java: pass exceptions thrown from contexts to joiners

This helps the invoker to determine if isolate executed successfuly or not.

java/runjava/src/main/java/io/osv/Context.java

@@ -26,6 +26,7 @@ public final class Context {
     private final Properties properties;
 
     private Thread mainThread;
+    private Throwable exception;
 
     public Context(ClassLoader systemClassLoader, Properties properties) {
         this.systemClassLoader = systemClassLoader;
@@ -53,8 +54,11 @@ public final class Context {
         return properties;
     }
 
-    public void join() throws InterruptedException {
+    public void join() throws InterruptedException, ContextFailedException {
         mainThread.join();
+        if (exception != null) {
+            throw new ContextFailedException(exception);
+        }
     }
 
     public LogManagerWrapper getLogManagerWrapper() {
@@ -64,4 +68,8 @@ public final class Context {
     public void interrupt() {
         mainThread.interrupt();
     }
+
+    void setException(Throwable exception) {
+        this.exception = exception;
+    }
 }

java/runjava/src/main/java/io/osv/ContextFailedException.java

+package io.osv;
+
+/*
+ * Copyright (C) 2014 Cloudius Systems, Ltd.
+ *
+ * This work is open source software, licensed under the terms of the
+ * BSD license as described in the LICENSE file in the top-level directory.
+ */
+public class ContextFailedException extends Exception {
+    public ContextFailedException(Throwable cause) {
+        super(cause);
+    }
+}

java/runjava/src/main/java/io/osv/ContextIsolator.java

@@ -111,6 +111,7 @@ public class ContextIsolator {
         thread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
             @Override
             public void uncaughtException(Thread t, Throwable e) {
+                context.setException(e);
                 e.printStackTrace();
             }
         });