Re: [9fans] off-topic linux threading bug complaint

[bs <bs@abc.com>]

Works for me...
[bs@rebox temp]$ uname -a
Linux rebox 2.4.20-31.9 #1 Tue Apr 13 17:41:45 EDT 2004 i686 i686 i386
GNU/Linux
[bs@rebox temp]$ cat /etc/redhat-release
Red Hat Linux release 9 (Shrike)
[bs@rebox temp]$ gcc x.c -lpthread
[bs@rebox temp]$ ./a.out &
[1] 3909
[bs@rebox temp]$ ps -ef|grep a.out
bs        3909  2249  0 14:13 pts/0    00:00:00 ./a.out
bs        3928  2281  0 14:14 pts/1    00:00:00 grep a.out
[bs@rebox temp]$ gdb a.out 3909
GNU gdb Red Hat Linux (5.3post-0.20021129.18rh)
Copyright 2003 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i386-redhat-linux-gnu"...
Attaching to program: /home/bs/temp/a.out, process 3909
Reading symbols from /lib/libpthread.so.0...done.
[New Thread 32769 (LWP 3911)]
[New Thread 16386 (LWP 3913)]
Loaded symbols for /lib/libpthread.so.0
Reading symbols from /lib/libc.so.6...done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib/ld-linux.so.2...done.
Loaded symbols for /lib/ld-linux.so.2
0x4002ae0d in __pthread_sigsuspend () from /lib/libpthread.so.0
(gdb) where
#0  0x4002ae0d in __pthread_sigsuspend () from /lib/libpthread.so.0
#1  0x4002a69d in __pthread_wait_for_restart_signal ()
    from /lib/libpthread.so.0
#2  0x40027506 in __pthread_do_exit () from /lib/libpthread.so.0
#3  0x40027398 in pthread_exit () from /lib/libpthread.so.0
#4  0x0804845c in main ()
#5  0x4008862d in __libc_start_main () from /lib/libc.so.6
(gdb) q
The program is running.  Quit anyway (and detach it)? (y or n) y
Detaching from program: /home/bs/temp/a.out, process 3909
[bs@rebox temp]$

> I'm sorry for the off-topic post, but I have no idea
> where to send this and I suspect there are still Linux
> experts lurking here who do.  Please feel free to forward.
>
> 	$ uname -a
> 	Linux t23 2.6.8-1-686 #1 Thu Oct 7 03:15:25 EDT 2004 i686 GNU/Linux
> 	$
>
> This program creates a second pthread and then
> lets the first pthread exit:
>
> 	$ cat x.c
> 	#include <stdio.h>
> 	#include <unistd.h>
> 	#include <pthread.h>
>
> 	void*
> 	sleeper(void *a)
> 	{
> 		for(;;)
> 			sleep(1000);
> 	}
>
> 	int
> 	main(void)
> 	{
> 		pthread_t id;
>
> 		pthread_create(&id, 0, sleeper, 0);
> 		pthread_exit(0);
> 	}
> 	$ gcc x.c -lpthread
> 	$ ./a.out &
> 	[1] 4723
> 	$
>
> Because the first pthread has exited, the ps listing
> makes it look like the process is a zombie, even
> though it's still running:
>
> 	$ ps axwwu|grep a.out |grep -v grep
> 	rsc       4723  0.0  0.0     0    0 pts/2    Z    13:29   0:00
> [a.out] <defunct>
> 	$
>
> The -T and -L flags to ps don't help:
>
> 	$ ps -T axwwu|grep a.out |grep -v grep
> 	$ ps -L axwwu|grep a.out |grep -v grep
> 	$
>
> It's not ps just misdisplaying information: gdb cannot attach either.
>
> 	$ gdb a.out 4723
> 	GNU gdb 6.1-debian
> 	Copyright 2004 Free Software Foundation, Inc.
> 	GDB is free software, covered by the GNU General Public License, and you are
> 	welcome to change it and/or distribute copies of it under certain conditions.
> 	Type "show copying" to see the conditions.
> 	There is absolutely no warranty for GDB.  Type "show warranty" for details.
> 	This GDB was configured as "i386-linux"...Using host libthread_db
> library "/lib/tls/libthread_db.so.1".
>
> 	Attaching to program: /home/rsc/a.out, process 4723
> 	ptrace: Operation not permitted.
> 	/home/rsc/4723: No such file or directory.
> 	(gdb) quit
> 	$
>
> On the other hand, if I guess the process/thread id of the
> second pthread, then I can still look at that:
>
> 	$ gdb a.out 4724
> 	GNU gdb 6.1-debian
> 	Copyright 2004 Free Software Foundation, Inc.
> 	GDB is free software, covered by the GNU General Public License, and you are
> 	welcome to change it and/or distribute copies of it under certain conditions.
> 	Type "show copying" to see the conditions.
> 	There is absolutely no warranty for GDB.  Type "show warranty" for details.
> 	This GDB was configured as "i386-linux"...Using host libthread_db
> library "/lib/tls/libthread_db.so.1".
>
> 	Attaching to program: /home/rsc/a.out, process 4724
> 	Reading symbols from /lib/tls/libpthread.so.0...done.
> 	[Thread debugging using libthread_db enabled]
> 	[New Thread 1083603888 (LWP 4724)]
> 	Loaded symbols for /lib/tls/libpthread.so.0
> 	Reading symbols from /lib/tls/libc.so.6...done.
> 	Loaded symbols for /lib/tls/libc.so.6
> 	Reading symbols from /lib/ld-linux.so.2...done.
> 	Loaded symbols for /lib/ld-linux.so.2
> 	Reading symbols from /lib/libgcc_s.so.1...done.
> 	Loaded symbols for /lib/libgcc_s.so.1
> 	0x400dc5dc in nanosleep () from /lib/tls/libc.so.6
> 	(gdb) quit
> 	The program is running.  Quit anyway (and detach it)? (y or n) y
> 	Detaching from program: /home/rsc/a.out, process 4724
> 	$
>
> But that's stupid.  The process known as 4723 has not
> exited, and it should be debuggable, even though the
> pthread known as 4723 _has_ exited.
>
> Russ
>