From: Ken Brown <kbrown@cornell.edu>
To: cygwin <cygwin@cygwin.com>
Cc: Michael Haubenwallner <michael.haubenwallner@ssi-schaefer.com>
Subject: Fork problems on master branch
Date: Sat, 08 Jun 2019 19:44:00 -0000 [thread overview]
Message-ID: <330c76fd-af22-beb9-08b6-707c73df3b75@cornell.edu> (raw)
[-- Attachment #1: Type: text/plain, Size: 1182 bytes --]
Earlier today I reported on the cygwin-patches list a fork problem with a
cygwin1.dll built from the master branch of the Cygwin source repo. See
https://cygwin.com/ml/cygwin-patches/2019-q2/msg00155.html. A bisection showed
that commit f03ea8e1 was the first bad commit for the problem being discussed there.
I've just run into a second fork problem for which I think the same commit is
the first bad one. I can't be positive, because the problem is sporadic, so I
might have marked some bad commits as good if I didn't run the test enough times.
The test case for this (attached) is one that I used when testing my new FIFO
code. Normally I run this program in one terminal and type
echo blah > /tmp/myfifo
in a second terminal. For the present purposes, however, you can skip the
second part and simply terminate fifo_fork_test with C-c.
In my testing, I found that running the test program would yield "read: Bad
address" about 1 out of 10 times. Occasionally I would get "read: Communication
error on send" instead. Both error messages indicate a problem with the child
process reading from an fd inherited from the parent.
Ken
[-- Attachment #2: fifo_fork_test.c --]
[-- Type: text/plain, Size: 1071 bytes --]
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/wait.h>
int
main ()
{
int fd;
ssize_t nbytes;
char buf[6];
if (mkfifo ("/tmp/myfifo", S_IRUSR | S_IWUSR | S_IWGRP) < 0
&& errno != EEXIST)
{
perror ("mkfifo");
exit (-1);
}
if ((fd = open ("/tmp/myfifo", O_RDWR)) < 0)
/* if ((fd = open ("/tmp/myfifo", O_RDONLY)) < 0) */
{
perror ("open");
exit (-1);
}
switch (fork ())
{
case -1:
perror ("fork");
exit (-1);
case 0: /* Child. */
nbytes = read (fd, buf, 5);
if (nbytes != 5)
{
perror ("read");
exit (-1);
}
buf[5] = '\0';
printf ("child read %d bytes: %s\n", nbytes, buf);
if (close (fd) < 0)
{
perror ("child close");
exit (-1);
}
exit (0);
default: /* Parent. */
if (close (fd) < 0)
{
perror ("parent close");
exit (-1);
}
printf ("parent waiting for child to read\n");
wait (NULL);
break;
}
}
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next reply other threads:[~2019-06-08 19:44 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-08 19:44 Ken Brown [this message]
2019-06-09 16:51 ` Ken Brown
2019-06-23 17:14 ` Ken Brown
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