Fixing issue cucumber#723. Made the Groovy backend instance a thread local so that tests can run in parallel in the same JVM

Author: Bradley Hart

groovy/src/main/code_generator/I18n.groovy.txt

@@ -8,11 +8,11 @@ import java.util.regex.Pattern;
 public class ${i18n.underscoredIsoCode.toUpperCase()} {
 <% i18n.codeKeywords.each { kw -> %>
     public static void ${kw}(Pattern regexp, Closure body) throws Throwable {
-        GroovyBackend.instance.addStepDefinition(regexp, 0, body);
+        GroovyBackend.getInstance().addStepDefinition(regexp, 0, body);
     }
 
     public static void ${java.text.Normalizer.normalize(kw, java.text.Normalizer.Form.NFC)}(Pattern regexp, long timeoutMillis, Closure body) throws Throwable {
-        GroovyBackend.instance.addStepDefinition(regexp, timeoutMillis, body);
+        GroovyBackend.getInstance().addStepDefinition(regexp, timeoutMillis, body);
     }
 <% } %>
 }

groovy/src/main/java/cucumber/api/groovy/Hooks.java

@@ -9,7 +9,7 @@
 
 public class Hooks {
     public static void World(Closure body) throws Throwable {
-        GroovyBackend.instance.registerWorld(body);
+        GroovyBackend.getInstance().registerWorld(body);
     }
 
     public static void Before(Object... args) throws Throwable {
@@ -37,9 +37,9 @@ private static void addHook(Object[] tagsExpressionsAndBody, boolean before) {
 
         TagExpression tagExpression = new TagExpression(tagExpressions);
         if (before) {
-            GroovyBackend.instance.addBeforeHook(tagExpression, timeoutMillis, body);
+            GroovyBackend.getInstance().addBeforeHook(tagExpression, timeoutMillis, body);
         } else {
-            GroovyBackend.instance.addAfterHook(tagExpression, timeoutMillis, body);
+            GroovyBackend.getInstance().addAfterHook(tagExpression, timeoutMillis, body);
         }
     }
 }

groovy/src/main/java/cucumber/runtime/groovy/GroovyBackend.java

@@ -30,7 +30,7 @@
 import static cucumber.runtime.io.MultiLoader.packageName;
 
 public class GroovyBackend implements Backend {
-    public static GroovyBackend instance;
+    public static ThreadLocal<GroovyBackend> instanceThreadLocal = new ThreadLocal<GroovyBackend>();
     private final Set<Class> scripts = new HashSet<Class>();
     private final SnippetGenerator snippetGenerator = new SnippetGenerator(new GroovySnippet());
     private final ResourceLoader resourceLoader;
@@ -41,6 +41,10 @@ public class GroovyBackend implements Backend {
     private Object world;
     private Glue glue;
 
+    public static GroovyBackend getInstance(){
+        return instanceThreadLocal.get();
+    }
+
     private static GroovyShell createShell() {
         CompilerConfiguration compilerConfig = new CompilerConfiguration();
         // Probably not needed:
@@ -55,7 +59,7 @@ public GroovyBackend(ResourceLoader resourceLoader) {
     public GroovyBackend(GroovyShell shell, ResourceLoader resourceLoader) {
         this.shell = shell;
         this.resourceLoader = resourceLoader;
-        instance = this;
+        instanceThreadLocal.set(this);
         classFinder = new ResourceLoaderClassFinder(resourceLoader, shell.getClassLoader());
     }