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package whut.readwritelock;public class Data
{ private final char[]
buffer; private final ReadWriteLock
lock=new ReadWriteLock(); public Data(int size) { this.buffer=new char[size]; for(int i=0;i<buffer.length;i++) buffer[i]='*'; } public char[]
read()throws InterruptedException { lock.readLock(); try{ return doRead(); }finally{ lock.readUnlock(); } } private char[]
doRead() { char[]
newbuf=new char[buffer.length]; for(int i=0;i<buffer.length;i++) newbuf[i]=buffer[i]; slowly(); return newbuf; } public void write(char c)throws InterruptedException { lock.writeLock(); try{ doWrite(c); }finally{ lock.writeUnlock(); } } private void doWrite(char c) { for(int i=0;i<buffer.length;i++) { buffer[i]=c; slowly(); //这里的sleep并不会切换到别的线程 //这里就是体现了使用while的好处 //当该线程sleep时候，其余等待读取的还在wait中，而要写入的线程会判断它的状态，还没有释放锁 } } private void slowly() { try{ Thread.sleep(50); }catch(InterruptedException
e) { } } } |
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package whut.readwritelock;public class ReaderThread extends Thread{ private final Data
data; public ReaderThread(Data
data) { this.data=data; } public void run() { try{ while(true) { char[]
readbuf=data.read(); System.out.println(Thread.currentThread().getName() +"
reads "+String.valueOf(readbuf)); } }catch(InterruptedException
e) { } }} |
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package whut.readwritelock;import java.util.Random;public class WriterThread extends Thread{ private static final Random
random=new Random(); private final Data
data; private final String
filler; private int index=0; public WriterThread(Data
data,String filler) { this.data=data; this.filler=filler; } public void run() { try{ while(true) { char c=nextChar(); data.write(c); Thread.sleep(random.nextInt(1000)); } }catch(InterruptedException
e) { } } private char nextChar() { char c=filler.charAt(index); index++; if(index>=filler.length()) index=0; return c; }} |
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package whut.readwritelock;//关键部分public class ReadWriteLock
{ private int readingReaders=0;//实际正在读取的线程数目 private int waitingWriters=0;//正在等待写入的线程数目 private int writingWriters=0;//实际正在写入的线程数目 private boolean preferWriter=true;//写入优先的话，值为true //读取的时候获取锁 public synchronized void readLock()throws InterruptedException { //当有写入的时候，或者写入为优先级并且有等待的写入线程 while(writingWriters>0||(preferWriter&&waitingWriters>0)) { wait(); } readingReaders++; } //读完毕后释放锁 public synchronized void readUnlock()throws InterruptedException { readingReaders--; preferWriter=true; notifyAll(); } //写入的时候获取锁 public synchronized void writeLock()throws InterruptedException { waitingWriters++;//正在等待的写入的线程数目 try{ //有写入或者读入的时候 while(readingReaders>0||writingWriters>0) { wait(); } }finally{ waitingWriters--;//被唤醒了，则就是进而真正写入 } writingWriters++; } //写入毕后释放锁 public synchronized void writeUnlock()throws InterruptedException { writingWriters--; preferWriter=false;//写入后马上更换优先级，让读者继续 notifyAll(); }} |
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package whut.readwritelock;public class ReadWriteMain
{ public static void main(String[]
args) { //
TODO Auto-generated method stub Data
data=new Data(10); //读取线程 new ReaderThread(data).start(); new ReaderThread(data).start(); new ReaderThread(data).start(); new ReaderThread(data).start(); new ReaderThread(data).start(); new ReaderThread(data).start(); //写入线程 new WriterThread(data,"ABCDEFGHIJKLMNOPQRSTUVWXYZ").start(); new WriterThread(data,"abcdefghijklmnopqrstuvwxyz").start(); }} |