Re: SIGTTOU on multi-threaded programs

[Daniel Jacobowitz <drow at false dot org>]

On Wed, Mar 24, 2004 at 01:28:38PM +0300, Vladimir Prus wrote:
> 
> Hello,
> I'm having trouble running multi-threaded programs under gdb, soon after 
> starting the shell says that gdb is "stopped" -- and it seems like it 
> receives SIGTTOU.
> 
> Here's a simple program:
> 
> #include <pthread.h>
> 
> void* thread(void*)
> {
>     for(;;);
> }
> 
> int main()
> {
>     pthread_t p1;
>     pthread_create(&p1, 0, thread, 0);
>     return 0;
> }
> 
> When I run
> 
>    stty tostop
>    g++ -g threads.cpp -pthread
>    gdb ./a.out
> 
> and then "run", I see:
> 
> [1]+  Stopped                 gdb a.out
> 
> The "stty tostop" makes the terminal send 'SIGTTOU' if background process 
> writes something to console. The problem is that midnight commander also sets 
> this flag -- which means I can't debug multi-threaded programs under MC.
> 
> The debugged program and gdb have different process group id, and debugged 
> program is initially in the foreground -- so gdb in in background. It looks 
> like gdb tries to output something while it's still in background, and 
> recieves the signal.
> 
> Is this a known issue? What can be done about it? I've worked this around for 
> one program using code that adds the program to the same process group as the 
> parent, so both the program and gdb are consired to be in foreground by the 
> terminal, but that does not look the right solution.
> 
> I'm using "GNU gdb 6.0".

It's not a known issue.  If you can just verify what is being printed
while GDB does not have the terminal, we can fix it - GDB already has
hooks to take and release the terminal but is obviously not using them
somewhere it should be.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer