学步园

    前几天无聊，按照《编程之美》第一题写了个控制CPU使用率的程序。本以为没什么，可是今天早上在ChinaUnix上看到完全复制书上的代码毫无原创的帖子居然很火。。。所以把自己的代码贴出来，供以后学习……

    效果图如下：

    其实程序的设计思想很简单，Windows任务管理器中CPU使用率基本上1s刷新一次，而CPU使用率其实就是在1s中CPU忙和闲时间的均值。因此，根据我们想要得到的CPU曲线的特点，我们首先做出忙闲时间的表，CPU根据忙闲时间选择执行或挂起。

代码如下：

 #include <windows.h><br /> #include <stdlib.h><br /> #include <math.h></p> <p>#define COUNT 200</p> <p>const double SPLIT = 0.01;<br /> const double PI = 3.14159265;<br /> const double SLOPE = 150;<br /> const int INTERVAL = 300;</p> <p>DWORD WINAPI SineThread(LPVOID Sine)<br /> {<br /> DWORD busySpan[COUNT];<br /> DWORD idleSpan[COUNT];<br /> int half = INTERVAL/2;<br /> double radian = 0.0;<br /> DWORD startTime;<br /> int i;</p> <p> for (i=0; i<COUNT; i++)<br /> {<br /> busySpan[i] = (DWORD)(half + half*sin(PI*radian));<br /> idleSpan[i] = (DWORD)(INTERVAL - busySpan[i]);<br /> radian += SPLIT;<br /> }<br /> i = 0;<br /> while(1)<br /> {<br /> i %= COUNT;<br /> startTime = GetTickCount();<br /> while((GetTickCount()-startTime) <= busySpan[i])<br /> ;<br /> Sleep(idleSpan[i]);<br /> i++;<br /> }<br /> return 0;<br /> }</p> <p>DWORD WINAPI SawThread(LPVOID Saw)<br /> {<br /> DWORD busySpan[COUNT];<br /> DWORD idleSpan[COUNT];<br /> int half = INTERVAL/2;<br /> double radian = 0.0;<br /> DWORD startTime;<br /> int i;</p> <p> for (i=0; i<COUNT; i++)<br /> {<br /> busySpan[i] = (DWORD)(SLOPE*radian);<br /> idleSpan[i] = (DWORD)(INTERVAL - busySpan[i]);<br /> radian += SPLIT;<br /> }<br /> i = 0;<br /> while(1)<br /> {<br /> i %= COUNT;<br /> startTime = GetTickCount();<br /> while((GetTickCount()-startTime) <= busySpan[i])<br /> ;<br /> Sleep(idleSpan[i]);<br /> i++;<br /> }<br /> return 0;<br /> }</p> <p>int main()<br /> {<br /> HANDLE hThread1, hThread2;<br /> DWORD dwThreadId1, dwThreadId2;</p> <p> hThread1 = CreateThread(NULL, 0, SineThread, 0, CREATE_SUSPENDED, &dwThreadId1);<br /> hThread2 = CreateThread(NULL, 0, SawThread, 0, CREATE_SUSPENDED, &dwThreadId2);<br /> SetThreadAffinityMask(hThread1, 1);<br /> SetThreadAffinityMask(hThread2, 2);<br /> ResumeThread(hThread1);<br /> ResumeThread(hThread2);<br /> SuspendThread(GetCurrentThread());<br /> return 0;<br /> }

    其中INTERVAL可以视为周期，而COUNT和SPLIT分别为采样点数和步长，SLOPE就是斜率了。。。另外，对于双核而言，编程之美上的代码并不完美，于是按照书上的指点，使用SetThreadAffinityMask()将两个线程分别在每个核去执行。

Linux下代码完全仿照Windows写出，知识获取时间的函数不同，另外，使用usleep实现微秒级定时：
#include <unistd.h><br /> #include <stdlib.h><br /> #include <math.h><br /> #include <time.h><br /> #include <sys/time.h></p> <p>#define COUNT 200<br /> #define SPLIT 0.01<br /> #define PI 3.14159265<br /> #define INTERVAL 100</p> <p>double get_time()<br /> {<br /> struct timeval tv;<br /> gettimeofday(&tv, NULL);<br /> return (tv.tv_sec*1000+tv.tv_usec*1.0/1000); /* ms */<br /> }</p> <p>int main()<br /> {<br /> double busy_span[COUNT]; /* need to modify */<br /> double idle_span[COUNT];<br /> int half = INTERVAL/2;<br /> double radian = 0.0;</p> <p> double start_time;</p> <p> int i;</p> <p> for(i=0; i<COUNT; i++)<br /> {<br /> busy_span[i] = (double)(half + half*sin(PI*radian));<br /> idle_span[i] = (double)(INTERVAL - busy_span[i]);<br /> radian += SPLIT;<br /> }</p> <p> i = 0;<br /> while(1)<br /> {<br /> i %= COUNT;<br /> start_time = get_time();<br /> while((get_time()-start_time) <= busy_span[i])<br /> ;<br /> usleep(idle_span[i]*1000);<br /> i++;<br /> }<br /> return 0;<br /> }