Keep heap lean during remote partition polling

Resolves #4598

Author: hpoettker

spring-batch-integration/src/main/java/org/springframework/batch/integration/partition/MessageChannelPartitionHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2009-2023 the original author or authors.
+ * Copyright 2009-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -251,24 +251,22 @@ protected Set<StepExecution> doHandle(StepExecution managerStepExecution,
 
 	private Set<StepExecution> pollReplies(final StepExecution managerStepExecution, final Set<StepExecution> split)
 			throws Exception {
-		final Set<StepExecution> result = new HashSet<>(split.size());
+		Set<Long> partitionStepExecutionIds = split.stream().map(StepExecution::getId).collect(Collectors.toSet());
 
 		Callable<Set<StepExecution>> callback = () -> {
-			Set<Long> currentStepExecutionIds = split.stream().map(StepExecution::getId).collect(Collectors.toSet());
 			JobExecution jobExecution = jobExplorer.getJobExecution(managerStepExecution.getJobExecutionId());
-			jobExecution.getStepExecutions()
+			Set<StepExecution> finishedStepExecutions = jobExecution.getStepExecutions()
 				.stream()
-				.filter(stepExecution -> currentStepExecutionIds.contains(stepExecution.getId()))
-				.filter(stepExecution -> !result.contains(stepExecution))
+				.filter(stepExecution -> partitionStepExecutionIds.contains(stepExecution.getId()))
 				.filter(stepExecution -> !stepExecution.getStatus().isRunning())
-				.forEach(result::add);
+				.collect(Collectors.toSet());
 
 			if (logger.isDebugEnabled()) {
 				logger.debug(String.format("Currently waiting on %s partitions to finish", split.size()));
 			}
 
-			if (result.size() == split.size()) {
-				return result;
+			if (finishedStepExecutions.size() == split.size()) {
+				return finishedStepExecutions;
 			}
 			else {
 				return null;