win32 getMessage 和 peekMessage的区别

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:

win32 getMessage 和 peekMessage的区别

 

 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?

 

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