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

[mp911de]

Thank you for your report. lettuce connections are in general threadsafe but not stateless. Issuing a MULTI command will turn lettuce connections into a transactional state. All commands issued after a MULTI command are then within the transaction scope until either EXEC or DISCARD are issued.

The connection state means also, that calling MULTI twice will initiate the transaction twice and then try again to start the transaction. The mentioned exception ERR MULTI calls can not be nested is issued by Redis. I assume, that your test case can change the connection in a state, where the first transaction state might be lost, but I have to check this first.

Can you tell me about your expectation in this case?

[benjamin-bader]

Thanks for the sensible explanation. I see now what you mean by “threadsafe but stateful”. Individual commands are sent in a threadsafe manner, but application logic (transactions) must be synchronized at a higher level.