Java高併發編程（8）

實現ReadWriteLock鎖

主要lock代碼

//讀寫鎖
public class ReadWriteLock {

    /**
     * 正在讀的線程數
     */
    private int readerReading = 0;

    /**
     * 等待讀的線程數
     */
    private int readerWaiting = 0;

    /**
     * 正在寫的線程數
     */
    private int writeWriting = 0;

    /**
     * 等待寫的線程數
     */
    private int writeWaiting = 0;

    /**
     * 是否更偏愛寫鎖
     */
    private boolean peferWrite;

    public ReadWriteLock(){
        this(true);
    }

    public ReadWriteLock(boolean peferWrite){
        this.peferWrite = peferWrite;
    }


    public synchronized void readLock() throws InterruptedException {
        //進來之後先將等待讀數量+1
        this.readerWaiting++;
        try{
            while(writeWriting>0||(peferWrite&&writeWaiting>0)){
                this.wait();
            }
            //正在讀鎖+1
            this.readerReading++;
        }finally {
            //退出時將等待讀數量-1
            this.readerWaiting--;
        }
    }

    public synchronized void readUnlock(){
        this.readerReading--;
        this.notifyAll();
    }

    public synchronized void writeLock() throws InterruptedException {
        this.writeWaiting++;
        try{
            while (writeWriting>0||readerReading>0){
                this.wait();
            }
            this.writeWriting++;
        }finally {
            this.writeWaiting--;
        }
    }

    public synchronized void writeUnlock(){
        this.writeWriting--;
        this.notifyAll();
    }
}

接下來是測試類了，創建一個共享數據類，提供read和write方法

public class ShareDate {

    private final char[] buffer;

    private final ReadWriteLock lock = new ReadWriteLock();

    public ShareDate(int size){
        buffer = new char[size];
        for (int i = 0; i < size; i++) {
            buffer[i] = '*';
        }

    }

    public void read(){
        try {
            lock.readLock();
            System.out.println("Reader："+ Arrays.toString(buffer));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            lock.readUnlock();
        }
    }

    public void write(String str){
        for (int i = 0; i < str.length(); i++) {
            this.doWrite(str.charAt(i));
        }
    }

    private void doWrite(char c){
        try {
            lock.writeLock();
            for (int i = 0; i < buffer.length; i++) {
                buffer[i] = c;
            }
            System.out.println("Writer："+ Arrays.toString(buffer));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            lock.writeUnlock();
        }
    }
}

兩個線程類read和writer

public class WriteThread extends Thread {

    private ShareDate shareDate;

    private String str;

    public WriteThread(ShareDate shareDate,String str){
        this.shareDate = shareDate;
        this.str = str;
    }

    @Override
    public void run() {
        while (true){
            shareDate.write(str);
        }
    }
}

public class ReadThread extends Thread{

    private ShareDate shareDate;

    public ReadThread(ShareDate shareDate){
        this.shareDate = shareDate;
    }

    @Override
    public void run() {
        while (true){
            shareDate.read();
        }
    }
}

測試主類

    public static void main(String[] args) {
        ShareDate shareDate = new ShareDate(20);
        new ReadThread(shareDate).start();
        new ReadThread(shareDate).start();
        new ReadThread(shareDate).start();
        new ReadThread(shareDate).start();
        new ReadThread(shareDate).start();
        new ReadThread(shareDate).start();
        new WriteThread(shareDate,"qwertyuiop").start();
        new WriteThread(shareDate,"QWERTYUIOP").start();
    }

完畢