介绍：
我正在尝试使用读取目录更改W在循环中异步进行。
下面的代码片段说明了我想要实现的目标：
DWORD example()
{
DWORD error = 0;
OVERLAPPED ovl = { 0 };
ovl.hEvent = ::CreateEvent(NULL, TRUE, FALSE, NULL);
if (NULL == ovl.hEvent) return ::GetLastError();
char buffer[1024];
while(1)
{
process_list_of_existing_files();
error = ::ReadDirectoryChangesW(
m_hDirectory, // I have added FILE_FLAG_OVERLAPPED in CreateFile
buffer, sizeof(buffer), FALSE,
FILE_NOTIFY_CHANGE_FILE_NAME,
NULL, &ovl, NULL);
// we have new files, append them to the list
if(error) append_new_files_to_the_list(buffer);
// just continue with the loop
else if(::GetLastError() == ERROR_IO_PENDING) continue;
// RDCW error, this is critical -> exit
else return ::GetLastError();
}
}
PROBLEM:
我不知道如何处理这个案子ReadDirectoryChangesW回报FALSE with GetLastError()代码是ERROR_IO_PENDING.
在这种情况下，我应该继续循环并继续循环直到ReadDirectoryChangesW回报buffer我可以处理。
我为解决这个问题所做的努力：
我尝试过使用WaitForSingleObject(ovl.hEvent, 1000)但它因错误而崩溃1450 ERROR_NO_SYSTEM_RESOURCES。下面是重现此行为的 MVCE：
#include <iostream>
#include <Windows.h>
DWORD processDirectoryChanges(const char *buffer)
{
DWORD offset = 0;
char fileName[MAX_PATH] = "";
FILE_NOTIFY_INFORMATION *fni = NULL;
do
{
fni = (FILE_NOTIFY_INFORMATION*)(&buffer[offset]);
// since we do not use UNICODE,
// we must convert fni->FileName from UNICODE to multibyte
int ret = ::WideCharToMultiByte(CP_ACP, 0, fni->FileName,
fni->FileNameLength / sizeof(WCHAR),
fileName, sizeof(fileName), NULL, NULL);
switch (fni->Action)
{
case FILE_ACTION_ADDED:
{
std::cout << fileName << std::endl;
}
break;
default:
break;
}
::memset(fileName, '\0', sizeof(fileName));
offset += fni->NextEntryOffset;
} while (fni->NextEntryOffset != 0);
return 0;
}
int main()
{
HANDLE hDir = ::CreateFile("C:\\Users\\nenad.smiljkovic\\Desktop\\test",
FILE_LIST_DIRECTORY,
FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
NULL, OPEN_EXISTING,
FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED, NULL);
if (INVALID_HANDLE_VALUE == hDir) return ::GetLastError();
OVERLAPPED ovl = { 0 };
ovl.hEvent = ::CreateEvent(NULL, TRUE, FALSE, NULL);
if (NULL == ovl.hEvent) return ::GetLastError();
DWORD error = 0, br;
char buffer[1024];
while (1)
{
error = ::ReadDirectoryChangesW(hDir,
buffer, sizeof(buffer), FALSE,
FILE_NOTIFY_CHANGE_FILE_NAME,
NULL, &ovl, NULL);
if (0 == error)
{
error = ::GetLastError();
if (ERROR_IO_PENDING != error)
{
::CloseHandle(ovl.hEvent);
::CloseHandle(hDir);
return error;
}
}
error = ::WaitForSingleObject(ovl.hEvent, 0);
switch (error)
{
case WAIT_TIMEOUT:
break;
case WAIT_OBJECT_0:
{
error = processDirectoryChanges(buffer);
if (error > 0)
{
::CloseHandle(ovl.hEvent);
::CloseHandle(hDir);
return error;
}
if (0 == ::ResetEvent(ovl.hEvent))
{
error = ::GetLastError();
::CloseHandle(ovl.hEvent);
::CloseHandle(hDir);
return error;
}
}
break;
default:
error = ::GetLastError();
::CloseHandle(ovl.hEvent);
::CloseHandle(hDir);
return error;
break;
}
}
return 0;
}
仔细阅读文档，我似乎需要获取重叠结果最后一个参数设置为FALSE但我不知道如何正确使用这个API。
问题：
由于 MVCE 很好地说明了我正在尝试执行的操作（打印新添加的文件的名称），您能否向我展示在 MVCE 中必须修复哪些内容？while循环才能使其工作？
再次强调，重点是使用ReadDirectoryChangesW异步地，在循环中，如简介中的片段所示。
