solver: rewrite to use Qspawn->psgi_qx and pi-httpd.async

The psgi_qx routine in the now-abandoned "repobrowse" branch
allows us to break down blob-solving at each process execution
point.  It reuses the Qspawn facility for git-http-backend(1),
allowing us to limit parallel subprocesses independently of Perl
worker count.

This is actually a 2-3% slower a fully-synchronous execution;
but it is fair to other clients as it won't monopolize the server
for hundreds of milliseconds (or even seconds) at a time.

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/PublicInbox/HTTPD/Async.pm b/lib/PublicInbox/HTTPD/Async.pm
index a1f75518..a647f10d 100644
--- a/lib/PublicInbox/HTTPD/Async.pm
+++ b/lib/PublicInbox/HTTPD/Async.pm
@@ -14,6 +14,15 @@ require PublicInbox::EvCleanup;
 
 sub new {
         my ($class, $io, $cb, $cleanup) = @_;
+
+        # no $io? call $cb at the top of the next event loop to
+        # avoid recursion:
+        unless (defined($io)) {
+                PublicInbox::EvCleanup::asap($cb) if $cb;
+                PublicInbox::EvCleanup::next_tick($cleanup) if $cleanup;
+                return;
+        }
+
         my $self = fields::new($class);
         IO::Handle::blocking($io, 0);
         $self->SUPER::new($io);