Re: gcopy_avma() is wasting stack memory compared to gcopy()

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

On Wed, Jul 05, 2017 at 06:44:33PM +0200, Bill Allombert wrote:
> > gcopy_avma is needed for pthread.c, but not with this semantic, since
> > the threads share the universal constants, but not the same PARI stack.
> 
> I have just found that gcopy_avma in pthread.c was causing problem
> because it does not handle stack overflow.
> 
> ? default(threadsize,"1M")
> ? my(P=polmodular(101));pareval(vector(10,i,()->P*Mod(1,101)))
>   *** polmodular: Warning: increasing stack size to 16000000.
>   *** polmodular: Warning: increasing stack size to 32000000.
>   ***   Warning: increasing stack size to 64000000.
>   ***   at top-level: my(P=polmodular(101));pareval(vector(10,i,()->
>   ***                                       ^------------------------
>   *** pareval: bug in PARI/GP (Segmentation Fault), please report.
> 
> So we need something better.

I have fixed this problem by switching the stack and using regular
gcopy. This is a bit ugly, but this handles stack overflow correctly.

For that reason, I find gcopy_avma rather dangerous to use.
Maybe we should replace it by a function that handle stack overflow
correctly.

Cheers,
Bill.