Re: How to abort a read from a socket after some time?

[Tomas Volf <~@wolfsden.cz>]

[-- Attachment #1: Type: text/plain, Size: 1502 bytes --]

Hello,

thank you very much for the email and the suggested approach, I will try it out.
I just have one more question:

On 2024-01-22 00:46:23 +0100, M wrote:
> >
> > All code below runs after handler is set:
> >
> >    (sigaction SIGALRM (lambda _ (display "Alarm!\n")))
>
> Assuming the read-char takes too long, the kernel sends a SIGALRM to Guile. Hence, the C signal handler is run (which sets some fields somewhere indicating that this handler should be run later in the sense of system-async-mark), and the syscall behind read-char returns EINTR.
>
> As this is a fake error (passing it on as a Scheme exception would result in rather messy semantics, e.g. consider the case where things are interrupted twice in a row, time such that the exception handler itself is interrupted with a new exception), Guile decides to retry the syscall

I am confused about this.  I read the documentation for sigaction, and there is
this text for the flags argument:

      -- Variable: SA_RESTART
          If a signal occurs while in a system call, deliver the signal
          then restart the system call (as opposed to returning an
          ‘EINTR’ error from that call).

Based on that my expectation was to get EINTR.  But since the syscall seems to
be restarted even without the SA_RESTART, what exactly does this flag do then?

Thank you,
Tomas Volf

--
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]