Subj : atexit handler: pthread_cancel, pthread_testcancel, pthread_join problem
To   : comp.programming.threads
From : annamalai.gurusami
Date : Thu Aug 18 2005 03:38 am

Hi All,

I am having a problem related to pthread_join.  The following short
program
demonstrates the problem.

There are two threads of execution involved.  The main program (A) and
another
thread (B).  The thread B runs continuously (in forever loop) doing its
work.
Every time in the loop, it once call pthread_testcancel to check if it
has to
continue or not.  This is its only cancellation point.

The thread A, calls pthread_cancel(B) in its atexit handler.  This is
followed
by a call to pthread_join(B, 0) (in atexit handler).  This seems to
create
problems.  Any thoughts on this much appreciated.

#include <iostream>
#include <unistd.h>
#include <signal.h>

pthread_t th;

void* start_thread(void *)
{
    for(;;)
    {
        std::cout << "testcancel()" << std::endl;
        pthread_testcancel();
    }
}

void atexit_handler(void)
{
    pthread_cancel(th);
    pthread_join(th, 0);
}

int main()
{
    atexit( atexit_handler );
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
    pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);
    pthread_create(&th, &attr, start_thread, 0 );
    exit(0);
}

Some information about my system.

$ uname -a
Linux redhatas.mct.com 2.6.9-5.ELsmp #1 SMP Wed Jan 5 19:29:47 EST 2005
x86_64 x86_64 x86_64 GNU/Linux

$ cat /etc/redhat-release
Red Hat Enterprise Linux AS release 4 (Nahant)

I have mailed this problem to nahant-list@redhat.com, but no response
yet (more
than 24 hours is not good tech. support)

BTW, I tried this with both -m32 and -m64 options of g++.  In 32-bit
version,
it is hanging, and in 64-bit version it is dumping core.

The core dump looks like this.

[anna@redhatas] $ gdb pj64 core.29275
GNU gdb Red Hat Linux (6.1post-1.20040607.62rh)
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 "x86_64-redhat-linux-gnu"...Using host
libthread_db library "/lib64/tls/libthread_db.so.1".

Core was generated by `./pj64'.
Program terminated with signal 6, Aborted.
Reading symbols from /usr/lib64/libstdc++.so.6...done.
Loaded symbols for /usr/lib64/libstdc++.so.6
Reading symbols from /lib64/tls/libm.so.6...done.
Loaded symbols for /lib64/tls/libm.so.6
Reading symbols from /lib64/libgcc_s.so.1...done.
Loaded symbols for /lib64/libgcc_s.so.1
Reading symbols from /lib64/tls/libpthread.so.0...done.
Loaded symbols for /lib64/tls/libpthread.so.0
Reading symbols from /lib64/tls/libc.so.6...done.
Loaded symbols for /lib64/tls/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
#0  0x00000036c712e4dd in raise () from /lib64/tls/libc.so.6
(gdb) where
#0  0x00000036c712e4dd in raise () from /lib64/tls/libc.so.6
#1  0x00000036c712fc8e in abort () from /lib64/tls/libc.so.6
#2  0x00000036c7c0ac21 in unwind_cleanup () from
/lib64/tls/libpthread.so.0
#3  0x00000036c9286ec1 in std::ostream::put () from
/usr/lib64/libstdc++.so.6
#4  0x00000036c9286f60 in std::endl<char, std::char_traits<char> > ()
from /usr/lib64/libstdc++.so.6
#5  0x0000000000400cda in start_thread () at pj.cc:14
#6  0x00000036c7c0613a in start_thread () from
/lib64/tls/libpthread.so.0
#7  0x00000036c71c52b3 in clone () from /lib64/tls/libc.so.6
#8  0x0000000000000000 in ?? ()
(gdb) 

Rgds,
anna

.