process-pool | PHP Process Pool | Web Framework library

I am looking for a way to start two functions in parallel, each executing over a given set of different arguments. I use pool.map to achieve this. I create two different processes and each process starts a pool executing the map. This works - the order of execution is a little bit wild, but I will save this for another question.

Now I have also found another approach here (see the first answer). They are using only one pool and call map_async two times in a row. So I was wondering, if there is a preferred way for doing this? Because I have read (sadly I don't remember where) that it is best to only use one pool, which would mean the second approach (using only one pool) is better. But when I measure the time, the first approch (using two pools in separate processes) is actually a little bit faster. Additionally in the first approach the functions are really running in parallel, whereas in the second approach first the first call of map_async executes, then the second call.

Here is my test code: