Java多线程编程中线程锁与读写锁的使用示例

线程锁lock
lock  相当于 当前对象的 synchronized

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(); 
    } 
  } 
} 

读写锁 reentrantreadwritelock

 读写锁：允许多条线程同时读；不能读中有写；不能写中有读；不能写中有写

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; 
  }