在ReadFileEx 和WriteFileEx时使用Synchronization and Overlapped Input and Output是正确的。
If the function succeeds, the calling thread has an asynchronous input/output (I/O) operation pending: the overlapped read operation from the file. When this I/O operation completes, and the calling thread is blocked in an alertable wait state, the system calls the function pointed to by lpCompletionRoutine, and the wait state completes with a return code of WAIT_IO_COMPLETION.
If the function succeeds, and the file reading operation completes, but the calling thread is not in an alertable wait state, the system queues the completion routine call, holding the call until the calling thread enters an alertable wait state. For information about alertable waits and overlapped input/output operations, see Synchronization and Overlapped Input and Output.