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Dikshunarees R gude!
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The "perlio" layer doesn't do read(2) syscalls over 8192 bytes
at the moment, and binmode($fh, ':unix') leaks[1]. So use
sysseek and sysread for now, since I can't see retaining
compatibility with PerlIO::scalar being worth the trouble.
[1] http://nntp.perl.org/group/perl.perl5.porters/256918
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We want to be able to inject existing file handles + offsets and
even lengths into this in the future, without going through the
->getline interface[1]
We also switch to using a 64K buffer size since we can safely
discard whatever got truncated on write and full writes can help
negotiate a larger TCP window for high-latency, high-bandwidth
links.
While we're at it, make it obvious that we're using O_APPEND for
our tmpfile() interface so we can seek freely for reading while
the writer always prints to the end of the file.
[1] the getline interface for serving static files may result
in us buffering on-FS data into another temporary file,
which is a waste.
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We can reduce the amount of small arrayrefs in memory
by flattening $EXPMAP. This forces us to properly clean
up references during deferred close handling, so NNTP
(and soon HTTP) connections no longer linger until expiry.
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No reason to have an empty arrayref lying around when not
everybody needs it.
Re-indent the later-related subs since we're changing a
bunch of lines, anyways.
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No need to create an arrayref until we need it, and fix up a
comment while we're in the area. Some aesthetic changes while
we're at it:
- Rename $WaitPids to $wait_pids to make it clear this is
unique to our implementation and not in Danga::Socket.
- rewrite dwaitpid() to reduce indentation level
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Another place we can delay creating arrays until needed.
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We can rely on autovification to turn `undef' value of {wbuf}
into an arrayref.
Furthermore, "push" returns the (new) size of the array since at
least Perl 5.0 (I didn't look further back), so we can use that
return value instead of calling "scalar" again.
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This does not affect our current code, but theoretically a
DESTROY callback could call PublicInbox::DS::close to enqueue
elements into the ToClose array. So take a similar strategy as
we do with other queues (e.g. $nextq) by swapping references to
arrays, rather than operating on the array itself.
Since close operations are relatively rare, we can rely on
auto-vivification via "push" ops to create the array on an
as-needed basis.
Since we're in the area, clean up the PostLoopCallback
invocation to use the ternary operator rather than a confusing
(to me) combination of statements.
Finally, add a prototype to strengthen compile-time checking,
and move it in front of our only caller to make use of
the prototype.
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It doesn't seem needed at the moment, and we can re-add it
in the future if needed.
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Inbox.pm accessing the $in_loop variable directly raises
warnings when Inbox is loaded without DS.
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The class parameter is pointless, especially for an internal
sub which only has one external caller in a test. Add a sub
prototype while we're at it to get some compile time checking.
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"fileno(undef)" already dies under "use strict", so there's no
need to check for it ourselves. As far as "fileno($closed_io)"
or "fileno($fake_io)" goes, we'll let epoll_ctl detect the
error, instead.
Our design should make DescriptorMap entries impossible to clobber,
so make it fatal via confess in case it does happen, because
inadvertantly clobbering a FD would be very bad. While we're at
it, remove a redundant return statement and rely on implicit
returns.
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Danga::Socket 1.62 was released a few months back and
the maintainer indicated it would be the last release.
We've diverged significantly in incompatible ways...
While most of this should've already been documented in
commit messages, putting it all into one document could
make it easier-to-digest.
It's also a strange design for anybody used to conventional
event loops. Maybe this is an unconventional project :P
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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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HTTP::getline_pull and NNTP::long_step will both populate {wbuf}
manually to avoid recursion, so we need to account for an
empty-but-present {wbuf} while dispatching msg_more().
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We need to use $PublicInbox::DS::in_loop instead of ::running().
The latter is not valid for systems with signalfd or kqueue and
is now gone, completely.
Not needing periodic cleanups at all to deal with unlinked pack
indices will be a tougher task...
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We'll be supporting idle timeout for the HTTP code in the
future to deal directly with Internet-exposed clients w/o
Varnish or nginx.
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EvCleanup only existed since Danga::Socket was a separate
component, and cleanup code belongs with the event loop.
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I haven't noticed this being a problem in practice, but
be consistent with the rest of the singleton stuff.
Since we always call Reset() at load time, only do
initialization in that sub and not at declaration.
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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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The perl-5.16.3-294.el7_6 RPM package on RHEL/CentOS 7 is
affected by a memory leak in Perl when calling `ref' on
blessed references. This resulted in a very slow leak that
manifests more quickly with a nonstop "git fetch" loop.
Use Scalar::Util::blessed to work around the issue.
Tested overnight on a CentOS 7 VM.
cf. https://rt.perl.org/Public/Bug/Display.html?id=114340
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Might as well share some code for temporary file creation
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* origin/nntp-compress:
nntp: improve error reporting for COMPRESS
nntp: reduce memory overhead of zlib
nntp: support COMPRESS DEFLATE per RFC 8054
nntp: move LINE_MAX constant to the top
nntp: use msg_more as a method
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While we're usually not stuck waiting on waitpid after
seeing a pipe EOF or even triggering SIGPIPE in the process
(e.g. git-http-backend) we're reading from, it MAY happen
and we should be careful to never hang the daemon process
on waitpid calls.
v2: use "eq" for string comparison against 'DEFAULT'
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Using Z_FULL_FLUSH at the right places in our event loop, it
appears we can share a single zlib deflate context across ALL
clients in a process.
The zlib deflate context is the biggest factor in per-client
memory use, so being able to share that across many clients
results in a large memory savings.
With 10K idle-but-did-something NNTP clients connected to a
single process on a 64-bit system, TLS+DEFLATE used around
1.8 GB of RSS before this change. It now uses around 300 MB.
TLS via IO::Socket::SSL alone uses <200MB in the same situation,
so the actual memory reduction is over 10x.
This makes compression less efficient and bandwidth increases
around 45% in informal testing, but it's far better than no
compression at all. It's likely around the same level of
compression gzip gives on the HTTP side.
Security implications with TLS? I don't know, but I don't
really care, either... public-inbox-nntpd doesn't support
authentication and it's up to the client to enable compression.
It's not too different than Varnish caching gzipped responses
on the HTTP side and having responses go to multiple HTTPS
clients.
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We need to ensure all these subroutines return false on
incomplete.
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Since we have EPOLL_CTL_DEL implemented for the poll(2) and
kqueue backends, we can rely on Perl refcounting to gently
close(2) the underlying file descriptors as references get
dropped.
This may be beneficial in the future if we want to drop a
descriptor from the event loop without actually closing it.
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With DS buffering to a temporary file nowadays, applying
backpressure to git-http-backend(1) hurts overall memory
usage of the system. Instead, try to get git-http-backend(1)
to finish as quickly as possible and use edge-triggered
notifications to reduce wakeups on our end.
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We need to be careful about handling EAGAIN on write(2)
failures deal with SSL_WANT_READ vs SSL_WANT_WRITE as
appropriate.
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Our hacks in EvCleanup::next_tick and EvCleanup::asap were due
to the fact "closed" sockets were deferred and could not wake
up the event loop, causing certain actions to be delayed until
an event fired.
Instead, ensure we don't sleep if there are pending sockets to
close.
We can then remove most of the EvCleanup stuff
While we're at it, split out immediate timer handling into a
separate array so we don't need to deal with time calculations
for the event loop.
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Don't use epoll or kqueue to watch for anything unless we hit
EAGAIN, since we don't know if a socket is SSL or not.
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We'll be reusing requeue in other places to reduce trips to
the kernel to retrieve "hot" descriptors.
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Doing this for HTTP cuts the memory usage of 10K
idle-after-one-request HTTP clients from 92 MB to 47 MB.
The savings over the equivalent NNTP change in commit
6f173864f5acac89769a67739b8c377510711d49,
("nntp: lazily allocate and stash rbuf") seems down to the
size of HTTP requests and the fact HTTP is a client-sends-first
protocol where as NNTP is server-sends-first.
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On Linux systems with epoll support, we don't want to be
clobbering defined subs in the t/ds-poll.t test; so use
OO ->method dispatch instead and require users to explicitly
import subs via EXPORT_OK.
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We need to account for ->write(CODE) calls doing ->write(SCALARREF),
otherwise flush_write may see the wrong ->{wbuf} field.
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We end up buffering giant things to the FS sometimes, and open()
is not a cheap syscall; so being forced to do it twice to get a
file description with O_APPEND is gross when we can just use
O_EXCL ourselves and loop on EEXIST.
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At least the subset of epoll we use. EPOLLET might be
difficult to emulate if we end up using it.
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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 may need to rely on cleanup code running in enqueued
callbacks, so ensure we call it when flush_write happens.
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kqueue EV_ONESHOT semantics are different than epoll
EPOLLONESHOT. epoll only disables watches for that event while
keeping the item in the rbtree for future EPOLL_CTL_MOD. kqueue
removes the watch from the filter set entirely, necessitating
the use of EV_ADD for future modifications.
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We can bypass buffering when wbuf is empty when it's called
from a CODE reference passed to ->write.
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This is in accordance with TLS standards and will be needed
to support session caching/reuse in the future. However, we
don't issue shutdown(2) since we know not to inadvertantly
share our sockets with other processes.
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IO::Socket::SSL will try to re-bless back to the original class
on TLS negotiation failure. Unfortunately, the original class
is 'GLOB', and re-blessing to 'GLOB' takes away all the IO::Handle
methods, because Filehandle/IO are a special case in Perl5.
Anyways, since we already use syswrite() and sysread() as functions
on our socket, we might as well use CORE::close(), as well (and
it plays nicely with tied classes).
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It kinda, barely works, and I'm most happy I got it working
without any modifications to the main NNTP::event_step callback
thanks to the DS->write(CODE) support we inherited from
Danga::Socket.
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Instead of ENOMEM (or fragmentation/swap storms), using tempfile
buffers opens us up to filesystem and storage-related errors
(e.g. ENOSPC, EFBIG, EIO, EROFS). Log these errors, drop the
particular client, and try to limp by with whateve we have left.
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It may make sense to use PerlIO::mmap or PerlIO::scalar for
DS write buffering with IO::Socket::SSL or similar (since we can't
use MSG_MORE), so that means we need to go through buffering
in userspace for the common case; while still being easily
compatible with slow clients.
And it also simplifies GitHTTPBackend slightly.
Maybe it can make sense for HTTP input buffering, too...
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Both NNTP and HTTP have common needs and we can factor
out some common code to make dealing with IO::Socket::SSL
easier.
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They're never called; the only way to break out of that loop
is the PostEventLoop callback.
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We can reduce the amount of short-lived anonymous subs we
create by passing $self to code references.
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