ipc: wq: support dynamic worker count change

Increasing/decreasing workers count will be useful in
some situations.

1 files changed, 72 insertions, 27 deletions

diff --git a/lib/PublicInbox/IPC.pm b/lib/PublicInbox/IPC.pm
index 0c5205c1..5bca3627 100644
--- a/lib/PublicInbox/IPC.pm
+++ b/lib/PublicInbox/IPC.pm
@@ -8,7 +8,7 @@ use v5.10.1;
 use Carp qw(confess croak);
 use PublicInbox::DS qw(dwaitpid);
 use PublicInbox::Spawn;
-use POSIX ();
+use POSIX qw(WNOHANG);
 use Socket qw(AF_UNIX MSG_EOR);
 my $SEQPACKET = eval { Socket::SOCK_SEQPACKET() }; # portable enough?
 use constant PIPE_BUF => $^O eq 'linux' ? 4096 : POSIX::_POSIX_PIPE_BUF();
@@ -112,7 +112,7 @@ sub ipc_worker_spawn {
                 $w_res->autoflush(1);
                 $SIG{$_} = 'IGNORE' for (qw(TERM INT QUIT));
                 local $0 = $ident;
-                PublicInbox::DS::sig_setmask($oldset);
+                PublicInbox::DS::sig_setmask($sigset);
                 my $on_destroy = $self->ipc_atfork_child;
                 eval { ipc_worker_loop($self, $r_req, $w_res) };
                 die "worker $ident PID:$$ died: $@\n" if $@;
@@ -229,12 +229,13 @@ sub ipc_sibling_atfork_child {
         $pid == $$ and die "BUG: $$ ipc_atfork_child called on itself";
 }
 
-sub wq_worker_loop ($$) {
-        my ($self, $s2) = @_;
+sub wq_worker_loop ($) {
+        my ($self) = @_;
         my $buf;
         my $len = $self->{wq_req_len} // (4096 * 33);
         my ($rec, $sub, @args);
-        while (1) {
+        my $s2 = $self->{-wq_s2} // die 'BUG: no -wq_s2';
+        until ($self->{-wq_quit}) {
                 my (@fds) = $recv_cmd->($s2, $buf, $len) or return; # EOF
                 my $i = 0;
                 my @m = @{$self->{wq_open_modes} // [qw( +<&= >&= >&= )]};
@@ -258,7 +259,7 @@ sub wq_worker_loop ($$) {
 
 sub wq_do { # always async
         my ($self, $sub, $in, $out, $err, @args) = @_;
-        if (my $s1 = $self->{-wq_seq}) { # run in worker
+        if (my $s1 = $self->{-wq_s1}) { # run in worker
                 $_ = fileno($_) for ($in, $out, $err);
                 $send_cmd->($s1, $in, $out, $err,
                                 freeze([$sub, @args]), MSG_EOR);
@@ -270,42 +271,86 @@ sub wq_do { # always async
         }
 }
 
+sub _wq_worker_start ($$) {
+        my ($self, $oldset) = @_;
+        my $pid = fork // die "fork: $!";
+        if ($pid == 0) {
+                eval { PublicInbox::DS->Reset };
+                close(delete $self->{-wq_s1});
+                delete $self->{qw(-wq_workers -wq_quit)};
+                my $quit = sub { $self->{-wq_quit} = 1 };
+                $SIG{$_} = $quit for (qw(TERM INT QUIT));
+                $SIG{$_} = 'IGNORE' for (qw(TTOU TTIN));
+                local $0 = $self->{-wq_ident};
+                PublicInbox::DS::sig_setmask($oldset);
+                my $on_destroy = $self->ipc_atfork_child;
+                eval { wq_worker_loop($self) };
+                die "worker $self->{-wq_ident} PID:$$ died: $@\n" if $@;
+                exit;
+        } else {
+                $self->{-wq_workers}->{$pid} = \undef;
+        }
+}
+
 # starts workqueue workers if Sereal or Storable is installed
 sub wq_workers_start {
         my ($self, $ident, $nr_workers, $oldset) = @_;
         ($enc && $send_cmd && $recv_cmd && defined($SEQPACKET)) or return;
-        return if $self->{-wq_seq}; # idempotent
+        return if $self->{-wq_s1}; # idempotent
         my ($s1, $s2);
         socketpair($s1, $s2, AF_UNIX, $SEQPACKET, 0) or die "socketpair: $!";
-        my $sigset = $oldset // PublicInbox::DS::block_signals();
         $self->ipc_atfork_parent;
         $nr_workers //= 4;
+        my $sigset = $oldset // PublicInbox::DS::block_signals();
         $self->{-wq_workers} = {};
-        for my $i (0..($nr_workers - 1)) {
-                defined(my $pid = fork) or die "fork: $!";
-                if ($pid == 0) {
-                        eval { PublicInbox::DS->Reset };
-                        $s1 = undef;
-                        $SIG{$_} = 'IGNORE' for (qw(TERM INT QUIT));
-                        local $0 = $ident."[$i]";
-                        PublicInbox::DS::sig_setmask($oldset);
-                        my $on_destroy = $self->ipc_atfork_child;
-                        eval { wq_worker_loop($self, $s2) };
-                        die "worker $ident PID:$$ died: $@\n" if $@;
-                        exit;
-                } else {
-                        $self->{-wq_workers}->{$pid} = $i;
-                }
-        }
+        $self->{-wq_ident} = $ident;
+        $self->{-wq_s1} = $s1;
+        $self->{-wq_s2} = $s2;
+        _wq_worker_start($self, $sigset) for (1..$nr_workers);
         PublicInbox::DS::sig_setmask($sigset) unless $oldset;
-        $s2 = undef;
-        $self->{-wq_seq} = $s1;
         $self->{-wq_ppid} = $$;
 }
 
+sub wq_worker_incr { # SIGTTIN handler
+        my ($self, $oldset) = @_;
+        $self->{-wq_s2} or return;
+        $self->ipc_atfork_parent;
+        my $sigset = $oldset // PublicInbox::DS::block_signals();
+        _wq_worker_start($self, $sigset);
+        PublicInbox::DS::sig_setmask($sigset) unless $oldset;
+}
+
+sub wq_exit { # wakes up wq_worker_decr_wait
+        send($_[0]->{-wq_s2}, $$, MSG_EOR) // die "$$ send: $!";
+        exit;
+}
+
+sub wq_worker_decr { # SIGTTOU handler, kills first idle worker
+        my ($self) = @_;
+        my $workers = $self->{-wq_workers} or return;
+        my $s2 = $self->{-wq_s2} // die 'BUG: no wq_s2';
+        $self->wq_do('wq_exit', $s2, $s2, $s2);
+        $self->{-wq_exit_pending}++;
+        # caller must call wq_worker_decr_wait in main loop
+}
+
+sub wq_worker_decr_wait {
+        my ($self, $timeout) = @_;
+        return if $self->{-wq_ppid} != $$; # can't reap siblings or parents
+        my $s1 = $self->{-wq_s1} // croak 'BUG: no wq_s1';
+        vec(my $rin = '', fileno($s1), 1) = 1;
+        select(my $rout = $rin, undef, undef, $timeout) or
+                croak 'timed out waiting for wq_exit';
+        recv($s1, my $pid, 64, 0) // croak "recv: $!";
+        my $workers = $self->{-wq_workers} // croak 'BUG: no wq_workers';
+        delete $workers->{$pid} // croak "BUG: PID:$pid invalid";
+        $self->{-wq_exit_pending}--;
+        dwaitpid($pid, \&ipc_worker_reap, $self);
+}
+
 sub wq_close {
         my ($self) = @_;
-        delete $self->{-wq_seq} or return;
+        delete @$self{qw(-wq_s1 -wq_s2)} or return;
         my $ppid = delete $self->{-wq_ppid} // die 'BUG: no wq_ppid';
         my $workers = delete $self->{-wq_workers} // die 'BUG: no wq_workers';
         return if $ppid != $$; # can't reap siblings or parents