[Freeciv-Dev] Re: autobacktrace (was: concerning the use of assert)

[Jason Short <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

Per I. Mathisen wrote:
> On Fri, 13 Sep 2002, Reinier Post wrote:
>
> > I'm not sure it makes that much of a difference, you can start gdb,
> > atach it to the pid of a current civserver process, stop it,
> > print the backtrace, continue, and detach.But I don't really
> > see what to look for while running, and keeping the debugger attached
> > all the time may slow the game down too much.I never tried this.
>
> We don't need to have it attached all the time. We can freeze the server
> on an error, launch and attach gdb, print a backtrace to a log, kill gdb
> and then thaw the server and continue execution. The users will notice a
> hiccup, but it is much better than a crash.
Yes.

> Another option may be to fork() off a clone of the current process, then
> abort() it so that you generate a core file from that. This should be
> faster, but I don't know how this will affect our open files and allocated
> memory.
For starters, what about the simple function:

  static void dump_core(void)
  {
    pid_t pid = fork();

    if (pid <= 0 || waitpid(pid, NULL, 0) <= 0)
      abort();
  }

which should work fine for getting core without interrupting the current 
process.  Fork is pretty nice about not messing with the parent process' 
resources.
The extra handling you've been talking about could take place right at 
the end of this function:
- Attach gdb to the core file (we must handle the case where gdb doesn't 
exist, or where cores are disallowed).
- Get a backtrace, and possibly other information.
- Save the current game (could be tricky if the save code is not 
re-entrant).
- Perhaps get some other data: like the version number, build time, etc.
- E-mail all the collected data to freeciv-reportbug@xxxxxxxxxxx. 
(Sending it to freeciv-dev is a bad idea since there could potentially 
be a *lot* of duplicates and not everyone will want the traffic).  We 
must handle the case where there is no means to send mail; also do we 
need to ask the user before doing this?
Note this would work for both server and client (although the client is 
less likely to have all of the helper programs present).
jason