Re: no alloca() available - alternative?

[CRPence <CRPbottle@xxxxxxxxx>]

  FWiW: Over-consumption of the Automatic Storage will terminate a 
thread\process; i.e. resource limited within the thread [stack frames], 
versus being limited across either the system [heap, etc.] storage or 
user profile limits.  May be best to avoid the use of MODASA for an 
application with many "large" allocations and highly recursive 
utilization, to avoid that limitation.  The most negative effect is when 
the application exhausts the Automatic Storage only to a point whereby 
an invoked system program fails, possibly obfuscating the origin; i.e. 
appearing to be a defect in the OS for termination within the OS 
program, but instead, being a side effect of the actions of the 
application.  If that system program is performing auditing, then beware 
the effect of a high-impact setting for QAUDENDACN :-Q

Regards, Chuck

On 12/6/10 7:37 AM, Mark S. Waterbury wrote:
> It is not simply just a matter of replacing every occurrence of
> alloca() with malloc() ... you must also insert the corresponding
> free() calls at the appropriate place -- at the "end of scope" for
> the function (just before the function returns) ... but you must also
> consider other ways that the function could implicitly exit this
> scope, such as a longjump ... or due to exception handling.
>
> I suggest you create your own include file, called e.g. "alloca.h"
> that looks something like this (for OS/400):
>
> #ifndef _alloca_
> #define _alloca_
> #include <mih/modasa.h>
> #define alloca(s1) (modasa(s1))
> #endif
>
> This will automatically include the MIH/MODASA header file, and
> define a macro named "alloca" that changes any occurence of alloca
> in your source code to a direct call to modasa. Then, you only need
> to include this near the beginning of any source that uses alloca,
> e.g.:
>
> #include "alloca.h"
>
> On 12/6/2010 1:30 AM, Schmidt, Mihael wrote:
> > Thanx. I'll probably go that route.
> >
> > Scott Klement on Sunday, December 05, 2010 7:45 PM wrote:
> > > I'd change the ported code to use malloc(), and add code to clean
> > > up the allocations (as appropriate)
> > >
> > > That way, your code would be portable, run anywhere, etc.
> > >
> > > If you use a MI call, such as _modasa, that code will only run on
> > > IBM i... if you try to port to another system that doesn't have
> > > alloca(), you'll need a separate workaround for that system, and
> > > you end up with 20+ sections of #define macros for
> > > compatibility.
> > >
> > > Better to use malloc/free and write it in a portable fashion in
> > > the first place. (I'd only write my own alloca() if changing to
> > > malloc() would be too time-consuming.)
> > >
> > > On 12/3/2010 1:46 PM, Schmidt, Mihael wrote:
> > > > the ported software uses alloca() at some locations. Obviously
> > > >  alloca() is not support on IBM i. What is the alternative?
> > > > malloc? What do I have to take into account when changing this
> > > > to malloc? (besides freeing the memory afterwards)