下水道井盖为什么是圆的
“下水道井盖是圆的，因为圆形不会掉进井口，而且圆形具有均匀分布压力的优势。”
如何写一个程序让 cpu 占用率保持在 50%？
不要用 if-else 来解决，要把比例转成不同的 worktime。
解法的精确与否其实取决于“多久时间内测度一次已占用的时间”和“睡眠”两类 api 的精度。
bash 版本
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| #!/bin/bash
L=${1:-50}
[ $L -lt 0 ] || [ $L -gt 100 ] && { echo "用法: $0 [0-100]"; exit 1; }
echo "CPU负载${L}%，Ctrl+C停止"
trap 'echo -e "\n停止"' INT
while true; do
for i in $(seq $L); do : > /dev/null; done
[ $((100-L)) -gt 0 ] && sleep 0.0$((100-L))
done
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用法：
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| chmod +x cpu.sh
./cpu.sh 90
./cpu.sh 30
./cpu.sh
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java 版本
单核
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| public class SimpleCPULoader {
public static void main(String[] args) {
double targetLoad = 0.5;
if (args.length > 0) {
try {
targetLoad = Double.parseDouble(args[0]) / 100.0;
targetLoad = Math.max(0.0, Math.min(1.0, targetLoad));
} catch (NumberFormatException e) {
System.err.println("参数格式错误，使用默认50%负载");
}
}
System.out.println("开始CPU负载测试，目标利用率: " + (targetLoad * 100) + "%");
System.out.println("按 Ctrl+C 停止");
executeCPULoad(targetLoad);
}
private static void executeCPULoad(double loadRatio) {
final long PERIOD_MS = 100;
while (true) {
long workTime = (long) (PERIOD_MS * loadRatio);
long sleepTime = PERIOD_MS - workTime;
long workStart = System.currentTimeMillis();
while (System.currentTimeMillis() - workStart < workTime) {
Math.sqrt(Math.random());
}
try {
if (sleepTime > 0) {
Thread.sleep(sleepTime);
}
} catch (InterruptedException e) {
System.out.println("\n程序被中断");
return;
}
}
}
}
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多核
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| import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class MultiCoreCPULoader {
public static void main(String[] args) {
double targetLoad = 0.5;
int cores = Runtime.getRuntime().availableProcessors();
for (int i = 0; i < args.length; i++) {
try {
if (args[i].equals("-load") && i + 1 < args.length) {
targetLoad = Double.parseDouble(args[++i]) / 100.0;
targetLoad = Math.max(0.0, Math.min(1.0, targetLoad));
} else if (args[i].equals("-cores") && i + 1 < args.length) {
cores = Integer.parseInt(args[++i]);
cores = Math.max(1, Math.min(cores, Runtime.getRuntime().availableProcessors()));
}
} catch (NumberFormatException e) {
System.err.println("参数格式错误");
printUsage();
return;
}
}
System.out.println("开始CPU负载测试");
System.out.println("目标利用率: " + (targetLoad * 100) + "%");
System.out.println("使用核心数: " + cores);
System.out.println("按 Ctrl+C 停止");
executeMultiCoreCPULoad(targetLoad, cores);
}
private static void executeMultiCoreCPULoad(double loadRatio, int cores) {
ExecutorService executor = Executors.newFixedThreadPool(cores);
for (int i = 0; i < cores; i++) {
final int coreId = i;
executor.submit(() -> {
System.out.println("核心 " + coreId + " 开始工作");
executeSingleCoreCPULoad(loadRatio);
});
}
try {
Runtime.getRuntime().addShutdownHook(new Thread(() -> {
System.out.println("\n正在停止所有核心...");
executor.shutdown();
try {
if (!executor.awaitTermination(5, TimeUnit.SECONDS)) {
executor.shutdownNow();
}
} catch (InterruptedException e) {
executor.shutdownNow();
}
}));
executor.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS);
} catch (InterruptedException e) {
System.out.println("\n程序被中断");
executor.shutdownNow();
}
}
private static void executeSingleCoreCPULoad(double loadRatio) {
final long PERIOD_MS = 100;
while (!Thread.currentThread().isInterrupted()) {
long workTime = (long) (PERIOD_MS * loadRatio);
long sleepTime = PERIOD_MS - workTime;
long workStart = System.currentTimeMillis();
while (System.currentTimeMillis() - workStart < workTime &&
!Thread.currentThread().isInterrupted()) {
Math.sqrt(Math.random());
}
try {
if (sleepTime > 0) {
Thread.sleep(sleepTime);
}
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
break;
}
}
}
private static void printUsage() {
System.out.println("用法: java MultiCoreCPULoader [选项]");
System.out.println("选项:");
System.out.println(" -load <百分比> 设置CPU负载 (0-100)，默认50");
System.out.println(" -cores <数量> 指定使用的核心数，默认使用所有核心");
System.out.println("示例:");
System.out.println(" java MultiCoreCPULoader -load 90 # 90%负载，所有核心");
System.out.println(" java MultiCoreCPULoader -load 70 -cores 2 # 70%负载，2个核心");
System.out.println(" java MultiCoreCPULoader # 50%负载，所有核心");
}
}
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多核和单核的差别是每个核用一个单独线程来处理 load，但是核心思路还是在 workTime 里面用一个 sqrt 的方法来对随机数开平方，其余时间睡眠。
正弦函数版本
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| public class SineWaveCPULoader {
private static final long PERIOD_MS = 100;
private static final int FREQUENCY = 1;
public static void main(String[] args) {
System.out.println("开始生成正弦波CPU负载...");
System.out.println("波形频率: " + FREQUENCY + "Hz");
System.out.println("按 Ctrl+C 停止");
generateSineWave();
}
private static void generateSineWave() {
long startTime = System.currentTimeMillis();
while (true) {
long currentTime = System.currentTimeMillis();
double timeInSeconds = (currentTime - startTime) / 1000.0;
double sineValue = Math.sin(2 * Math.PI * FREQUENCY * timeInSeconds);
double loadRatio = 0.5 + 0.4 * sineValue;
executeCPULoad(loadRatio);
if ((currentTime / 2000) % 1 == 0) {
System.out.printf("\r时间: %.1fs, 正弦值: %.2f, CPU负载: %.1f%%",
timeInSeconds, sineValue, loadRatio * 100);
System.out.flush();
}
}
}
private static void executeCPULoad(double loadRatio) {
long workTime = (long) (PERIOD_MS * loadRatio);
long sleepTime = PERIOD_MS - workTime;
long workStart = System.currentTimeMillis();
while (System.currentTimeMillis() - workStart < workTime) {
Math.sqrt(Math.random());
}
try {
if (sleepTime > 0) {
Thread.sleep(sleepTime);
}
} catch (InterruptedException e) {
System.out.println("\n程序被中断");
System.exit(0);
}
}
}
|
这个算法的核心是计算距离起点的距离，然后推算出这个阶段的点在正弦曲线上的的纵轴多高，然后再用 executeCPULoad 函数来操纵 CPU。
利用系统 cpu 的解
如果能够获取当前的 cpu 利用率，sleep一个最小循环，然后进到下个 while 里再获取一次。
利用cpu的理论执行时间
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| const DWORD _busyTime = 10;
const DWORD _idleTime = _busyTime;
_int64 _startTime = 0;
void letCpuControl_GetTickCount()
{
while(true)
{
DWORD startTime = GetTickCount();
while(GetTickCount() - startTime <= _busyTime);
_sleep(_idleTime);
}
}
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一个屋子有一个门（门是关闭的）和3盏电灯。屋外有3个开关，分别与这3盏灯相连。你可以随意操纵这些开关，可一旦你将门打开，就不能变换开关了。确定每个开关具体管哪盏灯？
答：将一盏灯开一段时间，再关掉，在剩余2盏灯里随机开一盏，进屋去看，发热的灯对应第一个碰的开关，亮着的灯对应开关开着的开关，灭的灯对应没碰过的开关。
