java读写锁代码实现

た入场券 2022-01-14 06:29 183阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

读写锁适用读多写少的场景，读写锁需求必须满足条件：

1.一个线程对共享数据read时，同时允许另外一个线程可以并行read操作

2.一个线程对共享数据read时，不允许同时另外一个线程进行write操作

3.一个线程对共享数据write时，不允许同时另外一个线程进行write操作

第一步：

创建一个读写锁，优先写操作进行，为了在读多写少的场景下，能更多执行写操作。

public class ReadWriteLock {
        private int readingReaders = 0;
        private int waitingReaders = 0;
        private int writingWriters = 0;
        private int waitingWriters = 0;
        private boolean preferWriter = true;
    
        public ReadWriteLock() {
            this(true);
        }
    
        public ReadWriteLock(boolean preferWriter) {
            this.preferWriter = preferWriter;
        }
    
        public synchronized void readLock() throws InterruptedException {
            try {
                this.waitingReaders++;
                while (writingWriters > 0 || (preferWriter && waitingWriters > 0)) {
                    this.wait();
                }
                this.readingReaders++;
            }finally {
                this.waitingReaders--;
            }
        }
    
        public synchronized void readUnLock() {
            this.readingReaders--;
            this.notifyAll();
        }
    
        public synchronized void writeLock() throws InterruptedException {
            try {
                this.waitingWriters++;
                while(writingWriters > 0 || readingReaders > 0) {
                    this.wait();
                }
                this.writingWriters++;
            }finally {
                this.waitingWriters--;
            }
        }
    
        public synchronized void writeUnLock() {
            this.writingWriters--;
            this.notifyAll();
        }
    }

第二步：

创建一个共享数据对象，用于读写操作

public class ShareData {
        private final char[] buffer;
    
        private final ReadWriteLock lock = new ReadWriteLock();
    
        public ShareData(int size) {
            this.buffer = new char[size];
            for (int i = 0; i < buffer.length; i++) {
                buffer[i] = '*';
            }
        }
    
        public char[] read() throws InterruptedException {
            try{
                lock.readLock();
                return this.doRead();
            }finally {
                lock.readUnLock();
            }
        }
    
        public void write(char c) throws InterruptedException {
            try{
                lock.writeLock();
                this.doWrite(c);
            }finally {
                lock.writeUnLock();
            }
        }
    
        private void doWrite(char c) {
            for (int i = 0; i < buffer.length; i++) {
                buffer[i] = c;
                slowly(10);
            }
        }
    
        private char[] doRead() {
            char[] newBuf = new char[buffer.length];
            for (int i = 0; i < buffer.length; i++) {
                newBuf[i] = buffer[i];
            }
            slowly(500);
            return newBuf;
        }
    
        private void slowly(int ms)  {
            try {
                Thread.sleep(ms);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

第三步：

创建一个写线程，对共享对象进行写操作

public class WriterWorker extends Thread{
        private static final Random random = new Random(System.currentTimeMillis());
    
        private final ShareData data;
    
        private final String filler;
    
        private int index;
    
        public WriterWorker(ShareData data, String filler) {
            this.data = data;
            this.filler = filler;
        }
    
        @Override
        public void run() {
            try {
                while(true) {
                    char c = nextChar();
                    data.write(c);
                    Thread.sleep(random.nextInt(1000));
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
        public char nextChar() {
            char c = filler.charAt(index);
            index++;
            if(index >= filler.length()) {
                index = 0;
            }
            return c;
        }
    }

第四步：

创建一个读线程，对共享对象进行读操作，并输出读数据内容

ublic class ReaderWorker extends Thread{
        private final ShareData data;
    
        public ReaderWorker(ShareData data) {
            this.data = data;
        }
    
        @Override
        public void run() {
            try {
                while (true) {
                    char[] readBuffer = data.read();
                    System.out.println(Thread.currentThread().getName() + " reads " + String.valueOf(readBuffer));
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

第五步：

创建一个读多写少的测试类

public class ReadWriteLockClient {
        public static void main(String[] args) {
            final ShareData shareData = new ShareData(10);
            new ReaderWorker(shareData).start();
            new ReaderWorker(shareData).start();
            new ReaderWorker(shareData).start();
            new ReaderWorker(shareData).start();
            new ReaderWorker(shareData).start();
    
            new WriterWorker(shareData, "ddjifjsidjfisd").start();
            new WriterWorker(shareData, "DDJIFJSIDJFISD").start();
        }
    }

第六步：

查看打印结果

Thread-0 reads **********
    Thread-1 reads **********
    Thread-2 reads **********
    Thread-4 reads **********
    Thread-3 reads **********
    Thread-0 reads DDDDDDDDDD
    Thread-1 reads DDDDDDDDDD
    Thread-2 reads DDDDDDDDDD
    Thread-4 reads DDDDDDDDDD
    Thread-3 reads DDDDDDDDDD
    Thread-3 reads dddddddddd
    Thread-1 reads dddddddddd
    Thread-0 reads dddddddddd
    Thread-2 reads dddddddddd
    Thread-4 reads dddddddddd
    Thread-4 reads JJJJJJJJJJ
    Thread-3 reads JJJJJJJJJJ
    Thread-0 reads JJJJJJJJJJ
    Thread-1 reads JJJJJJJJJJ
    Thread-2 reads JJJJJJJJJJ
    Thread-2 reads IIIIIIIIII
    Thread-3 reads IIIIIIIIII
    Thread-1 reads IIIIIIIIII
    Thread-0 reads IIIIIIIIII
    Thread-4 reads IIIIIIIIII

转载于:https://my.oschina.net/u/1017791/blog/3055456

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220114/c5513b00e56749348e233ba3bb3b425c.png