Optionally enforce algorithm to pick the default device

[keryell]

When using some weird devices or debugging OpenCL stacks & compilers, it does not make sense to run the application on anything else.

If I correctly understand find_default_device()algorithm in https://github.com/boostorg/compute/blob/master/include/boost/compute/system.hpp#L210 on using the very handyBOOST_COMPUTE_DEFAULT_ variables, when some criteria cannot be fulfilled we fall-back on returning the first GPU found, etc.

So I'd like to add another variable environment for example (BOOST_COMPUTE_DEFAULT_ENFORCE? Bike-sheding welcome! :-) ) to change the selection algorithm to throw when a BOOST_COMPUTE_DEFAULT_ variable is set but the criteria cannot be fulfilled.

Any comment?

I can write a PR.

[jszuppe]

How throwing an exception would be helpful in such situations? I mean if you forget to set environment variables so find_default_device() picks device you want to use, you can always forget about adding `BOOST_COMPUTE_DEFAULT_ENFORCE.

[jszuppe]

I mean, if it's not about forgetting to set environment variables, how otherwise would it be possible there is no device you want to use?

[kylelutz]

@keryell I think I understand what you're getting at. If you could submit a PR with the proposal that would be great! Thanks!

[jszuppe]

I'm waiting for that PR ;)

[keryell]

Yes I know. :-(
But I am quite busy with a lot of deadlines. Such as the Khronos face-to-face meeting next week.
Perhaps see you there?

[jszuppe]

Yes I know. :-( But I am quite busy with a lot of deadlines.

Sure :) I understand. Just remember it's assigned to you.

Such as the Khronos face-to-face meeting next week. Perhaps see you there?

Maybe you'll hear me :), but it seems I won't be there in person.

[ddemidov]

Do you guys mean something like ddemidov@a7aa6cb?

[jszuppe]

Yes, I think so :) @keryell?

[jszuppe]

Implemented in #712.

[keryell]

Amazing!
@ddemidov you are motivating me to procrastinate... :-)