[Fix #1354] ForExecutor was not properly implemented for multithread

experimental/test/src/test/java/io/serverlessworkflow/fluent/test/ForEachFuncTest.java

@@ -75,7 +75,7 @@ void testForEachEmit() {
             .build();
 
     List<CloudEvent> publishedEvents = new CopyOnWriteArrayList<>();
-    InMemoryEvents eventBroker = new InMemoryEvents();
+    InMemoryEvents eventBroker = new LaggedInMemoryEvents();
     eventBroker.register(eventType, ce -> publishedEvents.add(ce));
 
     try (WorkflowApplication app =

experimental/test/src/test/java/io/serverlessworkflow/fluent/test/LaggedInMemoryEvents.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2020-Present The Serverless Workflow Specification Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.serverlessworkflow.fluent.test;
+
+import io.cloudevents.CloudEvent;
+import io.serverlessworkflow.impl.events.InMemoryEvents;
+import java.util.concurrent.CompletableFuture;
+
+public class LaggedInMemoryEvents extends InMemoryEvents {
+
+  @Override
+  public CompletableFuture<Void> publish(CloudEvent ce) {
+
+    return super.publish(ce)
+        .thenRun(
+            () -> {
+              try {
+                Thread.sleep(50);
+              } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+              }
+            });
+  }
+}

impl/core/src/main/java/io/serverlessworkflow/impl/executors/ForExecutor.java

@@ -75,23 +75,30 @@ protected ForExecutor(ForExecutorBuilder builder) {
   @Override
   protected CompletableFuture<WorkflowModel> internalExecute(
       WorkflowContext workflow, TaskContext taskContext) {
-    Iterator<?> iter = collectionExpr.apply(workflow, taskContext, taskContext.input()).iterator();
-    int i = 0;
-    CompletableFuture<WorkflowModel> future =
-        CompletableFuture.completedFuture(taskContext.input());
-    while (iter.hasNext()) {
+    return buildLoopFuture(
+        workflow,
+        taskContext,
+        taskContext.input(),
+        collectionExpr.apply(workflow, taskContext, taskContext.input()).iterator(),
+        -1);
+  }
+
+  private CompletableFuture<WorkflowModel> buildLoopFuture(
+      WorkflowContext workflow,
+      TaskContext taskContext,
+      WorkflowModel input,
+      Iterator<?> iter,
+      int index) {
+    final int newIndex = index + 1;
+    if (iter.hasNext()) {
       taskContext.variables().put(task.getFor().getEach(), iter.next());
-      taskContext.variables().put(task.getFor().getAt(), i++);
-      if (whileExpr.map(w -> w.test(workflow, taskContext, taskContext.input())).orElse(true)) {
-        future =
-            future.thenCompose(
-                input ->
-                    TaskExecutorHelper.processTaskList(
-                        taskExecutor, workflow, Optional.of(taskContext), input));
-      } else {
-        break;
+      taskContext.variables().put(task.getFor().getAt(), newIndex);
+      if (whileExpr.map(w -> w.test(workflow, taskContext, input)).orElse(true)) {
+        return TaskExecutorHelper.processTaskList(
+                taskExecutor, workflow, Optional.of(taskContext), input)
+            .thenCompose(output -> buildLoopFuture(workflow, taskContext, output, iter, newIndex));
       }
     }
-    return future;
+    return CompletableFuture.completedFuture(input);
   }
 }