Re: Multithreading with C++

[Ron Michael Khu]

i've encountered a similar problem a few months ago...
have u tried declaring AND defining the threadfun() function OUTSIDE of 
the class??

Huber, George K RDECOM CERDEC STCD SRI wrote:
All,
This may be a little off topic, but I though I would try here first.
I am writting a multi-threaded program and would like to have each 
thread `managed' by a class.  I have attempted to do this like this,
using the pthreads library:

<code>
====================begin cthread.h
class CThread
{
public:
   CThread(void*);
   ~CThread();
   ....
private:
   static CThread*     m_pThis;
   pthread_t             m_tid;
   static void*           threadfun(void*);
  ....
}
==================== begin cthread.cpp
CThread*  CThread::m_pThis = NULL;
CThread::CThread(void* arg)
{
   int      ret;
   m_pThis = this;
   if(0 != (ret = pthread_create(&m_tid, NULL, threadfun, arg)))
   {
        fprintf(stderr, "Thread creation failed");
  }
}   

void*  threadfun(void* arg)
{
    printf("Starting thread\n");
    ....
}
</code>
The code compiles without warnings or errors, except when I try and 
run the application I get a segmentation fault at the pthread_create.  
Trying to run under GDB, I am able to examine the value of the 
variables and they seem consisten with what I would expect

// stop on the pthread_create line in the constructor...
(gdb) print m_pThis
$1 = (CThread*) 0xfee756b0
(gdb) print this
$2 = (CThread*0xfee756b0
(gdb) print m_tid
$3 = 134514818               // to be expected because I have not initialized 
m_tid yet
(gdb) print &m_tid
$4 = (pthread_t*)0xfee756d8
(gdb) print threadfun
$5=&CThread::threadfun(void*)
// attempt the pthread_create line ....
Program received signal SIGSEGV, Segmenatation fault
0x0000000 in ?? ()
(gdb) where 
#0 0x00000000 in ?? ( )
#1 0x0804a6bb in CThread (this=0xfee756b0, args=0x0) at ....
#2 0x08049aad in daemon_main(argc=3, argv=0xfeec42d4) at ....
#3 0x08049193 in main(argc=3, argv=0xfeec42d3) at main.cpp: 83

Any idea on what is going on, or how to fix?
Thanks, 
George Huber

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