[DROOLS-7496] fixing concurrency problems in TruthMaintenanceSystemIm…

…pl (#5374)

drools-test-coverage/test-suite/src/test/java/org/drools/testcoverage/regression/TruthMaintenanceSystemConcurrencyTest.java

@@ -0,0 +1,67 @@
+package org.drools.testcoverage.regression;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+import org.drools.kiesession.rulebase.InternalKnowledgeBase;
+import org.drools.kiesession.rulebase.KnowledgeBaseFactory;
+import org.drools.kiesession.session.StatefulKnowledgeSessionImpl;
+import org.drools.mvel.compiler.Cheese;
+import org.junit.Test;
+import org.kie.api.definition.KiePackage;
+import org.kie.api.io.ResourceType;
+import org.kie.api.runtime.ClassObjectFilter;
+import org.kie.internal.builder.KnowledgeBuilder;
+import org.kie.internal.builder.KnowledgeBuilderFactory;
+import org.kie.internal.io.ResourceFactory;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+
+public class TruthMaintenanceSystemConcurrencyTest {
+
+    @Test
+    public void testUsingMultipleSessionsConcurrently() throws InterruptedException {
+        final KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
+        kbuilder.add(
+            ResourceFactory.newClassPathResource(
+                "test_concurrency.drl",
+                getClass()
+            ),
+            ResourceType.DRL
+        );
+        Collection<KiePackage> kpkgs = kbuilder.getKnowledgePackages();
+
+        InternalKnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
+        kbase.addPackages(kpkgs);
+
+        final ExecutorService executorService = Executors.newFixedThreadPool(20);
+
+        final Collection<Throwable> errors =
+            Collections.synchronizedCollection(new LinkedList<>());
+        for (int i = 0; i < 2000; i++) {
+            executorService.submit(() -> {
+                try {
+                    StatefulKnowledgeSessionImpl ksession = (StatefulKnowledgeSessionImpl) kbase.newKieSession();
+
+                    ksession.fireAllRules();
+                    assertThat(ksession.getObjects(new ClassObjectFilter(Cheese.class)))
+                        .hasSize(2);
+                } catch (Throwable e) {
+                    errors.add(e);
+                }
+            });
+        }
+        executorService.shutdown();
+        assertThat(executorService.awaitTermination(2, TimeUnit.SECONDS))
+            .isTrue();
+
+        assertThat(errors)
+            .isEmpty();
+    }
+
+}

drools-test-coverage/test-suite/src/test/resources/org/drools/testcoverage/regression/test_concurrency.drl

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2015 Red Hat, Inc. and/or its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ *
+ *      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 org.drools.testcoverage.regression;
+
+import org.drools.mvel.compiler.Cheese;
+
+rule "default"
+    then
+        insert("cheeseType");
+        insert(new Cheese("cheeseType"));
+end
+
+
+rule "insert new Cheese"
+    when
+        $type : String(this == "cheeseType")
+        Cheese( type == $type )
+    then
+        insertLogical( new Cheese("success") );
+end

drools-tms/src/main/java/org/drools/tms/TruthMaintenanceSystemImpl.java

@@ -68,17 +68,14 @@ public TruthMaintenanceSystemImpl(InternalWorkingMemoryEntryPoint ep) {
     }
 
     private static class EqualityKeyPlaceholder {
-        private static final EqualityKeyPlaceholder INSTANCE = new EqualityKeyPlaceholder();
+        private final Object object;
 
-        private Object object;
-
-        public EqualityKeyPlaceholder withObject(Object object) {
+        private EqualityKeyPlaceholder(final Object object) {
             this.object = object;
-            return this;
         }
 
         private static Object transformEqualityKey(Object o) {
-            return o instanceof EqualityKey ? o : EqualityKeyPlaceholder.INSTANCE.withObject(o);
+            return o instanceof EqualityKey ? o : new EqualityKeyPlaceholder(o);
         }
 
         @Override