Working JRuby/Clojure dosync

dosync.java

// Hacked from headius' version here: https://github.com/headius/clojr/blob/master/src/main/java/com/headius/clojr/ClojrLibrary.java
// See also  https://jira.codehaus.org/browse/JRUBY-6149

       public static IRubyObject dosync(final ThreadContext context, final IRubyObject self, final Block block) throws Exception {
            final Ruby ruby = context.runtime;

            return (IRubyObject) LockingTransaction.runInTransaction(new Callable() {
                public Object call() throws Exception {
                    // re-get transaction in case this gets run in different threads
                    try {
                        final IRubyObject result = block.call(ruby.getCurrentContext());
                        return result;
                    } catch (RaiseException e) {
                        final RubyException rubyException = e.getException();
                        if(rubyException instanceof NativeException) {
                            // Peek in the native exception for RetryEx and retrow it raw.
                            // Otherwise retries won't work. The class name check is pretty
                            // kludgy, but RetryEx is package private :(
                            final NativeException ne = (NativeException) rubyException;
                            final Throwable cause = (Throwable) ne.getCause();
                            if(cause != null &&
                                "clojure.lang.LockingTransaction$RetryEx".equals(cause.getClass().getName())) {
                                throw (Error) cause;
                            }
                            else {
                                throw e;
                            }
                        }
                        else {
                            throw e;
                        }
                    }
                }
            });
        }