threading issues with D -> C -> Python

[Michael via Digitalmars-d-learn]

On Wednesday, 3 December 2014 at 02:41:11 UTC, ketmar via 
Digitalmars-d-learn wrote:
> On Wed, 03 Dec 2014 02:21:45 +0000
> Michael via Digitalmars-d-learn 
> <digitalmars-d-learn at puremagic.com>
> wrote:
>
>> Thanks for this. Its definitely a step in the right direction. 
>> Would you mind explaining a bit more about the problem here, 
>> if you can? I don't fully understand why the garbage collector 
>> needs to know about the threads, and if so for how long does 
>> it need to know? If I put in 
>> "thread_attachThis();scope(exit)thread_detachThis();" it 
>> doesn't appear to fix my problems, so I'm definitely curious 
>> as to what is going on under the hood.
> you have to call `thread_attachThis();` in "alien" thread, not 
> in D
> thread. i.e. if you created thread from python code, you have 
> to call
> `thread_attachThis();` in that python thread (i don't know how 
> you'll
> do that, but you must ;-). and you must call 
> `thread_detachThis();`
> from the same python thread before exiting from it.
>
> garbage collector must know about all running threads so it can 
> scan
> their stacks, variables and so on. as there is no portable way 
> to set
> application-wide hooks on thread creation and termination, you 
> must
> inform GC about that events manually.
>
> the other thing you can do is to not use any D allocated data in
> "alien" threads. i.e. don't pass anything that was allocated by 
> D code
> to python thread and vice versa. if you want to pass some data 
> to
> "alien" thread, `malloc()` the necessary space, copy data to it 
> and
> pass malloc'ed pointer. don't forget to free that data in 
> "alien"
> thread. but i think that this is not what you really want, as 
> it means
> alot of allocations and copying, and complicates the whole 
> thing alot.
>
>
> "alien" is the thread that was created outside of D code.

Okay. Well I am already not passing any D-allocated data. I'm 
specifically creating variables/arrays on the C-stack, and then 
passing the pointer of that to D and overwriting the data of the 
C-stack pointer for any return values. I was worried about that 
specific problem and I thought this would be a solution. I am 
then able to tell python to use the C-stack variable without 
having to worry about D trying to run any garbage collection on 
it.

Going the other way, I probably am passing some python strings 
etc.. into D, but I would assume they are valid for the lifetime 
of the function call, and that D would have no reason to try and 
perform any garbage collection on them.