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From: arman@oahu.cs.ucla.edu (Arman Bostani)
Newsgroups: comp.unix.wizards
Subject: problems with async. I/O on streams
Message-ID: <27197@shemp.CS.UCLA.EDU>
Date: 18 Sep 89 06:25:13 GMT
Sender: news@CS.UCLA.EDU
Reply-To: arman@oahu.cs.ucla.edu (Arman Bostani)
Organization: UCLA Computer Science Department
Lines: 100

Pardon me if this question has been asked already ...

I have been trying to get asynchronous I/O with streams working on
sys-V to no avail. I have written a small program doing async. I/O
with streams that works perfectly fine on a Sun-3 running 4.0.3. The
program works by performing an I_SETSIG ioctl operation on stdin.

When I have tried it on a couple of boxes running sys-V rel. 3.2,
however, the ioctl returns an EINVAL (invalid argument) error. 

The streamio(7) manual has a little blurb about the fact that one will
recieve an EINVAL if the file descriptor "is linked below a multiplexer". 

Has anyone seen this problem before?
Is it possible at all to do async. I/O on ttys?
If so, how does one go about it?

I have included the text of a small program which runs into the
problem mentioned above.

Thanx for the help,
arman.

---------------------------------

#include <fcntl.h>
#include <signal.h>
#include <stropts.h>
#include <stdio.h>

#if	defined(FNDELAY)
#   define NODELAY	FNDELAY
#elif	defined(O_NDELAY)
#   define NODELAY	O_NDELAY
#else
    CROAK
#endif

#ifndef SIGPOLL
#	define SIGPOLL SIGIO
#endif 

static	int 	flags;

/*
 * Called when we get a SIGPOLL. We read available input and spit it
 * out in hex.
 */
handler()
{
	int	c;

	fprintf(stderr, "got signal ...\n");

	while((c = getchar()) != EOF) {
		fprintf(stderr, "char == 0x%x\n", c);
	}
}

bye()
{
	fcntl(0, F_SETFL, flags &= ~NODELAY);	/* reset to blocking I/O */
	exit(0);
}

main()
{
	/* asynchronous I/O interrpt handler */

	signal(SIGPOLL, handler);

	/* reset to blocking mode and exit on intr, quit */

	signal(SIGINT, 	bye);
	signal(SIGQUIT, bye);

	/*
	 * put stdin in non-blocking mode.
	 */
	flags = fcntl(0, F_GETFL);
	fcntl(0, F_SETFL, flags |= NODELAY);

	/*
	 * request SIGPOLL when input is available
	 */
	if (ioctl( 0, I_SETSIG, S_INPUT ) < 0) {
		perror("ioctl"); 
		exit(1);
	}

	printf("type some chars followed by a carriage return to test.\n");
	printf("type interrupt key to exit.\n");

	/* loop forever, waiting for SIGPOLLs */
	for (;;) ;
}


-- Arman Bostani	// UCLA Computer Science Department
-- arman@CS.UCLA.EDU	// ...!(ucbvax,rutgers)!ucla-cs!arman