[Openmcl-devel] type specifier '(simple-vector n) in defmethod

[Nicolas Martyanoff]

David McClain <dbm at refined-audiometrics.com> writes:

> I have been using Async Socket I/O in Lispworks, qute successfully for several
> years now. Even with multiple connections, it requires only a single machine
> thread to run a dedicated socket handler. LW must be using a Select() down deep
> inside, but I haven’t looked. There is no problem with idle socket connections.
>
> The dedicated handler thread hands off incoming packet fragments to one or more
> of my own waiting user code fragments which run in one of my pool threads. The
> entire thing runs in my laboratory with 4 or more networked machines, where I
> have in each machine just one socket handler thread, and a pool of 8 worker
> threads for myself. None of my code sits waiting for incoming socket data, but
> responds whenever fresh data arrive.

Now expand your system to thousands of concurrent connections, and see
what happens when processing each requests means running other IO
requests (e.g. calling external systems, or even simply disk
operations). Processing is now split on a multitude of IO event
callbacks (this is the definition of callback hell), making code so much
more difficult to follow. And of course each callback now has the
potential to delay other IO callbacks since they all run on the same
thread. Very fun when you realize that your apparently inoffensive read
on a file actually reads a NFS-mounted volume and the 30 second timeout
will delay all other IO events.

None of this really matters for tiny applications running in controlled
environments. But on large scale production systems, they do.

I would also hope that LW uses at least poll, and hopefully
epoll/kqueue).

-- 
Nicolas Martyanoff
https://n16f.net
nicolas at n16f.net