BLPOP works only sometimes

[Raghava Mutharaju]

Hi,

I am using two separate Jedis instances. One instance is used for calling BLPOP (which gets blocked if the list is empty). Using the other Jedis instance (in a separate thread), I do an LPUSH on the same list. These two instances are run by separate threads.

Irrespective of whether BLPOP happens before or after LPUSH, sometimes, BLPOP does not pop out an element -- it continues to block and I can see an item in that list is available.

Sometimes it works fine.

I am using Redis-2.8.0-rc4. Any help is highly appreciated.

Regards,

Raghava.

[Dvir Volk]

Can you recreate it in a redis-cli? Can you make it happen with a stable redis 2.6?

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Dvir Volk

Chief Architect, Everything.me

http://everything.me 

[Raghava Mutharaju]

No, I couldn't recreate it in redis-cli. It works fine in cli. When I used redis-2.6.16, it happens again but in some cases, even though the item is not in the list anymore BLPOP -- another Jedis does insert an item but BLPOP gets blocked with the item not in the list anymore.

I was using Redis for my application and thought I would use it for synchronization as well. Hence used BLPOP. Now, I moved to using java feature (CountDownLatch) and it works fine now. I guess I used it for the wrong purpose to begin with.

Regards,

Raghava.

[Dvir Volk]

Redis is perfect for distributed synchronization, it seems to me like it's either a bug in Jedis or a bug in your code. 

But as you said, you could not recreate it in pure redis, so it's not a redis issue. You might want to ask on the jedis mailing list.

[Raghava Mutharaju]

Ok, good to know that it is not uncommon to use Redis in that way :). Yes, I think it is most probably a bug in my code which isn't obvious. I will keep looking.

Thank you.

Regards,

Raghava.