fork and pthreads

fork and pthreads

[Sébastien Roret]

Hi, 
 
I'm having some problems using fork() with threads. 
I'm using a debian linux on Intel, gdb 6.3, glibc 2.3.3 and 2.3.5 
If I call forks before using threads it's ok, but not the other way. 
The problem occurs only with gdb. 
See below the testcase and output I got. 
My question : is it a bug, or did I missed something ? 
 
Thanks for any ideas. 
 
 
 
#include <sys/types.h> 
#include <unistd.h> 
#include <pthread.h> 
 
void* start_routine(void *arg) 
{ 
        printf("start_routine\n"); 
} 
 
int main() 
{ 
  pid_t pid; 
  pthread_t thread; 
  int status; 
 
  printf("pid=%d\n", getpid()); 
 
  pthread_create(&thread, NULL, &start_routine, NULL); 
  pthread_join(thread, NULL); 
  perror("join"); 
 
  pid = fork(); 
 
  printf("fork pid = %d\n", pid); 
  if( pid == -1 ) 
  { 
         perror( "fork" ); 
         abort(); 
  } 
  else if( pid == 0 ) 
  { 
        printf("pid = %d\n", pid); 
        sleep(1); 
        return 0; 
  } 
  else 
  { 
       printf("waiting child pid = %d\n", pid); 
       printf("wait=%d\n", wait( &status )); 
       printf("status=%d\n", status ); 
       return 0; 
  } 
} 
 
Then : 
$ gcc pthread_fork.c -o pthread_fork -lpthread 
$ gdb ./pthread_fork 
GNU gdb 6.3-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". 
 
(gdb) r 
Starting program: /tmp/pthread_fork 
[Thread debugging using libthread_db enabled] 
[New Thread 1075145376 (LWP 10278)] 
pid=10278 
[New Thread 1083534256 (LWP 10283)] 
start_routine 
[Thread 1083534256 (LWP 10283) exited] 
join: Success 
ptrace: No such process. 
thread_db_get_info: cannot get thread info: generic error 
(gdb) fork pid = 0 
pid = 0 
fork pid = 10284 
waiting child pid = 10284 
 
 
 
 
 

Re: fork and pthreads

[Daniel Jacobowitz]

On Fri, Sep 30, 2005 at 09:58:05AM +0000, Sébastien Roret wrote:
> Hi, 
>  
> I'm having some problems using fork() with threads. 
> I'm using a debian linux on Intel, gdb 6.3, glibc 2.3.3 and 2.3.5 
> If I call forks before using threads it's ok, but not the other way. 
> The problem occurs only with gdb. 
> See below the testcase and output I got. 
> My question : is it a bug, or did I missed something ? 

Please try a CVS snapshot (6.3.50.*) and let us know if that works
better.


-- 
Daniel Jacobowitz
CodeSourcery, LLC

Re: fork and pthreads

[Sébastien Roret]

I tried GNU gdb 6.3.50.20050930 with no success. 
I still have : 
"thread_db_get_info: cannot get thread info: generic error" 
I also tried g++ (GCC) 4.0.1 (Debian 4.0.1-2) : it seems that gdb no longer 
blocks on this error and continues the execution.