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   1  package SelfLoader;
   2  
   3  use 5.009005; # due to new regexp features
   4  use strict;
   5  
   6  use Exporter;
   7  our @ISA = qw(Exporter);
   8  our @EXPORT = qw(AUTOLOAD);
   9  our $VERSION = "1.11";
  10  sub Version {$VERSION}
  11  sub DEBUG () { 0 }
  12  
  13  my %Cache;      # private cache for all SelfLoader's client packages
  14  
  15  # allow checking for valid ': attrlist' attachments
  16  # see also AutoSplit
  17  
  18  my $attr_list = qr{
  19      \s* : \s*
  20      (?:
  21      # one attribute
  22      (?> # no backtrack
  23          (?! \d) \w+
  24          (?<nested> \( (?: [^()]++ | (?&nested)++ )*+ \) ) ?
  25      )
  26      (?: \s* : \s* | \s+ (?! :) )
  27      )*
  28  }x;
  29  
  30  # in croak and carp, protect $@ from "require Carp;" RT #40216
  31  
  32  sub croak { { local $@; require Carp; } goto &Carp::croak }
  33  sub carp { { local $@; require Carp; } goto &Carp::carp }
  34  
  35  AUTOLOAD {
  36      our $AUTOLOAD;
  37      print STDERR "SelfLoader::AUTOLOAD for $AUTOLOAD\n" if DEBUG;
  38      my $SL_code = $Cache{$AUTOLOAD};
  39      my $save = $@; # evals in both AUTOLOAD and _load_stubs can corrupt $@
  40      unless ($SL_code) {
  41          # Maybe this pack had stubs before __DATA__, and never initialized.
  42          # Or, this maybe an automatic DESTROY method call when none exists.
  43          $AUTOLOAD =~ m/^(.*)::/;
  44          SelfLoader->_load_stubs($1) unless exists $Cache{"$1}::<DATA"};
  45          $SL_code = $Cache{$AUTOLOAD};
  46          $SL_code = "sub $AUTOLOAD { }"
  47              if (!$SL_code and $AUTOLOAD =~ m/::DESTROY$/);
  48          croak "Undefined subroutine $AUTOLOAD" unless $SL_code;
  49      }
  50      print STDERR "SelfLoader::AUTOLOAD eval: $SL_code\n" if DEBUG;
  51  
  52      {
  53      no strict;
  54      eval $SL_code;
  55      }
  56      if ($@) {
  57          $@ =~ s/ at .*\n//;
  58          croak $@;
  59      }
  60      $@ = $save;
  61      defined(&$AUTOLOAD) || die "SelfLoader inconsistency error";
  62      delete $Cache{$AUTOLOAD};
  63      goto &$AUTOLOAD
  64  }
  65  
  66  sub load_stubs { shift->_load_stubs((caller)[0]) }
  67  
  68  sub _load_stubs {
  69      # $endlines is used by Devel::SelfStubber to capture lines after __END__
  70      my($self, $callpack, $endlines) = @_;
  71      no strict "refs";
  72      my $fh = \*{"$callpack}::DATA"};
  73      use strict;
  74      my $currpack = $callpack;
  75      my($line,$name,@lines, @stubs, $protoype);
  76  
  77      print STDERR "SelfLoader::load_stubs($callpack)\n" if DEBUG;
  78      croak("$callpack doesn't contain an __DATA__ token")
  79          unless defined fileno($fh);
  80      # Protect: fork() shares the file pointer between the parent and the kid
  81      if(sysseek($fh, tell($fh), 0)) {
  82        open my $nfh, '<&', $fh or croak "reopen: $!";# dup() the fd
  83        close $fh or die "close: $1";                 # autocloses, but be paranoid
  84        open $fh, '<&', $nfh or croak "reopen2: $!";  # dup() the fd "back"
  85        close $nfh or die "close after reopen: $1";   # autocloses, but be paranoid
  86      }
  87      $Cache{"$currpack}::<DATA"} = 1;   # indicate package is cached
  88  
  89      local($/) = "\n";
  90      while(defined($line = <$fh>) and $line !~ m/^__END__/) {
  91      if ($line =~ m/^sub\s+([\w:]+)\s*((?:\([\\\$\@\%\&\*\;]*\))?(?:$attr_list)?)/) {
  92              push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype));
  93              $protoype = $2;
  94              @lines = ($line);
  95              if (index($1,'::') == -1) {         # simple sub name
  96                  $name = "$currpack}::$1";
  97              } else {                            # sub name with package
  98                  $name = $1;
  99                  $name =~ m/^(.*)::/;
 100                  if (defined(&{"$1}::AUTOLOAD"})) {
 101                      \&{"$1}::AUTOLOAD"} == \&SelfLoader::AUTOLOAD ||
 102                          die 'SelfLoader Error: attempt to specify Selfloading',
 103                              " sub $name in non-selfloading module $1";
 104                  } else {
 105                      $self->export($1,'AUTOLOAD');
 106                  }
 107              }
 108          } elsif ($line =~ m/^package\s+([\w:]+)/) { # A package declared
 109              push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype));
 110              $self->_package_defined($line);
 111              $name = '';
 112              @lines = ();
 113              $currpack = $1;
 114              $Cache{"$currpack}::<DATA"} = 1;   # indicate package is cached
 115              if (defined(&{"$1}::AUTOLOAD"})) {
 116                  \&{"$1}::AUTOLOAD"} == \&SelfLoader::AUTOLOAD ||
 117                      die 'SelfLoader Error: attempt to specify Selfloading',
 118                          " package $currpack which already has AUTOLOAD";
 119              } else {
 120                  $self->export($currpack,'AUTOLOAD');
 121              }
 122          } else {
 123              push(@lines,$line);
 124          }
 125      }
 126      if (defined($line) && $line =~ /^__END__/) { # __END__
 127          unless ($line =~ /^__END__\s*DATA/) {
 128              if ($endlines) {
 129                  # Devel::SelfStubber would like us to capture the lines after
 130                  # __END__ so it can write out the entire file
 131                  @$endlines = <$fh>;
 132              }
 133              close($fh);
 134          }
 135      }
 136      push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype));
 137      no strict;
 138      eval join('', @stubs) if @stubs;
 139  }
 140  
 141  
 142  sub _add_to_cache {
 143      my($self,$fullname,$pack,$lines, $protoype) = @_;
 144      return () unless $fullname;
 145      carp("Redefining sub $fullname")
 146        if exists $Cache{$fullname};
 147      $Cache{$fullname} = join('', "package $pack; ",@$lines);
 148      print STDERR "SelfLoader cached $fullname: $Cache{$fullname}" if DEBUG;
 149      # return stub to be eval'd
 150      defined($protoype) ? "sub $fullname $protoype;" : "sub $fullname;"
 151  }
 152  
 153  sub _package_defined {}
 154  
 155  1;
 156  __END__
 157  
 158  =head1 NAME
 159  
 160  SelfLoader - load functions only on demand
 161  
 162  =head1 SYNOPSIS
 163  
 164      package FOOBAR;
 165      use SelfLoader;
 166  
 167      ... (initializing code)
 168  
 169      __DATA__
 170      sub {....
 171  
 172  
 173  =head1 DESCRIPTION
 174  
 175  This module tells its users that functions in the FOOBAR package are to be
 176  autoloaded from after the C<__DATA__> token.  See also
 177  L<perlsub/"Autoloading">.
 178  
 179  =head2 The __DATA__ token
 180  
 181  The C<__DATA__> token tells the perl compiler that the perl code
 182  for compilation is finished. Everything after the C<__DATA__> token
 183  is available for reading via the filehandle FOOBAR::DATA,
 184  where FOOBAR is the name of the current package when the C<__DATA__>
 185  token is reached. This works just the same as C<__END__> does in
 186  package 'main', but for other modules data after C<__END__> is not
 187  automatically retrievable, whereas data after C<__DATA__> is.
 188  The C<__DATA__> token is not recognized in versions of perl prior to
 189  5.001m.
 190  
 191  Note that it is possible to have C<__DATA__> tokens in the same package
 192  in multiple files, and that the last C<__DATA__> token in a given
 193  package that is encountered by the compiler is the one accessible
 194  by the filehandle. This also applies to C<__END__> and main, i.e. if
 195  the 'main' program has an C<__END__>, but a module 'require'd (_not_ 'use'd)
 196  by that program has a 'package main;' declaration followed by an 'C<__DATA__>',
 197  then the C<DATA> filehandle is set to access the data after the C<__DATA__>
 198  in the module, _not_ the data after the C<__END__> token in the 'main'
 199  program, since the compiler encounters the 'require'd file later.
 200  
 201  =head2 SelfLoader autoloading
 202  
 203  The B<SelfLoader> works by the user placing the C<__DATA__>
 204  token I<after> perl code which needs to be compiled and
 205  run at 'require' time, but I<before> subroutine declarations
 206  that can be loaded in later - usually because they may never
 207  be called.
 208  
 209  The B<SelfLoader> will read from the FOOBAR::DATA filehandle to
 210  load in the data after C<__DATA__>, and load in any subroutine
 211  when it is called. The costs are the one-time parsing of the
 212  data after C<__DATA__>, and a load delay for the _first_
 213  call of any autoloaded function. The benefits (hopefully)
 214  are a speeded up compilation phase, with no need to load
 215  functions which are never used.
 216  
 217  The B<SelfLoader> will stop reading from C<__DATA__> if
 218  it encounters the C<__END__> token - just as you would expect.
 219  If the C<__END__> token is present, and is followed by the
 220  token DATA, then the B<SelfLoader> leaves the FOOBAR::DATA
 221  filehandle open on the line after that token.
 222  
 223  The B<SelfLoader> exports the C<AUTOLOAD> subroutine to the
 224  package using the B<SelfLoader>, and this loads the called
 225  subroutine when it is first called.
 226  
 227  There is no advantage to putting subroutines which will _always_
 228  be called after the C<__DATA__> token.
 229  
 230  =head2 Autoloading and package lexicals
 231  
 232  A 'my $pack_lexical' statement makes the variable $pack_lexical
 233  local _only_ to the file up to the C<__DATA__> token. Subroutines
 234  declared elsewhere _cannot_ see these types of variables,
 235  just as if you declared subroutines in the package but in another
 236  file, they cannot see these variables.
 237  
 238  So specifically, autoloaded functions cannot see package
 239  lexicals (this applies to both the B<SelfLoader> and the Autoloader).
 240  The C<vars> pragma provides an alternative to defining package-level
 241  globals that will be visible to autoloaded routines. See the documentation
 242  on B<vars> in the pragma section of L<perlmod>.
 243  
 244  =head2 SelfLoader and AutoLoader
 245  
 246  The B<SelfLoader> can replace the AutoLoader - just change 'use AutoLoader'
 247  to 'use SelfLoader' (though note that the B<SelfLoader> exports
 248  the AUTOLOAD function - but if you have your own AUTOLOAD and
 249  are using the AutoLoader too, you probably know what you're doing),
 250  and the C<__END__> token to C<__DATA__>. You will need perl version 5.001m
 251  or later to use this (version 5.001 with all patches up to patch m).
 252  
 253  There is no need to inherit from the B<SelfLoader>.
 254  
 255  The B<SelfLoader> works similarly to the AutoLoader, but picks up the
 256  subs from after the C<__DATA__> instead of in the 'lib/auto' directory.
 257  There is a maintenance gain in not needing to run AutoSplit on the module
 258  at installation, and a runtime gain in not needing to keep opening and
 259  closing files to load subs. There is a runtime loss in needing
 260  to parse the code after the C<__DATA__>. Details of the B<AutoLoader> and
 261  another view of these distinctions can be found in that module's
 262  documentation.
 263  
 264  =head2 __DATA__, __END__, and the FOOBAR::DATA filehandle.
 265  
 266  This section is only relevant if you want to use
 267  the C<FOOBAR::DATA> together with the B<SelfLoader>.
 268  
 269  Data after the C<__DATA__> token in a module is read using the
 270  FOOBAR::DATA filehandle. C<__END__> can still be used to denote the end
 271  of the C<__DATA__> section if followed by the token DATA - this is supported
 272  by the B<SelfLoader>. The C<FOOBAR::DATA> filehandle is left open if an
 273  C<__END__> followed by a DATA is found, with the filehandle positioned at
 274  the start of the line after the C<__END__> token. If no C<__END__> token is
 275  present, or an C<__END__> token with no DATA token on the same line, then
 276  the filehandle is closed.
 277  
 278  The B<SelfLoader> reads from wherever the current
 279  position of the C<FOOBAR::DATA> filehandle is, until the
 280  EOF or C<__END__>. This means that if you want to use
 281  that filehandle (and ONLY if you want to), you should either
 282  
 283  1. Put all your subroutine declarations immediately after
 284  the C<__DATA__> token and put your own data after those
 285  declarations, using the C<__END__> token to mark the end
 286  of subroutine declarations. You must also ensure that the B<SelfLoader>
 287  reads first by  calling 'SelfLoader-E<gt>load_stubs();', or by using a
 288  function which is selfloaded;
 289  
 290  or
 291  
 292  2. You should read the C<FOOBAR::DATA> filehandle first, leaving
 293  the handle open and positioned at the first line of subroutine
 294  declarations.
 295  
 296  You could conceivably do both.
 297  
 298  =head2 Classes and inherited methods.
 299  
 300  For modules which are not classes, this section is not relevant.
 301  This section is only relevant if you have methods which could
 302  be inherited.
 303  
 304  A subroutine stub (or forward declaration) looks like
 305  
 306    sub stub;
 307  
 308  i.e. it is a subroutine declaration without the body of the
 309  subroutine. For modules which are not classes, there is no real
 310  need for stubs as far as autoloading is concerned.
 311  
 312  For modules which ARE classes, and need to handle inherited methods,
 313  stubs are needed to ensure that the method inheritance mechanism works
 314  properly. You can load the stubs into the module at 'require' time, by
 315  adding the statement 'SelfLoader-E<gt>load_stubs();' to the module to do
 316  this.
 317  
 318  The alternative is to put the stubs in before the C<__DATA__> token BEFORE
 319  releasing the module, and for this purpose the C<Devel::SelfStubber>
 320  module is available.  However this does require the extra step of ensuring
 321  that the stubs are in the module. If this is done I strongly recommend
 322  that this is done BEFORE releasing the module - it should NOT be done
 323  at install time in general.
 324  
 325  =head1 Multiple packages and fully qualified subroutine names
 326  
 327  Subroutines in multiple packages within the same file are supported - but you
 328  should note that this requires exporting the C<SelfLoader::AUTOLOAD> to
 329  every package which requires it. This is done automatically by the
 330  B<SelfLoader> when it first loads the subs into the cache, but you should
 331  really specify it in the initialization before the C<__DATA__> by putting
 332  a 'use SelfLoader' statement in each package.
 333  
 334  Fully qualified subroutine names are also supported. For example,
 335  
 336     __DATA__
 337     sub foo::bar {23}
 338     package baz;
 339     sub dob {32}
 340  
 341  will all be loaded correctly by the B<SelfLoader>, and the B<SelfLoader>
 342  will ensure that the packages 'foo' and 'baz' correctly have the
 343  B<SelfLoader> C<AUTOLOAD> method when the data after C<__DATA__> is first
 344  parsed.
 345  
 346  =cut