From: cgf AT bbc DOT com (Christopher Faylor)
Subject: Re: Signals in b19 - please help
8 Mar 1998 16:27:42 -0800
Message-ID: <EpIC3G.9M0.cygnus.gnu-win32@bbc.com>
References: <C1A9DAABC292D111A4D90000F879A2BA0E86 AT NTMAIL>
Reply-To: cgf AT bbc DOT com
To: gnu-win32 AT cygnus DOT com

In article <C1A9DAABC292D111A4D90000F879A2BA0E86 AT NTMAIL>,
Ian Collins  <Ian AT kiwiplan DOT co DOT nz> wrote:
>Can someone help me. I have a problem with signal handling (notably
>alarm calls) on b19. The problem was also around in b18, but I was
>hoping....
>
>The problem can be shown in an example program, as follows,
>
>#include <stdio.h>
>#include <signal.h>
>
>/*
> Designed to test the alarm calls.
> */
>main()
>{
>  int ch;
>  extern void handler();
>  while (1) {
>    printf("Setting alarm\n");
>    if (signal(SIGALRM, handler) == SIG_ERR) return -1;
>    alarm(5);
>    printf("Set alarm. Getting input\n");
>    ch = getchar();
>    printf("getchar returned %d\n", ch);
>  }
>}
>
>void handler()
>{
>  printf("In handler. I want getchar to return now like Unix does\n");
>}
>
>When this program is run on most Unix machines (OK, AIX needs kicking to
>get it to work), the getchar will return after the timeout occurs.
>What we see however is that after the timeout handler is called, the
>getchar does not return, it still waits for a character to be input.
>
>Is there any way I can get getchar to interrupt and return? This is a
>showstopper for me ar present. Can anyone help!

You've hit one of the biggest problems in cygwin but I don't know of any
way around this behavior due to Win32 behavior.  It is not possible to
interrupt a blocking read in Win32.  That's what you're expecting in the
code above.

I wish there was some way to do this in a way that worked on all
implementations of Win32 but I'm not aware of any.  Sorry.
-- 
http://www.bbc.com/	cgf AT bbc DOT com			"Strange how unreal
VMS=>UNIX Solutions	Boston Business Computing	 the real can be."
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