All overlapped operations are guaranteed to be executed in the order that the application issued them. However, the completion notifications returned from a completion port are not guaranteed to be in that same order.That is, if an application posts two overlapped WSARecv operations, one with a 10 KB buffer and the next with a 12 KB buffer, the 10 KB buffer is filled first, followed by the 12 KB buffer. The application's worker thread may receive notification from GetQueuedCompletionStatus for the 12 KB WSARecv before the completion event for the 10 KB operation. Of course, this is only an issue when multiple operations are posted on a socket.