[PATCH] [Lit] Use multiprocessing instead of threading

[NAKAMURA Takumi]

Daniel, FYI, --use-processes has a couple of issues on win32;

- "python llvm-lit --use-processes" fails, although lit.py runs.

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "c:\Python27\lib\multiprocessing\forking.py", line 346, in main
    prepare(preparation_data)
  File "c:\Python27\lib\multiprocessing\forking.py", line 455, in prepare
    file, path_name, etc = imp.find_module(main_name, dirs)
ImportError: No module named llvm-lit

To rename (generated) bin/llvm-lit to bin/llvm-lit.py can appease
python in this case. That said...

- Spawning spends much time by seconds. I haven't measured yet.
  I guess it would cost to pickle many objects.

Rather, I expect yet another runner, for example ninja runner on win32. ;)

2013/10/23 Daniel Dunbar <daniel at zuster.org>:
> I wanted to have a little bit of time to check out how things were on
> Windows, but I haven't found it.
>
> Off the top of my head, I think that was the main thing, other than also
> just giving it a little bake time.
>
> We could go ahead and switch the default for non-Windows and see what
> happens if you are interested...
>
>  - Daniel
>
>
> On Tue, Oct 22, 2013 at 9:23 PM, Rafael Espíndola
> <rafael.espindola at gmail.com> wrote:
>>
>> I noticed that this is still not the default. On linux check-clang
>> goes from 0m27.526s to 0m25.277s, so it would be nice to enable it.
>>
>> What is blocking switching the default?
>>
>> Cheers,
>> Rafael
>
>
>
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