[cmake-developers] kwsysProcess threadsafety

[Sebastian Holtermann]

Hello!

As you might have noticed I tried to parallelize AUTOMOC/UIC.
https://gitlab.kitware.com/cmake/cmake/merge_requests/1632
The issue that's blocking it now is that the kwsysProcess framework
isn't thread safe. As a consequence it is not possible for threads to
start processes concurrently using the kwsysProcess framework.

There are three options I see

1) Make kwsysProcess thread safe

I don't think it's impossible but it's not a small task.
Looking through the code I found a few issues that
would block the whole idea for me.
  - OpenVMS: I have little to no knowledge about OpenVMS. 
    Wikipedia says it is basically abandoned. 
    Can the OpenVMS code be removed? I couldn't test it anyway.

  - C vs. C++
    There's a lot of C in processUNIX.c (list allocation etc.).
    I would prefer to use C++11 (or higher), especially
    std::array, std::vector, std::thread,  std::mutex, etc..
    Is C++11 acceptable in kwsysProcess?
    This would make processUNIX.c processUNIX.cpp?

2) Use libuv instead

Using the libuv event loop is overkill and would probably imply that
more threads are started than necessary
(the libuv thread pool will be started anyway).
But it would allow to start multiple concurrent  (moc/uic) processes.
Is there a reason to not use libuv?

3) Abandon the idea to parallelize AUTOMOC/UIC

Well, I liked the idea.


Any thoughts?

-Sebastian