Is a thread-safe ItemReader needed in a multi-threaded step with the new concurrency model of Spring Batch 6 ?

[ctrung]

Hi,

With the new concurrency model of Spring Batch 6, ItemReader.read() is accessed by the main thread whereas it was accessed by the threads of the taskExecutor before.

It seems that the reader doesn't need to be thread-safe anymore (I have verified that myself, and the behaviour is the same with or without a thread-safe reader).

Chapter https://docs.spring.io/spring-batch/reference/scalability.html#multithreadedStep of the reference documentation still mentions the need for a thread safe reader.

Are there other usecases where a thread-safe reader is still needed ?

My step definition :

var step = new StepBuilder("my_step", jobRepository)
                         .<I, O>chunk(5)
                         .transactionManeger(transactionManager)
                         .reader(reader)
                         .writer(writer)
                         .taskExecutor(taskExecutor)
                         .build();

[fmbenhassine]

Yes, with the new concurrency model, the reader is only called by a single thread and does not have to be thread-safe. I gave some details about that here: #4955 (comment). Does that clarify things better for you?

I need to write about that elsewhere for more visibility.

Chapter https://docs.spring.io/spring-batch/reference/scalability.html#multithreadedStep of the reference documentation still mentions the need for a thread safe reader.

That's an oversight, I will update the documentation accordingly.

Are there other usecases where a thread-safe reader is still needed ?

Not with the step implementations provided by Spring Batch. We kept the synchronised wrappers around for anyone implementing a custom step and who might need to wrap the reader/writer in a synchronized decorator.

[ctrung]

Thanks for your answer !

Also, for those who are using multi-threaded chunk steps, the writing part is not concurrent anymore. By using local-chunking (introduced in this version too, needs an additional dependency to spring-batch-integration), I managed to have a behaviour similar to that of Spring Batch 5.

[fmbenhassine]

Thanks! We still need to update the documentation with that change. I created #5228 for that and planned it for the upcoming 6.0.2.