Allow semaphore to acquire more than one token/lock/resource per call about redis-semaphore HOT 4 CLOSED

MultiSemaphore was added in v3.2.0

from redis-semaphore.

Hi!
Adding int argument to acquire is not quite correct, because there are several ways how to make multiple lock. For your example, lets say there are serveral running instances of application which should connect to service (some of them needs 1 lock to open single connection, other needs 2). Instance1 locks two slots, Instance2 locks one slot, after that there are one free slot left. What should instance3 do? Waits until two slots become available (possibly may never happend, cause there are instance2 which can always lock "third" slot)? Or should it lock one slot and waits until other one will be released? If second UX is what you want, then you can do it with current interface: create two instances of Semaphore with same key and call await Promise.all([semaphore1.acquire(), semaphore2.acquire()]), which is more clear I guess. (offtop: calling .acquire on single semaphore instance multiple times doesn't locks multiple slots, because internall semaphore based on sorted set in redis, so only one slot for single semaphore identifier will be "relocked")
For that UX it's better to create something like "MultiSemaphore" class with acquire which will internally create multiple Semaphores and call acquire for each of them, I guess. What do you think? Thanks

from redis-semaphore.

So i believe that instance3 here should throw on the acquire if it requires 2 but only 1 slot is available. That really depends if you hold locks for a long time or if it is a temporary lock. I think that should be left to the application developer.
A MultiSemaphore class could work, but I would expect it to be atomic and in the case of using multiple classes of Semaphore under it, it won't be.
I feel this script https://github.com/swarthy/redis-semaphore/blob/master/src/semaphore/acquire/lua.ts#L14-L18
could be adapted to to do something like (not a lua programmer, so probably wrong but you get the gist):

if redis.call('zcard', key) + ask <= limit then
    array = {}
    for i= 0, ask do
        array[i*2] = now
        array[i+1] = identifier
    end
    redis.call('zadd', key, unpack(array))

Thanks!

from redis-semaphore.

Wow so fast, thank you so much, this is awesome!

from redis-semaphore.