update-xfonts-traditional: process fonts in parallel

Exploit multicore systems to speed up the runtime when processing
needs to be done.

Some timing results on a dual-core 1.50GHz Atom N550 laptop:

-j1
  real    0m43.035s
  user    0m43.319s
  sys     0m37.830s

-j2
  real    0m23.113s
  user    0m40.643s
  sys     0m30.486s

-j3
  real    0m21.910s
  user    0m43.707s
  sys     0m30.674s

-j4
  real    0m22.038s
  user    0m44.695s
  sys     0m31.058s

This system has hyperthreading so looks like 4 cores.  Based on this
I have set the number of processing threads to the number of cpus.

1 files changed, 63 insertions, 16 deletions

diff --git a/update-xfonts-traditional b/update-xfonts-traditional
index 65d1d08..8e04e60 100755
--- a/update-xfonts-traditional
+++ b/update-xfonts-traditional
@@ -7,6 +7,7 @@ use File::Glob qw(:glob);
 use Data::Dumper;
 use IO::Pipe;
 use File::Find;
+use Sys::CPU;
 
 our $prefix="/usr/local";
 our $package='xfonts-traditional';
@@ -22,6 +23,7 @@ our $verbose=0;
 our $reportfh;
 our $foundryinfo;
 our %props;
+our $wanted_parallel;
 
 sub reportloaded {
     return unless $verbose;
@@ -251,13 +253,44 @@ sub processfontdir ($) {
 	$changed = 1;
     }
     my $newdone = { '' => $foundryinfo };
-    my $log = new IO::File "$fontdir/$logfile", "w" 
-	or die "$fontdir/$logfile $!";
     my %outfiles; # bitmask: 1 /*exists*/ | 2 /*wanted*/
     my $updated=0;
     my $reported=0;
     my $anypcfs=0;
 
+    my $logpath = "$fontdir/$logfile";
+    unlink "$logpath" or $!==&ENOENT or die "$logpath $!";
+    my $log = new IO::File $logpath, ">>" or die "$logpath $!";
+
+    if (!$wanted_parallel) {
+	$wanted_parallel = Sys::CPU::cpu_count();
+	printf $reportfh "parallelism: %d\n", $wanted_parallel if $verbose>=2;
+    }
+    $wanted_parallel = 1 if $wanted_parallel < 1;
+
+    our %inprogress;
+
+    my $await = sub {
+	my $child = wait;
+	die $! unless defined $child;
+	my $job = $inprogress{$child};
+	die $child unless $job;
+
+	my $dent = $job->{Dent};
+	my $outdent = $job->{Outdent};
+	my $stats = $job->{Stats};
+	if ($?==0) {
+	    $updated++;
+	    $outfiles{$outdent} |= 3;
+	} elsif ($?==2*256) {
+	} else {
+	    die "[$child] $dent $outdent $?";
+	}
+	$newdone->{$dent} = $stats;
+	$changed = 1;
+	delete $inprogress{$child};
+    };
+
     flush $reportfh or die $!;
     while (my $dent = scalar readdir FD) {
 	if ($dent =~ m/^\Q$fontprefix\E.*\.new$/) {
@@ -287,21 +320,34 @@ sub processfontdir ($) {
 	    next;
 	}
 
-	my $r = processpcfgz("$fontdir/$dent",
-			     "$fontdir/$outdent.new",
-			     $log, $dent);
-	if ($r !~ m/^\d/) {
-	    printf $log "%s: unchanged - %s\n", $dent, $r;
-	    unlink "$fontdir/$outdent.new" or die "$fontdir $outdent $!";
-	} else {
-	    rename "$fontdir/$outdent.new", "$fontdir/$outdent"
-		or die "$fontdir $outdent $!";
-	    $updated++;
-	    $outfiles{$outdent} |= 3;
+	$await->() while scalar keys %inprogress >= $wanted_parallel;
+
+	my $child = fork;  die unless defined $child;
+	if (!$child) {
+	    my $r = processpcfgz("$fontdir/$dent",
+				 "$fontdir/$outdent.new",
+				 $log, $dent);
+	    my $rc;
+	    if ($r !~ m/^\d/) {
+		printf $log "%s: unchanged - %s\n", $dent, $r;
+		unlink "$fontdir/$outdent.new" or die "$fontdir $outdent $!";
+		$rc = 2;
+	    } else {
+		rename "$fontdir/$outdent.new", "$fontdir/$outdent"
+		    or die "$fontdir $outdent $!";
+		$rc = 0;
+	    }
+	    $log->flush or die "$logpath $!";
+	    exit $rc;
 	}
-	$newdone->{$dent} = $stats;
-	$changed = 1;
+	$inprogress{$child} = {
+	    Dent => $dent,
+	    Outdent => $outdent,
+	    Stats => $stats,
+	};
     }
+    $await->() while scalar keys %inprogress;
+
     my $affected=0;
     foreach my $olddent (keys %outfiles) {
 	my $state = $outfiles{$olddent};
@@ -320,7 +366,7 @@ sub processfontdir ($) {
 	die "$fontdir $? $!" if $? or $!;
     }
     if (!$anypcfs) {
-	unlink "$fontdir/$logfile" or die "$fontdir $!";
+	unlink "$logpath" or die "$fontdir $!";
 	unlink "$fontdir/$donefile" or $!==&ENOENT or die "$fontdir $!";
     } elsif ($changed) {
 	my $newdoneh = new IO::File "$fontdir/$donefile.new", 'w' 
@@ -357,6 +403,7 @@ our (@options)=(
     'R|rules-include=s@' => \@rulespath,
     'share-dir=s' => \$sharedir,
     'verbose|v+' => \$verbose,
+    'j|parallel=i' => \$wanted_parallel,
     );
 
 sub define_mode ($$) {