Xref: utzoo comp.unix.internals:1982 alt.sys.sun:2650
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!island!hue
From: hue@island.COM (Pond Scum)
Newsgroups: comp.unix.internals,alt.sys.sun
Subject: fast writes interruptable on SunOS 4.1.1
Message-ID: <3666@island.COM>
Date: 7 Feb 91 09:03:19 GMT
Followup-To: alt.sys.sun
Organization: Island Graphics Corp., San Rafael, CA
Lines: 75


(It's sorta internals - it has to do with sleeping at PZERO or lower, right?)

Here is a program that shows that writes to a regular file are interruptable
and not restartable under SunOS 4.1.1.  Under SunOS 4.0.3 on Sun 3 and 4c,
HP-UX 7.0 on a 9000/370, and AIX 3.1 on an RS/6000 (no particular reason for
choosing them, that's just what's near my cube) the writes are not interrupted
and always complete.  Under SunOS 4.1.1 on a 4c, the writes are interrupted.


-----------
#include <sys/types.h>
#include <fcntl.h>
#include <sys/time.h>
#include <signal.h>
#include <stdio.h>
#include <errno.h>

static void alrm();
static char bigbuf[0x100000];
static struct sigvec v = {alrm, 0, 0};
static struct itimerval it = {{0, 500000}, {0, 500000}};	/* half sec */

static void
alrm()
{
    fputs("Ow, my head!\n", stderr);
}


main(argc, argv)
int argc;
char **argv;
{
    int i, fd, nw;

    for (i = 0; i < 0x100000; i++)
	bigbuf[i] = i & 0xff;
    sigvec(SIGALRM, &v, 0);
    setitimer(ITIMER_REAL, &it, 0);
    if ((fd = open("bigfile", O_WRONLY | O_CREAT | O_TRUNC, 0666)) < 0)
    {
	perror("bigfile");
	exit(1);
    }
    for (i = 0; i < 10; i++)
    {
	errno = 0;
	nw = write(fd, bigbuf, sizeof(bigbuf));
	if (nw < 0)
	{
	    perror("bigfile");
	}
	else if (nw != sizeof(bigbuf))
	{
	    if (errno)
	    {
		fprintf(stderr, "interrupted write, %d of %d got written\n",
			nw, sizeof(bigbuf));
	    }
	    else
	    {
		fprintf(stderr, "short write, %d of %d got written\n",
			nw, sizeof(bigbuf));
	    }
	}
    }
    return(0);
}
--
"It reminds me of how in the computer industry they use the word "user", which
 to them means "idiot"" -Dave Barry

Jonathan Hue, Senior Coding Pig	   Island Grapics Corp.  Graphic Arts Division
4000 Civic Center Drive San Rafael, CA  {uunet,sun}!island!hue  hue@island.com