status, the kernel will check the threads of the APC queue, have the APC, if the queue will be executed in sequence according to the FIFO method. If the queue is empty, the thread will hang wait for event object. Sometime later, once the APC enters the queue, the thread will be awakened APC execution.