ERR MULTI calls can not be nested

my code: public static void main(String[] args) throws Exception { final RedisConnection<String, byte[]> sync = new RedisClient(“10.58.52.60”, 5021) .connect(new BytesCodec()); sync.flushall();

     final CountDownLatch c = new CountDownLatch(1);
        new Thread(new Runnable() {
            public void run() {
                try {
                    c.await();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                sync.multi();
                sync.set("a", Thread.currentThread().getName().getBytes());
                sync.set("a1", Thread.currentThread().getName().getBytes());
                System.out.println(1234);
            }
        }).start();
        new Thread(new Runnable() {
            public void run() {
                try {
                    c.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                sync.multi();
                sync.set("a", Thread.currentThread().getName().getBytes());
                sync.set("a1", Thread.currentThread().getName().getBytes());
                sync.exec();
                System.out.println(5678);
            }
        }).start();

        c.countDown();


}

output: Exception in thread “Thread-2” com.lambdaworks.redis.RedisCommandExecutionException: ERR MULTI calls can not be nested at com.lambdaworks.redis.LettuceFutures.await(LettuceFutures.java:76) at com.lambdaworks.redis.FutureSyncInvocationHandler.handleInvocation(FutureSyncInvocationHandler.java:59) at com.google.common.reflect.AbstractInvocationHandler.invoke(AbstractInvocationHandler.java:87) at $Proxy5.multi(Unknown Source) at com.lambdaworks.redis.AsyncConnectionConcurrentTest$2.run(AsyncConnectionConcurrentTest.java:44) at java.lang.Thread.run(Thread.java:662) 1234