I'm considering writing a manager for background processes --- such as send a 
batch of e-mail or other process that takes a while to finish --- for a web 

I see the challenge here as just writing something that will look like a
very basic UNIX shell --- so I'll call it ``web-api-shell'' from now on.
(``Web'' because it will be used by a web system through some HTTP API.)

This thing has to be flawless. I'm looking for design principles and advice.

I don't know which language I will use, but I'd like to use Racket at
least as a prototype. I am looking at section 15.4 at


and I'm not sure it gives me all the control I need. I have a more
lower view of the job --- fork(), execve(), waitpid(), SIGCHLD. But I
suppose Racket handles this much more elegantly that I would in C.

Your advice will be very appreciated.

(*) Where will it run

It will run on GNU systems running the Linux kernel.

(*) My own thoughts

The interface to shell will be through HTTP requests, so this shell will
likely be a web server of some sort. But before I get involved in the
web at all, I need the shell working flawlessly.

So I need a laboratory first. I could write a program that reads some
named pipe on disk to get commands such as ``run this or that'' while I
work. (Later I can write a web server replacing this named-pipe

Just like a UNIX shell, this web-api-shell must know all every process
it runs. I suppose the work is essentially fork(), execve() followed by

One concern I have is the following. Is it possible for a process to
simply ``get out of'' the shell? What do I mean by that? A process
that does fork() and puts itself into background would leave the
web-api-shell's control, wouldn't it?

I think I must avoid that. Perhaps I can't let just any process run.
Perhaps the web-api-shell must only offer a few processes carefully
written by myself --- so that I know they won't put themselves in
background. (For instance, I can't let them change PIDs, otherwise I
won't have any idea who they are and that's a mess. I'd love to somehow
restrict system calls such as fork().)

(*) Serialization

I also think this web-api-shell must not be invoked in parallel. So I
guess I must use some queue of requests with no race condition and
pull each request as it comes. Any pointers on how to do this basic
thing with my zero experience?

(*) What is my level of training?

In the past I've studied many parts of

Advanced Programming in the UNIX Environment
W. Richard Stevens

I will definitely have to read it again to get work on this project.
Can you mention any UNIX concepts that are of great relevance for this
project? I don't think I ever got my mind wrapped around things like
sessions, session leaders and so on. Are these concepts relevant to
this application?

Thank you very much.

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