v2writable: more ways to detect online CPU count

OpenBSD and FreeBSD support `getconf NPROCESSORS_ONLN` (no
leading underscore).  They may also have GNU nproc installed as
"gnproc".

We may also encounter Linux systems w/o GNU coreutils, but able
to use `getconf _NPROCESSORS_ONLN` (with leading underscore).

diff --git a/lib/PublicInbox/V2Writable.pm b/lib/PublicInbox/V2Writable.pm
index 72d8d5af6641aac8e0080132a92d26a11642c173..82843241f50a507ad4001723f632b976b30c33c1 100644 (file)
--- a/lib/PublicInbox/V2Writable.pm
+++ b/lib/PublicInbox/V2Writable.pm
@@ -7,6 +7,7 @@ package PublicInbox::V2Writable;
 use strict;
 use warnings;
 use base qw(PublicInbox::Lock);
+use 5.010_001;
 use PublicInbox::SearchIdxShard;
 use PublicInbox::MIME;
 use PublicInbox::Git;
@@ -32,14 +33,29 @@ my $PACKING_FACTOR = 0.4;
 # to increase Xapian shards
 our $NPROC_MAX_DEFAULT = 4;
 
+sub detect_nproc () {
+       for my $nproc (qw(nproc gnproc)) { # GNU coreutils nproc
+               `$nproc 2>/dev/null` =~ /^(\d+)$/ and return $1;
+       }
+
+       # getconf(1) is POSIX, but *NPROCESSORS* vars are not
+       for (qw(_NPROCESSORS_ONLN NPROCESSORS_ONLN)) {
+               `getconf $_ 2>/dev/null` =~ /^(\d+)$/ and return $1;
+       }
+
+       # should we bother with `sysctl hw.ncpu`?  Those only give
+       # us total processor count, not online processor count.
+       undef
+}
+
 sub nproc_shards ($) {
        my ($creat_opt) = @_;
        my $n = $creat_opt->{nproc} if ref($creat_opt) eq 'HASH';
        $n //= $ENV{NPROC};
        if (!$n) {
-               chomp($n = `nproc 2>/dev/null`);
-               # assume 2 cores if GNU nproc(1) is not available
-               $n = 2 if !$n;
+               # assume 2 cores if not detectable or zero
+               state $NPROC_DETECTED = detect_nproc() || 2;
+               $n = $NPROC_DETECTED;
                $n = $NPROC_MAX_DEFAULT if $n > $NPROC_MAX_DEFAULT;
        }