qspawn: allow configurable limiters

And bump the default limit to 32 so we match git-daemon
behavior.  This shall allow us to configure different levels
of concurrency for different repositories and prevent clones
of giant repos from stalling service to small repos.

2 files changed, 33 insertions, 11 deletions

diff --git a/lib/PublicInbox/GitHTTPBackend.pm b/lib/PublicInbox/GitHTTPBackend.pm
index ebb0850a..ed8fdf00 100644
--- a/lib/PublicInbox/GitHTTPBackend.pm
+++ b/lib/PublicInbox/GitHTTPBackend.pm
@@ -13,6 +13,9 @@ use HTTP::Status qw(status_message);
 use Plack::Util;
 use PublicInbox::Qspawn;
 
+# 32 is same as the git-daemon connection limit
+my $default_limiter = PublicInbox::Qspawn::Limiter->new(32);
+
 # n.b. serving "description" and "cloneurl" should be innocuous enough to
 # not cause problems.  serving "config" might...
 my @text = qw[HEAD info/refs
@@ -176,6 +179,7 @@ sub prepare_range {
 # returns undef if 403 so it falls back to dumb HTTP
 sub serve_smart {
         my ($env, $git, $path) = @_;
+        my $limiter = $default_limiter;
         my $in = $env->{'psgi.input'};
         my $fd = eval { fileno($in) };
         unless (defined $fd && $fd >= 0) {
@@ -248,7 +252,7 @@ sub serve_smart {
                 # holding the input here is a waste of FDs and memory
                 $env->{'psgi.input'} = undef;
 
-                $x->start(sub { # may run later, much later...
+                $x->start($limiter, sub { # may run later, much later...
                         ($rpipe) = @_;
                         $in = undef;
                         if ($async) {
diff --git a/lib/PublicInbox/Qspawn.pm b/lib/PublicInbox/Qspawn.pm
index 9299096a..cc9c340d 100644
--- a/lib/PublicInbox/Qspawn.pm
+++ b/lib/PublicInbox/Qspawn.pm
@@ -1,12 +1,14 @@
 # Copyright (C) 2016 all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# Limits the number of processes spawned
+# This does not depend on Danga::Socket or any other external
+# scheduling mechanism, you just need to call start and finish
+# appropriately
 package PublicInbox::Qspawn;
 use strict;
 use warnings;
 use PublicInbox::Spawn qw(popen_rd);
-our $LIMIT = 1;
-my $running = 0;
-my @run_queue;
 
 sub new ($$$;) {
         my ($class, $cmd, $env, $opt) = @_;
@@ -16,9 +18,10 @@ sub new ($$$;) {
 sub _do_spawn {
         my ($self, $cb) = @_;
         my $err;
+
         ($self->{rpipe}, $self->{pid}) = popen_rd(@{$self->{args}});
         if (defined $self->{pid}) {
-                $running++;
+                $self->{limiter}->{running}++;
         } else {
                 $self->{err} = $!;
         }
@@ -27,26 +30,41 @@ sub _do_spawn {
 
 sub finish ($) {
         my ($self) = @_;
+        my $limiter = $self->{limiter};
         if (delete $self->{rpipe}) {
                 my $pid = delete $self->{pid};
                 $self->{err} = $pid == waitpid($pid, 0) ? $? :
                                 "PID:$pid still running?";
-                $running--;
+                $limiter->{running}--;
         }
-        if (my $next = shift @run_queue) {
+        if (my $next = shift @{$limiter->{run_queue}}) {
                 _do_spawn(@$next);
         }
         $self->{err};
 }
 
-sub start ($$) {
-        my ($self, $cb) = @_;
+sub start {
+        my ($self, $limiter, $cb) = @_;
+        $self->{limiter} = $limiter;
 
-        if ($running < $LIMIT) {
+        if ($limiter->{running} < $limiter->{limit}) {
                 _do_spawn($self, $cb);
         } else {
-                push @run_queue, [ $self, $cb ];
+                push @{$limiter->{run_queue}}, [ $self, $cb ];
         }
 }
 
+package PublicInbox::Qspawn::Limiter;
+use strict;
+use warnings;
+
+sub new {
+        my ($class, $limit) = @_;
+        bless {
+                limit => $limit || 1,
+                running => 0,
+                run_queue => [],
+        }, $class;
+}
+
 1;