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Using "make update-copyrights" after setting GNULIB_PATH in my
config.mak
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Since the removal of pseudo-hash support in Perl 5.10, the
"fields" module no longer provides the space or speed benefits
it did in 5.8. It also does not allow for compile-time checks,
only run-time checks.
To me, the extra developer overhead in maintaining "use fields"
args has become a hassle. None of our non-DS-related code uses
fields.pm, nor do any of our current dependencies. In fact,
Danga::Socket (which DS was originally forked from) and its
subclasses are the only fields.pm users I've ever encountered in
the wild. Removing fields may make our code more approachable
to other Perl hackers.
So stop using fields.pm and locked hashes, but continue to
document what fields do for non-trivial classes.
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I didn't wait until September to do it, this year!
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EPOLL_CTL_ADD may fail with transient ENOMEM or ENOSPC errors,
so don't tear down the process when that happens.
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There's a bunch of leftover "require" and "use" statements we no
longer need and can get rid of, along with some excessive
imports via "use".
IO::Handle usage isn't always obvious, so add comments
describing why a package loads it. Along the same lines,
document the tmpdir support as the reason we depend on
File::Temp 0.19, even though every Perl 5.10.1+ user has it.
While we're at it, favor "use" over "require", since it it gives
us extra compile-time checking.
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We need to warn when hitting file or socket memory limits
or misconfigurations which clear O_NONBLOCK to make it easier
to diagnose configuration problems. We'll also warn on
some other errors in case bugs creep in...
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For users relying on socket activation via service manager (e.g.
systemd) and running multiple service instances (@1, @2),
we need to ensure configuration of the socket is NonBlocking.
Otherwise, service managers such as systemd may clear the
O_NONBLOCK flag for a small window where accept/accept4
blocks:
public-inbox-nntpd@1 |systemd |public-inbox-nntpd@2
--------------------------+----------------+--------------------
F_SETFL,O_NONBLOCK|O_RDWR | | (not running, yet)
|F_SETFL, O_RDWR |
|fork+exec @2... |
accept(...) # blocks! | |(started by systemd)
| |F_SETFL,O_NONBLOCK|O_RDWR
| |accept(...) non-blocking
It's a very small window where O_NONBLOCK can be cleared,
but it exists, and I finally hit it after many years.
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We don't need extra wakeups from the kernel when we know a
listener is already active.
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We can avoid the EPOLL_CTL_ADD && EPOLL_CTL_MOD sequence with
a single EPOLL_CTL_ADD.
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Having separate read/write callbacks in every class is too
confusing to my easily-confused mind. Instead, give every class
an "event_step" callback which is easier to wrap my head around.
This will make future code to support IO::Socket::SSL-wrapped
sockets easier-to-digest, since SSL_write() can require waiting
on POLLIN events, and SSL_read() can require waiting on POLLOUT
events.
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Since our listen sockets are non-blocking and we may run
multiple httpd|nntpd processes; we need a way to avoid
thundering herds when there are multiple httpd|nntpd worker
processes.
EPOLLEXCLUSIVE was added just for that in Linux 4.5
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These modules are unmaintained upstream at the moment, but I'll
be able to help with the intended maintainer once/if CPAN
ownership is transferred. OTOH, we've been waiting for that
transfer for several years, now...
Changes I intend to make:
* EPOLLEXCLUSIVE for Linux
* remove unused fields wasting memory
* kqueue bugfixes e.g. https://rt.cpan.org/Ticket/Display.html?id=116615
* accept4 support
And some lower priority experiments:
* switch to EV_ONESHOT / EPOLLONESHOT (incompatible changes)
* nginx-style buffering to tmpfile instead of string array
* sendfile off tmpfile buffers
* io_uring maybe?
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Using update-copyrights from gnulib
While we're at it, use the SPDX identifier for AGPL-3.0+ to
ease mechanical processing.
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Notes for future developers (myself included) since we
can't assume people can read my mind.
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This is meant to provide an easy starting point for server admins.
It provides a basic HTTP server for admins unfamiliar with
configuring PSGI applications as well as being an identical
interface for management as our nntpd implementation.
This HTTP server may also be a generic Plack/PSGI server for
existing Plack/PSGI applications.
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We can avoid making getpeername syscalls this way.
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Hopefully this gives new hackers a better overview of
how the components relate to each other.
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We'll probably be supporting read-only IMAP, or maybe
we'll just implement a custom HTTP server so users can
manage/upgrade the same way as the nntpd while being
immune to slow clients.
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