[PATCH 25/26] xcpdb|compact: support --jobs/-j flag like gmake(1)

[Eric Wong <e@80x24.org>]

We don't have to be tied to the number of partitions in case
we made a bad choice at initialization.  This doesn't affect
reindexing, but the copying phase is already intensive.

And optimize away the extra process when we only have a single
job which won't parallelize.

The wording for the (v2) reindexing phase could be improved,
later.  I also plan to allow repartitioning of existing
Xapian DBs.
---
 lib/PublicInbox/Xapcmd.pm | 44 +++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/lib/PublicInbox/Xapcmd.pm b/lib/PublicInbox/Xapcmd.pm
index 5b6d06b..a294d53 100644
--- a/lib/PublicInbox/Xapcmd.pm
+++ b/lib/PublicInbox/Xapcmd.pm
@@ -13,7 +13,7 @@ use File::Basename qw(dirname);
 # support testing with dev versions of Xapian which installs
 # commands with a version number suffix (e.g. "xapian-compact-1.5")
 our $XAPIAN_COMPACT = $ENV{XAPIAN_COMPACT} || 'xapian-compact';
-our @COMPACT_OPT = qw(quiet|q blocksize|b=s no-full|n fuller|F);
+our @COMPACT_OPT = qw(jobs|j=i quiet|q blocksize|b=s no-full|n fuller|F);
 
 sub commit_changes ($$$) {
 	my ($ibx, $tmp, $opt) = @_;
@@ -54,8 +54,7 @@ sub cb_spawn {
 	my ($cb, $args, $opt) = @_; # $cb = cpdb() or compact()
 	defined(my $pid = fork) or die "fork: $!";
 	return $pid if $pid > 0;
-	eval { $cb->($args, $opt) };
-	die $@ if $@;
+	$cb->($args, $opt);
 	exit 0;
 }
 
@@ -103,6 +102,31 @@ sub same_fs_or_die ($$) {
 	die "$x and $y reside on different filesystems\n";
 }
 
+sub process_queue {
+	my ($queue, $cb, $max, $opt) = @_;
+	if ($max <= 1) {
+		while (defined(my $args = shift @$queue)) {
+			$cb->($args, $opt);
+		}
+		return;
+	}
+
+	# run in parallel:
+	my %pids;
+	while (@$queue) {
+		while (scalar(keys(%pids)) < $max && scalar(@$queue)) {
+			my $args = shift @$queue;
+			$pids{cb_spawn($cb, $args, $opt)} = $args;
+		}
+
+		while (scalar keys %pids) {
+			my $pid = waitpid(-1, 0);
+			my $args = delete $pids{$pid};
+			die join(' ', @$args)." failed: $?\n" if $?;
+		}
+	}
+}
+
 sub run {
 	my ($ibx, $task, $opt) = @_; # task = 'cpdb' or 'compact'
 	my $cb = \&${\"PublicInbox::Xapcmd::$task"};
@@ -163,19 +187,7 @@ sub run {
 		}
 
 		delete($ibx->{$_}) for (qw(mm over search)); # cleanup
-		my %pids;
-		while (@q) {
-			while (scalar(keys(%pids)) < $max && scalar(@q)) {
-				my $args = shift @q;
-				$pids{cb_spawn($cb, $args, $opt)} = $args;
-			}
-
-			while (scalar keys %pids) {
-				my $pid = waitpid(-1, 0);
-				my $args = delete $pids{$pid};
-				die join(' ', @$args)." failed: $?\n" if $?;
-			}
-		}
+		process_queue(\@q, $cb, $max, $opt);
 		commit_changes($ibx, $tmp, $opt);
 	});
 }
-- 
EW