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Re: Query about Emacs Process API | Asynchronous processes

From: Narendra Joshi
Subject: Re: Query about Emacs Process API | Asynchronous processes
Date: Wed, 08 Jul 2020 00:26:38 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)

Narendra Joshi <> writes:

> Stefan Monnier <> writes:
>>> I read that section of the manual. I am still not sure what will be the
>>> use cases for this. Where in Emacs (or the package ecosystem) is this
>>> feature being used currently?
>> I think it's used for `ielm`.
>>         Stefan
> `ielm` seems to be adding a dummy process to its buffer using either
> `cat` or `hexl` binary.
>   ;; A dummy process to keep comint happy. It will never get any input
>   (unless (comint-check-proc (current-buffer))
>     ;; Was cat, but on non-Unix platforms that might not exist, so
>     ;; use hexl instead, which is part of the Emacs distribution.
>     (condition-case nil
>         (start-process "ielm" (current-buffer) "hexl")
>       (file-error (start-process "ielm" (current-buffer) "cat")))
>     (set-process-query-on-exit-flag (ielm-process) nil)
>     (goto-char (point-max))

I, finally, found the reason for adding it. It's being used by
`gdb-mi.el`. I am still not sure how and why because I am not familiar
with `gdb-mi`.

#+begin_src emacs-lisp
;; We want to use comint because it has various nifty and familiar features.
(define-derived-mode gdb-inferior-io-mode comint-mode "Inferior I/O"
  "Major mode for gdb inferior-io."
  :syntax-table nil :abbrev-table nil
  (make-comint-in-buffer "gdb-inferior" (current-buffer) nil))

The feature was added to `make-process` for `gdb-mi.el` in this commit: 

#+begin_src vc-git-log-view
Author: Nick Roberts <>
Date:   Thu Aug 13 13:22:55 2009 +0000

    (create_pty): New function.
    (Fstart_process): Use it to allow Emacs to just associate a pty
    with the buffer.  See associated change in gdb-mi.el.
    (list_processes_1): Deal with no program name.
    (start_process_unwind): Use pid == -2 to mean no process.

Narendra Joshi

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