improved thread id reporting

[Mark Kettenis]

> Date: Sat,  4 Apr 2009 11:46:04 -0700 (PDT)
> From: dje@google.com (Doug Evans)
> 
> Hi.
> 
> GDB's current reporting of thread ids has (at least) three problems (IMO):
> 1) Reporting the pthread id (e.g. 0x0xf7e5cbb0) has a very low S/N ratio.

Uh?  I'd say it has a very high S/N ratio; it's the only thing that
you can actually use to identify a thread to a particular thread
created by the code you're debugging.

Also realize that whatever is printed now between () is OS-specific
information that varies from OS to OS and may even be completely
absent in the case of user-level threads libraries.

> 2) When switching to a thread IWBN to also report the thread being switched
>    from, otherwise one has to scrollback through the session to find it
>    (assuming that's even possible).

That's not an unreasonable suggestion.

> 3) When reporting thread ids the only usable number in the gdb session
>    (gdb's internal thread number) is not included.

I don't consider this to be a big issue.  If I need a GDB internal
thread number, I find it no problem to just use the "info threads"
command and make decisions based on that.  I'd expect that to be much
more convenient than scrollback through the session ;)

That said, if it's possible to print them without creating additional
line breaks on an 80-column wide screen, I have no objections.

> To fix (1) I'd like to simply remove the pthread id from the output.

I think that's a bad idea.