Re: [PATCH RFA] lin-lwp.c: Block SIGCHLD events when attaching

H . J . Lu
2001-11-20T07:55:34Z

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On Tue, Nov 20, 2001 at 12:17:10AM -0700, Kevin Buettner wrote:
> On Nov 19, 11:53pm, Kevin Buettner wrote:
>
> > I just tried it. It seems to behave about the same. It usually attaches
> > okay, but I am able to reproduce the "Cannot find new threads: generic error"
> > by using Jim's trick of repeatedly attaching and detaching.
>
> I now know a little bit more about this problem.
>
> First, I should explain that I'm using Jim Blandy's trick of
>
> set height 0
> break <somewhere that will be hit by one or more threads>
> while 1
> attach <pid of main process>
> continue
> detach
> end
>
> The "Cannot find new threads: generic error" seems to occur just (or
> shortly) after one of the early threads has exited. Tomorrow, I'll
> write a test to see if it's possible at all to attach to a
> multithreaded process in which one of the threads has exited.

Here is a modified ex11.c. It is easier to reproduce the gdb bug.

H.J.

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/* Test program for timedout read/write lock functions.
Copyright (C) 2000 Free Software Foundation, Inc.
Contributed by Ulrich Drepper <drepper@redhat.com>, 2000.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */

#include <errno.h>
#include <error.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>

#define NWRITERS 15
#define WRITETRIES 10
#define NREADERS 15
#define READTRIES 15

#define TIMEOUT 1000000
#define DELAY 1000000

static pthread_rwlock_t lock = PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP;

static void *
writer_thread (void *nr)
{
struct timespec ts;
struct timespec delay;
int n;

ts.tv_sec = 1000000;
ts.tv_nsec = TIMEOUT;

delay.tv_sec = 1000;
delay.tv_nsec = DELAY;

for (n = 0; n < WRITETRIES; ++n)
{
do
{
clock_gettime (CLOCK_REALTIME, &ts);

ts.tv_nsec += 2 * TIMEOUT;

// printf ("writer thread %ld tries again\n", (long int) nr);
}
//while (pthread_rwlock_wrlock (&lock), 0);
while (pthread_rwlock_timedwrlock (&lock, &ts) == ETIMEDOUT);

printf ("writer thread %ld succeeded\n", (long int) nr);

nanosleep (&delay, NULL);

pthread_rwlock_unlock (&lock);

printf ("writer thread %ld released\n", (long int) nr);
}

return NULL;
}

static void *
reader_thread (void *nr)
{
struct timespec ts;
struct timespec delay;
int n;

delay.tv_sec = 1000000;
delay.tv_nsec = DELAY;

for (n = 0; n < READTRIES; ++n)
{
do
{
clock_gettime (CLOCK_REALTIME, &ts);

ts.tv_nsec += TIMEOUT;

// printf ("reader thread %ld tries again\n", (long int) nr);
}
//while (pthread_rwlock_rdlock (&lock), 0);
while (pthread_rwlock_timedrdlock (&lock, &ts) == ETIMEDOUT);

printf ("reader thread %ld succeeded\n", (long int) nr);

nanosleep (&delay, NULL);

pthread_rwlock_unlock (&lock);

printf ("reader thread %ld released\n", (long int) nr);
}

return NULL;
}

int
main (void)
{
pthread_t thwr[NWRITERS];
pthread_t thrd[NREADERS];
int n;
void *res;

/* Make standard error the same as standard output. */
dup2 (1, 2);

/* Make sure we see all message, even those on stdout. */
setvbuf (stdout, NULL, _IONBF, 0);

for (n = 0; n < NWRITERS; ++n)
{
int err = pthread_create (&thwr[n], NULL, writer_thread,
(void *) (long int) n);

if (err != 0)
error (EXIT_FAILURE, err, "cannot create writer thread");
}

for (n = 0; n < NREADERS; ++n)
{
int err = pthread_create (&thrd[n], NULL, reader_thread,
(void *) (long int) n);

if (err != 0)
error (EXIT_FAILURE, err, "cannot create reader thread");
}

/* Wait for all the threads. */
for (n = 0; n < NWRITERS; ++n)
pthread_join (thwr[n], &res);
for (n = 0; n < NREADERS; ++n)
pthread_join (thrd[n], &res);

return 0;
}