Fix for jruby/jruby#8178 by only allowing a RubyArray into Argv

fix_8178_attempt_2.diff

diff --git a/core/src/main/java/org/jruby/embed/variable/AbstractVariable.java b/core/src/main/java/org/jruby/embed/variable/AbstractVariable.java
index 46177487d7..3c5f9cb821 100644
--- a/core/src/main/java/org/jruby/embed/variable/AbstractVariable.java
+++ b/core/src/main/java/org/jruby/embed/variable/AbstractVariable.java
@@ -94,7 +94,7 @@ abstract class AbstractVariable implements BiVariable {
         return (RubyObject) receiver.getRuntime().getTopSelf();
     }
 
-    protected void updateByJavaObject(final Ruby runtime, Object... values) {
+    protected synchronized void updateByJavaObject(final Ruby runtime, Object... values) {
         assert values != null;
         javaObject = values[0];
         if (javaObject == null) {
@@ -108,7 +108,7 @@ abstract class AbstractVariable implements BiVariable {
         fromRuby = false;
     }
 
-    protected void updateRubyObject(final IRubyObject rubyObject) {
+    protected synchronized void updateRubyObject(final IRubyObject rubyObject) {
         if ( rubyObject == null ) return;
         this.rubyObject = rubyObject;
         this.javaType = null;
@@ -134,7 +134,7 @@ abstract class AbstractVariable implements BiVariable {
         return name;
     }
 
-    public Object getJavaObject() {
+    public synchronized Object getJavaObject() {
         if (rubyObject == null) return javaObject;
 
         if (javaType != null) { // Java originated variables
diff --git a/core/src/main/java/org/jruby/embed/variable/Argv.java b/core/src/main/java/org/jruby/embed/variable/Argv.java
index ad8559f10c..0040990cbb 100644
--- a/core/src/main/java/org/jruby/embed/variable/Argv.java
+++ b/core/src/main/java/org/jruby/embed/variable/Argv.java
@@ -114,7 +114,7 @@ public class Argv extends AbstractVariable {
      * invoked during EvalUnit#run() is executed.
      */
     @Override
-    public void inject() {
+    public synchronized void inject() {
         final Ruby runtime = getRuntime();
 
         final RubyArray argv = RubyArray.newArray(runtime);
@@ -141,7 +141,7 @@ public class Argv extends AbstractVariable {
      * this variable in top self.
      */
     @Override
-    public void remove() {
+    public synchronized void remove() {
         this.javaObject = new ArrayList();
         inject();
     }
@@ -173,7 +173,7 @@ public class Argv extends AbstractVariable {
     }
 
     // ARGV appears to require special treatment, leaving javaType intact
-    protected void updateRubyObject(final IRubyObject rubyObject) {
+    protected synchronized void updateRubyObject(final IRubyObject rubyObject) {
         if ( rubyObject == null ) return;
         this.rubyObject = rubyObject;
     }
@@ -193,7 +193,7 @@ public class Argv extends AbstractVariable {
 
     @Override
     @SuppressWarnings("unchecked")
-    public Object getJavaObject() {
+    public synchronized Object getJavaObject() {
         if ( rubyObject == null || ! fromRuby ) return javaObject;
 
         final RubyArray ary = (RubyArray) rubyObject;