Redis Locking for a KEY

[Madhu Sudhanarao palepu]

Hi,

Can I lock a particular KEY in Redis?

import redis

import time

conn = redis.StrictRedis(host='localhost', port=6379, db=0)

print ("previous Connected Key value is :" + conn.get('connected'))

print ("previous Operational Key value is :" + conn.get('operational'))

have_lock = False

my_lock = redis.Redis().lock("my_key")

try:

    have_lock = my_lock.acquire(blocking=False)

    #have_lock = my_lock.acquire(timeout=5)

    if have_lock:

        print("Got lock. Doing some stuff...")

        time.sleep(15)

        conn.set('connected', 'false')

        conn.set('operational', 'false')

    else:

        print("Did not acquire lock.")

finally:

    if have_lock:

        my_lock.release()

print ("After Connected Key value is :" + conn.get('connected'))

print ('After Operational Key value is :' + conn.get('operational'))

I tried with above example but it didn't work, the KEY still accessible from redis-cli and I can set even lock is acquired.

Any help is appreciated.

-Thanks,

[Marc Gravell]

Redis does not have a locking mechanism in the sense of blocking other connections. Instead, it relies on connections agreeing on common rules and respecting them. For example, it is common to use a key to *indicate* that you have a notional lock. That doesn't block anyone, but it is expected that other connections will try to acquire the same key, and if they can't: *then they don't do their thing* - they might do a pause / retry until they successfully take the lock, for example.

Marc

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[Madhu Sudhanarao palepu]

Thanks for your reply!

My requirement is:

I want to execute a script through which I can set some KEYS, at the same time I can execute a java based application where the same KEY can be reset.

This whole process should be synchronized.

I tried the above script where executing multiple instances, it is acquiring the lock properly 

but from java based or using redis-cli still I can access the KEY.

Can I do synchronize KEY from multiple access?

-Madhu

[Marc Gravell]

> Can I do synchronize KEY from multiple access?

Not from inside redis; to repeat - it does not support a blocking-style lock mechanism. You need to co-ordinate this from the calling code by following some convention. Two such conventions are discussed in the documentation; "redlock": http://redis.io/topics/distlock and something simpler using set with nx: http://redis.io/commands/set

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Regards,

Marc

[Madhu Sudhanarao palepu]

Okay.

Thanks for the reply.

Regards,

Marc