QT在windows下的机制,是采用PeekMessage的策略,所以我就想,在没有事件产生时,会发生什么,按照微软文档的解释,getmessage在没有消息时,会被阻塞。如果peekmessage没有消息时,就返回。那它所处的while不就一直占用cpu?
测试一个例子,用了qt的机制:
// 消息机制.cpp : 定义应用程序的入口点。 // #include "framework.h" #include "消息机制.h" #define MAX_LOADSTRING 100 // 全局变量: HINSTANCE hInst; // 当前实例 WCHAR szTitle[MAX_LOADSTRING]; // 标题栏文本 WCHAR szWindowClass[MAX_LOADSTRING]; // 主窗口类名 int cxClient, cyClient; HWND hWnd; // 此代码模块中包含的函数的前向声明: ATOM MyRegisterClass(HINSTANCE hInstance); BOOL InitInstance(HINSTANCE, int); LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM); INT_PTR CALLBACK About(HWND, UINT, WPARAM, LPARAM); void DrawRectangle(HWND hwnd) { HBRUSH hBrush; HDC hdc; RECT rect; if (cxClient == 0 || cyClient == 0) return; SetRect(&rect, rand() % cxClient, rand() % cyClient, rand() % cxClient, rand() % cyClient); hBrush = CreateSolidBrush( RGB(rand() % 256, rand() % 256, rand() % 256)); hdc = GetDC(hwnd); FillRect(hdc, &rect, hBrush); ReleaseDC(hwnd, hdc); DeleteObject(hBrush); } int APIENTRY wWinMain(_In_ HINSTANCE hInstance, _In_opt_ HINSTANCE hPrevInstance, _In_ LPWSTR lpCmdLine, _In_ int nCmdShow) { UNREFERENCED_PARAMETER(hPrevInstance); UNREFERENCED_PARAMETER(lpCmdLine); // TODO: 在此处放置代码。 // 初始化全局字符串 LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING); LoadStringW(hInstance, IDC_MY, szWindowClass, MAX_LOADSTRING); MyRegisterClass(hInstance); // 执行应用程序初始化: if (!InitInstance (hInstance, nCmdShow)) { return FALSE; } HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_MY)); MSG msg; // 主消息循环: while (TRUE) { if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) { if (msg.message == WM_QUIT) break; TranslateMessage(&msg); DispatchMessage(&msg); } else if (MsgWaitForMultipleObjectsEx(0, NULL, 0, QS_ALLINPUT, MWMO_ALERTABLE) == WAIT_OBJECT_0) { // a new message has arrived, process it continue; } else DrawRectangle(hWnd); MsgWaitForMultipleObjectsEx(0, NULL, INFINITE, QS_ALLINPUT, MWMO_ALERTABLE | MWMO_INPUTAVAILABLE); } return (int) msg.wParam; } // // 函数: MyRegisterClass() // // 目标: 注册窗口类。 // ATOM MyRegisterClass(HINSTANCE hInstance) { WNDCLASSEXW wcex; wcex.cbSize = sizeof(WNDCLASSEX); wcex.style = CS_HREDRAW | CS_VREDRAW; wcex.lpfnWndProc = WndProc; wcex.cbClsExtra = 0; wcex.cbWndExtra = 0; wcex.hInstance = hInstance; wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_MY)); wcex.hCursor = LoadCursor(nullptr, IDC_ARROW); wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1); wcex.lpszMenuName = MAKEINTRESOURCEW(IDC_MY); wcex.lpszClassName = szWindowClass; wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL)); return RegisterClassExW(&wcex); } // // 函数: InitInstance(HINSTANCE, int) // // 目标: 保存实例句柄并创建主窗口 // // 注释: // // 在此函数中,我们在全局变量中保存实例句柄并 // 创建和显示主程序窗口。 // BOOL InitInstance(HINSTANCE hInstance, int nCmdShow) { hInst = hInstance; // 将实例句柄存储在全局变量中 hWnd = CreateWindowW(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr); if (!hWnd) { return FALSE; } ShowWindow(hWnd, nCmdShow); UpdateWindow(hWnd); return TRUE; } // // 函数: WndProc(HWND, UINT, WPARAM, LPARAM) // // 目标: 处理主窗口的消息。 // // WM_COMMAND - 处理应用程序菜单 // WM_PAINT - 绘制主窗口 // WM_DESTROY - 发送退出消息并返回 // // LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam) { switch (message) { case WM_COMMAND: { int wmId = LOWORD(wParam); // 分析菜单选择: switch (wmId) { case IDM_ABOUT: DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About); break; case IDM_EXIT: DestroyWindow(hWnd); break; default: return DefWindowProc(hWnd, message, wParam, lParam); } } break; case WM_PAINT: { PAINTSTRUCT ps; HDC hdc = BeginPaint(hWnd, &ps); // TODO: 在此处添加使用 hdc 的任何绘图代码... EndPaint(hWnd, &ps); } break; case WM_SIZE: cxClient = LOWORD(lParam); cyClient = HIWORD(lParam); return 0; case WM_DESTROY: PostQuitMessage(0); return 0; default: return DefWindowProc(hWnd, message, wParam, lParam); } return 0; } // “关于”框的消息处理程序。 INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam) { UNREFERENCED_PARAMETER(lParam); switch (message) { case WM_INITDIALOG: return (INT_PTR)TRUE; case WM_COMMAND: if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL) { EndDialog(hDlg, LOWORD(wParam)); return (INT_PTR)TRUE; } break; } return (INT_PTR)FALSE; }
可以看到有两处地方用了MsgWaitForMultipleObjectsEx(0, NULL, 0, QS_ALLINPUT, MWMO_ALERTABLE),另外一处:
MsgWaitForMultipleObjectsEx(0, NULL, INFINITE, QS_ALLINPUT, MWMO_ALERTABLE | MWMO_INPUTAVAILABLE);
如果没有加这两处代码,程序是一直占用cpu的。加上之后,用process Explore监测程序的cpu情况:
在没有输入的情况下,cpu是不是进行上下文切换调度该线程的。从而达到与getmessage相同的效果,微软文档对相应的参数也做了解释,但是我查了很久,都找不到前两个参数为0,null时所代表的意义,默认本线程吗?