🚀 go-pugleaf

In article <92245.122042A10742@TRMETU.BITNET> A10742@TRMETU.BITNET (Pinar Aydemir) writes:

>I almost hear everyday that msdos is non-reentrant.
>It is non re-entrant so dont call a dos funcion from a Interrupt Service
>Routine.
>Since It is non reentrant, bla bla bla.

>I looked at some books about OS, and the definition of reentrancy is
>given as being unmodified (pure) code.So, what makes msdos non reentrant ?
>Any information  is appreciated.
>-Yasemin

When performing a DOS call, some routines use Static data space, (rather than
allocating memory on a stack). If you interrupt a DOS call to perform the 
same function(or on fro the same family, (even if you save all the 
registers) you can still trash the original data. And after your TSR exits
DOS continues with corrupted data. 

Reentrancy is not dependent on pure code, it simply requires that a 
routine may call itself, or be interupted and called by another routine
WITHOUT SIDE EFFECTS. To wit (I always wanted to say that) each time 
the code begins, all data must be allocated on a stack (no static data 
blocks!!!!!).