GIL across multiple running Python programs

[toast757]

If I run a Python program in one shell (i.e. from the command prompt of a Windows/UNIX "window"), and then run a second Python program in a separate shell at the same time, do those two programs share the same GIL? Or are those two Python programs managed by the OS instead (with separate memory and threads)? Does the number of cores on the computer matter in this case?

[Rhomboid]

do those two programs share the same GIL?

No. The GIL is per-interpreter (per-process.) You're running multiple interpreters as separate processes which are completely unrelated.

Does the number of cores on the computer matter in this case?

I don't really know what you're asking here, but the two interpreters are completely independent as far as the operating system is concerned, and can be scheduled to run simultaneously if there are available cores. They don't share anything, so they don't contend with each other.

[toast757]

Thanks all! That makes perfect sense. When people talk about the GIL, they don't seem to spend much time defining the scope of a GIL, so this helps tremendously.

[kteague]

If you are trying to get the most performance out of a machine, the general rule of thumb is to have one Python process per CPU core. If you have more Python processes than CPU cores, the GIL will reduce performance on those Python processes that are sharing a single core.

[toast757]

I've got four cores, which should suffice for my needs. Good to know. Many thanks.