I need to parallelize a single step of a batch spring job. Before the step to be parallelized, tasklets are run that put some results in the parameters of the job. The results produced by the tasklets, are necessary to execute the Partitioner and the Items of the step to be parallelized. A doubt is arising that I really can't solve. Since I can have the same job running simultaneously multiple times with different initial parameters, are the tasklets and step items safe thread-safe?
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2 Answers
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No, tasklets and chunk-oriented step components are not thread-safe. If they are shared between multiple job instances/executions running concurrently, you need to make them thread-safe.
You can achieve this by using JobScoped steps and StepScoped readers/writers. You can also use the SynchronizedItemStreamReader and the (upcoming) SynchronizedItemStreamWriter to make readers and writers thread-safe. All item readers and writers provided by Spring Batch have a mention about their thread-safety in the Javadoc.
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You do not want to run multiple instances of the same job. It would be better to run multiple tasks or processes in the same step and or job. You might want to lookup job partitioning, and or Remote Chucking to do concurrent processing.
If it has to be isolated jobs then you might have your concurrent jobs write out to say a message que as their end (writer) step, and then have another job listen to read from that que.
https://docs.spring.io/spring-batch/2.1.x/cases/parallel.html
