git-svn: lazy load some modules

We can delay loading some modules until we need them for uncommon
code paths.  For example, persistent memoization is not often
needed, so we can avoid loading the modules for it until we
encounter svn::mergeinfo during fetch.

This gives a tiny reduction in syscalls (from 15641 to 15305) when
running "git svn info" and counting via "strace -fc".  Further,
more invasive work will be needed to noticeably improve performance.

Signed-off-by: Eric Wong <normalperson@yhbt.net>

1 files changed, 13 insertions, 9 deletions

diff --git a/perl/Git/SVN.pm b/perl/Git/SVN.pm
index 8e4af7153e..afa562c8b9 100644
--- a/perl/Git/SVN.pm
+++ b/perl/Git/SVN.pm
@@ -9,10 +9,8 @@ use vars qw/$_no_metadata
 	    $_use_log_author $_add_author_from $_localtime/;
 use Carp qw/croak/;
 use File::Path qw/mkpath/;
-use File::Copy qw/copy/;
 use IPC::Open3;
 use Memoize;  # core since 5.8.0, Jul 2002
-use Memoize::Storable;
 use POSIX qw(:signal_h);
 
 use Git qw(
@@ -32,11 +30,7 @@ use Git::SVN::Utils qw(
 	add_path_to_url
 );
 
-my $can_use_yaml;
-BEGIN {
-	$can_use_yaml = eval { require Git::SVN::Memoize::YAML; 1};
-}
-
+my $memo_backend;
 our $_follow_parent  = 1;
 our $_minimize_url   = 'unset';
 our $default_repo_id = 'svn';
@@ -1578,7 +1572,16 @@ sub tie_for_persistent_memoization {
 	my $hash = shift;
 	my $path = shift;
 
-	if ($can_use_yaml) {
+	unless ($memo_backend) {
+		if (eval { require Git::SVN::Memoize::YAML; 1}) {
+			$memo_backend = 1;
+		} else {
+			require Memoize::Storable;
+			$memo_backend = -1;
+		}
+	}
+
+	if ($memo_backend > 0) {
 		tie %$hash => 'Git::SVN::Memoize::YAML', "$path.yaml";
 	} else {
 		tie %$hash => 'Memoize::Storable', "$path.db", 'nstore';
@@ -2188,8 +2191,9 @@ sub rev_map_set {
 	# both of these options make our .rev_db file very, very important
 	# and we can't afford to lose it because rebuild() won't work
 	if ($self->use_svm_props || $self->no_metadata) {
+		require File::Copy;
 		$sync = 1;
-		copy($db, $db_lock) or die "rev_map_set(@_): ",
+		File::Copy::copy($db, $db_lock) or die "rev_map_set(@_): ",
 					   "Failed to copy: ",
 					   "$db => $db_lock ($!)\n";
 	} else {