content: /*
   * Copyright 2025 the original author or authors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      https://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.alibaba.cloud.ai.studio.core.utils.common;
  
  import java.sql.Timestamp;
  import java.util.concurrent.Executors;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.TimeUnit;
  
  /**
   * System clock implementation that provides efficient time access. Uses a background
   * thread to update the current time at regular intervals.
   *
   * @since 1.0.0.3
   */
  public class SystemClock {
  
  	/**
  	 * Clock update interval in milliseconds
  	 */
  	private final long period;
  
  	/**
  	 * Current time in milliseconds
  	 */
  	private volatile long now;
  
  	/**
  	 * Constructor
  	 */
  	private SystemClock(long period) {
  		this.period = period;
  		this.now = System.currentTimeMillis();
  		scheduleClockUpdating();
  	}
  
  	/**
  	 * Starts the clock update scheduler
  	 */
  	private void scheduleClockUpdating() {
  		ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor(runnable -> {
  			Thread thread = new Thread(runnable, "System Clock");
  			thread.setDaemon(true);
  			return thread;
  		});
  		scheduler.scheduleAtFixedRate(new Runnable() {
  			public void run() {
  				now = System.currentTimeMillis();
  			}
  		}, period, period, TimeUnit.MILLISECONDS);
  	}
  
  	/**
  	 * @return Current time in milliseconds
  	 */
  	private long currentTimeMillis() {
  		return now;
  	}
  
  	// ------------------------------------------------------------------------ static
  
  	/**
  	 * Singleton holder
  	 */
  	private static class InstanceHolder {
  
  		public static final SystemClock INSTANCE = new SystemClock(1);
  
  	}
  
  	/**
  	 * @return Singleton instance
  	 */
  	private static SystemClock instance() {
  		return InstanceHolder.INSTANCE;
  	}
  
  	/**
  	 * @return Current time in milliseconds
  	 */
  	public static long now() {
  		return instance().currentTimeMillis();
  	}
  
  	/**
  	 * @return Current time as a string
  	 */
  	public static String nowDate() {
  		return new Timestamp(instance().currentTimeMillis()).toString();
  	}
  
  }
  