Method execute

src/main/java/groovy/concurrent/Agent.java:341–346

Queues a task for serial execution. @param command the task to execute

(Runnable command)

         * @param command the task to execute
         */
        @Override
        public void execute(Runnable command) {
            if (shutdown) throw new RejectedExecutionException("shutdown");
            queue.add(command);
            scheduleNext();
        }

        private void scheduleNext() {
            if (!queue.isEmpty() && active.compareAndSet(false, true)) {