On Mon, 18 Nov 2024 22:50:41 -0500, 186282@ud0s4.net wrote:

> yer passing "blocks of information" between processes.

Pipes actually pass streams of information. And they won’t let you read
what hasn’t been written yet, or write too much beyond what hasn’t been
read yet.

In other words, they provide automatic synchronization between readers and
writers.

On 19 Nov 2024 04:50:15 GMT, Robert Riches wrote:

> A named pipe let mplayer write to a named file.

Another example is playing an audio file to a phone call made through the
Asterisk telephony engine. It wants the audio to be in a specific format
(e.g. GSM), while the original file might be in an entirely different
format. It’s easy enough to use FFmpeg to convert on the fly in real time.
The Asterisk playback command expects a file name, and I found that a
named pipe would work (bar a warning or two about it not being seekable).
Net result -- no need to pre-convert the audio or save temporary files
anywhere. And the pipe itself provides automatic synchronization between
the source (FFmpeg) and the sink (Asterisk).

On 19/11/2024 03:50, 186282@ud0s4.net wrote:
> Temporary files on a RAMdisk are fine (but slower).
not if it never gets to disk, but is all in cache

--
The New Left are the people they warned you about.

"186282@ud0s4.net" <186283@ud0s4.net> writes:
> Dunno why everybody seems so keen to slag anybody
> who doesn't do it/see it exactly like some high-holy
> manual from 1982 says you're supposed to. That's
> no fun !

Without comment:

| As I said somewhere, if your child processes are sending
| megabytes back to the parent you're DOING SOMETHING WRONG.

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

On 11/18/24 17:54, rbowman wrote:
> On Mon, 18 Nov 2024 11:05:03 +0000, Pancho wrote:
>
>> I don't know if Linux provides message queues as a primitive, or not. I
>> meant I used message queue protocols (MQTT,zeroMQ, ActiveMQ).
>
>
> https://www.softprayog.in/programming/interprocess-communication-using-
> system-v-message-queues-in-linux
>
> https://www.softprayog.in/programming/interprocess-communication-using-
> posix-message-queues-in-linux
>
> I've only used System V queues. Neither work like ActiveMQ.

I was never particularly interested in the nitty gritty, when I say I
used ActiveMQ, I meant I used a wrapper API that used ActiveMQ, I think
JMS. I generally liked to decouple my software development from specific
implementations. It made my skills more transferable, less dependent on
a specific development stack.

So, for me all queues tended to be just Enqueue/Dequeue, FIFO, data
structures. The queue provider was mainly to shield me from the
complexity of dealing with monitoring and reliability issues involved in
handling a remote service.

I was just curious when this thread started commenting on what pipes
were and I realised I had never programmed them, and hence gained a
proper understanding. That has a knock on effect that I don't really
understand the behaviour of programs which do use pipes. I'm presuming
bash commands uses pipes.

On Tue, 19 Nov 2024 09:57:47 +0000, Pancho wrote:

> That has a knock on effect that I don't really
> understand the behaviour of programs which do use pipes. I'm presuming
> bash commands uses pipes.

As should be apparent by now, pipes are more than a substitute for
temporary files, they are an IPC/synchronization mechanism.

Consider this C program <https://gitlab.com/ldo/slow_dbus_server>, and see
how a pipe is used to send a termination notification from a worker thread
back to the main thread.