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：

1 2	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

 

1 2	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。