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Jedis线程池returnResource异常

Erica_1230 人气:0

在线上环境发现了一个工作线程异常终止

看日志先是一些SocketTimeoutException,然后突然有一个ClassCastException

redis.clients.jedis.exceptions.JedisConnectionException: java.net.SocketTimeoutException: Read timed out
...
java.lang.ClassCastException: [B cannot be cast to java.lang.Long
        at redis.clients.jedis.Connection.getIntegerReply(Connection.java:208)
        at redis.clients.jedis.Jedis.sismember(Jedis.java:1307)

经过在本地人工模拟网络异常的情境,最终复现了线上的这一异常。

又经过深入分析(提出假设-->验证假设),最终找出了导致这一问题的原因。

见如下示例代码

JedisPool pool = ...;
Jedis jedis = pool.getResource();
String value = jedis.get("foo");
System.out.println("Make SocketTimeoutException");
System.in.read(); //等待制造SocketTimeoutException
try {
    value = jedis.get("foo");
    System.out.println(value);
} catch (JedisConnectionException e) {
    e.printStackTrace();
}
System.out.println("Recover from SocketTimeoutException");
System.in.read();  //等待恢复
Thread.sleep(5000); // 继续休眠一段时间 等待网络完全恢复
boolean isMember = jedis.sismember("urls", "baidu.com");

以及日志输出

bar
Make SocketTimeoutException
redis.clients.jedis.exceptions.JedisConnectionException: java.net.SocketTimeoutException: Read timed out
Recover from SocketTimeoutException
    at redis.clients.util.RedisInputStream.ensureFill(RedisInputStream.java:210)
    at redis.clients.util.RedisInputStream.readByte(RedisInputStream.java:47)
    at redis.clients.jedis.Protocol.process(Protocol.java:131)
    at redis.clients.jedis.Protocol.read(Protocol.java:196)
    at redis.clients.jedis.Connection.readProtocolWithCheckingBroken(Connection.java:283)
    at redis.clients.jedis.Connection.getBinaryBulkReply(Connection.java:202)
    at redis.clients.jedis.Connection.getBulkReply(Connection.java:191)
    at redis.clients.jedis.Jedis.get(Jedis.java:101)
    at com.tcl.recipevideohunter.JedisTest.main(JedisTest.java:23)
Caused by: java.net.SocketTimeoutException: Read timed out
    at java.net.SocketInputStream.socketRead0(Native Method)
    at java.net.SocketInputStream.read(SocketInputStream.java:152)
    at java.net.SocketInputStream.read(SocketInputStream.java:122)
    at java.net.SocketInputStream.read(SocketInputStream.java:108)
    at redis.clients.util.RedisInputStream.ensureFill(RedisInputStream.java:204)
    ... 8 more
Exception in thread "main" java.lang.ClassCastException: [B cannot be cast to java.lang.Long
    at redis.clients.jedis.Connection.getIntegerReply(Connection.java:208)
    at redis.clients.jedis.Jedis.sismember(Jedis.java:1307)
    at com.tcl.recipevideohunter.JedisTest.main(JedisTest.java:32)

分析

等执行第二遍的get("foo")时,网络超时,并未实际发送 get foo 命令,等执行sismember时,网络已恢复正常,并且是同一个jedis实例,于是将之前的get foo命令(已在输出流缓存中)一并发送。

执行顺序如下所示

127.0.0.1:9379> get foo"bar"127.0.0.1:9379> sismember urls baidu.com(integer) 1127.0.0.1:9379> get foo
"bar"
127.0.0.1:9379> sismember urls baidu.com
(integer) 1

故在上述示例代码中最后的sismember得到的结果是get foo的结果,即一个字符串,而sismember需要的是一个Long型,故导致了ClassCastException。

执行redis的逻辑

为什么线上会出现这一问题呢?原因是其执行redis的逻辑类似这样:

while(true){
        Jedis jedis = null;
    try {
        jedis = pool.getResource();
        //some redis operation here.
    } catch (Exception e) {
       logger.error(e);
    } finally {
        pool.returnResource(jedis);
    }
}

因若是网络异常的话,pool.returnResource(jedis)仍能成功执行,即能将其返回到池中(这时jedis并不为空)。等网络恢复后,并是多线程环境,导致后续其他某个线程获得了同一个Jedis实例(pool.getResource()),

若该线程中的jedis操作返回类型与该jedis实例在网络异常期间第一条未执行成功的jedis操作的返回类型不匹配(如一个是get,一个是sismember),则就会出现ClassCastException异常。

这还算幸运的,若返回的是同一类型的话(如lpop("queue_order_pay_failed"),lpop("queue_order_pay_success")),那我真不敢想象。

如在上述示例代码中的sismember前插入一get("nonexist-key")(redis中不存在该key,即应该返回空).

value = jedis.get("nonexist-key");
System.out.println(value);
boolean isMember = jedis.sismember("urls", "baidu.com");
System.out.println(isMember);

实际的日志输出为

bar
Exception in thread "main" java.lang.NullPointerException
    at redis.clients.jedis.Jedis.sismember(Jedis.java:1307)
    at com.tcl.recipevideohunter.JedisTest.main(JedisTest.java:37)

分析:

get("nonexist-key")得到是之前的get("foo")的结果, 而sismember得到的是get("nonexist-key")的结果,而get("nonexist-key")返回为空,于是这时是报空指针异常了.

解决方法:

不能不管什么情况都一律使用returnResource。更健壮可靠以及优雅的处理方式如下所示:

while(true){
    Jedis jedis = null;
    boolean broken = false;
    try {
        jedis = jedisPool.getResource();
        return jedisAction.action(jedis); //模板方法
    } catch (JedisException e) {
        broken = handleJedisException(e);
        throw e;
    } finally {
        closeResource(jedis, broken);
    }
}

/**
 * Handle jedisException, write log and return whether the connection is broken.
 */
protected boolean handleJedisException(JedisException jedisException) {
    if (jedisException instanceof JedisConnectionException) {
        logger.error("Redis connection " + jedisPool.getAddress() + " lost.", jedisException);
    } else if (jedisException instanceof JedisDataException) {
        if ((jedisException.getMessage() != null) && (jedisException.getMessage().indexOf("READONLY") != -1)) {
            logger.error("Redis connection " + jedisPool.getAddress() + " are read-only slave.", jedisException);
        } else {
            // dataException, isBroken=false
            return false;
        }
    } else {
        logger.error("Jedis exception happen.", jedisException);
    }
    return true;
}
/**
 * Return jedis connection to the pool, call different return methods depends on the conectionBroken status.
 */
protected void closeResource(Jedis jedis, boolean conectionBroken) {
    try {
        if (conectionBroken) {
            jedisPool.returnBrokenResource(jedis);
        } else {
            jedisPool.returnResource(jedis);
        }
    } catch (Exception e) {
        logger.error("return back jedis failed, will fore close the jedis.", e);
        JedisUtils.destroyJedis(jedis);
    }
}

补充

Ubuntu本地模拟访问redis网络超时:

sudo iptables -A INPUT -p tcp --dport 6379 -j DROP

恢复网络:

sudo iptables -F

补充:

若jedis操作逻辑类似下面所示的话,

Jedis jedis = null;
try {
    jedis = jedisSentinelPool.getResource();
    return jedis.get(key);
}catch(JedisConnectionException e) {
    jedisSentinelPool.returnBrokenResource(jedis);
    logger.error("", e);
    throw e;
}catch (Exception e) {
    logger.error("", e);
    throw e;
}
finally {
    jedisSentinelPool.returnResource(jedis);
}

若一旦发生了JedisConnectionException,如网络异常,会先执行returnBrokenResource,这时jedis已被destroy了。然后进入了finally,再一次执行returnResource,这时会报错:

redis.clients.jedis.exceptions.JedisException: Could not return the resource to the pool
    at redis.clients.util.Pool.returnResourceObject(Pool.java:65)
    at redis.clients.jedis.JedisSentinelPool.returnResource(JedisSentinelPool.java:221)

临时解决方法

jedisSentinelPool.returnBrokenResource(jedis);
jedis=null; //这时不会实际执行returnResource中的相关动作了

但不建议这样处理,更严谨的释放资源方法见前文所述。

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