Fixes coalesce and case operators in multithreaded environments with …

…different number of arguments

The bug is described in the issue eclipse-ee4j#2136

TestArgumentListFunctionExpressionConcurrency.java - adds tests that reproduce the bug.
ExpressionOperator.java - fixes getArgumentIndices by disabling the caching of the dynamically created argument indexes.

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

@@ -97,10 +97,10 @@ public void setOperator(ExpressionOperator theOperator) {
      */
     @Override
     public void printSQL(ExpressionSQLPrinter printer) {
-        ListExpressionOperator operator = (ListExpressionOperator) this.operator;
-
-        operator.setIsComplete(true);
-        operator.printCollection(this.children, printer);
+        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

@@ -47,11 +47,12 @@ 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, p.string1, '" + cacheBuster(i) + "')";
-            } else {
                 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);
         });
     }