开卷有益 union/substact/intersect/difference
Java线程池处理子线程超时问题
起因
近几天,某个正常运行了近两个月的项目,单日处理请求条数锐减,排查日志发现如下异常:
Mon Apr 29 18:12:01 CST 2019, org.apache.hadoop.hbase.client.RpcRetryingCaller@34f04eb2, java.io.IOException: java.io.IOException: Could not seek StoreFileScanner[HFileScanner for reader reader=hdfs://Ucluster5/hbase/data/default/video_search_shot/5402a6d8800f28541d456a50367cc757/d/b98d69cfc81f4903a3ddb94e95114454, compression=none, cacheConf=CacheConfig:enabled [cacheDataOnRead=true] [cacheDataOnWrite=false] [cacheIndexesOnWrite=false] [cacheBloomsOnWrite=false] [cacheEvictOnClose=false] [cacheCompressed=false], firstKey=8bfc17007695e96ae27e049a11b42792:11.000_0.133/d:dhash128/1554703137033/Put, lastKey=8e00dfe4801a80988f7fe7944120317b:14.000_1.000/d:video/1554768240786/Put, avgKeyLen=65, avgValueLen=398, entries=356358, length=168414223, cur=null] to key 8de584f3a3f112d2cbe581f1f8e30588:0.000_1.000/d:/LATEST_TIMESTAMP/DeleteFamily/vlen=0/mvcc=0 at org.apache.hadoop.hbase.regionserver.StoreFileScanner.seek(StoreFileScanner.java:157) at org.apache.hadoop.hbase.regionserver.StoreScanner.<init>(StoreScanner.java:168) at org.apache.hadoop.hbase.regionserver.HStore.getScanner(HStore.java:1648) at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.<init>(HRegion.java:3513) at org.apache.hadoop.hbase.regionserver.HRegion.instantiateRegionScanner(HRegion.java:1816) at org.apache.hadoop.hbase.regionserver.HRegion.getScanner(HRegion.java:1808) at org.apache.hadoop.hbase.regionserver.HRegion.getScanner(HRegion.java:1785) at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:4538) at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:4513) at org.apache.hadoop.hbase.regionserver.HRegionServer.get(HRegionServer.java:2780) at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:26925) at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2141) at org.apache.hadoop.hbase.ipc.RpcServer$Handler.run(RpcServer.java:1844) Caused by: java.io.IOException: Failed to read compressed block at 159280276, onDiskSizeWithoutHeader=67484, preReadHeaderSize=33, header.length=33, header bytes: DATABLK*\x00\x01\x07:\x00\x01\x07&\x00\x00\x00\x00\x07\x97\x02\xD9\x01\x00\x00@\x00\x00\x01\x07G at org.apache.hadoop.hbase.io.hfile.HFileBlock$FSReaderV2.readBlockDataInternal(HFileBlock.java:1495) at org.apache.hadoop.hbase.io.hfile.HFileBlock$FSReaderV2.readBlockData(HFileBlock.java:1358) at org.apache.hadoop.hbase.io.hfile.HFileReaderV2.readBlock(HFileReaderV2.java:335) at org.apache.hadoop.hbase.io.hfile.HFileBlockIndex$BlockIndexReader.loadDataBlockWithScanInfo(HFileBlockIndex.java:253) at org.apache.hadoop.hbase.io.hfile.HFileReaderV2$AbstractScannerV2.seekTo(HFileReaderV2.java:474) at org.apache.hadoop.hbase.io.hfile.HFileReaderV2$AbstractScannerV2.seekTo(HFileReaderV2.java:495) at org.apache.hadoop.hbase.regionserver.StoreFileScanner.seekAtOrAfter(StoreFileScanner.java:225) at org.apache.hadoop.hbase.regionserver.StoreFileScanner.seek(StoreFileScanner.java:145) ... 12 more Caused by: java.io.IOException: Invalid HFile block magic: \x00\x00\x00\x00\x00\x00\x00\x00 at org.apache.hadoop.hbase.io.hfile.BlockType.parse(BlockType.java:154) at org.apache.hadoop.hbase.io.hfile.BlockType.read(BlockType.java:165) at org.apache.hadoop.hbase.io.hfile.HFileBlock.<init>(HFileBlock.java:258) at org.apache.hadoop.hbase.io.hfile.HFileBlock$FSReaderV2.readBlockDataInternal(HFileBlock.java:1492) ... 19 more
协调大数据与运维部门,最终定位错误为Hadoop集群某个节点磁盘坏块,随后运维更换磁盘,速度略微提升,该异常仍然存在(最终排查确认仍有其他节点磁盘坏块,全部更换后问题解决).这就造成一个问题,业务代码操作video_search_shot这张表时,将因此阻塞,时长达到数分钟.考虑到磁盘坏块客观存在,数据库连接超时过久,故设置线程超时时间成了必然选择.
线程超时解决方案
常用的线程超时处理方法有很多,例如Thread.join(long timeout)/Future.get(long timeout,TimeUnit unit)/ExecutorService的超时方法...实际应用中,偏爱使用第二种 Future.get(long timeout,TimeUnit unit),因为其相对来说更灵活,关键是该类更熟悉,而且相对于针对线程池的超时处理,该方案处理粒度更小,便于掌控.
实操
既然选择使用Future的get方法去处理线程超时问题,这里就需要考虑线程池子线程的处理时机,在调用get方法时,子线程应处于未执行状态,否则超时处理就没有意义.故排除ExecutorService.invokeAll(Collection<? extends Callable<T> tasks>)/ExecutorService.invokeAny(Collection<? extends Callable<T> tasks>)及二者对应的线程池超时方法.这时往线程池提交子线程的选择就剩下了ExecutorService.submit(....),其次,需要处理的异常,首先是TimeoutException,其次是,InterruptedIOException,因为将调用Future.cancel(boolean mayInterruptIfRunning)方法中断子线程.
代码
ExecutorService exec = Executors.newFixedThreadPool(4); List<Future<Boolean>> futures = new ArrayList<>(); Callable<Integer> task; for (int i = 0;i<4;i++) { task = () -> { TimeUnit.SECONDS.sleep(50); return true; }; Future<Boolean> futureNow = exec.submit(task); futures.add(futureNow); } for (Future<Integer> future : futures) { try { Integer intRes = future.get(2000, TimeUnit.MILLISECONDS); System.out.println("result : " + intRes); } catch (InterruptedException ex) { System.out.println("子线程被中断 "); } catch (ExecutionException e) { System.out.println("子线程执行出错"); } catch (TimeoutException e) { System.out.println("处理超时"); } finally { future.cancel(true); // 中断子线程 } } exec.shutdown();