[Info-vax] What is a section file? How is it helpful? Is a TPU$SECTION file a section file?

[Johnny Billquist]

On 2022-09-02 02:36, Arne Vajhøj wrote:
> On 9/1/2022 12:53 PM, Stephen Hoffman wrote:
>> On 2022-08-31 00:07:29 +0000, Arne Vajhj said:
>>
>>> On 8/30/2022 6:10 PM, Stephen Hoffman wrote:
>>>>
>>>> A section file...
>>>>
>>>> ...is a form of persistent storage available for in-memory data 
>>>> structures.
>>>>
>>>> ...can be used to persist a user-written or third-party in-memory 
>>>> database.  Or can persist a pile of shared data structures. Or other 
>>>> such.
>>>>
>>>> ...lacks any database-like APIs and features; it's a means to map 
>>>> (transfer) arbitrary user data from persistent storage into memory, 
>>>> and from memory into persistent storage.
>>>>
>>>> ...sections are the underpinning of Fortran COMMON, the C/Unix 
>>>> mmap() APIs, of parts of TPU customizations, and related mechanisms.
>>>
>>> I agree with everything except the Fortran common block thing.
>>>
>>> A Fortran common block is a psect, but not this kind of section (per 
>>> default - it can of course be mapped like any other memory).
>>
>> Sure.
>>
>> It's a section of virtual memory with backing (and sharable) storage, 
>> with the salient difference being whether it uses static 
>> mapping—Fortran, BASIC, C, etc., common storage involving the 
>> linker—or use dynamic mapping—run-time calls to $crmpsc, etc.
> 
> ????
> 
> A Fortran common block does not share data between processes
> and does not map data to disk.
> 
> It is basically just a named bundle of global variables.
> 
> (VAX C and DEC C with /EXTERN=COMMON_BLOCK use the same
> construct for global variables)
> 
> To share with other processes or map data to disk something
> more is needed like mapping it via SYS$CRMPSC or SYS$MGLBSC.
> 
> Or a bit more old fashioned. Use the common block in
> a block data and build that to a shareable installed
> writeable image.

I just love how this is identical to RSX (again). :-D

   Johnny