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 system.
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 https://docs.racket-lang.org/reference/os.html 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 interface.) 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 waitpid(). 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. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/hRIrZF2NP2tUKP8_HV2lLkFr95li_XmhSrzbJCuR1ruwDxy2qyWgC-vREZPyrJMn0oUWj3N6gzSlQ1PBvs_FrwErvOInegt-CQGpPjDG2gw%3D%40protonmail.com.
