cn.jiangzeyin.SystemClock Maven / Gradle / Ivy
package cn.jiangzeyin;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
/**
* 高并发场景下System.currentTimeMillis()的性能问题的优化
* 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）
* System.currentTimeMillis()之所以慢是因为去跟系统打了一次交道
* 后台定时更新时钟，JVM退出时，线程自动回收
* 10亿：43410,206,210.72815533980582%
* 1亿：4699,29,162.0344827586207%
* 1000万：480,12,40.0%
* 100万：50,10,5.0%
* Created by jiangzeyin on 2018/6/20.
*/
public final class SystemClock {
private final long period;
private final AtomicLong now;
private SystemClock(long period) {
this.period = period;
this.now = new AtomicLong(System.currentTimeMillis());
scheduleClockUpdating();
}
private static class InstanceHolder {
static final SystemClock INSTANCE = new SystemClock(1);
}
private static SystemClock instance() {
return InstanceHolder.INSTANCE;
}
private void scheduleClockUpdating() {
ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor(runnable -> {
Thread thread = new Thread(runnable, "System Clock");
thread.setDaemon(true);
return thread;
});
scheduler.scheduleAtFixedRate(() -> now.set(System.currentTimeMillis()), period, period, TimeUnit.MILLISECONDS);
}
private long currentTimeMillis() {
return now.get();
}
public static long now() {
return instance().currentTimeMillis();
}
}