Path: utzoo!attcan!uunet!wuarchive!udel!princeton!jonlab!jon
From: jon@jonlab.UUCP (Jon H. LaBadie)
Newsgroups: comp.unix.aix
Subject: Re: read ignores SIGINTR
Summary: sounds like aix tty reads are not interruptable
Message-ID: <812@jonlab.UUCP>
Date: 23 Oct 89 05:18:41 GMT
References: <1162@msa3b.UUCP>
Organization: 4455 Province Line Rd., Princeton, NJ 08540
Lines: 39

For starts, let me say I have not mucked around in the AIX kernel;
I have played with the System V kernel and my comments are based on
that experience.

In article <1162@msa3b.UUCP>, kevin@msa3b.UUCP (Kevin P. Kleinfelter) writes:
> I have a "read(2)" call in a ported program.  DEL is defined as the "intr"
> key.  The program has an exception handler for the SIGINT interrupt.
> When the read call is executed, I hit DEL, and the interrupt handler is NOT
> executed.  Then I hit RETURN, and the signal handler IS executed.
> I don't think the terminal is in RAW mode, because the signal handler is
> executed once the newline is read. ...

When a process executes a system call and enters a sleep state, the
process priority is set to a high priority level, typically between
1 and 40 (low numerically, high priority).  Within this range, two
sub-ranges exist, interuptable and non-interuptable.  Typically they
are 1-25 (non-interuptable) and 26-40 (interuptable).  Non-interuptable
priorities are used for those types of events that are pretty certain
to finish quickly.  For example, disk I/O.  Interuptable priorities are
assigned to those events that have less certain completions; for example
terminal I/O - humans can be so SSLLOOWW..

System calls at a non-interuptable only check for signals upon entry and
exit from the system call.  Your description (interupt handler invoked
upon hitting RETURN, not the DEL key) sounds like terminal I/O under AIX
is not interuptable.  Thus, signals pending would only be checked upon
exit from the system call.

> How do I make my read be in cooked mode (to allow backspace processing)
> and receive signals such as SIGINT immediately?

Now this is a different question!  Investigate "cbreak" mode to allow
cannonical processing.  It is kind of like not "raw", not "cooked",
but "rare" terminal I/O.

-- 
Jon LaBadie
{att, princeton, bcr}!jonlab!jon
{att, attmail, bcr}!auxnj!jon