高并发场景下System.currentTimeMillis()的性能问题的优化
package cn.ucaner.alpaca.common.util.key; import java.sql.Timestamp;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicLong; /**
* 高并发场景下System.currentTimeMillis()的性能问题的优化
* <p><p>
* System.currentTimeMillis()的调用比new一个普通对象要耗时的多（具体耗时高出多少我还没测试过，有人说是100倍左右）<p>
* System.currentTimeMillis()之所以慢是因为去跟系统打了一次交道<p>
* 后台定时更新时钟，JVM退出时，线程自动回收<p>
* 10亿：43410,206,210.72815533980582%<p>
* 1亿：4699,29,162.0344827586207%<p>
* 1000万：480,12,40.0%<p>
* 100万：50,10,5.0%<p>
* @author lry
*/
public class SystemClock { private final long period; private final AtomicLong now; ExecutorService executor = Executors.newSingleThreadExecutor(); private SystemClock(long period) {
this.period = period;
this.now = new AtomicLong(System.currentTimeMillis());
scheduleClockUpdating();
} private static class InstanceHolder {
public static final SystemClock INSTANCE = new SystemClock(1);
} private static SystemClock instance() {
return InstanceHolder.INSTANCE;
} private void scheduleClockUpdating() {
ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor(new ThreadFactory() {
@Override
public Thread newThread(Runnable runnable) {
Thread thread = new Thread(runnable, "System Clock");
thread.setDaemon(true);
return thread;
}
});
scheduler.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
now.set(System.currentTimeMillis());
}
}, period, period, TimeUnit.MILLISECONDS);
} private long currentTimeMillis() {
return now.get();
} public static long now() {
return instance().currentTimeMillis();
} public static String nowDate() {
return new Timestamp(instance().currentTimeMillis()).toString();
} /**
* @Description: Just for test
* @param args void
* @throws InterruptedException
* @Autor: Jason - [email protected]
*/
public static void main(String[] args) throws InterruptedException {
for (int i = 0; i < 100; i++) {
System.out.println(nowDate());
Thread.sleep(1000);
}
}
}
//Outputs
//2018-05-10 15:37:18.774
//2018-05-10 15:37:19.784
//2018-05-10 15:37:20.784
//2018-05-10 15:37:21.785
//2018-05-10 15:37:22.784
//2018-05-10 15:37:23.784
//2018-05-10 15:37:24.785
//2018-05-10 15:37:25.784
//2018-05-10 15:37:26.785
//2018-05-10 15:37:27.786
//2018-05-10 15:37:28.785
//2018-05-10 15:37:29.785
//2018-05-10 15:37:30.785
//2018-05-10 15:37:31.785