ReadWriteLock

ReadWriteLock

• 

• /**
   * 独占锁（写锁）
   * 一次只能被一个线程占有
   * 共享锁（读锁） 多个线程可以同时占有
   *
   * ReadWriteLock
   * 读-读  可以共存！
   * 读-写  不能共存！
   * 写-写  不能共存！
   */
  public class Test04 {
      public static void main(String[] args) throws InterruptedException {
          MyCacheLock myCache = new MyCacheLock();
          //写入
          for (int i = 0; i < 5; i++) {
              final int count = i;
              new Thread(() -> {
                  myCache.put(count + " ", count + " ");
              }, String.valueOf(i)).start();
          }
          //写入
          for (int i = 0; i < 5; i++) {
              final int count = i;
              new Thread(() -> {
                  myCache.get(count + " ");
              }, String.valueOf(i)).start();
          }
      }
  }
  
  //加锁的自定义缓存
  class MyCacheLock {
      private volatile Map<String, Object> map = new HashMap<>();
      //读写锁: 更加细粒度的控制
      private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
  
      //存,写入的时候 只能有一个线程写入
      public void put(String key, Object value) {
          readWriteLock.writeLock().lock();
          try {
              System.out.println(Thread.currentThread().getName() + "写入" + key);
              map.put(key, value);
              System.out.println(Thread.currentThread().getName() + "写入完成");
          } catch (Exception e) {
              e.printStackTrace();
          } finally {
              readWriteLock.writeLock().unlock();
          }
      }
  
      //取，读的时候允许多个线程读取
      public void get(String key) {
          readWriteLock.readLock().lock();
          try {
              System.out.println(Thread.currentThread().getName() + "读取" + key);
              Object obj = map.get(key);
              System.out.println(Thread.currentThread().getName() + "读取完成");
          } catch (Exception e) {
              e.printStackTrace();
          } finally {
              readWriteLock.readLock().unlock();
          }
      }
  }
  
  //自定义缓存  : 会出现插队写入
  /* 会出现插队写入   ：
          0写入0
          4写入4
          4写入完成
          3写入3
          3写入完成*/
  class MyCache {
      private volatile Map<String, Object> map = new HashMap<>();
      //存,写
      public void put(String key, Object value) {
          System.out.println(Thread.currentThread().getName() + "写入" + key);
          map.put(key, value);
          System.out.println(Thread.currentThread().getName() + "写入完成");
      }
      //取，读
      public void get(String key) {
          System.out.println(Thread.currentThread().getName() + "读取" + key);
          Object obj = map.get(key);
          System.out.println(Thread.currentThread().getName() + "读取完成");
      }
  }
  

标签：Thread,currentThread,ReadWriteLock,getName,写入,System,key
来源： https://www.cnblogs.com/saxonsong/p/14728887.html