http: constrain getline/close responses by time

This allows us to yield control to other clients gracefully if
getline takes too long to generate a chunk.  This is more
expensive but should not cost a syscall on modern 64-bit systems.

diff --git a/lib/PublicInbox/HTTP.pm b/lib/PublicInbox/HTTP.pm
index e0ed2d15e95e6bba6eb3662ec5048619717affb5..800b2401e3cb6b2fc70ea963e3f9738bc7ddd05c 100644 (file)
--- a/lib/PublicInbox/HTTP.pm
+++ b/lib/PublicInbox/HTTP.pm
@@ -16,6 +16,7 @@ use Fcntl qw(:seek);
 use Plack::HTTPParser qw(parse_http_request); # XS or pure Perl
 use HTTP::Status qw(status_message);
 use HTTP::Date qw(time2str);
+use Time::HiRes qw(clock_gettime CLOCK_MONOTONIC);
 use Scalar::Util qw(weaken);
 use IO::File;
 use constant {
@@ -25,6 +26,8 @@ use constant {
        CHUNK_MAX_HDR => 256,
 };
 
+sub now () { clock_gettime(CLOCK_MONOTONIC) }
+
 # FIXME: duplicated code with NNTP.pm, layering violation
 my $WEAKEN = {}; # string(inbox) -> inbox
 my $weakt;
@@ -267,14 +270,14 @@ sub getline_response {
                my $forward = $self->{forward};
                # limit our own running time for fairness with other
                # clients and to avoid buffering too much:
-               my $n = 100;
+               my $end = now() + 0.1;
                while ($forward && defined(my $buf = $forward->getline)) {
                        $write->($buf);
                        last if $self->{closed};
                        if ($self->{write_buf_size}) {
                                $self->write($self->{pull});
                                return;
-                       } elsif ((--$n) <= 0) {
+                       } elsif (now() > $end) {
                                PublicInbox::EvCleanup::asap($self->{pull});
                                return;
                        }