Re: occasional threading in lua

["Russ Cox" <rsc@...>]

> On 11/16/06, Russ Cox <rsc@swtch.com> wrote:
> > This program ends up using just two pthreads.
>
> is this true in the current implementation - both cases seem to create
> a sequence of pthreads?

You're right -- there is a third pthread that gets created
and then almost immediately deleted every time a sleep happens.
This could be easily optimized away.

> > I'd be happy to hear comments or suggestions for even
> > simpler ways to accomplish this.
>
> it seems like sched_mutex is acquired iff vm_mutex is held - could we
> get by with just one mutex?

Yes, indeed.  Originally they did not overlap, but in their
current form the sched_mutex can definitely be dropped.

> on linux 2.6 x86, i noticed that the vmsize and rss keep increasing
> (until vmsize maxes out at 3GB).  since the pthreads are created as
> "joinable" by default, their memory isn't reclaimed when they exit.
>
> i added a global pthread_attr_t object, initialize it in luaopen_thread()
>
>   pthread_attr_init(&attr);
>   if(pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED) != 0)
>     luaG_runerror(L, "setdetachstate");

Aha, thanks!

> and passed it as the second argument to pthread_create() in
> luaT_vm_unlock().  another option would be to call
> pthread_detach(pthread_self()) in luaT_scheduler().
>
> i also noticed that the default stack size for each pthread is a
> whopping 8MB (RLIMIT_STACK) on my linux box.  depending on how many
> concurrent threads one expects, is it worth having an option to reduce
> this by using pthread_attr_setstacksize()?

It probably is worthwhile, though the only real issue here is
address space, not actual memory, since the memory will be
paged in on demand.

Russ