jedis和lettuce的对比

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

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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：

 
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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：

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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

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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

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

　　

线程2执行到了：

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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：

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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）

 
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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)
 

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

 
 
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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();
            }
        }
 
    }
 
}
Lettuce的连接是基于Netty的，连接实例（StatefulRedisConnection）可以在多个线程间并发访问，应为StatefulRedisConnection是线程安全的，所以一个连接实例（StatefulRedisConnection）就可以满足多线程环境下的并发访问，当然这个也是可伸缩的设计，一个连接实例不够的情况也可以按需增加连接实例。

posted on 2020-09-28 17:14  缘在此季  阅读(12673)  评论(0)  编辑  收藏  举报

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