Fixes coalesce and case operators in multithreaded environments with different number of arguments (#2259)

The bug is described in the issue #2136

TestArgumentListFunctionExpressionConcurrency.java - adds tests that reproduce the bug.
ArgumentListFunctionExpression.java - fixes printSQL to use the operator itself and not the common instance of it
ExpressionOperator.java - fixes getArgumentIndices by disabling the caching of the dynamically created argument indexes.

---------

Co-authored-by: Igor Mukhin <[email protected]>

Author: igormukhin

foundation/org.eclipse.persistence.core/src/main/java/org/eclipse/persistence/expressions/ExpressionOperator.java

@@ -2618,7 +2618,7 @@ public void setArgumentIndices(int[] indices) {
     }
 
     /**
-     * Return the argumentIndices if set, otherwise initialize argumentIndices to the provided size
+     * Returns the argumentIndices if set, otherwise returns an array of indexes of the provided size.
      */
     public int[] getArgumentIndices(int size) {
         int[] indices = this.argumentIndices;
@@ -2630,7 +2630,11 @@ public int[] getArgumentIndices(int size) {
         for (int i = 0; i < indices.length; i++) {
             indices[i] = i;
         }
-        this.argumentIndices = indices;
+
+        // NOTE: Why not cache the newly generated array of indexes like "this.argumentIndices = indices" here?
+        // The reason is that some operators have variable number of arguments like COALESCE and CASE WHEN.
+        // As instances of this class are shared between threads we cannot cache the array of indexes.
+
         return indices;
     }
 

foundation/org.eclipse.persistence.core/src/main/java/org/eclipse/persistence/internal/expressions/ArgumentListFunctionExpression.java

@@ -97,8 +97,7 @@ public void setOperator(ExpressionOperator theOperator) {
      */
     @Override
     public void printSQL(ExpressionSQLPrinter printer) {
-        ListExpressionOperator realOperator;
-        realOperator = (ListExpressionOperator)getPlatformOperator(printer.getPlatform());
+        ListExpressionOperator realOperator = (ListExpressionOperator) getPlatformOperator(printer.getPlatform());
         operator.copyTo(realOperator);
         realOperator.setIsComplete(true);
         realOperator.printCollection(this.children, printer);

jpa/eclipselink.jpa.test.jse/src/it/java/org/eclipse/persistence/jpa/test/jpql/TestArgumentListFunctionExpressionConcurrency.java

@@ -0,0 +1,126 @@
+/*
+ * Copyright (c) 2024 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2024 IBM Corporation. All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0,
+ * or the Eclipse Distribution License v. 1.0 which is available at
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
+ */
+package org.eclipse.persistence.jpa.test.jpql;
+
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.ObjIntConsumer;
+
+import org.eclipse.persistence.jpa.test.framework.DDLGen;
+import org.eclipse.persistence.jpa.test.framework.Emf;
+import org.eclipse.persistence.jpa.test.framework.EmfRunner;
+import org.eclipse.persistence.jpa.test.jpql.model.JPQLEntity;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import jakarta.persistence.EntityManager;
+import jakarta.persistence.EntityManagerFactory;
+
+/**
+ * This test reproduces the issues #2136, #1867 and #1717.
+ *
+ * @author Igor Mukhin
+ */
+@RunWith(EmfRunner.class)
+public class TestArgumentListFunctionExpressionConcurrency {
+
+    private static final int MAX_THREADS = Math.min(Runtime.getRuntime().availableProcessors(), 4);
+    private static final int ITERATIONS_PER_THREAD = 1000;
+
+    @Emf(name = "argumentListFunctionExpressionConcurrencyEMF", createTables = DDLGen.DROP_CREATE, classes = { JPQLEntity.class })
+    private EntityManagerFactory emf;
+
+    @Test
+    public void testConcurrentUseOfCoalesce() throws Exception {
+        runInParallel((em, i) -> {
+            String jpql;
+            if (i % 2 == 0) {
+                jpql = "SELECT p FROM JPQLEntity p  WHERE p.string1 = coalesce(p.string2, '" + cacheBuster(i) + "')";
+            } else {
+                jpql = "SELECT p FROM JPQLEntity p  WHERE p.string1 = coalesce(p.string2, p.string1, '" + cacheBuster(i) + "')";
+            }
+            em.createQuery(jpql, JPQLEntity.class).getResultList();
+            System.out.println(Thread.currentThread().getName() + " - " + i % 2);
+        });
+    }
+
+    @Test
+    public void testConcurrentUseOfCaseCondition() throws Exception {
+        runInParallel((em, i) -> {
+            String jpql;
+            if (i % 2 == 0) {
+                jpql = "SELECT p FROM JPQLEntity p"
+                        + " WHERE p.string1 = case "
+                        + "   when p.string2 = '" + cacheBuster(i) + "' then p.string1 "
+                        + "   else null "
+                        + "   end";
+            } else {
+                jpql = "SELECT p FROM JPQLEntity p"
+                        + " WHERE p.string1 = case "
+                        + "   when p.string2 = '" + cacheBuster(i) + "' then p.string1"
+                        + "   when p.string2 = 'x' then p.string2"
+                        + "   else null "
+                        + "   end";
+
+            }
+            em.createQuery(jpql, JPQLEntity.class).getResultList();
+        });
+    }
+
+    private static String cacheBuster(Integer i) {
+        return "cacheBuster." + Thread.currentThread().getName() + "." + i;
+    }
+
+    private void runInParallel(ObjIntConsumer<EntityManager> runnable) throws Exception {
+        AtomicReference<Exception> exception = new AtomicReference<>();
+
+        // start all threads
+        List<Thread> threads = new ArrayList<>();
+        for (int t = 0; t < MAX_THREADS; t++) {
+            Thread thread = new Thread(() -> {
+                try {
+                    for (int i = 0; i < ITERATIONS_PER_THREAD; i++) {
+                        if (exception.get() != null) {
+                            return;
+                        }
+
+                        try (EntityManager em = emf.createEntityManager()) {
+                            runnable.accept(em, i);
+                        }
+
+                    }
+                } catch (Exception e) {
+                    exception.set(e);
+                }
+            });
+            threads.add(thread);
+            thread.start();
+        }
+
+        // wait for all threads to finish
+        threads.forEach(thread -> {
+            try {
+                thread.join();
+            } catch (InterruptedException e) {
+                exception.set(e);
+            }
+        });
+
+        // throw the first exception that occurred
+        if (exception.get() != null) {
+            throw exception.get();
+        }
+    }
+}