From owner-freebsd-hackers  Mon Feb 26 12:58:46 2001
Delivered-To: freebsd-hackers@freebsd.org
Received: from akira.lanfear.com (akira.lanfear.com [208.12.11.174])
	by hub.freebsd.org (Postfix) with ESMTP id 5854737B491
	for <freebsd-hackers@freebsd.org>; Mon, 26 Feb 2001 12:58:37 -0800 (PST)
	(envelope-from mwlist@lanfear.com)
Received: from sapporo.lanfear.com (h-64-105-36-216.snvacaid.covad.net [64.105.36.216])
	by akira.lanfear.com (8.9.3/8.9.3) with SMTP id MAA39013
	for freebsd-hackers@freebsd.org; Mon, 26 Feb 2001 12:58:36 -0800 (PST)
	(envelope-from mwlist@lanfear.com)
Date: Mon, 26 Feb 2001 12:58:36 -0800 (PST)
From: Marc W <mwlist@lanfear.com>
Message-Id: <200102262058.MAA39013@akira.lanfear.com>
To: freebsd-hackers@freebsd.org
Subject: Why does a named pipe (FIFO) give me my data twice ???
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
X-Mailer: Kiltdown 0.7
Sender: owner-freebsd-hackers@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG


hello!

    I've got a program that creates a named pipe, and then spawns a
thread
which sits in a loop:

    // error checking snipped.
    //
    while (1) {
        int fifo = open(fifoPath, O_RDONLY);  // this blocks
        fprintf(stderr, "somebody opened the other end!\n");
        read(fifo, buf, sizeof(buf));
        fprintf(stderr, "got the following data: %s\n", buf);
        close(fifo);
    }

    i then have another instance of the same program do the following:

    fifo = open(fifoPath, O_WRONLY);
    write(fifo, buf, strlen(buf);


    now, the problem is that the first process succeeds suddenly for
the
open, reads the data, closes the fifo, and IMMEDIATELY SUCCEEDS THE
open(2)
again, reading in the same data.
 After that, all is as expected.  

    Note that this doesn't happen ALL the time -- only about 80% of the
time.

    Any idea why this would happen?

    Thanks!

    marc.



To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message