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java多线程有关问题，求帮忙

日期：2014-05-20　浏览次数：20752 次

java多线程问题，求帮忙
要求:
1. 线程x在读取共享内存时必须确保读取的内容可靠, 因此在读取过程中, Shared Memory存储的内容不能被其他线程改变.
2. 所有线程(无论读或写)无序且并发执行.
3. 线程x写内存Shared Memory时, 为保证其他线程读取的内容真实可靠, 在写操作未完成时, 不允许任何线程读取.
4. 当线程x读取Shared Memory时, 其他线程也可以读取.
5. 当线程x 写内存Shared Memory时, 未保证数据一致性, 其他线程不允许写.
我自己写的代码如下：

Java code


public class MuitipleThread {
public static void main(String[] args) {
Buffer sharedLocation = new UnsynchronizedBuffer();
Producer p = new Producer(sharedLocation);     Consumer s = new Consumer(sharedLocation);     for (int i = 1; i <= 20; i++) {     int j = 0;     j = (int) (Math.random() * 10 + 1);     if (j <= 3) {     Thread tdj = new Thread(p);     tdj.start();     } else {     Thread tdj = new Thread(s);     tdj.start();     }     }
}
interface Buffer {     public void set();
public void get();    }
static class Consumer extends Thread {     private Buffer ShareLocation;
public Consumer(Buffer shared) {
ShareLocation = shared;
}
public void run() {
synchronized (ShareLocation) {
try {     // while (Producer.i != 0) {     // ShareLocation.wait();     // }
ShareLocation.get();     System.out.println(Thread.currentThread().getName()     + "读出完成");
} catch (Exception e) {
e.printStackTrace();     }
}
}
}
static class Producer extends Thread {
private static Buffer ShareLocation;     public static int i = 1;
public Producer(Buffer shared) {     ShareLocation = shared;
}
public void run() {
synchronized (ShareLocation) {     try {
ShareLocation.set();     i = 0;     ShareLocation.notify();
} catch (Exception e) {
e.printStackTrace();     }
}
}
}
static class UnsynchronizedBuffer implements Buffer {
public void set() {
try {
System.err.println(Thread.currentThread().getName() + "写入");     Thread.sleep(3000); System.err.println(Thread.currentThread().getName() + "写入完成");
} catch (Exception e) {     // TODO: handle exception     }
}
public void get() {     try {
System.out.println(Thread.currentThread().getName() + "读出");     Thread.sleep(300);
} catch (Exception e) {     // TODO: handle exception     }     }    }}

虽然输出上像多个线程可以同时读出，但看代码实际上是解锁一次一次的读的，怎么在此基础上实现真正的多个线程同时读？

------解决方案--------------------

Java code


//给你个现成的例子，jdk里面的
import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import javax.xml.crypto.Data;

class RWDictionary {
    private final Map<String, Data> m = new TreeMap<String, Data>();
    private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
    private final Lock r = rwl.readLock();
    private final Lock w = rwl.writeLock();
    
    public Data get(String key) {
        r.lock();
        try {
            return m.get(key);
        } finally {
            r.unlock();
        }
    }

    public String[] allKeys() {
        r.lock();
        try {
            return m.keySet().toArray(new String[0]);
        } finally {
            r.unlock();
        }
    }

    public Data put(String key, Data value) {
        w.lock();
        try {
            return m.put(key, value);
        } finally {
            w.unlock();
        }
    }
    public void clear() {
        w.lock();
        try {
            m.clear();
        } finally {
            w.unlock();
        }
    }
}

------解决方案--------------------

Java code

static String aa="内存共享模块";

static final String lock ="锁";
static int power = 1;

public Object operateAA(String action)throws Exception{
    Object o = null;
    if(-1==power){
        throw new Exception("有一线程在进行修改动作");
    }

    if("写".equals(action)){
        synchronized(lock){
            power = -1;
            ......
            power = 1;
        }
    }else{
    
    }
    return o;
}

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java多线程有关问题，求帮忙

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