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From: John Birrell <cimaxp1!jb@werple.net.au>
Subject: Nonblocking writes to pipes hang
To: hackers@FreeBSD.org
Date: Fri, 14 Jun 1996 18:27:37 +1000 (EST)
Cc: jb@cimlogic.com.au
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G'day,

We're having problems with non-blocking writes to pipes under
FreeBSD 2.1R and 2.2-current (supped middle of last week). The
test program (below) gives the following results:

OSF/1 V3.1        65536 bytes written to pipe
HPUX  V10.01       8192 bytes written to pipe
NetBSD 1.1A/i386   4096 bytes written to pipe

The program on either FreeBSD 2.1R or 2.2-current just hangs.
Only a kill -9 will interrupt it.

Can anyone explain what is going on?


#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

int 
main()
{
	char           *p_buff;
	int             desc[2];
	int             ierr = 0;
	long            num;
	size_t          buffsize = 100000;

	if ((p_buff = (char *) malloc(buffsize)) == NULL) {
		printf("Error allocating %lu bytes\n", (unsigned long) buffsize);
		ierr = 1;
	} else {
		memset(p_buff, 'a', buffsize);
		*(p_buff + buffsize - 1) = '\0';

		if (pipe(desc) != 0) {
			printf("Error %d from pipe()\n", errno);
			ierr = 1;
		} else if (fcntl(desc[1], F_SETFL, O_NONBLOCK) != 0) {
			printf("Error %d from pipe()\n", errno);
			ierr = 1;
		} else if ((num = write(desc[1], p_buff, buffsize)) < 0) {
			printf("Error %d from write()\n", errno);
			ierr = 1;
		} else {
			printf("%ld bytes written to pipe\n", num);
		}
	}

	return (ierr);
}

Thanks,

-- 
John Birrell                                CIMlogic Pty Ltd
jb@cimlogic.com.au                          119 Cecil Street
Ph  +61  3 9690 6900                        South Melbourne Vic 3205
Fax +61  3 9690 6650                        Australia
Mob +61 18  353  137