Java多线程编程中线程锁与读写锁的使用示例

import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /*  * Lock lock = new ReentrantLock();  * lock.lock();  lock.unLock();  * 类似于 synchronized，但不能与synchronized 混用  */ public class LockTest {   public static void main(String[] args) {     final Outer outer = new LockTest().new Outer();     new Thread(new Runnable() {        @Override       public void run() {         // TODO Auto-generated method stub         while (true) {           outer.out1("zhangxiaoxiao");           outer.out2("lihuoming");         }       }      }).start();     new Thread(new Runnable() {        @Override       public void run() {         // TODO Auto-generated method stub         while (true) {           outer.out1("zhangxiaoxiao");           outer.out2("lihuoming");         }       }      }).start();    }   class Outer {     Lock lock = new ReentrantLock();     void out1(String name) {       lock.lock();       int len = name.length();       for (int i = 0; i < len; i++) {         System.out.print(name.charAt(i));       }       System.out.println();       lock.unlock();     }     void out2(String name) {       lock.lock();       int len = name.length();       for (int i = 0; i < len; i++) {         System.out.print(name.charAt(i));       }       System.out.println();       lock.unlock();     }   } } 

import java.util.HashMap; import java.util.Map; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; /*  * 问题：设计一个 缓存机制 的 伪代码  *  从集合中读取数据，读取不到，就写入，再考虑多线程并发的情况   */ public class ReadWriteLockTest2 {   private Map<String, Object> data = new HashMap<String, Object>();   private ReadWriteLock lock = new ReentrantReadWriteLock();    //读写锁   public Object getInstance1(String key, Object obj) {     lock.readLock().lock();     Object value = null;     try {       value = data.get(key);       if (value == null) {//一条线程进入这里，         lock.readLock().unlock();//读锁解了，其他线程就可能也到这了         lock.writeLock().lock();//只能有一条线程到这，写锁开启，要写入数据了         if (data.get(key) == null) {           value = obj;               /*先判断数据，如果不存在，才写入，，因为 界时当写锁解除后，其他               线程，再想写入时， 判断到数据存在 ，就跳过了。就不会发生同时写入的情况             */              data.put(key, value);          }         lock.writeLock().unlock();//写完了，解锁         lock.readLock().lock();       }     } finally {       lock.readLock().unlock();     }       return value;   }