java多线程设计模式(8) ReadWriteLock（４）-优快云博客

本文通过实现ReadingThread和WritingThread两个类，展示了如何利用读写锁（ReadWriteLock）来确保多线程环境下数据的安全访问。通过5个读线程和2个写线程的实例，验证了即使在高并发情况下，读写操作也能保持原子性和一致性。

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public方法read()和write()完全封装了底层的ReadWriteLock，因此，多线程可以安全地调用这两个方法：

// ReadingThread不断读取数据：
package com.crackj2ee.thread;
public class ReadingThread extends Thread {
private DataHandler handler;
public ReadingThread(DataHandler handler) {
this.handler = handler;
}
public void run() {
for(;;) {
try {
char[] data = handler.read(getName());
Thread.sleep((long)(Math.random()*1000+100));
}
catch(InterruptedException ie) {
break;
}
}
}
}

// WritingThread不断写入数据，每次写入的都是10个相同的字符：
package com.crackj2ee.thread;
public class WritingThread extends Thread {
private DataHandler handler;
public WritingThread(DataHandler handler) {
this.handler = handler;
}
public void run() {
char[] data = new char[10];
for(;;) {
try {
fill(data);
handler.write(getName(), data);
Thread.sleep((long)(Math.random()*1000+100));
}
catch(InterruptedException ie) {
break;
}
}
}
// 产生一个A-Z随机字符，填入char[10]:
private void fill(char[] data) {
char c = (char)(Math.random()*26+'A');
for(int i=0; i<data.length; i++)
data[i] = c;
}
}

最后Main负责启动这些线程：

package com.crackj2ee.thread;
public class Main {
public static void main(String[] args) {
DataHandler handler = new DataHandler();
Thread[] ts = new Thread[] {
new ReadingThread(handler),
new ReadingThread(handler),
new ReadingThread(handler),
new ReadingThread(handler),
new ReadingThread(handler),
new WritingThread(handler),
new WritingThread(handler)
};
for(int i=0; i<ts.length; i++) {
ts[i].start();
}
}
}

我们启动了5个读线程和2个写线程，运行结果如下：

Thread-0 waiting for read...
Thread-1 waiting for read...
Thread-2 waiting for read...
Thread-3 waiting for read...
Thread-4 waiting for read...
Thread-5 waiting for write...
Thread-6 waiting for write...
Thread-4 reads data: AAAAAAAAAA
Thread-3 reads data: AAAAAAAAAA
Thread-2 reads data: AAAAAAAAAA
Thread-1 reads data: AAAAAAAAAA
Thread-0 reads data: AAAAAAAAAA
Thread-5 wrote data: EEEEEEEEEE
Thread-6 wrote data: MMMMMMMMMM
Thread-1 waiting for read...
Thread-4 waiting for read...
Thread-1 reads data: MMMMMMMMMM
Thread-4 reads data: MMMMMMMMMM
Thread-2 waiting for read...
Thread-2 reads data: MMMMMMMMMM
Thread-0 waiting for read...
Thread-0 reads data: MMMMMMMMMM
Thread-4 waiting for read...
Thread-4 reads data: MMMMMMMMMM
Thread-2 waiting for read...
Thread-5 waiting for write...
Thread-2 reads data: MMMMMMMMMM
Thread-5 wrote data: GGGGGGGGGG
Thread-6 waiting for write...
Thread-6 wrote data: AAAAAAAAAA
Thread-3 waiting for read...
Thread-3 reads data: AAAAAAAAAA
......

可以看到，每次读/写都是完整的原子操作，因为我们每次写入的都是10个相同字符。并且，每次读出的都是最近一次写入的内容。