Redis Functionality

Question

I am trying to use redis for a simple process.
Process :- Read value for a key and update it.
Example :- (a,1) Read a value and update 1 to 2.
The problem here is that in multithreaded environment ,multiple thread (say 4) read at same time and then update it to 2, actually it should have been 4 .Is there a way where in I can impose locking in redis such that if one thread reads a value it imposes a lock so that other threads are kept in waiting state?

Answer 1

Use INCRBY to do an atomic increment:

redis> SET mykey "10"
"OK"
redis> INCRBY mykey 5
(integer) 15
redis> 

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Or, if you need something more sophisticated, use an uninterruptible MULTI command.

Answer 2

you do not need the lock. In multithreaded environment, suppose 4, they send read and update commands to Redis not in right order. may be:

1:read->2:read->1:update->2:update->3:read->3:update->4:read->4:update

you need combine 1:read and 1:update to an atomic operation, that is Lua Script.

you can write a Lua script for all operation and execute it whit EVAL command, the multithreaded commands will in right order.