java多线程设计模式(8) ReadWriteLock （２）

最新推荐文章于 2025-08-09 17:15:54 发布

原创最新推荐文章于 2025-08-09 17:15:54 发布 · 88 阅读

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文章标签：

#多线程 #设计模式 #Java #IE #thread

本文介绍了一种自定义ReadWriteLock的实现方式，通过同步方法控制多个线程的读写操作，确保了数据的一致性和线程安全性。

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为了让多线程能安全读写，我们设计了一个ReadWriteLock：

package com.crackj2ee.thread;
public class ReadWriteLock {
private int readingThreads = 0;
private int writingThreads = 0;
private int waitingThreads = 0; // waiting for write
private boolean preferWrite = true;

public synchronized void readLock() throws InterruptedException {
while(writingThreads>0 || (preferWrite && waitingThreads>0))
this.wait();
readingThreads++;
}

public synchronized void readUnlock() {
readingThreads--;
preferWrite = true;
notifyAll();
}

public synchronized void writeLock() throws InterruptedException {
waitingThreads++;
try {
while(readingThreads>0 || writingThreads>0)
this.wait();
}
finally {
waitingThreads--;
}
writingThreads++;
}

public synchronized void writeUnlock() {
writingThreads--;
preferWrite = false;
notifyAll();
}
}

readLock()用于获得读锁，readUnlock()释放读锁，writeLock()和writeUnlock()一样。由于锁用完必须释放，因此，必须保证lock和unlock匹配。我们修改DataHandler，加入ReadWriteLock：

package com.crackj2ee.thread;
public class DataHandler {
// store data:
private char[] buffer = "AAAAAAAAAA".toCharArray();
// lock:
private ReadWriteLock lock = new ReadWriteLock();

public char[] read(String name) throws InterruptedException {
System.out.println(name + " waiting for read...");
lock.readLock();
try {
char[] data = doRead();
System.out.println(name + " reads data: " + new String(data));
return data;
}
finally {
lock.readUnlock();
}
}

public void write(String name, char[] data) throws InterruptedException {
System.out.println(name + " waiting for write...");
lock.writeLock();
try {
System.out.println(name + " wrote data: " + new String(data));
doWrite(data);
}
finally {
lock.writeUnlock();
}
}

private char[] doRead() {
char[] ret = new char[buffer.length];
for(int i=0; i<buffer.length; i++) {
ret[i] = buffer[i];
sleep(3);
}
return ret;
}
private void doWrite(char[] data) {
if(data!=null) {
buffer = new char[data.length];
for(int i=0; i<buffer.length; i++) {
buffer[i] = data[i];
sleep(10);
}
}
}
private void sleep(int ms) {
try {
Thread.sleep(ms);
}
catch(InterruptedException ie) {}
}
}