[Info-vax] Shared Stream IO (SSIO) beta kit available for OpenVMS

[Johnny Billquist]

On 2013-01-28 14:31, Stephen Hoffman wrote:
> On 2013-01-28 12:54:57 +0000, Neil Rieck said:
>
>> This is great news. Thanks for working with HP OpenVMS Engineering to
>> have this developed. (speaking of UNIX portability, any idea if you
>> can get them to implement a true fork?)
>
> I can save Bill the trouble, here.
>
> Fork is not going to happen on VMS.
>
> Ever.
>
> There are existing DEC/Compaq/HP C fork-related routines available which
> make porting ~95%[1] of the C code using fork() fairly easy, but that
> last ~5%[1] of the C code around is really using the true, full
> capabilities of fork(), and analogs of those capabilities are not
> available on VMS due to the low-level architectural differences between
> VMS and Unix.  The copy-on-write memory management and the differences
> in I/O channel contexts being two examples of this.
>
> Could fork() be implemented?  Sure.  But that means either massive
> complexity and untenable overhead, or ripping up the kernel.  Or both.

copy on write is not a semantic of fork. It's just a very nice optimization.
However, the file handle duplication of fork would be more or less 
impossible to achieve in VMS. (Yes, I suppose everything is possible 
with enough work, but this one would probably be enormous.)

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol