c++ - ReadDirectoryChangesW 拒绝 CreateIoCompletionPort 接受的 HANDLE

Question

我正在向我的(基于 Qt 的)应用程序添加功能，以递归地监视我的 Windows 系统上的任意文件夹的任何事件(这是 Qt 变体 QFileSystemWatcher 所缺少的)。使用 CreatFileW() 打开文件夹后，我创建了一个完成端口来接收重叠的 I/O，然后使用 ReadDirectoryChangesW() 对读取进行排队。

我已将所有这些放在下面的“简单”Win32 控制台应用程序中进行演示(请注意，“stdafx.h” header 已被修改为包含“windows.h”，但除此之外与 Visual Studio 2013 IDE 相同生成它):

#include "stdafx.h"

#define MAX_BUFFER 4096

struct ThreadData
{;
    DWORD           winerr;
    HANDLE          handle;
    unsigned int    flags;
    int             recursive;
    HANDLE          completion_port;
    CHAR            buffer[MAX_BUFFER];
    DWORD           buffer_len;
    OVERLAPPED      overlapped;
};

int _tmain(int argc, _TCHAR* argv[])
{
    DWORD winerr;
    ThreadData td;

    td.flags = FILE_NOTIFY_CHANGE_FILE_NAME|
               FILE_NOTIFY_CHANGE_DIR_NAME|
               FILE_NOTIFY_CHANGE_ATTRIBUTES|
               FILE_NOTIFY_CHANGE_SIZE|
               FILE_NOTIFY_CHANGE_LAST_WRITE|
               FILE_NOTIFY_CHANGE_LAST_ACCESS|
               FILE_NOTIFY_CHANGE_CREATION|
               FILE_NOTIFY_CHANGE_SECURITY;
    td.recursive = 1;
    td.completion_port = INVALID_HANDLE_VALUE;
    td.handle = INVALID_HANDLE_VALUE;

    td.handle = CreateFileW(L"J:\\Font",         // arbitrary folder
                            FILE_LIST_DIRECTORY, // required
                            FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
                            NULL,
                            OPEN_EXISTING,
                            // Use FILE_FLAG_OVERLAPPED for asynchronous operation with ReadDirectoryChangesW.
                            FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
                            NULL);

    if(td.handle == INVALID_HANDLE_VALUE)
    {
        winerr = GetLastError();
        CloseHandle(td->handle);
        return 0;
    }

    td.completion_port = CreateIoCompletionPort(td.handle,
                                                td.completion_port,
                                                (ULONG_PTR)td,
                                                0);    // max num processors
    if(td.completion_port == INVALID_HANDLE_VALUE)
    {
        winerr = GetLastError();
        CloseHandle(td.completion_port);
        CloseHandle(td.handle);
        return 0;
    }

    BOOL rdc = ReadDirectoryChangesW(td.handle,
                                     td.buffer,    // read results
                                     MAX_BUFFER,
                                     td.recursive, // watch subdirectories
                                     // NOTE: At least one flag is required!
                                     td.flags,     // see Notify Filters below
                                     &td.buffer_len,
                                     &td.overlapped,
                                     NULL);         // completion routine
    if(rdc == 0)
    {
        winerr = GetLastError();     // "The handle is invalid. (0x6)"
        CloseHandle(td.completion_port);
        CloseHandle(td.handle);
        return 0;
    }

    // Launch thread here to handle completions and trigger new ones
    ...

    // Clean up when the thread is done
    CloseHandle(td.completion_port);
    CloseHandle(td.handle);

    return 0;
}

关于此代码需要注意的一点是，它是根据用 C 语言编写的 Python 模块(“watcher”)建模的，该模块提供与 Python 环境类似的功能。我已经在 Python 中使用过它，并且在这个 C++ 片段中使用所有相同的设置，它可以按预期工作。

在上面的代码中，CreateIoCompletionPort()接受了CreateFileW()生成的HANDLE，但是ReadDirectoryChangesW()不接受。它返回 0，并且 GetLastError() 返回“句柄无效。(0x6)”。我在 32 位和 64 位编译下都试过了，以防万一(我使用的是 64 位版本的 Python)。此外，指定的目录似乎并不重要:我指定的所有目录都产生相同的结果，这表明某处的设置有问题。

CreateFileW() 调用中是否有某些东西可能导致 HANDLE 对生成完成端口有效，但会给 ReadDirectoryChangesW() 函数带来胃灼热？

Answer 1

您没有正确初始化 I/O 完成端口，您根本没有初始化 OVERLAPPED 结构。 ReadDirectoryChangesW() 失败，因为 OVERLAPPED::hEvent 字段包含无效的事件对象句柄。这是错误代码所指的无效句柄，而不是目录句柄。

试试这个:

#include "stdafx.h"

#define MAX_BUFFER 4096

struct ThreadData
{
    DWORD           winerr;
    HANDLE          handle;
    DWORD           flags;
    BOOL            recursive;
    HANDLE          completion_port;
    CHAR            buffer[MAX_BUFFER];
    DWORD           buffer_len;
    OVERLAPPED      overlapped;
};

int _tmain(int argc, _TCHAR* argv[])
{
    DWORD winerr;
    ThreadData td;

    td.flags = FILE_NOTIFY_CHANGE_FILE_NAME|
               FILE_NOTIFY_CHANGE_DIR_NAME|
               FILE_NOTIFY_CHANGE_ATTRIBUTES|
               FILE_NOTIFY_CHANGE_SIZE|
               FILE_NOTIFY_CHANGE_LAST_WRITE|
               FILE_NOTIFY_CHANGE_LAST_ACCESS|
               FILE_NOTIFY_CHANGE_CREATION|
               FILE_NOTIFY_CHANGE_SECURITY;
    td.recursive = TRUE;
    td.completion_port = NULL;
    td.handle = CreateFileW(L"J:\\Font",         // arbitrary folder
                            FILE_LIST_DIRECTORY, // required
                            FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
                            NULL,
                            OPEN_EXISTING,
                            // Use FILE_FLAG_OVERLAPPED for asynchronous operation with ReadDirectoryChangesW.
                            FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
                            NULL);

    if(td.handle == INVALID_HANDLE_VALUE)
    {
        winerr = GetLastError();
        return 0;
    }

    td.completion_port = CreateIoCompletionPort(td.handle,
                                                NULL,
                                                (ULONG_PTR)&td,
                                                0);    // max num processors
    if(td.completion_port == NULL)
    {
        winerr = GetLastError();
        CloseHandle(td.handle);
        return 0;
    }

    ZeroMemory(&td.overlapped, sizeof(td.overlapped)); // <-- add this!

    // required if the thread uses GetOverlappedResult()...
    // optional if the thread uses GetQueuedCompletionStatus()...
    /*
    td.overlapped.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
    if(td.overlapped.hEvent == NULL)
    {
        winerr = GetLastError();
        CloseHandle(td.completion_port);
        CloseHandle(td.handle);
        return 0;
    }
    */

    BOOL rdc = ReadDirectoryChangesW(td.handle,
                                     td.buffer,    // read results
                                     MAX_BUFFER,
                                     td.recursive, // watch subdirectories
                                     // NOTE: At least one flag is required!
                                     td.flags,     // see Notify Filters below
                                     &td.buffer_len,
                                     &td.overlapped,
                                     NULL);         // completion routine
    if(rdc == FALSE)
    {
        winerr = GetLastError();
        //CloseHandle(td.overlapped.hEvent);
        CloseHandle(td.completion_port);
        CloseHandle(td.handle);
        return 0;
    }

    // Launch thread here to handle completions and trigger new ones
    ...

    // Clean up when the thread is done
    //CloseHandle(td.overlapped.hEvent);
    CloseHandle(td.completion_port);
    CloseHandle(td.handle);

    return 0;
}