《Windows核心编程》第七章——进程优先级实验

其实就是做个实验，看看SetPriorityClass是否真的会生效。

设计思路：主线程一直在进行某种操作（这里是写文件操作），以保证有一定的CPU占用率；生成的子线程来接收你的命令，决定将进程改变为什么级别。

代码逻辑如下：

#include <iostream>
#include <windows.h>
#include <tchar.h>
#include <process.h>
#include <fstream>

using namespace std;
unsigned int WINAPI ThreadFunc(PVOID pvParam){
    HANDLE hPThread = (HANDLE)pvParam;
    printf("Enter thread
");
    while (true){
        char cPriority = getchar();
        //SuspendThread(hPThread);
        if (cPriority == 'a')
        {
            if (!SetPriorityClass(GetCurrentProcess(), IDLE_PRIORITY_CLASS))
            {
                printf("SetPriorityClass failed:%d
", GetLastError());
                return FALSE;
            }
            printf("IDLE_PRIORITY_CLASS
");
        }
        if (cPriority == 'b')
        {
            if (!SetPriorityClass(GetCurrentProcess(), BELOW_NORMAL_PRIORITY_CLASS))
            {
                printf("SetPriorityClass failed:%d
", GetLastError());
                return FALSE;
            }
            printf("BELOW_NORMAL_PRIORITY_CLASS
");
        }
        if (cPriority == 'c')
        {
            if (!SetPriorityClass(GetCurrentProcess(), NORMAL_PRIORITY_CLASS))
            {
                printf("SetPriorityClass failed:%d
", GetLastError());
                return FALSE;
            }
            printf("NORMAL_PRIORITY_CLASS
");
        }
        if (cPriority == 'd')
        {
            if (!SetPriorityClass(GetCurrentProcess(), ABOVE_NORMAL_PRIORITY_CLASS))
            {
                printf("SetPriorityClass failed:%d
", GetLastError());
                return FALSE;
            }
            printf("ABOVE_NORMAL_PRIORITY_CLASS
");
        }
        if (cPriority == 'e')
        {
            if (!SetPriorityClass(GetCurrentProcess(), HIGH_PRIORITY_CLASS))
            {
                printf("SetPriorityClass failed:%d
", GetLastError());
                return FALSE;
            }
            printf("HIGH_PRIORITY_CLASS
");
        }
        if (cPriority == 'f')
        {
            if (!SetPriorityClass(GetCurrentProcess(), REALTIME_PRIORITY_CLASS))
            {
                printf("SetPriorityClass failed:%d
", GetLastError());
                return FALSE;
            }
            printf("REALTIME_PRIORITY_CLASS
");
        }
        /*if (cPriority == 's')
        {
            Sleep(30000);
            printf("Sleeping..
");
        }*/
        //ResumeThread(hPThread);
    }
    CloseHandle(hPThread);
    return TRUE;
}

BOOL main(){
    HANDLE hPThread;
    if (!DuplicateHandle(GetCurrentProcess(), GetCurrentThread(), GetCurrentProcess(),
    &hPThread, THREAD_SUSPEND_RESUME, FALSE, DUPLICATE_SAME_ACCESS))
    {
    printf("Dupilicate failed:%d", GetLastError());
    return FALSE;
    }

    _beginthreadex(NULL, 0, ThreadFunc, NULL, 0, NULL);

    int i = 0;
    printf("Enter while
");
    while (TRUE){
        i++;
        ofstream outfile;
        outfile.open("E:\Coding\test\test2.txt");
        outfile << "Run service success..
" << endl;
        outfile.close();
    }
    return TRUE;
}

当启动这个线程和它的副本的时候，二者CPU占用率差不多：

现在调低188.exe的优先级，调到IDLE优先级后，其CPU占用率立即下降：

如果改成实时的优先级，其CUP占用率就会提升：

确实会有变化，但是并不像书中说的那么明显。