I had a go at getting the asynchronous version of ReadDirectoryChangesW working. As I mentioned, it is pretty complicated. Note:
are used to call the callback function. These require a special message loop to be despatched. Therefore, calling functions that block and run their own message loop (such as MessageBox and DialogBox) will also block change notifications.
Code:
#define _WIN32_WINNT 0x0400
#include <windows.h>
#include <windowsx.h>
#include <commctrl.h>
#include <shlwapi.h>
#if defined(_MSC_VER)
#pragma comment(lib, "comctl32.lib")
#pragma comment(lib, "user32.lib")
#pragma comment(lib, "ole32.lib")
#endif
HINSTANCE g_hinst;
typedef void (CALLBACK *FileChangeCallback)(LPTSTR, DWORD, LPARAM);
typedef struct tagDIR_MONITOR
{
OVERLAPPED ol;
HANDLE hDir;
BYTE buffer[32 * 1024];
LPARAM lParam;
DWORD notifyFilter;
BOOL fStop;
FileChangeCallback callback;
} *HDIR_MONITOR;
/*
* Unpacks events and passes them to a user defined callback.
*/
VOID CALLBACK MonitorCallback(DWORD dwErrorCode, DWORD dwNumberOfBytesTransfered, LPOVERLAPPED lpOverlapped)
{
TCHAR szFile[MAX_PATH];
PFILE_NOTIFY_INFORMATION pNotify;
HDIR_MONITOR pMonitor = (HDIR_MONITOR) lpOverlapped;
size_t offset = 0;
BOOL RefreshMonitoring(HDIR_MONITOR pMonitor);
if (dwErrorCode == ERROR_SUCCESS)
{
do
{
pNotify = (PFILE_NOTIFY_INFORMATION) &pMonitor->buffer[offset];
offset += pNotify->NextEntryOffset;
# if defined(UNICODE)
{
lstrcpynW(szFile, pNotify->FileName,
min(MAX_PATH, pNotify->FileNameLength / sizeof(WCHAR) + 1));
}
# else
{
int count = WideCharToMultiByte(CP_ACP, 0, pNotify->FileName,
pNotify->FileNameLength / sizeof(WCHAR),
szFile, MAX_PATH - 1, NULL, NULL);
szFile[count] = TEXT('\0');
}
# endif
pMonitor->callback(szFile, pNotify->Action, pMonitor->lParam);
} while (pNotify->NextEntryOffset != 0);
}
if (!pMonitor->fStop)
{
RefreshMonitoring(pMonitor);
}
}
/*
* Refreshes the directory monitoring.
*/
BOOL RefreshMonitoring(HDIR_MONITOR pMonitor)
{
return
ReadDirectoryChangesW(pMonitor->hDir, pMonitor->buffer, sizeof(pMonitor->buffer), FALSE,
pMonitor->notifyFilter, NULL, &pMonitor->ol, MonitorCallback);
}
/*
* Stops monitoring a directory.
*/
void StopMonitoring(HDIR_MONITOR pMonitor)
{
if (pMonitor)
{
pMonitor->fStop = TRUE;
CancelIo(pMonitor->hDir);
if (!HasOverlappedIoCompleted(&pMonitor->ol))
{
SleepEx(5, TRUE);
}
CloseHandle(pMonitor->ol.hEvent);
CloseHandle(pMonitor->hDir);
HeapFree(GetProcessHeap(), 0, pMonitor);
}
}
/*
* Starts monitoring a directory.
*/
HDIR_MONITOR StartMonitoring(LPCTSTR szDirectory, DWORD notifyFilter, FileChangeCallback callback)
{
HDIR_MONITOR pMonitor = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(*pMonitor));
pMonitor->hDir = CreateFile(szDirectory, FILE_LIST_DIRECTORY, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED, NULL);
if (pMonitor->hDir != INVALID_HANDLE_VALUE)
{
pMonitor->ol.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
pMonitor->notifyFilter = notifyFilter;
pMonitor->callback = callback;
if (RefreshMonitoring(pMonitor))
{
return pMonitor;
}
else
{
CloseHandle(pMonitor->ol.hEvent);
CloseHandle(pMonitor->hDir);
}
}
HeapFree(GetProcessHeap(), 0, pMonitor);
return NULL;
}
/*
* Runs a message loop that allows APCs to be despatched.
*/
int RunAPCMessageLoop(void)
{
BOOL done = FALSE;
MSG msg = { 0 };
while (!done)
{
/* Wait for either an APC or a message. */
while (WAIT_IO_COMPLETION ==
MsgWaitForMultipleObjectsEx(0, NULL, INFINITE, QS_ALLINPUT, MWMO_ALERTABLE)) /* Do nothing */;
/* One or more messages have arrived. */
while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
{
if (msg.message == WM_QUIT)
{
done = TRUE;
break;
}
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
return (int) msg.wParam;
}
void CALLBACK FileCallback(LPTSTR szFile, DWORD action, LPARAM lParam)
{
/* Shouldn't call MessageBox as it will block new notifications coming in. */
MessageBox(NULL, szFile, NULL, 0);
}
HDIR_MONITOR h;
BOOL OnCreate(HWND hwnd, LPCREATESTRUCT lpcs)
{
h = StartMonitoring(TEXT("C:\\Documents and Settings\\USER\\My Documents"),
FILE_NOTIFY_CHANGE_CREATION | FILE_NOTIFY_CHANGE_SIZE | FILE_NOTIFY_CHANGE_FILE_NAME,
FileCallback);
return TRUE;
}
void OnDestroy(HWND hwnd)
{
if (h) StopMonitoring(h);
PostQuitMessage(0);
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT uiMsg, WPARAM wParam, LPARAM lParam)
{
switch (uiMsg)
{
HANDLE_MSG(hwnd, WM_CREATE, OnCreate);
HANDLE_MSG(hwnd, WM_DESTROY, OnDestroy);
}
return DefWindowProc(hwnd, uiMsg, wParam, lParam);
}
BOOL InitApp(void)
{
WNDCLASS wc = { 0 };
wc.style = 0;
wc.lpfnWndProc = WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = g_hinst;
wc.hIcon = NULL;
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
wc.lpszMenuName = NULL;
wc.lpszClassName = TEXT("Scratch");
if (!RegisterClass(&wc)) return FALSE;
return TRUE;
}
int WINAPI WinMain(HINSTANCE hinst, HINSTANCE hinstPrev,
LPSTR lpCmdLine, int nShowCmd)
{
HWND hwnd;
int result;
g_hinst = hinst;
if (!InitApp()) return 0;
hwnd = CreateWindow(
TEXT("Scratch"), /* Class Name */
TEXT("Scratch"), /* Title */
WS_OVERLAPPEDWINDOW, /* Style */
CW_USEDEFAULT, CW_USEDEFAULT, /* Position */
CW_USEDEFAULT, CW_USEDEFAULT, /* Size */
NULL, /* Parent */
NULL, /* No menu */
hinst, /* Instance */
0); /* No special parameters */
ShowWindow(hwnd, nShowCmd);
result = RunAPCMessageLoop();
return result;
}
Originally Posted by anonytmouse
I had a go at getting the asynchronous version of ReadDirectoryChangesW working. As I mentioned, it is pretty complicated. Note: APCs are used to call the callback function. These require a special message loop to be despatched. Therefore, calling functions that block and run their own message loop (such as MessageBox and DialogBox) will also block change notifications.
