Bug #31025 for AutoLoader: AutoLoader slowness in "can"

Hi p5p, I just received the following bug report for AutoLoader from Slaven Rezic. Apparently, AutoLoader > 5.60, $obj->can("foo") tries to autoload the foo method. (Given that the package of $obj uses AutoLoader's AUTOLOAD.) Slaven points out that this inflicts a stat() call, which is suboptimal. If I find some time today, I'll investigate this, but I can't make any promises. I'm not sure Slaven's proposed patch is a good solution at first sight. Any input is appreciated. Best regards, Steffen Tue Nov 27 17:40:08 2007: Request 31016 was acted upon. Transaction: Ticket created by SREZIC Queue: AutoLoader Subject: AutoLoader:can: Slowness because of numerous stat(2) calls Broken in: 5.63 Severity: Critical Owner: Nobody Requestors: SREZIC@cpan.org Status: new Ticket <URL: http://rt.cpan.org/Ticket/Display.html?id=31016 > An OO program, which uses AutoLoader 5.63 and can(), may have performance problems because of many stat(2) calls. Consider the following program package Bla; use AutoLoader qw(AUTOLOAD); my $x = bless {}, __PACKAGE__; for (1..100) { $x->can("not_existent"); } __END__ With 5.8.8 and AutoLoader 5.60, it seems that there is no attempt to autoload the "not_existent" method: $ truss perl5.8.8 Bla.pm | & grep 'stat.*not_existent.al' | wc -l 0 With 5.10.0 or 5.8.8 with AutoLoader 5.63, every can() call would cause a stat() call, which may be expensive: $ truss perl5.8.8 -Mblib=/usr/local/src/CPAN/build/AutoLoader-5.63-zw4plq Bla.pm | & grep 'stat.*not_existent.al' | wc -l 900 $ truss perl5.10.0 Bla.pm | & grep 'stat.*not_existent.al' | wc -l 500 The root of the problem is that the "require" in AutoLoader::can is called every time. A possible fix is to fake %INC so that require is called only once. See the attached patch. I see two minor problems with the patch, though probably not really relevant: * Programs which use the keys or values of %INC (e.g. for reloading) will be misleaded * Formerly a (long-running) program would benefit from a late installation of the missing autoloaded file. See also ticket where this problem was reported originally: http://rt.cpan.org/Ticket/Display.html?id=30929 Regards, Slaven #### Patch data follows #### diff -up '../build/AutoLoader-5.63-zw4plq/lib/AutoLoader.pm' 'AutoLoader-5.63/lib/AutoLoader.pm' Index: ./lib/AutoLoader.pm --- ./lib/AutoLoader.pm Wed Jan 17 14:18:54 2007 +++ ./lib/AutoLoader.pm Tue Nov 27 23:29:04 2007 @@ -60,7 +60,7 @@ sub can { my $package = ref( $self ) || $self; my $filename = AutoLoader::find_filename( $package . '::' . $method ); local $@; - return unless eval { require $filename }; + $INC{$filename} = undef, return unless eval { require $filename }; no strict 'refs'; return \&{ $package . '::' . $method }; #### End of Patch data ####