# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
# base class for remote IPC calls and workqueues, requires Storable or Sereal
+# - ipc_do and ipc_worker_* is for a single worker/producer and uses pipes
+# - wq_io_do and wq_worker* is for a single producer and multiple workers,
+# using SOCK_SEQPACKET for work distribution
+# use ipc_do when you need work done on a certain process
+# use wq_io_do when your work can be done on any idle worker
package PublicInbox::IPC;
use strict;
use v5.10.1;
-use Carp qw(confess croak);
+use parent qw(Exporter);
+use Carp qw(croak);
use PublicInbox::DS qw(dwaitpid);
use PublicInbox::Spawn;
-use POSIX qw(mkfifo WNOHANG);
+use PublicInbox::OnDestroy;
+use PublicInbox::WQWorker;
use Socket qw(AF_UNIX MSG_EOR SOCK_STREAM);
-use Errno qw(EMSGSIZE);
-use File::Temp 0.19 (); # 0.19 for ->newdir
+my $MY_MAX_ARG_STRLEN = 4096 * 33; # extra 4K for serialization
my $SEQPACKET = eval { Socket::SOCK_SEQPACKET() }; # portable enough?
-use constant PIPE_BUF => $^O eq 'linux' ? 4096 : POSIX::_POSIX_PIPE_BUF();
-my $WQ_MAX_WORKERS = 4096;
+our @EXPORT_OK = qw(ipc_freeze ipc_thaw);
my ($enc, $dec);
# ->imports at BEGIN turns sereal_*_with_object into custom ops on 5.14+
# and eliminate method call overhead
};
if ($enc && $dec) { # should be custom ops
- *freeze = sub ($) { sereal_encode_with_object $enc, $_[0] };
- *thaw = sub ($) { sereal_decode_with_object $dec, $_[0], my $ret };
+ *ipc_freeze = sub ($) { sereal_encode_with_object $enc, $_[0] };
+ *ipc_thaw = sub ($) { sereal_decode_with_object $dec, $_[0], my $ret };
} else {
- eval { # some distros have Storable as a separate package from Perl
- require Storable;
- Storable->import(qw(freeze thaw));
- $enc = 1;
- } // warn("Storable (part of Perl) missing: $@\n");
+ require Storable;
+ *ipc_freeze = \&Storable::freeze;
+ *ipc_thaw = \&Storable::thaw;
}
my $recv_cmd = PublicInbox::Spawn->can('recv_cmd4');
chop($len) eq "\n" or croak "no LF byte in $len";
defined(my $n = read($r, my $buf, $len)) or croak "read error: $!";
$n == $len or croak "short read: $n != $len";
- thaw($buf);
-}
-
-sub _pack_rec ($) {
- my ($ref) = @_;
- my $buf = freeze($ref);
- length($buf) . "\n" . $buf;
+ ipc_thaw($buf);
}
sub _send_rec ($$) {
my ($w, $ref) = @_;
- print $w _pack_rec($ref) or croak "print: $!";
+ my $buf = ipc_freeze($ref);
+ print $w length($buf), "\n", $buf or croak "print: $!";
}
sub ipc_return ($$$) {
# starts a worker if Sereal or Storable is installed
sub ipc_worker_spawn {
- my ($self, $ident, $oldset) = @_;
- return unless $enc; # no Sereal or Storable
+ my ($self, $ident, $oldset, $fields) = @_;
return if ($self->{-ipc_ppid} // -1) == $$; # idempotent
delete(@$self{qw(-ipc_req -ipc_res -ipc_ppid -ipc_pid)});
pipe(my ($r_req, $w_req)) or die "pipe: $!";
my $pid = fork // die "fork: $!";
if ($pid == 0) {
srand($seed);
+ eval { Net::SSLeay::randomize() };
eval { PublicInbox::DS->Reset };
- delete @$self{qw(-wq_s1 -wq_workers -wq_ppid)};
+ delete @$self{qw(-wq_s1 -wq_s2 -wq_workers -wq_ppid)};
$w_req = $r_res = undef;
$w_res->autoflush(1);
$SIG{$_} = 'IGNORE' for (qw(TERM INT QUIT));
local $0 = $ident;
- PublicInbox::DS::sig_setmask($sigset);
- my $on_destroy = $self->ipc_atfork_child;
- eval { ipc_worker_loop($self, $r_req, $w_res) };
- die "worker $ident PID:$$ died: $@\n" if $@;
- exit;
+ # ensure we properly exit even if warn() dies:
+ my $end = PublicInbox::OnDestroy->new($$, sub { exit(!!$@) });
+ eval {
+ $fields //= {};
+ local @$self{keys %$fields} = values(%$fields);
+ my $on_destroy = $self->ipc_atfork_child;
+ local @SIG{keys %SIG} = values %SIG;
+ PublicInbox::DS::sig_setmask($sigset);
+ ipc_worker_loop($self, $r_req, $w_res);
+ };
+ warn "worker $ident PID:$$ died: $@\n" if $@;
+ undef $end; # trigger exit
}
PublicInbox::DS::sig_setmask($sigset) unless $oldset;
$r_req = $w_res = undef;
}
sub ipc_worker_reap { # dwaitpid callback
- my ($self, $pid) = @_;
- # SIGTERM (15) is our default exit signal
- warn "PID:$pid died with \$?=$?\n" if $? && ($? & 127) != 15;
+ my ($args, $pid) = @_;
+ my ($self, @uargs) = @$args;
+ delete $self->{-wq_workers}->{$pid};
+ return $self->{-reap_do}->($args, $pid) if $self->{-reap_do};
+ return if !$?;
+ my $s = $? & 127;
+ # TERM(15) is our default exit signal, PIPE(13) is likely w/ pager
+ warn "$self->{-wq_ident} PID:$pid died \$?=$?\n" if $s != 15 && $s != 13
}
-sub wq_wait_old {
- my ($self) = @_;
- my $pids = delete $self->{"-wq_old_pids.$$"} or return;
- dwaitpid($_, \&ipc_worker_reap, $self) for @$pids;
+sub wq_wait_async {
+ my ($self, $cb, @uargs) = @_;
+ local $PublicInbox::DS::in_loop = 1;
+ $self->{-reap_async} = 1;
+ $self->{-reap_do} = $cb;
+ my @pids = keys %{$self->{-wq_workers}};
+ dwaitpid($_, \&ipc_worker_reap, [ $self, @uargs ]) for @pids;
}
# for base class, override in sub classes
sub ipc_atfork_prepare {}
+sub wq_atexit_child {}
+
sub ipc_atfork_child {
my ($self) = @_;
my $io = delete($self->{-ipc_atfork_child_close}) or return;
# idempotent, can be called regardless of whether worker is active or not
sub ipc_worker_stop {
- my ($self) = @_;
+ my ($self, $args) = @_;
my ($pid, $ppid) = delete(@$self{qw(-ipc_pid -ipc_ppid)});
my ($w_req, $r_res) = delete(@$self{qw(-ipc_req -ipc_res)});
if (!$w_req && !$r_res) {
$w_req = $r_res = undef;
return if $$ != $ppid;
- dwaitpid($pid, \&ipc_worker_reap, $self);
+ dwaitpid($pid, \&ipc_worker_reap, [$self, $args]);
}
# use this if we have multiple readers reading curl or "pigz -dc"
# and writing to the same store
sub ipc_lock_init {
my ($self, $f) = @_;
+ $f // die 'BUG: no filename given';
require PublicInbox::Lock;
$self->{-ipc_lock} //= bless { lock_path => $f }, 'PublicInbox::Lock'
}
-sub ipc_async_wait ($$) {
- my ($self, $max) = @_; # max == -1 to wait for all
- my $aif = $self->{-async_inflight} or return;
- my $r_res = $self->{-ipc_res} or die 'BUG: no ipc_res';
- while (my ($sub, $bytes, $cb, $cb_arg) = splice(@$aif, 0, 4)) {
- my $ret = _get_rec($r_res) //
- die "no response on $sub (req.size=$bytes)";
- $self->{-async_inflight_bytes} -= $bytes;
-
- eval { $cb->($cb_arg, $ret) };
- warn "E: $sub callback error: $@\n" if $@;
- return if --$max == 0;
- }
+sub _wait_return ($$) {
+ my ($r_res, $sub) = @_;
+ my $ret = _get_rec($r_res) // die "no response on $sub";
+ die $$ret if ref($ret) eq 'PublicInbox::IPC::Die';
+ wantarray ? @$ret : $$ret;
}
# call $self->$sub(@args), on a worker if ipc_worker_spawn was used
my $ipc_lock = $self->{-ipc_lock};
my $lock = $ipc_lock ? $ipc_lock->lock_for_scope : undef;
if (defined(wantarray)) {
- my $r_res = $self->{-ipc_res} or die 'BUG: no ipc_res';
- ipc_async_wait($self, -1);
+ my $r_res = $self->{-ipc_res} or die 'no ipc_res';
_send_rec($w_req, [ wantarray, $sub, @args ]);
- my $ret = _get_rec($r_res) // die "no response on $sub";
- die $$ret if ref($ret) eq 'PublicInbox::IPC::Die';
- wantarray ? @$ret : $$ret;
+ _wait_return($r_res, $sub);
} else { # likely, fire-and-forget into pipe
_send_rec($w_req, [ undef , $sub, @args ]);
}
}
}
-sub ipc_async {
- my ($self, $sub, $sub_args, $cb, $cb_arg) = @_;
- if (my $w_req = $self->{-ipc_req}) { # run in worker
- my $rec = _pack_rec([ 1, $sub, @$sub_args ]);
- my $cur_bytes = \($self->{-async_inflight_bytes} //= 0);
- while (($$cur_bytes + length($rec)) > PIPE_BUF) {
- ipc_async_wait($self, 1);
- }
- my $ipc_lock = $self->{-ipc_lock};
- my $lock = $ipc_lock ? $ipc_lock->lock_for_scope : undef;
- print $w_req $rec or croak "print: $!";
- $$cur_bytes += length($rec);
- push @{$self->{-async_inflight}},
- $sub, length($rec), $cb, $cb_arg;
- } else {
- my $ret = [ eval { $self->$sub(@$sub_args) } ];
- if (my $exc = $@) {
- $ret = ( bless(\$exc, 'PublicInbox::IPC::Die') );
- }
- eval { $cb->($cb_arg, $ret) };
- warn "E: $sub callback error: $@\n" if $@;
- }
-}
-
# needed when there's multiple IPC workers and the parent forking
# causes newer siblings to inherit older siblings sockets
sub ipc_sibling_atfork_child {
$pid == $$ and die "BUG: $$ ipc_atfork_child called on itself";
}
-sub _recv_and_run {
+sub recv_and_run {
my ($self, $s2, $len, $full_stream) = @_;
- my @fds = $recv_cmd->($s2, my $buf, $len);
- my $n = length($buf // '') or return;
+ my @fds = $recv_cmd->($s2, my $buf, $len // $MY_MAX_ARG_STRLEN);
+ return if scalar(@fds) && !defined($fds[0]);
+ my $n = length($buf) or return 0;
my $nfd = 0;
for my $fd (@fds) {
if (open(my $cmdfh, '+<&=', $fd)) {
$n = length($buf);
}
# Sereal dies on truncated data, Storable returns undef
- my $args = thaw($buf) // die "thaw error on buffer of size: $n";
+ my $args = ipc_thaw($buf) // die "thaw error on buffer of size: $n";
undef $buf;
my $sub = shift @$args;
eval { $self->$sub(@$args) };
- warn "$$ wq_worker: $@" if $@ && ref($@) ne 'PublicInbox::SIGPIPE';
+ warn "$$ $0 wq_worker: $sub: $@" if $@;
delete @$self{0..($nfd-1)};
$n;
}
-sub wq_worker_loop ($) {
- my ($self) = @_;
- my $len = $self->{wq_req_len} // (4096 * 33);
- my $s2 = $self->{-wq_s2} // die 'BUG: no -wq_s2';
- 1 while (_recv_and_run($self, $s2, $len));
+sub wq_worker_loop ($$) {
+ my ($self, $bcast2) = @_;
+ my $wqw = PublicInbox::WQWorker->new($self, $self->{-wq_s2});
+ PublicInbox::WQWorker->new($self, $bcast2) if $bcast2;
+ PublicInbox::DS->SetPostLoopCallback(sub { $wqw->{sock} });
+ PublicInbox::DS::event_loop();
+ PublicInbox::DS->Reset;
}
-sub do_sock_stream { # via wq_do, for big requests
+sub do_sock_stream { # via wq_io_do, for big requests
my ($self, $len) = @_;
- _recv_and_run($self, delete $self->{0}, $len, 1);
+ recv_and_run($self, my $s2 = delete $self->{0}, $len, 1);
+}
+
+sub wq_broadcast {
+ my ($self, $sub, @args) = @_;
+ if (my $wkr = $self->{-wq_workers}) {
+ my $buf = ipc_freeze([$sub, @args]);
+ for my $bcast1 (values %$wkr) {
+ my $sock = $bcast1 // $self->{-wq_s1} // next;
+ send($sock, $buf, MSG_EOR) // croak "send: $!";
+ # XXX shouldn't have to deal with EMSGSIZE here...
+ }
+ } else {
+ eval { $self->$sub(@args) };
+ warn "wq_broadcast: $@" if $@;
+ }
+}
+
+sub stream_in_full ($$$) {
+ my ($s1, $fds, $buf) = @_;
+ socketpair(my $r, my $w, AF_UNIX, SOCK_STREAM, 0) or
+ croak "socketpair: $!";
+ my $n = $send_cmd->($s1, [ fileno($r) ],
+ ipc_freeze(['do_sock_stream', length($buf)]),
+ MSG_EOR) // croak "sendmsg: $!";
+ undef $r;
+ $n = $send_cmd->($w, $fds, $buf, 0) // croak "sendmsg: $!";
+ while ($n < length($buf)) {
+ my $x = syswrite($w, $buf, length($buf) - $n, $n) //
+ croak "syswrite: $!";
+ croak "syswrite wrote 0 bytes" if $x == 0;
+ $n += $x;
+ }
}
-sub wq_do { # always async
+sub wq_io_do { # always async
my ($self, $sub, $ios, @args) = @_;
if (my $s1 = $self->{-wq_s1}) { # run in worker
my $fds = [ map { fileno($_) } @$ios ];
- my $n = $send_cmd->($s1, $fds, freeze([$sub, @args]), MSG_EOR);
- return if defined($n);
- croak "sendmsg error: $!" if $! != EMSGSIZE;
- socketpair(my $r, my $w, AF_UNIX, SOCK_STREAM, 0) or
- croak "socketpair: $!";
- my $buf = freeze([$sub, @args]);
- $n = $send_cmd->($s1, [ fileno($r) ],
- freeze(['do_sock_stream', length($buf)]),
- MSG_EOR) // croak "sendmsg: $!";
- undef $r;
- $n = $send_cmd->($w, $fds, $buf, 0) // croak "sendmsg: $!";
- while ($n < length($buf)) {
- my $x = syswrite($w, $buf, length($buf) - $n, $n) //
- croak "syswrite: $!";
- croak "syswrite wrote 0 bytes" if $x == 0;
- $n += $x;
+ my $buf = ipc_freeze([$sub, @args]);
+ if (length($buf) > $MY_MAX_ARG_STRLEN) {
+ stream_in_full($s1, $fds, $buf);
+ } else {
+ my $n = $send_cmd->($s1, $fds, $buf, MSG_EOR);
+ return if defined($n); # likely
+ $!{ETOOMANYREFS} and
+ croak "sendmsg: $! (check RLIMIT_NOFILE)";
+ $!{EMSGSIZE} ? stream_in_full($s1, $fds, $buf) :
+ croak("sendmsg: $!");
}
} else {
@$self{0..$#$ios} = @$ios;
eval { $self->$sub(@args) };
- warn "wq_do: $@" if $@ && ref($@) ne 'PublicInbox::SIGPIPE';
+ warn "wq_io_do: $@" if $@;
delete @$self{0..$#$ios}; # don't close
}
}
-sub _wq_worker_start ($$$) {
- my ($self, $oldset, $fields) = @_;
+sub wq_sync_run {
+ my ($self, $wantarray, $sub, @args) = @_;
+ if ($wantarray) {
+ my @ret = eval { $self->$sub(@args) };
+ ipc_return($self->{0}, \@ret, $@);
+ } else { # '' => wantscalar
+ my $ret = eval { $self->$sub(@args) };
+ ipc_return($self->{0}, \$ret, $@);
+ }
+}
+
+sub wq_do {
+ my ($self, $sub, @args) = @_;
+ if (defined(wantarray)) {
+ pipe(my ($r, $w)) or die "pipe: $!";
+ wq_io_do($self, 'wq_sync_run', [ $w ], wantarray, $sub, @args);
+ undef $w;
+ _wait_return($r, $sub);
+ } else {
+ wq_io_do($self, $sub, [], @args);
+ }
+}
+
+sub _wq_worker_start ($$$$) {
+ my ($self, $oldset, $fields, $one) = @_;
+ my ($bcast1, $bcast2);
+ $one or socketpair($bcast1, $bcast2, AF_UNIX, $SEQPACKET, 0) or
+ die "socketpair: $!";
my $seed = rand(0xffffffff);
my $pid = fork // die "fork: $!";
if ($pid == 0) {
srand($seed);
+ eval { Net::SSLeay::randomize() };
+ undef $bcast1;
eval { PublicInbox::DS->Reset };
- delete @$self{qw(-wq_s1 -wq_workers -wq_ppid)};
- @$self{keys %$fields} = values(%$fields) if $fields;
- $SIG{$_} = 'IGNORE' for (qw(PIPE TTOU TTIN));
- $SIG{$_} = 'DEFAULT' for (qw(TERM QUIT INT CHLD));
- local $0 = $self->{-wq_ident};
- PublicInbox::DS::sig_setmask($oldset);
+ delete @$self{qw(-wq_s1 -wq_ppid)};
+ $self->{-wq_worker_nr} =
+ keys %{delete($self->{-wq_workers}) // {}};
+ $SIG{$_} = 'DEFAULT' for (qw(TTOU TTIN TERM QUIT INT CHLD));
+ local $0 = $one ? $self->{-wq_ident} :
+ "$self->{-wq_ident} $self->{-wq_worker_nr}";
# ensure we properly exit even if warn() dies:
my $end = PublicInbox::OnDestroy->new($$, sub { exit(!!$@) });
- my $on_destroy = $self->ipc_atfork_child;
- eval { wq_worker_loop($self) };
+ eval {
+ $fields //= {};
+ local @$self{keys %$fields} = values(%$fields);
+ my $on_destroy = $self->ipc_atfork_child;
+ local @SIG{keys %SIG} = values %SIG;
+ PublicInbox::DS::sig_setmask($oldset);
+ wq_worker_loop($self, $bcast2);
+ };
warn "worker $self->{-wq_ident} PID:$$ died: $@" if $@;
- undef $on_destroy;
undef $end; # trigger exit
} else {
- $self->{-wq_workers}->{$pid} = \undef;
+ $self->{-wq_workers}->{$pid} = $bcast1;
}
}
# starts workqueue workers if Sereal or Storable is installed
sub wq_workers_start {
my ($self, $ident, $nr_workers, $oldset, $fields) = @_;
- ($enc && $send_cmd && $recv_cmd && defined($SEQPACKET)) or return;
+ ($send_cmd && $recv_cmd && defined($SEQPACKET)) or return;
return if $self->{-wq_s1}; # idempotent
$self->{-wq_s1} = $self->{-wq_s2} = undef;
socketpair($self->{-wq_s1}, $self->{-wq_s2}, AF_UNIX, $SEQPACKET, 0) or
die "socketpair: $!";
$self->ipc_atfork_prepare;
- $nr_workers //= 4;
- $nr_workers = $WQ_MAX_WORKERS if $nr_workers > $WQ_MAX_WORKERS;
+ $nr_workers //= $self->{-wq_nr_workers}; # was set earlier
my $sigset = $oldset // PublicInbox::DS::block_signals();
$self->{-wq_workers} = {};
$self->{-wq_ident} = $ident;
- _wq_worker_start($self, $sigset, $fields) for (1..$nr_workers);
+ my $one = $nr_workers == 1;
+ $self->{-wq_nr_workers} = $nr_workers;
+ _wq_worker_start($self, $sigset, $fields, $one) for (1..$nr_workers);
PublicInbox::DS::sig_setmask($sigset) unless $oldset;
$self->{-wq_ppid} = $$;
}
-sub wq_worker_incr { # SIGTTIN handler
- my ($self, $oldset, $fields) = @_;
- $self->{-wq_s2} or return;
- return if wq_workers($self) >= $WQ_MAX_WORKERS;
- $self->ipc_atfork_prepare;
- my $sigset = $oldset // PublicInbox::DS::block_signals();
- _wq_worker_start($self, $sigset, $fields);
- PublicInbox::DS::sig_setmask($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) = @_;
- return unless wq_workers($self);
- my $s2 = $self->{-wq_s2} // die 'BUG: no wq_s2';
- $self->wq_do('wq_exit', [ $s2, $s2, $s2 ]);
- # caller must call wq_worker_decr_wait in main loop
-}
-
-sub wq_worker_decr_wait {
- my ($self, $timeout) = @_;
- return if $self->{-wq_ppid} != $$; # can't reap siblings or parents
- my $s1 = $self->{-wq_s1} // croak 'BUG: no wq_s1';
- vec(my $rin = '', fileno($s1), 1) = 1;
- select(my $rout = $rin, undef, undef, $timeout) or
- croak 'timed out waiting for wq_exit';
- recv($s1, my $pid, 64, 0) // croak "recv: $!";
- my $workers = $self->{-wq_workers} // croak 'BUG: no wq_workers';
- delete $workers->{$pid} // croak "BUG: PID:$pid invalid";
- dwaitpid($pid, \&ipc_worker_reap, $self);
-}
-
-# set or retrieve number of workers
-sub wq_workers {
- my ($self, $nr) = @_;
- my $cur = $self->{-wq_workers} or return;
- if (defined $nr) {
- while (scalar(keys(%$cur)) > $nr) {
- $self->wq_worker_decr;
- $self->wq_worker_decr_wait;
- }
- $self->wq_worker_incr while scalar(keys(%$cur)) < $nr;
- }
- scalar(keys(%$cur));
-}
-
sub wq_close {
- my ($self, $nohang) = @_;
- delete @$self{qw(-wq_s1 -wq_s2)} or return;
- my $ppid = delete $self->{-wq_ppid} or return;
- my $workers = delete $self->{-wq_workers} // die 'BUG: no wq_workers';
- return if $ppid != $$; # can't reap siblings or parents
- my @pids = map { $_ + 0 } keys %$workers;
- if ($nohang) {
- push @{$self->{"-wq_old_pids.$$"}}, @pids;
- } else {
- dwaitpid($_, \&ipc_worker_reap, $self) for @pids;
- }
-}
-
-sub wq_kill_old {
my ($self) = @_;
- my $pids = $self->{"-wq_old_pids.$$"} or return;
- kill 'TERM', @$pids;
+ delete @$self{qw(-wq_s1 -wq_s2)} or return;
+ return if $self->{-reap_async};
+ my @pids = keys %{$self->{-wq_workers}};
+ dwaitpid($_, \&ipc_worker_reap, [ $self ]) for @pids;
}
sub wq_kill {
my ($self, $sig) = @_;
- my $workers = $self->{-wq_workers} or return;
- kill($sig // 'TERM', keys %$workers);
+ kill($sig // 'TERM', keys %{$self->{-wq_workers}});
}
-sub WQ_MAX_WORKERS { $WQ_MAX_WORKERS }
-
sub DESTROY {
my ($self) = @_;
my $ppid = $self->{-wq_ppid};
wq_kill($self) if $ppid && $ppid == $$;
wq_close($self);
- wq_wait_old($self);
ipc_worker_stop($self);
}
-# Sereal doesn't have dclone
-sub deep_clone { thaw(freeze($_[-1])) }
+sub detect_nproc () {
+ # _SC_NPROCESSORS_ONLN = 84 on both Linux glibc and musl
+ return POSIX::sysconf(84) if $^O eq 'linux';
+ return POSIX::sysconf(58) if $^O eq 'freebsd';
+ # TODO: more OSes
+
+ # getconf(1) is POSIX, but *NPROCESSORS* vars are not
+ for (qw(_NPROCESSORS_ONLN NPROCESSORS_ONLN)) {
+ `getconf $_ 2>/dev/null` =~ /^(\d+)$/ and return $1;
+ }
+ for my $nproc (qw(nproc gnproc)) { # GNU coreutils nproc
+ `$nproc 2>/dev/null` =~ /^(\d+)$/ and return $1;
+ }
+
+ # should we bother with `sysctl hw.ncpu`? Those only give
+ # us total processor count, not online processor count.
+ undef
+}
1;