Re: Enhancement - show old and new thread info when switching during debugging

["pfee at talk21 dot com" <pfee at talk21 dot com>]

> > What he wants is the last user selected  thread,

> >  not the thread that happens to be current when switch_to_thread
> > is   called.
> > 
> > - user resumes with thread 1 selected
> > - thread  2 hits  breakpoint, gdb switches to thread 2
> >   - breakpoint  doesn't cause stop,  target is re-resumed
> > - thread 3 hits  breakpoint, gdb switches to thread  3
> >   - breakpoint causes  stop, previous_inferior_ptid is
> >      thread 1, but the  last switch_to_thread would have
> >     recorded   $previous_thread as thread 2
> > 
> > If you want a convenience  variable, please  model it on
> > $_thread --- see end of  thread.c:_initialize_thread.
> > 
> > Note  that the previously  selected thread may not exist anymore,
> > it may have exited   meanwhile, for example, or the inferior
> > exec'ed.
> > 
> > -- 
> > Pedro  Alves
> >
> 
> Hi Pedro,
> 
> I agree with your  example, the previous_inferior_ptid in infrun.c, 
>normal_stop() 
>
> has the  information I need.  I'll try and use that to populate the new 
> convenience variable.
> 
> I'll a try to construct a test program that  creates a scenario where the 
> previous thread as died by the time  normal_stop() executes.
> 

Hello again,

I've looked into convenience variables and have developed a new patch.  The gdb 
output when switching threads is no longer altered, instead the $_prev_thread 
convenience variable can be used to switch back to the previous thread.

When making this patch I renamed an existing variable from 
previous_inferior_ptid to current_inferior_ptid.  That way we have values that 
move from inferior_ptid (the new ptid) to current_inferior_ptid and finally to  
previous_inferior_ptid (which is exposed via the convenience variable).  This 
seemed better than leaving the variables names as was and introducing something 

confusing like previous_previous_inferior_ptid.

By the way, I've made the patches against GDB trunk, I presume that's preferred 
over GDB 7.3.


Comments welcome.
Thanks,
Paul

2011-08-08  Paul Fee <pfee@talk21.com>

    * inferior.h: Add function for handling $_prev_thread convenience variable
    * infrun.c: Rename previous_inferior_ptid to current_inferior_ptid.
    Add function for handling $_prev_thread convenience variable
    * thread.c: Add $_prev_thread convenience variable

Attachment: prev_thread.patch
Description: Binary data