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

[David Leimbach <leimy2k@gmail.com>]

I tried it on solaris:


sultan% ps -p 1362 -o "lwp user pid ppid taskid pcpu pmem fname"
   LWP     USER   PID  PPID TASKID %CPU %MEM COMMAND
     1     dave  1362  1354    59    -  0.1 <defunct>
     2     dave  1362  1354    59  0.0  0.1 x


2 Light Weight processes, one of which is defunct.  Sounds similar to
the linux behavior.

Dave

On Thu, 10 Feb 2005 13:35:46 -0500, Russ Cox <russcox@gmail.com> wrote:
> 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
>