C++第四十二篇 -- CPU Usage

前言

目的：读取并控制CPU占用率

近期在做CPU Usage方面的事情，让CPU以一种高占用率的状态运行一定的时间，需要读取CPU各个核的占用率，网上关于这方面的资料好少，FQ也只找到了一个WMI的方法，但是感觉对比任务管理器里面的结果偏小。目前也只能读取CPU总的占用率，和任务管理器看起来差不多，也不是完全相同。

虽然还没有实现结果，但是想记录一下历程。

参考链接：

https://blog.csdn.net/wangting627/article/details/22931337

https://blog.csdn.net/fyxichen/article/details/50577580

内容

1. 任务管理器查看CPU占用率。

方法一：

方法二：

2. C++读取CPU的占用率

原理：先读取一次CPU的当前的空闲时间，内核时间和用户时间，间隔一秒，再次读取三个时间，经过公式演算，得到CPU在这一秒内的占用率。

第一次读取：

    FILETIME ftIdle, ftKernel, ftUser;
    BOOL flag = FALSE;
    if (flag = GetSystemTimes(&ftIdle, &ftKernel, &ftUser))
    {
        m_fOldCPUIdleTime = FileTimeToDouble(&ftIdle);
        m_fOldCPUKernelTime = FileTimeToDouble(&ftKernel);
        m_fOldCPUUserTime = FileTimeToDouble(&ftUser);

    }
    return flag;

View Code

第二次读取：

    FILETIME ftIdle, ftKernel, ftUser;
    //检索系统定时信息，对于多处理器系统，返回值是各处理器总和的时间
    //参数1：空闲时间
    //参数2：内核时间
    //参数3：用户时间
    //函数成功，返回值为非零。函数失败，返回值为零
    if (GetSystemTimes(&ftIdle, &ftKernel, &ftUser))
    {
        double fCPUIdleTime = FileTimeToDouble(&ftIdle);
        double fCPUKernelTime = FileTimeToDouble(&ftKernel);
        double fCPUUserTime = FileTimeToDouble(&ftUser);}

View Code

计算占用率：

//CPU使用率 = （总的时间-空闲时间) / 总的时间
nCPUUseRate = (int)(100.0 - (fCPUIdleTime - m_fOldCPUIdleTime) / (fCPUKernelTime - m_fOldCPUKernelTime + fCPUUserTime - m_fOldCPUUserTime)*100.0);

View Code

3. 控制CPU占用率

原理：CPU的占用率 = （CPU总时间 - CPU空闲时间）/ CPU总时间。

举几个例子看看：

占用率	num值	空闲时间：运行时间
50%	1	1:1
66.7%	2	1:2
80%	4	1:4
90%	9	1:9

如果想要控制CPU的占用率是50%，那么就设置num = 1，空闲时间和运行时间的比例为1:1。不过这些都有个前提是，电脑中并没有运行其他的程序。但是显然不可能，所以这个占用率也只是个大概。并且想要数据比较准确，一秒之内的空闲和运行最好是间隔运行，如果控制前0.5s运行，后0.5秒Sleep，效果也是不好的，在代码中设置的是0.1s休息。

    int busytime = 100;
    int idletime = busytime;
    long starttime = 0;
    while (true)
    {
        starttime = GetTickCount();
        //std::cout<<starttime<<std::endl;//调试用
        while ((GetTickCount() - starttime) <= busytime * num)
            ;
        Sleep(idletime);
    }

View Code

4. 效果图

以1:9的代码运行结果如下：

可以看到其实任务管理器中的值每隔一秒刷新一次，我写的程序是每隔一秒刷新一次，然后任务管理器中的值看起来比代码中的偏高一些，大胆猜测一下是因为我的程序也在运行，运行过程中也会增加占用率。

5. WMI读取CPU各个核的使用率

代码是google找到的，链接我忘了，后续找到补上，需要FQ

bool getCpuLoadInfo() {
    HRESULT hres;

    // Step 1: --------------------------------------------------
    // Initialize COM. ------------------------------------------

    hres = CoInitializeEx(0, COINIT_MULTITHREADED);
    if (FAILED(hres)) {
        cout << "Failed to initialize COM library. Error code = 0x" << hex << hres << endl;
        return 0;                  // Program has failed.
    }

    // Step 2: --------------------------------------------------
    // Set general COM security levels --------------------------
    // Note: If you are using Windows 2000, you need to specify -
    // the default authentication credentials for a user by using
    // a SOLE_AUTHENTICATION_LIST structure in the pAuthList ----
    // parameter of CoInitializeSecurity ------------------------

    hres = CoInitializeSecurity(
        NULL,
        -1,                          // COM authentication
        NULL,                        // Authentication services
        NULL,                        // Reserved
        RPC_C_AUTHN_LEVEL_DEFAULT,   // Default authentication
        RPC_C_IMP_LEVEL_IMPERSONATE, // Default Impersonation  
        NULL,                        // Authentication info
        EOAC_NONE,                   // Additional capabilities
        NULL                         // Reserved
    );


    if (FAILED(hres)) {
        cout << "Failed to initialize security. Error code = 0x"
            << hex << hres << endl;
        CoUninitialize();
        return 0;                    // Program has failed.
    }

    // Step 3: ---------------------------------------------------
    // Obtain the initial locator to WMI -------------------------

    IWbemLocator *pLoc = NULL;

    hres = CoCreateInstance(
        CLSID_WbemLocator,
        0,
        CLSCTX_INPROC_SERVER,
        IID_IWbemLocator, (LPVOID *)&pLoc);

    if (FAILED(hres)) {
        cout << "Failed to create IWbemLocator object."
            << " Err code = 0x"
            << hex << hres << endl;
        CoUninitialize();
        return 0;                 // Program has failed.
    }

    // Step 4: -----------------------------------------------------
    // Connect to WMI through the IWbemLocator::ConnectServer method

    IWbemServices *pSvc = NULL;

    // Connect to the root\cimv2 namespace with
    // the current user and obtain pointer pSvc
    // to make IWbemServices calls.
    hres = pLoc->ConnectServer(
        _bstr_t(L"ROOT\\CIMV2"), // Object path of WMI namespace
        NULL,                    // User name. NULL = current user
        NULL,                    // User password. NULL = current
        0,                       // Locale. NULL indicates current
        NULL,                    // Security flags.
        0,                       // Authority (e.g. Kerberos)
        0,                       // Context object
        &pSvc                    // pointer to IWbemServices proxy
    );

    if (FAILED(hres)) {
        cout << "Could not connect. Error code = 0x" << hex << hres << endl;
        pLoc->Release();
        CoUninitialize();
        return 0;                // Program has failed.
    }

    cout << "Connected to ROOT\\CIMV2 WMI namespace" << endl;


    // Step 5: --------------------------------------------------
    // Set security levels on the proxy -------------------------

    hres = CoSetProxyBlanket(
        pSvc,                        // Indicates the proxy to set
        RPC_C_AUTHN_WINNT,           // RPC_C_AUTHN_xxx
        RPC_C_AUTHZ_NONE,            // RPC_C_AUTHZ_xxx
        NULL,                        // Server principal name
        RPC_C_AUTHN_LEVEL_CALL,      // RPC_C_AUTHN_LEVEL_xxx
        RPC_C_IMP_LEVEL_IMPERSONATE, // RPC_C_IMP_LEVEL_xxx
        NULL,                        // client identity
        EOAC_NONE                    // proxy capabilities
    );

    if (FAILED(hres)) {
        cout << "Could not set proxy blanket. Error code = 0x"
            << hex << hres << endl;
        pSvc->Release();
        pLoc->Release();
        CoUninitialize();
        return 0;               // Program has failed.
    }

    // Step 6: --------------------------------------------------
    // Use the IWbemServices pointer to make requests of WMI ----

    // For example, get the name of the operating system
    IEnumWbemClassObject* pEnumerator = NULL;
    IWbemClassObject *pclsObj;
    int i;
    //while (1) {
        i = 1;
        hres = pSvc->ExecQuery(
            bstr_t("WQL"),
            bstr_t("SELECT * FROM Win32_PerfFormattedData_PerfOS_Processor"),

            WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY,
            NULL,
            &pEnumerator);

        if (FAILED(hres)) {
            cout << "Query for operating system name failed."
                << " Error code = 0x"
                << hex << hres << endl;
            pSvc->Release();
            pLoc->Release();
            CoUninitialize();
            return 0;               // Program has failed.
        }

        // Step 7: -------------------------------------------------
        // Get the data from the query in step 6 -------------------


        ULONG uReturn = 0;

        while (pEnumerator) {
            HRESULT hr = pEnumerator->Next(WBEM_INFINITE, 1,
                &pclsObj, &uReturn);

            if (0 == uReturn) {
                break;
            }

            VARIANT vtProp;

            // Get the value of the Name property
            //hr = pclsObj->Get(L"Name", 0, &vtProp, 0, 0);
            hr = pclsObj->Get(L"PercentProcessorTime", 0, &vtProp, 0, 0);
            wcout << " CPU Usage of CPU " << i << " : " << vtProp.bstrVal << endl;
            VariantClear(&vtProp);

            //IMPORTANT!!
            pclsObj->Release();

            i++;
        }

    //}

    // Cleanup
    // ========

    pSvc->Release();
    pLoc->Release();
    pEnumerator->Release();
    //pclsObj->Release();
    CoUninitialize();

    return 0;   // Program successfully completed.
}