使用Jedis面临的非线程安全问题详解

目录

• 1. jedis类图
• 2. 为什么jedis不是线程安全的
• 2.1 共享socket引起的异常
• 2.2 共享数据流引起的异常
• 3、jedis多线程操作

网上都说jedis实例是非线程安全的，常常通过JedisPool连接池去管理实例，在多线程情况下让每个线程有自己独立的jedis实例，但都没有具体说明为啥jedis实例时非线程安全的，下面详细看一下非线程安全主要从哪个角度来看。

1. jedis类图

2. 为什么jedis不是线程安全的

由上述类图可知，Jedis类中有RedisInputStream和RedisOutputStream两个属性，而发送命令和获取返回值都是使用这两个成员变量，显然，这很容易引发多线程问题。测试代码如

public class BadConcurrentJedisTest {

    private static final ExecutorService pool = Executors.newFixedThreadPool(20);

    private static final Jedis jedis = new Jedis("192.168.58.99", 6379);

    public static void main(String[] args) {
        for(int i=0;i<20;i++){
            pool.execute(new RedisSet());
        }
    }

    static class RedisSet implements Runnable{

        @Override
        public void run() {
            while(true){
                jedis.set("hello", "world");
            }
        }

    }

报错：

Exception in thread "pool-1-thread-4" redis.clients.jedis.exceptions.JedisConnectionException: java.net.SocketException: Socket Closed
    at redis.clients.jedis.Connection.connect(Connection.java:164)
    at redis.clients.jedis.BinaryClient.connect(BinaryClient.java:80)
    at redis.clients.jedis.Connection.sendCommand(Connection.java:100)
    at redis.clients.jedis.BinaryClient.set(BinaryClient.java:97)
    at redis.clients.jedis.Client.set(Client.java:32)
    at redis.clients.jedis.Jedis.set(Jedis.java:68)
    at threadsafe.BadConcurrentJedisTest$RedisSet.run(BadConcurrentJedisTest.java:26)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.net.SocketException: Socket Closed
    at java.net.AbstractPlainSocketImpl.setOption(AbstractPlainSocketImpl.java:212)
    at java.net.Socket.setKeepAlive(Socket.java:1310)
    at redis.clients.jedis.Connection.connect(Connection.java:149)
    ... 9 more
redis.clients.jedis.exceptions.JedisConnectionException: java.net.SocketException: Socket Closed
    at redis.clients.jedis.Connection.connect(Connection.java:164)
    at redis.clients.jedis.BinaryClient.connect(BinaryClient.java:80)
    at redis.clients.jedis.Connection.sendCommand(Connection.java:100)
    at redis.clients.jedis.BinaryClient.set(BinaryClient.java:97)
    at redis.clients.jedis.Client.set(Client.java:32)
    at redis.clients.jedis.Jedis.set(Jedis.java:68)
    at threadsafe.BadConcurrentJedisTest$RedisSet.run(BadConcurrentJedisTest.java:26)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
.......

主要错误：

ava.net.SocketException: Socket closed
java.net.SocketException: Socket is not connected　　

2.1 共享socket引起的异常

为什么会出现这2个错误呢？ 我们可以很容易的通过堆栈信息定位到redis.clients.jedis.Connection的connect方法

public void connect() {
    if (!isConnected()) {
      try {
        socket = new Socket();
        // ->@wjw_add
        socket.setReuseAddress(true);
        socket.setKeepAlive(true); // Will monitor the TCP connection is
        // valid
        socket.setTcpNoDelay(true); // Socket buffer Whetherclosed, to
        // ensure timely delivery of data
        socket.setSoLinger(true, 0); // Control calls close () method,
        // the underlying socket is closed
        // immediately
        // <-@wjw_add

        socket.connect(new InetSocketAddress(host, port), connectionTimeout);
        socket.setSoTimeout(soTimeout);

        if (ssl) {
          if (null == sslSocketFactory) {
            sslSocketFactory = (SSLSocketFactory)SSLSocketFactory.getDefault();
          }
          socket = (SSLSocket) sslSocketFactory.createSocket(socket, host, port, true);
          if (null != sslParameters) {
            ((SSLSocket) socket).setSSLParameters(sslParameters);
          }
          if ((null != hostnameVerifier) &&
              (!hostnameVerifier.verify(host, ((SSLSocket) socket).getSession()))) {
            String message = String.format(
                "The connection to '%s' failed ssl/tls hostname verification.", host);
            throw new JedisConnectionException(message);
          }
        }

        outputStream = new RedisOutputStream(socket.getOutputStream());
        inputStream = new RedisInputStream(socket.getInputStream());
      } catch (IOException ex) {
        broken = true;
        throw new JedisConnectionException(ex);
      }
    }
  }

jedis在执行每一个命令之前都会先执行connect方法，socket是一个共享变量，在多线程的情况下可能存在：线程1执行到了

outputStream = new RedisOutputStream(socket.getOutputStream());
inputStream = new RedisInputStream(socket.getInputStream());　　

线程2执行到了：

socket = new Socket();
//线程2
socket.connect(new InetSocketAddress(host, port), connectionTimeout);　　

因为线程2重新初始化了socket但是还没有执行connect，所以线程1执行socket.getOutputStream()或者socket.getInputStream()就会抛出java.net.SocketException: Socket is not connected。java.net.SocketException: Socket closed是因为socket异常导致共享变量socket关闭了引起的。

2.2 共享数据流引起的异常

上面是因为多个线程共享jedis引起的socket异常。除了socket连接引起的异常之外，还有共享数据流引起的异常。下面就看一下，因为共享jedis实例引起的共享数据流错误问题。

为了避免多线程连接的时候引起的错误，我们在初始化的时候就先执行一下connect操作：

public class BadConcurrentJedisTest1 {

    private static final ExecutorService pool = Executors.newCachedThreadPool();

    private static final Jedis jedis = new Jedis("192.168.58.99", 6379);

    static{
        jedis.connect();
    }

    public static void main(String[] args) {
        for(int i=0;i<20;i++){
            pool.execute(new RedisTest());
        }

    }

    static class RedisTest implements Runnable{

        @Override
        public void run() {
            while(true){
                jedis.set("hello", "world");
            }
        }

    }

}　

报错：（每次报的错可能不完全一样）

Exception in thread "pool-1-thread-7" Exception in thread "pool-1-thread-1" redis.clients.jedis.exceptions.JedisDataException: ERR Protocol error: invalid multibulk length
    at redis.clients.jedis.Protocol.processError(Protocol.java:123)
    at redis.clients.jedis.Protocol.process(Protocol.java:157)
    at redis.clients.jedis.Protocol.read(Protocol.java:211)
    at redis.clients.jedis.Connection.readProtocolWithCheckingBroken(Connection.java:297)
    at redis.clients.jedis.Connection.getStatusCodeReply(Connection.java:196)
    at redis.clients.jedis.Jedis.set(Jedis.java:69)
    at threadsafe.BadConcurrentJedisTest1$RedisTest.run(BadConcurrentJedisTest1.java:30)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Exception in thread "pool-1-thread-4" redis.clients.jedis.exceptions.JedisConnectionException: java.net.SocketException: Broken pipe (Write failed)
    at redis.clients.jedis.Connection.flush(Connection.java:291)
    at redis.clients.jedis.Connection.getStatusCodeReply(Connection.java:194)
    at redis.clients.jedis.Jedis.set(Jedis.java:69)
    at threadsafe.BadConcurrentJedisTest1$RedisTest.run(BadConcurrentJedisTest1.java:30)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.net.SocketException: Broken pipe (Write failed)

Protocol error: invalid multibulk lengt是因为多线程通过RedisInputStream和RedisOutputStream读写缓冲区的时候引起的问题造成的数据问题不满足RESP协议引起的。举个简单的例子，例如多个线程执行命令,线程1执行 set hello world命令。本来应该发送：

*3\r\n$3\r\nSET\r\n$5\r\nhello\r\n$5\r\nworld\r\n

但是线程执行写到

*3\r\n$3\r\nSET\r\n$5\r\nhello\r\n

然后被挂起了，线程2执行了写操作写入了' '，然后线程1继续执行，最后发送到redis服务器端的数据可能就是：

*3\r\n$3\r\nSET\r\n$5\r\nhello\r\n' '$5\r\nworld\r\n

至于java.net.SocketException: Connection reset或ReadTimeout错误，是因为redis服务器接受到错误的命令，执行了socket.close这样的操作，关闭了连接。服务器会返回复位标志"RST"，但是客户端还在继续执行读写数据操作。

3、jedis多线程操作

jedis本身不是多线程安全的，这并不是jedis的bug，而是jedis的设计与redis本身就是单线程相关，jedis实例抽象的是发送命令相关，一个jedis实例使用一个线程与使用100个线程去发送命令没有本质上的区别，所以没必要设置为线程安全的。但是如果需要用多线程方式访问redis服务器怎么做呢？那就使用多个jedis实例，每个线程对应一个jedis实例，而不是一个jedis实例多个线程共享。一个jedis关联一个Client，相当于一个客户端，Client继承了Connection，Connection维护了Socket连接，对于Socket这种昂贵的连接，一般都会做池化，jedis提供了JedisPool。

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;

public class JedisPoolTest {

    private static final ExecutorService pool = Executors.newCachedThreadPool();

    private static final CountDownLatch latch = new CountDownLatch(20);

    private static final JedisPool jPool = new JedisPool("192.168.58.99", 6379);

    public static void main(String[] args) {
        long start = System.currentTimeMillis();
        for(int i=0;i<20;i++){
            pool.execute(new RedisTest());
        }
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(System.currentTimeMillis() - start);
        pool.shutdownNow();

    }

    static class RedisTest implements Runnable{

        @Override
        public void run() {
            Jedis jedis = jPool.getResource();
            int i = 1000;
            try{
                while(i-->0){
                        jedis.set("hello", "world");
                }
            }finally{
                jedis.close();
                latch.countDown();
            }
        }

    }

}

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