使用Jedis面临的非线程安全问题详解
作者：小勇DW3
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();
}
}
}
}到此这篇关于使用Jedis面临的非线程安全问题详解的文章就介绍到这了,更多相关Jedis非线程安全问题内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！