读写锁

来源：互联网发布：linux sys 编辑：程序博客网时间：2024/04/30 08:14

本文摘自电子书

Data类

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();
  }
}

public void write(char c) throws InterruptedException{
  lock.writeLock();
  try{
   doWrite(c);
  }finally{
   lock.writeUnlock();
  }
}

private char[] doRead(){
  char[] newbuf = new char[buffer.length];
  for(int i = 0;i<buffer.length;i++){
   newbuf[i] = buffer[i];
  }
  slowly();
  return newbuf;
}

private void doWrite(char c){
  for(int i = 0;i<buffer.length;i++){
   buffer[i] = c;
   slowly();
  }
}

private void slowly(){
  try{
   Thread.sleep(50);
  }catch(InterruptedException e){

  }
}
}

读线程

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()+String.valueOf(readbuf));
   }
  }catch(InterruptedException e){

  }
}
}

写线程

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(3000));
   }
  }catch(InterruptedException e){

  }
}

private char nextchar(){
  char c = filler.charAt(index);
  index++;
  if(index >= filler.length()){
   index = 0;
  }
  return c;
}
}

读写锁

public final class ReadWriteLock {
private int readingReaders = 0;//(A)...实际正在读取的线程数量
private int waitingWriters = 0;//(B)...正在等待写入的线程数量
private int writingWriters = 0;//(c)...实际正在写入的线程数量
private boolean preferWriter = true;//写入优先的话，值为true

public synchronized void readLock() throws InterruptedException{
  while(writingWriters>0 || (preferWriter && waitingWriters > 0)){
   wait();
  }

  readingReaders++;//(A)实际正在读取的线程数量加1
}

public synchronized void readUnlock(){
  readingReaders--; //(A)实际正在读取的线程数量减1
  preferWriter = true;
  notifyAll();
}

public synchronized void writeLock() throws InterruptedException{
  waitingWriters++;//(B)正在等待写入的线程数量加1
  try{
   while(readingReaders > 0 || writingWriters > 0){
    wait();
   }
  }finally{
   waitingWriters--;//(B)正在等待写入的线程数量减1
  }
  writingWriters++;//(C)实际正在写入的线程数量加1
}

public synchronized void writeUnlock(){
  writingWriters--;//(C)实际正在写入的线程数量减1
  preferWriter = false;
  notifyAll();
}
}

测试类

public class MainReadWriteLock {
public static void main(String[] args){
  Data data = new Data(10);
  new ReaderThread(data).start();
  new ReaderThread(data).start();
  new ReaderThread(data).start();
  new ReaderThread(data).start();
  new ReaderThread(data).start();
  new ReaderThread(data).start();
  new WriterThread(data,"ABCDEFGHIJKLMNOPQRSTUVWXYZ").start();
  new WriterThread(data,"abcdefghijklmnopqrstuvwxyz").start();

}
}

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