记一次jstack命令定位问题

今天天气不错，但是赶上恶意加班心情就不爽，怀着不爽的心情干活，总能创造出更多的问题，这不，今天就自己挖了一个坑，自己跳进去了，好在上来了

经过是这样的，开始调试canal采集binlog时，由于添加了一个上报数量大小，随手打印了一个日志

logger.info("batchData:{}", batchData);
pipeline.put(batchData);

发到sit环境测试一把，卧槽。。。，怎么不同步数据了，开始排查问题，是我改的代码有问题？于是回退了，还是不同步数据，但是发现在停止任务时会中断读线程，这时数据同步过来了，试了几次都是这样，开始怀疑读线程被阻塞了，于是乎祭出许久未用的jstack去看一下读线程状态：jstack pid

"canal-binlog-encrypt-wangbd-test-001,219025,ReaderTask_CanalReader_0_0" #32 prio=5 os_prio=0 tid=0x00007fdfdc010800 nid=0x4199 waiting on condition [0x00007fe044653000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000800ad988> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
        at java.util.concurrent.ArrayBlockingQueue.take(ArrayBlockingQueue.java:403)
        at com.data.integration.engine.stream.core.cache.memory.MemoryDataCache.get(MemoryDataCache.java:135)
        at com.data.integration.engine.stream.core.cache.DataCache.get(DataCache.java:65)
        at com.data.integration.engine.stream.core.cache.DataCache.get(DataCache.java:61)
        at com.data.integration.engine.stream.core.config.pipeline.Pipeline.getBatchData(Pipeline.java:74)
        at com.alibaba.fastjson.serializer.ASMSerializer_4_Pipeline.write(Unknown Source)
        at com.alibaba.fastjson.serializer.ASMSerializer_1_DefaultBatchData.write(Unknown Source)
        at com.alibaba.fastjson.serializer.JSONSerializer.write(JSONSerializer.java:285)
        at com.alibaba.fastjson.JSON.toJSONString(JSON.java:740)
        at com.alibaba.fastjson.JSON.toJSONString(JSON.java:678)
        at com.alibaba.fastjson.JSON.toJSONString(JSON.java:643)
        at com.data.integration.engine.stream.plugin.reader.canalreader.CanalReader.start(CanalReader.java:127)
        at com.data.integration.engine.stream.plugin.reader.ReaderTask$ReaderThread.run(ReaderTask.java:138)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

发现居然在使用fastjson转换json时阻塞在缓存队列上了，说一下缓存队列读线程只会向里面写，写现场才会读，于是乎开始怀疑打印的这个日志，顺着思路找到了如下代码：

pipeline的batchData属性居然是从缓存中获取的对象

public BatchData getBatchData(){
        return dataCache.get();
    }

这就难怪了，由于缓存队列是空的，在toJson时阻塞了，导致整个读线程被阻塞，把这个日志去掉后就正常了,正常的读线程栈是这样的：

"canal-binlog-encrypt-wangbd-test-001,219023,ReaderTask_CanalReader_0_0" #32 prio=5 os_prio=0 tid=0x00007f7c8c00b000 nid=0xefb waiting on condition [0x00007f7d0476d000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000807bf660> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
        at com.alibaba.otter.canal.store.memory.MemoryEventStoreWithBuffer.get(MemoryEventStoreWithBuffer.java:219)
        at com.alibaba.otter.canal.server.embedded.CanalServerWithEmbedded.getEvents(CanalServerWithEmbedded.java:538)
        at com.alibaba.otter.canal.server.embedded.CanalServerWithEmbedded.getWithoutAck(CanalServerWithEmbedded.java:347)
        - locked <0x00000000808a3448> (a com.alibaba.otter.canal.instance.manager.CanalInstanceWithManager)
        at com.data.integration.engine.stream.plugin.reader.canalreader.CanalReader.start(CanalReader.java:101)
        at com.data.integration.engine.stream.plugin.reader.ReaderTask$ReaderThread.run(ReaderTask.java:138)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)