Re: [PATCH 0/6] Support kernel-backed user threads on FreeBSD

Pedro Alves
2016-01-12T19:24:49Z

On 01/12/2016 07:06 PM, Paul_Koning@Dell.com wrote:
>
>> On Jan 12, 2016, at 1:55 PM, John Baldwin <jhb@freebsd.org> wrote:
>>
>> On Monday, January 11, 2016 10:53:50 AM John Baldwin wrote:

>> One other note I forgot to mention is that currently I leave the ptid for
>> single-threaded processes as (pid, 0, 0) (i.e. I only use LWPs in PTIDs
>> when there is more than one thread). What is the best practice? Should
>> I always use LWPs in ptids instead?
>
> I would say always use the LWP.
>
> For one thing, the process might start out single-threaded, then at some point midway through the debug session start more threads. If you always use the LWP, the main thread doesn't change identity. But if you fake the PTID to (pid,0,0) then that ID no longer applies once the new thread starts. You'd end up with the confusion of apparently seeing a thread disappear and a new one appear in its place, when in reality that's just the main thread continuing in existence.

We have thread_change_ptid to handle that scenario, but it's indeed best
to avoid it if possible.

Thanks,
Pedro Alves