Automatic multithreading systems and resources/queries

[Tonaion02]

Hello guys, i have a question.
I know that if you put in arguments of a function the resources to retrieve and the queries to make, the systems are automatically parallelized.
I know that you can retrieve resources or make query in the corpe of a function, but in the case where i do in that way, what happens to automatic multithreading between systems? It doesn't work anymore?

[SkiFire13]

I know that you can retrieve resources or make query in the corpe of a function

Do you mean when using a &mut World parameter? In that case while your system is running no other system can, since your system is the only one that can access any part of the world.

[SkiFire13]

Yes, a Commands parameter won't prevent your system from being run in parallel with other systems.

However note that the phase when the commands are applied later on will not run in parallel because it takes a &mut World.

[Tonaion02]

Thx a lot!

[Tonaion02]

Hello, i have another doubt, if i have multiple systems with a Commands parameter, they can run in parallel? The documentation suggested that Commands is really a queue, so probably can run in parallel, am i wrong?

[SkiFire13]

Yes, two systems with Commands can run in parallel (of course the other parameters must also be compatible with each other). Each system has its own queue, so they don't conflict on that (as opposed to for example EventWriter, which writes to a queue but that's a in a resource and so it's shared between all systems)

[Tonaion02]

Ok thx a lot!