我正在向基于Qt的应用程序中添加功能，以便以递归方式监视Windows系统上的任意文件夹的任何活动（Qt变体QFileSystemWatcher缺少此功能）。使用CreatFileW（）打开文件夹后，我创建一个完成端口以接收重叠的I / O，然后使用ReadDirectoryChangesW（）将读取排队。
我已将所有这些内容放置在下面的“简单” Win32控制台应用程序中进行演示（请注意，“ stdafx.h”标头已被修改为包括“ windows.h”，但Visual Studio 2013 IDE生成了该标头） ：
#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;
}
关于此代码的注意事项是，它是以C语言编写的Python模块（“观察程序”）为模型的，该模块提供与Python环境类似的功能。我已经在Python中使用了它，并且可以在此C ++片段中的所有相同设置下按预期工作。
在上面的代码中，CreateIoCompletionPort（）接受CreateFileW（）生成的HANDLE，但ReadDirectoryChangesW（）不接受。它返回0，并且GetLastError（）返回“句柄无效。（0x6）”。我已经在32位和64位编译器中进行了尝试，以防万一有所不同（我使用的是64位版本的Python）。另外，指定的目录似乎无关紧要：我指定的所有目录都产生相同的结果，这表明某处的设置存在问题。
在CreateFileW（）调用中是否有可能导致HANDLE对生成补全端口有效的东西，但会给ReadDirectoryChangesW（）函数带来灼热感？
最佳答案
您没有正确初始化I / O完成端口，也根本没有初始化OVERLAPPED结构。 ReadDirectoryChangesW()失败，因为OVERLAPPED::hEvent字段包含无效的事件对象句柄。那是错误代码所指的无效句柄，而不是目录句柄。
尝试以下方法：
#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;
}