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From: Richard Kettlewell <invalid@invalid.invalid>
Newsgroups: comp.os.linux.misc
Subject: Re: The joy of pipes
Date: Sun, 17 Nov 2024 08:42:12 +0000
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"186282@ud0s4.net" <186283@ud0s4.net> writes:
> On 11/16/24 5:31 AM, Richard Kettlewell wrote:
>> Louis Krupp <lkrupp@invalid.pssw.com.invalid> writes:

>>>> But, really, they're just temp files the parent process can access.
>>>
>>> Pipes *could* be implemented with temporary disk files, at least to an
>>> extent, but as far as I can tell, they're not.
>>
>> “Temporary files the parent can access” is not a good model for a
>> couple of reasons:
>>
>> * The semantics are different. Bytes read from a regular file are
>>   still there to be read again if you rewind the file; bytes read from
>>   a pipe are gone. Empty/full files behave differently to empty/full
>>   pipes.
>>
>> * Temporary regular files can already be accessed by other processes
>>   by name, by file descriptor inheritance, or file descriptor passing.
>
>   Didn't say temp disk files were necessarily SUPERIOR,

Indeed. You said they’re really the same, which they’re not.

>   just that they CAN do most of the stuff pipes are used for and in an
>   easier user/code-friendly fashion.

There’s certainly an overlap in the end goals you can meet with them,
but even within that overlap they’re used in slightly different ways.

>   SIZE is almost unlimited too.

Capacity is one of the ways in which they are very different, already
alluded to above.

>   Anyway, I'd made some TCP/UDP servers but the parent needed
>   to know the status of the children in a little more detail
>   than just a tiny return code - might want to terminate the
>   child if it'd been idle for awhile, might want to know how
>   much bandwidth was being used, might want to pick a good
>   time to do some maint routines, might want to know WHO the
>   connections were from. Pipes were the (relatively) easy
>   'C'-approved method and did the job very well.

I’ve no idea what you think “’C’-approved” means. C is a programming
language, not a set of guidelines. Pipes are an OS concept, not
appearing in the C language standard.

-- 
https://www.greenend.org.uk/rjk/