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One syscall is better than two for atomicity in Maildirs. This
means there's no window where another process can see both the
old and new file at the same time (link && unlink), nor a window
where we might inadvertantly clobber an existing file if we were
to do `stat && rename'.
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Since signalfd is often combined with our event loop, give it a
convenient API and reduce the code duplication required to use it.
EventLoop is replaced with ::event_loop to allow consistent
parameter passing and avoid needlessly passing the package name
on stack.
We also avoid exporting SFD_NONBLOCK since it's the only flag we
support. There's no sense in having the memory overhead of a
constant function when it's in cold code.
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We'll be supporting inotify directly as we do with epoll so so
Linux users won't have to deal with XS, extra DSOs or install
Linux::Inotify2 (and common::sense) modules.
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FreeBSD (and other *BSDs) do not have stable syscall numbers, so
drop no-op checks for it and add a note to use Inline::C,
instead. Drop an implicit return for the syscall.ph loading
while we're at it, too.
On Linux, epoll_create(2) ignores the size arg since Linux
2.6.8, so just hard code it to some non-zero value.
On a side note, we can probably drop epoll_create(2) support
soon and just use epoll_create1(2) which appeared in 2.6.27+
(2008-10-09). Our userspace (Perl and git) requirements are
already further ahead.
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Older Perls (tested 5.16.3) would warn on uninitialized scalars while
newer (tested 5.28.1) do not. Just initialize it to an empty string
since it'll be filled in by `vec'.
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Using "make update-copyrights" after setting GNULIB_PATH in my
config.mak
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Since Perl exposes O_NONBLOCK as a constant, we can safely make
SFD_NONBLOCK a constant, too. This is not the case for
SFD_CLOEXEC, since O_CLOEXEC is not exposed by Perl despite
being used internally in the interpreter.
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Consistently returning the equivalent of pollfd.revents in a
portable manner was never worth the effort for us, as we use the
same ->event_step callback regardless of POLLIN/POLLOUT/POLLHUP.
Being a Perl, @events knows it size and we don't have to return
a maximum index for the caller to iterate on.
We can also avoid redundant integer coercion ("+0") since we
ensure everything is an IV in other places.
Finally, vec() is preferable to ("\0" x $size) for resizing
buffers because it only needs to write the extended portion
and not overwrite the entire buffer.
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Thanks to the GCC compile farm project, we can wire up syscalls
for sparc64 and set system-specific SFD_* constants properly.
I've FINALLY figured out how to use POSIX::SigSet to generate
a usable buffer for the syscall perlfunc. This is required
for endian-neutral behavior and relevant to sparc64, at least.
There's no need for signalfd-related stuff to be constants,
either. signalfd initialization is never a hot path and a stub
subroutine for constants uses several KB of memory in the
interpreter.
We'll drop the needless SEEK_CUR import while we're importing
O_NONBLOCK, too.
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The x32 ABI allows users to take advantage of the extra
registers on x86-64 without the bloat of 64-bit pointers and
longs.
This ought to be significant since Perl was designed when 32-bit
was prevalent; and the common structs for ops, hashes, scalars,
and arrays use longs (SSize_t/Size_t) for things which should
never need 64-bits when processing emails.
Debian's x32 port seems to work quite nicely under a chroot
on an amd64 Linux system. All tests pass under x32, now.
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I didn't wait until September to do it, this year!
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"use vars" was superseded by "our" in Perl 5.6, and we
can "use parent qw(Exporter)" in favor of manipulating
@ISA directly (or the bigger "use base ...");
While we're at it, avoid multiple invocations of constant->import
by passing a hashref as a "use" parameter.
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Our attempt at using a self-pipe in signal handlers was
ineffective, since pure Perl code execution is deferred
and Perl doesn't use an internal self-pipe/eventfd. In
retrospect, I actually prefer the simplicity of Perl in
this regard...
We can use sigprocmask() from Perl, so we can introduce
signalfd(2) and EVFILT_SIGNAL support on Linux and *BSD-based
systems, respectively. These OS primitives allow us to avoid a
race where Perl checks for signals right before epoll_wait() or
kevent() puts the process to sleep.
The (few) systems nowadays without signalfd(2) or IO::KQueue
will now see wakeups every second to avoid missed signals.
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I'm not sure they'll make a measurable difference or will
be worth the effort in the future given the prevalance
of HTTPS and giant socket buffers.
Using Inline::C for this may make more sense in the
future, too, especially if we want to be able to use
GnuTLS.
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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 don't need to code multiple event loops or have branches in
watch() if we can easily make the IO::KQueue-based interface
look like our lower-level epoll_* API.
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We don't need to keep track of that field since we always
know what events we're interested in when using one-shot
wakeups.
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We don't need to keep information from uname(2) around outside
of startup.
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EPOLLRDBAND is used for DECnet; and I'm pretty sure I won't be
updating any of our code to work with DECnet.
I've never found use for EPOLLHUP or EPOLLERR, either; so
disable those for now and add comments for things I might
actually use: EPOLLET and EPOLLONESHOT.
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No backwards compatibility to worry about for us; and fadvise
is superior anyways.
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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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