异步使用 ReadDirectoryChangesW 时线程死锁

Question

我想在一个线程中实时监控多个目录的更改，因此我决定使用 ReadDirectoryChangesW() 方法与 GetQueuedCompletionStatus 异步使用。 这是我的代码：

static DWORD WINAPI Routine( LPVOID lParam )
{
    FileSystemWatcher* obj = (FileSystemWatcher*)lParam;

    obj->hDir[0] = CreateFile(
        obj->WatchedDir[0].c_str(),
        GENERIC_READ|GENERIC_WRITE,
        FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
        NULL,
        OPEN_EXISTING,
        FILE_FLAG_BACKUP_SEMANTICS|FILE_FLAG_OVERLAPPED,
        NULL
    );

    obj->hDir[1] = CreateFile(
   obj->WatchedDir[1].c_str(),
   GENERIC_READ|GENERIC_WRITE,
   FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
   NULL,
   OPEN_EXISTING,
   FILE_FLAG_BACKUP_SEMANTICS|FILE_FLAG_OVERLAPPED,
   NULL
    );

    if( INVALID_HANDLE_VALUE == obj->hDir[0] || INVALID_HANDLE_VALUE == obj->hDir     [1] ) 
{
    return false;
}

obj->IOCPHandle[0] = CreateIoCompletionPort(obj->hDir[0], NULL, 0, 1);
obj->IOCPHandle[1] = CreateIoCompletionPort(obj->hDir[1], NULL, 0, 1);

if (obj->IOCPHandle[0] == INVALID_HANDLE_VALUE || obj->IOCPHandle[1] ==  INVALID_HANDLE_VALUE)
{
    return false;
}

    char buf[ 2*(sizeof(FILE_NOTIFY_INFORMATION)+MAX_PATH) ];
    FILE_NOTIFY_INFORMATION* pNotify=(FILE_NOTIFY_INFORMATION *)buf;
    DWORD BytesReturned;
    LPOVERLAPPED overLap = NULL;

    m_pFileNotifyInfo = pNotify;
    dirEvents[0] = CreateEvent(NULL, TRUE, FALSE, NULL);
    dirEvents[1] = CreateEvent(NULL, TRUE, FALSE, NULL);*/

    while(true)
    {

    BOOL success = ReadDirectoryChangesW( obj->hDir[0],
    pNotify,
    sizeof(buf),
    true,
    FILE_NOTIFY_CHANGE_FILE_NAME|FILE_NOTIFY_CHANGE_DIR_NAME,
    &BytesReturned,
    overLap,
    NULL );
    BOOL success1 = ReadDirectoryChangesW( obj->hDir[1],
    pNotify,
    sizeof(buf),
    true,
    FILE_NOTIFY_CHANGE_FILE_NAME|FILE_NOTIFY_CHANGE_DIR_NAME,
    &BytesReturned,
    overLap,    
                 NULL );

    LPOVERLAPPED theOverLap;
    PULONG_PTR lpCompKey = NULL;
    if (GetQueuedCompletionStatus(obj->IOCPHandle[0], &BytesReturned, lpCompKey, &overLap, 100))
    {
    cout<<"First Dir Changed"<<endl;
    }

    if (GetQueuedCompletionStatus(obj->IOCPHandle[1], &BytesReturned, lpCompKey, &overLap, 100))
    {
    cout<<"Second Dir Changed"<<endl;
    }

    cout<<"Nothing happened yet"<<endl;

       }

    return 0;
}

当我运行代码时，无论我为 GetQueuedCompletionStatus() 函数的最后一个参数设置什么值，我的线程都会无缘无故地阻塞。 我不知道为什么我遇到这个问题。 谁能告诉我原因吗？ 非常感谢！

Answer 1

1. 您必须指定有效的 OVERLAPPED 结构才能使异步 I/O 工作。 您正在使用 NULL (LPOVERLAPPED overLap = NULL;)。

2. 并发 I/O 操作必须使用单独的 OVERLAPPED 结构，而不仅仅是一个。

3. 您确定需要 IOCP 吗？ 我只需在 OVERLAPPED 结构中填写 hEvent 并对这些事件执行 WaitForMultipleObjects。