最近在做一个监控系统，用来监控网站上各个业务功能的调用量以及处理时间，以便及时发现问题，及时处理。做这种实时统计处理系统，自然首先想到了storm，于是现学现用，自然遇到了一些坑，而且不少是网上也难以找到的问题。在这里就做个记录，记录下这个最让我苦恼的错误。
首先我的业务逻辑是按分钟统计一分钟中的调用次数的数据，所以我在bolt里跑了一个定时器，定时将统计数据发到下一个bolt入库。所在我在定时器执行的代码里调用了OutputCollector发射到下一个bolt。本地调试没啥问题，就部署到外网环境测试。通常也没发现问题，但是偶尔会出现这种错误，作为开发人员最讨厌的就是这种可复现率很低的错误 。
这里是错误日志：
5675 [Thread-7-disruptor-executor[2 2]-send-queue] ERROR backtype.storm.daemon.executor -
java.lang.RuntimeException: java.lang.NullPointerException
at backtype.storm.utils.DisruptorQueue.consumeBatchToCursor(DisruptorQueue.java:128) ~[storm-core-0.9.3.jar:0.9.3]
at backtype.storm.utils.DisruptorQueue.consumeBatchWhenAvailable(DisruptorQueue.java:99) ~[storm-core-0.9.3.jar:0.9.3]
at backtype.storm.disruptor$consume_batch_when_available.invoke(disruptor.clj:80) ~[storm-core-0.9.3.jar:0.9.3]
at backtype.storm.disruptor$consume_loop_STAR_$fn__1460.invoke(disruptor.clj:94) ~[storm-core-0.9.3.jar:0.9.3]
at backtype.storm.util$async_loop$fn__464.invoke(util.clj:463) ~[storm-core-0.9.3.jar:0.9.3]
at clojure.lang.AFn.run(AFn.java:24) [clojure-1.5.1.jar:na]
at java.lang.Thread.run(Thread.java:722) [na:1.7.0_15]
Caused by: java.lang.NullPointerException: null
at clojure.lang.RT.intCast(RT.java:1087) ~[clojure-1.5.1.jar:na]
at backtype.storm.daemon.worker$mk_transfer_fn$fn__3549.invoke(worker.clj:129) ~[storm-core-0.9.3.jar:0.9.3]
at backtype.storm.daemon.executor$start_batch_transfer__GT_worker_handler_BANG_$fn__3283.invoke(executor.clj:258) ~[storm-core-0.9.3.jar:0.9.3]
at backtype.storm.disruptor$clojure_handler$reify__1447.onEvent(disruptor.clj:58) ~[storm-core-0.9.3.jar:0.9.3]
at backtype.storm.utils.DisruptorQueue.consumeBatchToCursor(DisruptorQueue.java:125) ~[storm-core-0.9.3.jar:0.9.3]
... 6 common frames omitted 5697 [Thread-7-disruptor-executor[2 2]-send-queue] ERROR backtype.storm.util - Halting process: ("Worker died")
java.lang.RuntimeException: ("Worker died")
at backtype.storm.util$exit_process_BANG_.doInvoke(util.clj:325) [storm-core-0.9.3.jar:0.9.3]
at clojure.lang.RestFn.invoke(RestFn.java:423) [clojure-1.5.1.jar:na]
at backtype.storm.daemon.worker$fn__3808$fn__3809.invoke(worker.clj:452) [storm-core-0.9.3.jar:0.9.3]
at backtype.storm.daemon.executor$mk_executor_data$fn__3274$fn__3275.invoke(executor.clj:240) [storm-core-0.9.3.jar:0.9.3]
at backtype.storm.util$async_loop$fn__464.invoke(util.clj:473) [storm-core-0.9.3.jar:0.9.3]
at clojure.lang.AFn.run(AFn.java:24) [clojure-1.5.1.jar:na]
at java.lang.Thread.run(Thread.java:722) [na:1.7.0_15]
如果你也遇到这个问题，相信你第一次看到这个错误一定很痛苦，因为错误日志中没有任何与自己的业务代码相关的记录。所以实在是无从定位问题的所在。痛苦至极的是复现还不那么容易。
经过我多次猜测尝试，终于测出了问题的所在。下面我先贴出一个会报这个错误的例子代码：
public class Main {
public static void main(String[] args) {
TopologyBuilder builder = new TopologyBuilder();
builder.setSpout("spout",new TestWordSpout());
builder.setBolt("dispatch", new WordDispatchBolt()).shuffleGrouping("spout");
builder.setBolt("print",new PrintBolt()).fieldsGrouping("dispatch", new Fields("word"));
Config conf = new Config();
conf.setDebug(false);
conf.setNumWorkers(1);
//conf.put(Config.TOPOLOGY_MAX_SPOUT_PENDING, 1);
LocalCluster cluster = new LocalCluster();
cluster.submitTopology("test-kafka-1", conf, builder.createTopology());
}
}
public class TestWordSpout extends BaseRichSpout {
private static final long serialVersionUID = 1L;
boolean _isDistributed;
SpoutOutputCollector _collector;
String[] words = new String[] {"nathan", "mike", "jackson", "golda", "bertels"};
public TestWordSpout() {
this(true);
}
public TestWordSpout(boolean isDistributed) {
_isDistributed = isDistributed;
}
public void open(Map conf, TopologyContext context, SpoutOutputCollector collector) {
_collector = collector;
}
public void close() {
}
public void nextTuple() {
Utils.sleep(1000);
final Random rand = new Random();
final String word = words[rand.nextInt(words.length)];
_collector.emit(new Values(word), word+new Random().nextDouble());
}
public void ack(Object msgId) {
System.out.println("### ack:"+msgId);
}
public void fail(Object msgId) {
System.out.println("### fail:"+msgId);
}
public void declareOutputFields(OutputFieldsDeclarer declarer) {
declarer.declare(new Fields("word"));
}
public class WordDispatchBolt extends BaseRichBolt{
private OutputCollector collector;
@Override
public void prepare(Map stormConf, TopologyContext context,
OutputCollector collector) {
this.collector = collector;
new Thread(new Runnable() {
@Override
public void run() {
while(true){
send();//不做sleep休眠，否则抛出此异常的几率太小，不容易观察到
}
}
}).start();
}
public void send(){
this.collector.emit(new Values(new Random().nextDouble()));
}
@Override
public void execute(Tuple input) {
String word = input.getStringByField("word");
this.collector.emit(new Values(word));
this.collector.ack(input);
}
@Override
public void declareOutputFields(OutputFieldsDeclarer declarer) {
declarer.declare(new Fields("word"));
}
}
public class PrintBolt extends BaseRichBolt {
private static final long serialVersionUID = 1L;
@Override
public void prepare(Map stormConf, TopologyContext context,
OutputCollector collector) {
}
@Override
public void execute(Tuple input) {
System.out.println(input.getValue(0));
}
@Override
public void declareOutputFields(OutputFieldsDeclarer declarer) {
}
}
这个代码很简单，就不做详细介绍了。在WordDispatchBolt类里我启动了另一个线程来发射数据到下一个bolt。我的业务代码中与此类似，是通过Timer定时发送数据的（Timer底层其实也是线程，就不多说了）。但是Timer是按分钟调用的，所以出现问题的几率小的可怜，这里我故意零停顿的调用，让此异常发生的几率更大一些。
如果运行以上例子代码，你也肯定遇到前边贴出的错误异常。如果不知道是OutputCollector的同步问题，相信解决起来绝对让人痛不欲生。既然知道了是同步问题，要么避免在别的线程里调用collector,要么改成同步的。以下是我简单想到的解决方案。（如果有大神还有更好的，希望留言指教）
对WordDispatchBolt类做如下修改：
public class WordDispatchBolt extends BaseRichBolt{
private OutputCollector collector;
@Override
public void prepare(Map stormConf, TopologyContext context,
OutputCollector collector) {
this.collector = collector;
new Thread(new Runnable() {
@Override
public void run() {
while(true){
send(new Values(new Random().nextDouble()));//不做sleep休眠，否则抛出此异常的几率太小，不容易观察到
}
}
}).start();
}
public synchronized void send(List<Object> tuple){
this.collector.emit(tuple);
}
@Override
public void execute(Tuple input) {
String word = input.getStringByField("word");
send(new Values(word));
this.collector.ack(input);
}
@Override
public void declareOutputFields(OutputFieldsDeclarer declarer) {
declarer.declare(new Fields("word"));
}
}
到这里，这个坑算是基本得到解决了。之后可能还要大量使用到storm，遇到坑是再做记录。
”把遇到的坑记录下来，让后遇到者可以有更多的网络资源查询，以减少排查问题的时间和纠结“