如何使用带有完成例程的 ReadDirectoryChangesW() 方法？答案

【问题标题】：How to use ReadDirectoryChangesW() method with completion routine?如何使用带有完成例程的 ReadDirectoryChangesW() 方法？
【发布时间】：2008-12-05 01:38:33
【问题描述】：

我想在异步模式下使用函数ReadDirectoryChangesW()，并提供 I/O 完成例程。

问题是我不知道如何检索有关完成例程中更改的确切信息（CALLBACK 函数）。完成例程定义如下：

VOID CALLBACK FileIOCompletionRoutine(
  [in]                 DWORD dwErrorCode,
  [in]                 DWORD dwNumberOfBytesTransfered,
  [in]                 LPOVERLAPPED lpOverlapped
);

我想知道这些信息是否包含在LPOVERLAPPED 结构中。但我不知道如何得到它。

【问题讨论】：

标签： windows asynchronous readdirectorychangesw

【解决方案1】：

很好的问题！已经晚了 7 年，但这里有一个答案，或者更重要的是，如何找到它。所以，ReadDirectoryChangesW 的文档：

https://msdn.microsoft.com/en-us/library/windows/desktop/aa365465%28v=vs.85%29.aspx

在参数部分给出了 FileIOCompletionRoutine 的链接：

https://msdn.microsoft.com/en-us/library/windows/desktop/aa364052%28v=vs.85%29.aspx

在示例部分中提供了使用完成例程的命名管道服务器的链接：

https://msdn.microsoft.com/en-us/library/windows/desktop/aa365601%28v=vs.85%29.aspx

信不信由你甚至不使用ReadDirectoryChangesW，但实际上给出了一个使用ReadFileEx的例子，也使用了FileIOCompletionRoutine：

https://msdn.microsoft.com/en-us/library/windows/desktop/aa365468%28v=vs.85%29.aspx

您可以在这段代码中看到使用这两个函数（ReadFileEx 和 CompletedReadRoutine（这是应用程序定义的回调函数 FileIOCompletionRoutine 的实现））的示例：

// CompletedWriteRoutine(DWORD, DWORD, LPOVERLAPPED) 
// This routine is called as a completion routine after writing to 
// the pipe, or when a new client has connected to a pipe instance.
// It starts another read operation. 
    
VOID WINAPI CompletedWriteRoutine(DWORD dwErr, DWORD cbWritten, 
    LPOVERLAPPED lpOverLap) 
{ 
    LPPIPEINST lpPipeInst; 
    BOOL fRead = FALSE; 
    
// lpOverlap points to storage for this instance. 
    
    lpPipeInst = (LPPIPEINST) lpOverLap; 
    
// The write operation has finished, so read the next request (if 
// there is no error). 
    
    if ((dwErr == 0) && (cbWritten == lpPipeInst->cbToWrite)) 
        fRead = ReadFileEx( 
            lpPipeInst->hPipeInst, 
            lpPipeInst->chRequest, 
            BUFSIZE*sizeof(TCHAR), 
            (LPOVERLAPPED) lpPipeInst, 
            (LPOVERLAPPED_COMPLETION_ROUTINE) CompletedReadRoutine); 
    
// Disconnect if an error occurred. 
    
    if (! fRead) 
        DisconnectAndClose(lpPipeInst); 
} 
    
// CompletedReadRoutine(DWORD, DWORD, LPOVERLAPPED) 
// This routine is called as an I/O completion routine after reading 
// a request from the client. It gets data and writes it to the pipe. 
    
VOID WINAPI CompletedReadRoutine(DWORD dwErr, DWORD cbBytesRead, 
    LPOVERLAPPED lpOverLap) 
{ 
    LPPIPEINST lpPipeInst; 
    BOOL fWrite = FALSE; 
    
// lpOverlap points to storage for this instance. 
    
    lpPipeInst = (LPPIPEINST) lpOverLap; 
    
// The read operation has finished, so write a response (if no 
// error occurred). 
    
    if ((dwErr == 0) && (cbBytesRead != 0)) 
    { 
        GetAnswerToRequest(lpPipeInst); 
    
        fWrite = WriteFileEx( 
            lpPipeInst->hPipeInst, 
            lpPipeInst->chReply, 
            lpPipeInst->cbToWrite, 
            (LPOVERLAPPED) lpPipeInst, 
            (LPOVERLAPPED_COMPLETION_ROUTINE) CompletedWriteRoutine); 
    } 
    
// Disconnect if an error occurred. 
    
    if (! fWrite) 
        DisconnectAndClose(lpPipeInst); 
}

这不是一个很好的答案（我只是在探索我自己是否想使用这些功能），但它应该可以帮助人们入门。

另见：

https://msdn.microsoft.com/en-us/library/windows/desktop/aa365261%28v=vs.85%29.aspx

【讨论】：