package com.hikvision.cms.rvs.common.util;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
 * Created by lihong10 on 2017/8/9.
 * 一個(gè)循環(huán)計(jì)數(shù)器，每天從1開始計(jì)數(shù)，隔天重置為1。
 * 可以創(chuàng)建一個(gè)該類的全局對(duì)象，然后每次使用時(shí)候調(diào)用其get方法即可，可以保證線程安全性
 */
public class CircularCounter {
  private static final AtomicReferenceFieldUpdater<CircularCounter, AtomicInteger> valueUpdater =
      AtomicReferenceFieldUpdater.newUpdater(CircularCounter.class, AtomicInteger.class, "value");
  //保證內(nèi)存可見性
  private volatile String key;
  //保證內(nèi)存可見性
  private volatile AtomicInteger value;
  private static final String DATE_PATTERN = "yyyy-MM-dd";
  public CircularCounter() {
    /**
     * 這里將key設(shè)置為getCurrentDateString() + "sssssssssss" 是為了測(cè)試addAndGet()方法中日期發(fā)生變化的情況
     * 正常使用應(yīng)該將key初始化為getCurrentDateString()
     */
    this.key = getCurrentDateString() + "sssssssssss";
    this.value = new AtomicInteger(0);
  }
  /**
   * 獲取計(jì)數(shù)器加1以后的值
   *
   * @return
   */
  public Integer addAndGet() {
    AtomicInteger oldValue = value;
    AtomicInteger newInteger = new AtomicInteger(0);
    int newVal = -1;
    String newDateStr = getCurrentDateString();
    //日期一致，計(jì)數(shù)器加1后返回
    if (isDateEquals(newDateStr)) {
      newVal = add(1);
      return newVal;
    }
    //日期不一致，保證有一個(gè)線程重置技術(shù)器
    reSet(oldValue, newInteger, newDateStr);
    this.key = newDateStr;
    //重置后加1返回
    newVal = add(1);
    return newVal;
  }
  /**
   * 獲取計(jì)數(shù)器的當(dāng)前值
   * @return
   */
  public Integer get() {
    return value.get();
  }
  /**
   * 判斷當(dāng)前日期與老的日期（也即key成員變量記錄的值）是否一致
   *
   * @return
   */
  private boolean isDateEquals(String newDateStr) {
    String oldDateStr = key;
    if (!isBlank(oldDateStr) && oldDateStr.equals(newDateStr)) {
      return true;
    }
    return false;
  }
  /**
   * 如果日期發(fā)生變化，重置計(jì)數(shù)器，也即將key設(shè)置為當(dāng)前日期，并將value重置為0，重置后才能接著累加，
   */
  private void reSet(AtomicInteger oldValue, AtomicInteger newValue, String newDateStr) {
    if(valueUpdater.compareAndSet(this, oldValue, newValue)) {
      System.out.println("線程" + Thread.currentThread().getName() + "發(fā)現(xiàn)日期發(fā)生變化");
    }
  }
  /**
   * 獲取當(dāng)前日期字符串
   *
   * @return
   */
  private String getCurrentDateString() {
    Date date = new Date();
    String newDateStr = new SimpleDateFormat(DATE_PATTERN).format(date);
    return newDateStr;
  }
  /**
   * 計(jì)數(shù)器的值加1。采用CAS保證線程安全性
   *
   * @param increment
   */
  private int add(int increment) {
    return value.addAndGet(increment);
  }
  public static boolean isBlank(CharSequence cs) {
    int strLen;
    if(cs != null && (strLen = cs.length()) != 0) {
      for(int i = 0; i < strLen; ++i) {
        if(!Character.isWhitespace(cs.charAt(i))) {
          return false;
        }
      }
      return true;
    } else {
      return true;
    }
  }
  public static void test() {
    CircularCounter c = new CircularCounter();
    AtomicInteger count = new AtomicInteger(0);
    List<Thread> li = new ArrayList<Thread>();
    int size = 10;
    CountDownLatch latch1 = new CountDownLatch(1);
    CountDownLatch latch2 = new CountDownLatch(size);
    for (int i = 0; i < size; i++) {
      Thread t = new Thread(new CounterRunner(c, latch1, latch2, count), "thread-" + i);
      li.add(t);
      t.start();
    }
    System.out.println("start");
    latch1.countDown();
    try {
      latch2.await();
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    System.out.println(count.get());
    System.out.println(c.get());
    if(count.get() == c.get()) {
      System.out.println("該計(jì)數(shù)器是線程安全的?。?！");
    }
  }
  public static void main(String... args) {
    for(int i = 0; i < 15; i++) {
      test();
    }
  }
}
/**
 * 測(cè)試使用的Runnable對(duì)象
 */
class CounterRunner implements Runnable {
  private CircularCounter counter;
  private CountDownLatch latch1;
  private CountDownLatch latch2;
  private AtomicInteger count;
  public CounterRunner(CircularCounter counter, CountDownLatch latch1, CountDownLatch latch2, AtomicInteger count) {
    this.latch1 = latch1;
    this.latch2 = latch2;
    this.counter = counter;
    this.count = count;
  }
  @Override
  public void run() {
    try {
      latch1.await();
      System.out.println("****************");
      for (int i = 0; i < 20; i++) {
        counter.addAndGet();
        count.addAndGet(1);
      }
      latch2.countDown();
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}