macOS - fix deadlock on reqrep socket close

[alzix]

when an aio has no a_cancel_fn and the task is in task_prepstate abort it on nni_aio_stop call

fixes #1813 Deadlock during nng_close() - multi platform

[gdamore]

This looks like a good find. Furthermore, it looks like nni_aio_abort also suffers from the same flaw.

I want to look at this in more detail later today before I move forward.

[gdamore]

I think I've convinced myself that this is precisely the right fix, and we just need to add the same change to the implementation of nni_aio_abort.

[alzix]

i'm on it

[gdamore]

So there are other callers.

Basically we also need the same logic in nni_aio_cancel, and I think nni_aio_fini. It looks like it was missed in all the paths where we tear down or abort an aio.

[gdamore]

This was an excellent find, and probably tricky to do so as well. Thank you for your contribution!

[alzix]

it does not solve the Windows issue though :(
On Windows the issue seems to be different

it seems that on Windows it is a TOCTOU issue in the nni_sock_shutdown

it is stuck on

// We have to wait for pipes to be removed.
while (!nni_list_empty(&sock->s_pipes)) {
=>	nni_cv_wait(&sock->s_cv);
}

while s_pipes is already empty

the issue predates the fix - so it is better to address it in another PR

[gdamore]

I'm merging this... the hang waiting for pipes to be empty feels like a missed cv_wake somewhere. I'll look for it later. I'm out of time for today.

[alzix]

created a new ticket for this #1827