chainlint.pl: validate test scripts in parallel

Although chainlint.pl has undergone a good deal of optimization during
its development -- increasing in speed significantly -- parsing and
validating 1050+ scripts and 16500+ tests via Perl is not exactly
instantaneous. However, perceived performance can be improved by taking
advantage of the fact that there is no interdependence between test
scripts or test definitions, thus parsing and validating can be done in
parallel. The number of available cores is determined automatically but
can be overridden via the --jobs option.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/chainlint.pl

@@ -15,9 +15,11 @@
 
 use warnings;
 use strict;
+use Config;
 use File::Glob;
 use Getopt::Long;
 
+my $jobs = -1;
 my $show_stats;
 my $emit_all;
 
@@ -569,6 +571,16 @@ package main;
 	$interval = sub { return Time::HiRes::tv_interval(shift); };
 }
 
+sub ncores {
+	# Windows
+	return $ENV{NUMBER_OF_PROCESSORS} if exists($ENV{NUMBER_OF_PROCESSORS});
+	# Linux / MSYS2 / Cygwin / WSL
+	do { local @ARGV='/proc/cpuinfo'; return scalar(grep(/^processor\s*:/, <>)); } if -r '/proc/cpuinfo';
+	# macOS & BSD
+	return qx/sysctl -n hw.ncpu/ if $^O =~ /(?:^darwin$|bsd)/;
+	return 1;
+}
+
 sub show_stats {
 	my ($start_time, $stats) = @_;
 	my $walltime = $interval->($start_time);
@@ -621,7 +633,9 @@ sub exit_code {
 Getopt::Long::Configure(qw{bundling});
 GetOptions(
 	"emit-all!" => \$emit_all,
+	"jobs|j=i" => \$jobs,
 	"stats|show-stats!" => \$show_stats) or die("option error\n");
+$jobs = ncores() if $jobs < 1;
 
 my $start_time = $getnow->();
 my @stats;
@@ -633,6 +647,40 @@ sub exit_code {
 	exit;
 }
 
-push(@stats, check_script(1, sub { shift(@scripts); }, sub { print(@_); }));
+unless ($Config{useithreads} && eval {
+	require threads; threads->import();
+	require Thread::Queue; Thread::Queue->import();
+	1;
+	}) {
+	push(@stats, check_script(1, sub { shift(@scripts); }, sub { print(@_); }));
+	show_stats($start_time, \@stats) if $show_stats;
+	exit(exit_code(\@stats));
+}
+
+my $script_queue = Thread::Queue->new();
+my $output_queue = Thread::Queue->new();
+
+sub next_script { return $script_queue->dequeue(); }
+sub emit { $output_queue->enqueue(@_); }
+
+sub monitor {
+	while (my $s = $output_queue->dequeue()) {
+		print($s);
+	}
+}
+
+my $mon = threads->create({'context' => 'void'}, \&monitor);
+threads->create({'context' => 'list'}, \&check_script, $_, \&next_script, \&emit) for 1..$jobs;
+
+$script_queue->enqueue(@scripts);
+$script_queue->end();
+
+for (threads->list()) {
+	push(@stats, $_->join()) unless $_ == $mon;
+}
+
+$output_queue->end();
+$mon->join();
+
 show_stats($start_time, \@stats) if $show_stats;
 exit(exit_code(\@stats));