Re: Interrupting computations using signals

[Daniel Mendler <mail@daniel-mendler.de>]

On 5/24/21 2:53 PM, Eli Zaretskii wrote:
>> I've read something in the manual about SIGUSR1/SIGUSR2 but I could not
>> get these handlers to work in an Emacs running in daemon or batch mode.
> 
> Show us the code.

I have a file "interrupt.el" containing this code:

~~~
(defun sigusr-handler ()
  (interactive)
  (message "Caught signal %S" last-input-event))

(define-key special-event-map [sigusr1] 'sigusr-handler)
(define-key special-event-map [sigusr2] 'sigusr-handler)

(condition-case nil
    (while t
      (with-local-quit
        (while t
          (sleep-for 0.1)))
      (message "QUIT"))
  (t (message "OUTER QUIT")))
~~~

1. I start the batch process with "emacs -Q --batch -l interrupt.el" or
"emacs -Q --fg-daemon -l interrupt.el".

2. I send a SIGUSR1 signal to the process. The signal is ignored.
Nothing happens, in particular the handler is not called.

3. I send a SIGUSR2 signal to the process. The process terminates with
the message "Debugger entered--beginning evaluation of function call
form: * (setq quit-flag t)...". I neither see the "QUIT" nor the "OUTER
QUIT" message.

Daniel