Re: [Sbcl-devel] RFC: exiting SBCL vs returning from a thread vs aborting a thread

[Nikodemus S. <nik...@ra...>]

On 30 April 2012 03:14, Jianshi Huang <jia...@gm...> wrote:
> Some feedback for further discussion:
>
> *exit-hooks* are invoked before calling %exit-other-threads, which
> seems controversial to me. It means I can't use it for to free
> resources or to guarantee all buffers are flushed since other threads
> might still operating on them.

The reason *EXIT-HOOKS* are called first now is threefold:

(1) make it possible to use them to guarantee an orderly shut-down,
which for me includes non-asynch termination of other threads.

(2) since it is possible that we cannot cleanly terminate a thread
(eg. because it's stuck inside a WITHOUT-INTERRUPTS.), there is now
way to guarantee that we will reach a state where all threads are
running before *EXIT-HOOKS* are called.

(3) calling them early means that it's sane (well, almost) to still
spawn new threads from exit hooks. If we did that after thread
termination, we could not allow it and call the shutdown orderly.
While I don't expect exit hooks spawning threads to be a regular
occurrence, I can still image it happening by both design and harmless
accident.

Still, your point and use-case are both perfectly valid. Maybe we need
a second series of exit hooks as well. Name suggestions?

 *AFTER-EXIT-HOOKS* ?

 *FINAL-HOOKS* ?

Or maybe have *EXIT-HOOKS* act as you suggest, and add

 *BEFORE-EXIT-HOOKS* ?

which could even be called before from the current thread. I think I
like this option the best -- if there's a hook which is called after
unwinding everything, it doesn't matter if the initial hook is called
before.

Thoughts?

> It would be nicer if we have *thread-exit-hooks* for each thread.

Can you clarify this a bit?

As a thread-local binding? Can do that, but don't quite see the point
-- how would it be different from sticking an UNWIND-PROTECT clause to
do the same?

Or do you mean as a global variable, called per thread? I guess that
makes sense, but don't see an immediate application.

Cheers,

 -- Nikodemus