线程中的QEventLoop::exec是怎么实现的

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在Qt Creator中添加如下测试代码：

void myThread::run(){    QEventLoop eventLoop;    eventLoop.exec();}

//C:\Qt\Qt5.7.0\5.7\Src\qtbase\src\corelib\kernel\qeventloop.cppint QEventLoop::exec(ProcessEventsFlags flags){    //...    while (!d->exit.loadAcquire())        processEvents(flags | WaitForMoreEvents | EventLoopExec);    //...}

//C:\Qt\Qt5.7.0\5.7\Src\qtbase\src\corelib\kernel\qeventdispatcher_win.cppbool QEventDispatcherWin32::processEvents(QEventLoop::ProcessEventsFlags flags){    //...    if (!d->internalHwnd) {        createInternalHwnd();        wakeUp(); // trigger a call to sendPostedEvents()    }    //...    haveMessage = PeekMessage(&msg, 0, 0, 0, PM_REMOVE);    //...    if (!filterNativeEvent(QByteArrayLiteral("windows_generic_MSG"), &msg, 0)) {                    TranslateMessage(&msg);                    DispatchMessage(&msg);                }    //...    waitRet = MsgWaitForMultipleObjectsEx(nCount, pHandles, INFINITE, QS_ALLINPUT, MWMO_ALERTABLE | MWMO_INPUTAVAILABLE);    //...}

其中createInternalHwnd()调用了qt_create_internal_window

static HWND qt_create_internal_window(const QEventDispatcherWin32 *eventDispatcher){    QWindowsMessageWindowClassContext *ctx = qWindowsMessageWindowClassContext();    if (!ctx->atom)        return 0;#ifdef Q_OS_WINCE    HWND parent = 0;#else    HWND parent = HWND_MESSAGE;#endif    HWND wnd = CreateWindow(ctx->className,    // classname                            ctx->className,    // window name                            0,                 // style                            0, 0, 0, 0,        // geometry                            parent,            // parent                            0,                 // menu handle                            qWinAppInst(),     // application                            0);                // windows creation data.    if (!wnd) {        qErrnoWarning("CreateWindow() for QEventDispatcherWin32 internal window failed");        return 0;    }#ifdef GWLP_USERDATA    SetWindowLongPtr(wnd, GWLP_USERDATA, (LONG_PTR)eventDispatcher);#else    SetWindowLong(wnd, GWL_USERDATA, (LONG)eventDispatcher);#endif    return wnd;}

创建了一个"message-only window"

https://msdn.microsoft.com/en-us/library/windows/desktop/ms632599(v=vs.85).aspx#message_only

Message-Only Windows

A message-only window enables you to send and receive messages. It is not visible, has no z-order, cannot be enumerated, and does not receive broadcast messages. The window simply dispatches messages.

To create a message-only window, specify the HWND_MESSAGE constant or a handle to an existing message-only window in the hWndParent parameter of the CreateWindowEx function. You can also change an existing window to a message-only window by specifying HWND_MESSAGE in thehWndNewParent parameter of theSetParent function.

To find message-only windows, specify HWND_MESSAGE in the hwndParent parameter of the FindWindowEx function. In addition, FindWindowEx searches message-only windows as well as top-level windows if both thehwndParent andhwndChildAfter parameters are NULL.

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