網上都說jedis實例是非線程安全的，常常通過JedisPool連接池去管理實例，在多線程情況下讓每個線程有自己獨立的jedis實例，但都沒有具體說明為啥jedis實例時非線程安全的，下面詳細看一下非線程安全主要從哪個角度來看。
1. jedis類圖
2. 為什么jedis不是線程安全的？
由上述類圖可知，Jedis類中有RedisInputStream和RedisOutputStream兩個屬性，而發送命令和獲取返回值都是使用這兩個成員變量，顯然，這很容易引發多線程問題。測試代碼如
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");
}
}
}
報錯：
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)
.......
主要錯誤：
ava.net.SocketException: Socket closed java.net.SocketException: Socket is not connected
2.1 共享socket引起的異常
為什么會出現這2個錯誤呢？ 我們可以很容易的通過堆棧信息定位到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在執行每一個命令之前都會先執行connect方法，socket是一個共享變量，在多線程的情況下可能存在：線程1執行到了
outputStream = new RedisOutputStream(socket.getOutputStream()); inputStream = new RedisInputStream(socket.getInputStream());
線程2執行到了：
socket = new Socket(); 線程2 socket.connect(new InetSocketAddress(host, port), connectionTimeout);
因為線程2重新初始化了socket但是還沒有執行connect，所以線程1執行socket.getOutputStream()或者socket.getInputStream()就會拋出java.net.SocketException: Socket is not connected。java.net.SocketException: Socket closed是因為socket異常導致共享變量socket關閉了引起的。
2.2 共享數據流引起的異常
上面是因為多個線程共享jedis引起的socket異常。除了socket連接引起的異常之外，還有共享數據流引起的異常。下面就看一下，因為共享jedis實例引起的共享數據流錯誤問題。
為了避免多線程連接的時候引起的錯誤，我們在初始化的時候就先執行一下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");
}
}
}
}
報錯：（每次報的錯可能不完全一樣）
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是因為多線程通過RedisInputStream和RedisOutputStream讀寫緩沖區的時候引起的問題造成的數據問題不滿足RESP協議引起的。舉個簡單的例子，例如多個線程執行命令,線程1執行 set hello world命令。本來應該發送：
*3\r\n$3\r\nSET\r\n$5\r\nhello\r\n$5\r\nworld\r\n
但是線程執行寫到
*3\r\n$3\r\nSET\r\n$5\r\nhello\r\n
然后被掛起了，線程2執行了寫操作寫入了' '，然后線程1繼續執行，最后發送到redis服務器端的數據可能就是：
*3\r\n$3\r\nSET\r\n$5\r\nhello\r\n' '$5\r\nworld\r\n
至於java.net.SocketException: Connection reset或ReadTimeout錯誤，是因為redis服務器接受到錯誤的命令，執行了socket.close這樣的操作，關閉了連接。服務器會返回復位標志"RST"，但是客戶端還在繼續執行讀寫數據操作。
3、jedis多線程操作
jedis本身不是多線程安全的，這並不是jedis的bug，而是jedis的設計與redis本身就是單線程相關，jedis實例抽象的是發送命令相關，一個jedis實例使用一個線程與使用100個線程去發送命令沒有本質上的區別，所以沒必要設置為線程安全的。但是如果需要用多線程方式訪問redis服務器怎么做呢？那就使用多個jedis實例，每個線程對應一個jedis實例，而不是一個jedis實例多個線程共享。一個jedis關聯一個Client，相當於一個客戶端，Client繼承了Connection，Connection維護了Socket連接，對於Socket這種昂貴的連接，一般都會做池化，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();
}
}
}
}