Spring Batch: taskExecutor exception when adding skip limit

Question

I'm using Spring 4.0.5 and Spring Batch 3.0.1

I have a simple step like this, and it works perfectly:

<step id="myStep" next="nextStep">
    <tasklet transaction-manager="myTxManager" task-executor="myTaskExecutor" throttle-limit="10">
        <batch:chunk reader="myItemReader" processor="myPDFItemProcessor" writer="myItemWriter" commit-interval="20">
        </batch:chunk>
    </tasklet>
</step>

I have tried a simple skip-limit example (Configuring Skip Logic) like this:

<step id="myStep" next="nextStep">
    <tasklet transaction-manager="myTxManager" task-executor="myTaskExecutor" throttle-limit="10">
        <batch:chunk reader="myItemReader" processor="myPDFItemProcessor" writer="myItemWriter" commit-interval="20" skip-limit="10000000">
            <batch:skippable-exception-classes>
                <batch:include class="java.lang.Exception" />
            </batch:skippable-exception-classes>
        </batch:chunk>
    </tasklet>
</step>

When I try to add this logic, this warning is writen in log files:

2015-03-24 16:03:50 [WARN ] [org.springframework.batch.core.step.builder.FaultTolerantStepBuilder.detectStreamInReader(FaultTolerantStepBuilder.java:504)] Asynchronous TaskExecutor detected with ItemStream reader.  This is probably an error, and may lead to incorrect restart data being stored.
2015-03-24 16:04:18 [WARN ] [org.springframework.batch.core.step.item.ChunkMonitor.open(ChunkMonitor.java:118)] No ItemReader set (must be concurrent step), so ignoring offset data.
2015-03-24 16:04:18 [WARN ] [org.springframework.batch.core.step.item.ChunkMonitor.getData(ChunkMonitor.java:155)] ItemStream was opened in a different thread.  Restart data could be compromised.

The reader is JdbcPagingItemReader with saveState setted to false.

The processor is a CompositeItemProcessor.

The writer is a CompositeItemWriter.

Is there anything wrong with my configuration? Maybe do I need any additional configuration for skip logic to work?

Any help is very appreciated. Thanks

I think its not because of skip logic, its because its multi threaded. Try HibernatePagingItemReader or in case if you cannot use Hibernate then try writing a threadsafe implementation of ItemReader. — Bilbo Baggins
@SamwiseGamgee, thanks for your suggestion. Bean myItemReader is a JdbcPagingItemReader reader, with scope=step and saveState=false . As it does not seem to be thread-safe, I have tested a simple custom ItemReader with a synchronized read method, which delegates in myItemReader and it hasn't work. So, what can I do to make a thread-safe reader? Or what can I do to make myItemReader a thread-safe one? Thanks a lot. — yaki_nuka
forum.spring.io/forum/spring-projects/batch/… this link explains how to achieve the thread safety. — Bilbo Baggins

yaki_nuka yaki_nuka · Accepted Answer · 2015-03-27T16:23:54

Finally, I could solve my issue with Samwise's hint.

When you have an ItemReader in a multithreaded step, to make that reader thread safe, the code is:

public SynchronizedItemReader<T> implements ItemReader<T> {
  private final ItemReader<T> delegate; 
  public SynchronizedItemReader(ItemReader<T> delegate) {
    this.delegate = delegate;
  }
  public synchronized T read () {
    return delegate.read();
  }
}

The delegated ItemReader in this class is the current ItemReader you want to make thread-safe.

This sample class is in the link suggested by Samwise.

IMPORTANT EDIT: Docs in Item Readers and Writers, section 6.5, explain that delegated reader must be injected as a stream. I don't know why, but in my current issue in this question, the delegate reader must not be injected as a stream reader in the chunk. When I injected it, it failed.

Hope it would be helpful. Thanks.

Spring Batch: taskExecutor exception when adding skip limit

1 Answers