Deprecate --[kokkos-]threads command line argument in favor of --[kokkos-]num-threads

[dalg24]

Rational: consistency

environment variable	command line argument
N/A	--[kokkos-]help
KOKKOS_DISABLE_WARNINGS	--kokkos-disable-warnings
KOKKOS_TUNE_INTERNALS	--kokkos-tune-internals
KOKKOS_NUM_THREADS	--[kokkos-]threads
KOKKOS_NUMA	--[kokkos-]numa
KOKKOS_DEVICE_ID	--[kokkos-]device-id
KOKKOS_NUM_DEVICES	--[kokkos-]num-devices (optional 2nd INT to skip)
KOKKOS_SKIP_DEVICE	2nd INT value with --[kokkos-]num-devices
KOKKOS_RAND_DEVICES

It was pointed out on the developer channel on Slack that --kokkos-disable-warnings and --kokkos-tune-internals do not have without the kokkos- prefix. I would prefer not settling this here. I tend to think we should only have supported --help.

[dalg24]

Here is a link to the documentation https://github.com/kokkos/kokkos/wiki/Initialization#51-initialization-by-command-line-arguments

Note that the changes proposed here are consistent with the naming of the data member Kokkos::InitArguments::num_threads
https://github.com/kokkos/kokkos/wiki/Initialization#52-initialization-by-struct

[dalg24]

Wiki is actually outdated (missing tune_internals and other kokkos-tools options)

kokkos/core/src/Kokkos_Core.hpp

Lines 84 to 94 in 999c208

	struct InitArguments {
	int num_threads;
	int num_numa;
	int device_id;
	int ndevices;
	int skip_device;
	bool disable_warnings;
	bool tune_internals;
	bool tool_help = false;
	std::string tool_lib = {};
	std::string tool_args = {};

For reference, below is a table that includes the data members from the Kokkos::InitArguments struct

environment variable	command line argument	Kokkos::InitArguments data member
N/A	--[kokkos-]help
KOKKOS_DISABLE_WARNINGS	--kokkos-disable-warnings	disable_warnings
KOKKOS_TUNE_INTERNALS	--kokkos-tune-internals	tune_internals
KOKKOS_NUM_THREADS	--[kokkos-]threads	num_threads
KOKKOS_NUMA	--[kokkos-]numa	num_numa
KOKKOS_DEVICE_ID	--[kokkos-]device-id	device_id
KOKKOS_NUM_DEVICES	--[kokkos-]num-devices (optional 2nd INT to skip)	ndevices
KOKKOS_SKIP_DEVICE	2nd INT value with --[kokkos-]num-devices	skip_device
KOKKOS_RAND_DEVICES

[JBludau]

Strongly in favor of this change. Just makes perfect sense to have a consistent naming prefix

[fnrizzi]

@dalg24 now there is this:

• KOKKOS_NUMA, --[kokkos-]numa, num_numa
  why not changing it to:
• KOKKOS_NUM_NUMA, --[kokkos-]numa, num_numa
  so that it is consistent with threads?
  If we want to keep KOKKOS_NUMA then I personally would do numa for the InitAguments

[dalg24]

I noticed the inconsistency (so did I for Kokkos::InitArguments::ndevices) but these may be more controversial and I did not want to tie the fate of the PR to them.
Note that making changes to the data members in the struct might be tricky with respect to backward compatibility.