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f8881bd9 AD |
1 | package SelfLoader; |
2 | use Carp; | |
3 | require Exporter; | |
4 | @ISA = qw(Exporter); | |
5 | @EXPORT = qw(AUTOLOAD); | |
6 | $VERSION = 1.06; sub Version {$VERSION} | |
7 | $DEBUG = 0; | |
8 | ||
9 | my %Cache; # private cache for all SelfLoader's client packages | |
10 | ||
11 | AUTOLOAD { | |
12 | print STDERR "SelfLoader::AUTOLOAD for $AUTOLOAD\n" if $DEBUG; | |
13 | my $code = $Cache{$AUTOLOAD}; | |
14 | unless ($code) { | |
15 | # Maybe this pack had stubs before __DATA__, and never initialized. | |
16 | # Or, this maybe an automatic DESTROY method call when none exists. | |
17 | $AUTOLOAD =~ m/^(.*)::/; | |
18 | SelfLoader->_load_stubs($1) unless exists $Cache{"${1}::<DATA"}; | |
19 | $code = $Cache{$AUTOLOAD}; | |
20 | $code = "sub $AUTOLOAD { }" if (!$code and $AUTOLOAD =~ m/::DESTROY$/); | |
21 | croak "Undefined subroutine $AUTOLOAD" unless $code; | |
22 | } | |
23 | print STDERR "SelfLoader::AUTOLOAD eval: $code\n" if $DEBUG; | |
24 | eval $code; | |
25 | if ($@) { | |
26 | $@ =~ s/ at .*\n//; | |
27 | croak $@; | |
28 | } | |
29 | defined(&$AUTOLOAD) || die "SelfLoader inconsistency error"; | |
30 | delete $Cache{$AUTOLOAD}; | |
31 | goto &$AUTOLOAD | |
32 | } | |
33 | ||
34 | sub load_stubs { shift->_load_stubs((caller)[0]) } | |
35 | ||
36 | sub _load_stubs { | |
37 | my($self, $callpack) = @_; | |
38 | my $fh = \*{"${callpack}::DATA"}; | |
39 | my $currpack = $callpack; | |
40 | my($line,$name,@lines, @stubs, $protoype); | |
41 | ||
42 | print STDERR "SelfLoader::load_stubs($callpack)\n" if $DEBUG; | |
43 | croak("$callpack doesn't contain an __DATA__ token") | |
44 | unless fileno($fh); | |
45 | $Cache{"${currpack}::<DATA"} = 1; # indicate package is cached | |
46 | ||
40da2db3 | 47 | while(defined($line = <$fh>) and $line !~ m/^__END__/) { |
f8881bd9 AD |
48 | if ($line =~ m/^sub\s+([\w:]+)\s*(\([\$\@\;\%\\]*\))?/) { # A sub declared |
49 | push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype)); | |
50 | $protoype = $2; | |
51 | @lines = ($line); | |
52 | if (index($1,'::') == -1) { # simple sub name | |
53 | $name = "${currpack}::$1"; | |
54 | } else { # sub name with package | |
55 | $name = $1; | |
56 | $name =~ m/^(.*)::/; | |
57 | if (defined(&{"${1}::AUTOLOAD"})) { | |
58 | \&{"${1}::AUTOLOAD"} == \&SelfLoader::AUTOLOAD || | |
59 | die 'SelfLoader Error: attempt to specify Selfloading', | |
60 | " sub $name in non-selfloading module $1"; | |
61 | } else { | |
62 | $self->export($1,'AUTOLOAD'); | |
63 | } | |
64 | } | |
65 | } elsif ($line =~ m/^package\s+([\w:]+)/) { # A package declared | |
66 | push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype)); | |
67 | $self->_package_defined($line); | |
68 | $name = ''; | |
69 | @lines = (); | |
70 | $currpack = $1; | |
71 | $Cache{"${currpack}::<DATA"} = 1; # indicate package is cached | |
72 | if (defined(&{"${1}::AUTOLOAD"})) { | |
73 | \&{"${1}::AUTOLOAD"} == \&SelfLoader::AUTOLOAD || | |
74 | die 'SelfLoader Error: attempt to specify Selfloading', | |
75 | " package $currpack which already has AUTOLOAD"; | |
76 | } else { | |
77 | $self->export($currpack,'AUTOLOAD'); | |
78 | } | |
79 | } else { | |
80 | push(@lines,$line); | |
81 | } | |
82 | } | |
83 | close($fh) unless defined($line) && $line =~ /^__END__\s*DATA/; # __END__ | |
84 | push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype)); | |
85 | eval join('', @stubs) if @stubs; | |
86 | } | |
87 | ||
88 | ||
89 | sub _add_to_cache { | |
90 | my($self,$fullname,$pack,$lines, $protoype) = @_; | |
91 | return () unless $fullname; | |
92 | carp("Redefining sub $fullname") if exists $Cache{$fullname}; | |
93 | $Cache{$fullname} = join('', "package $pack; ",@$lines); | |
94 | print STDERR "SelfLoader cached $fullname: $Cache{$fullname}" if $DEBUG; | |
95 | # return stub to be eval'd | |
96 | defined($protoype) ? "sub $fullname $protoype;" : "sub $fullname;" | |
97 | } | |
98 | ||
99 | sub _package_defined {} | |
100 | ||
101 | 1; | |
102 | __END__ | |
cb1a09d0 | 103 | |
f8881bd9 AD |
104 | =head1 NAME |
105 | ||
106 | SelfLoader - load functions only on demand | |
107 | ||
108 | =head1 SYNOPSIS | |
109 | ||
110 | package FOOBAR; | |
111 | use SelfLoader; | |
112 | ||
113 | ... (initializing code) | |
114 | ||
115 | __DATA__ | |
116 | sub {.... | |
117 | ||
118 | ||
119 | =head1 DESCRIPTION | |
120 | ||
121 | This module tells its users that functions in the FOOBAR package are to be | |
463e8aa9 | 122 | autoloaded from after the C<__DATA__> token. See also |
123 | L<perlsub/"Autoloading">. | |
f8881bd9 AD |
124 | |
125 | =head2 The __DATA__ token | |
126 | ||
463e8aa9 | 127 | The C<__DATA__> token tells the perl compiler that the perl code |
128 | for compilation is finished. Everything after the C<__DATA__> token | |
f8881bd9 | 129 | is available for reading via the filehandle FOOBAR::DATA, |
463e8aa9 | 130 | where FOOBAR is the name of the current package when the C<__DATA__> |
131 | token is reached. This works just the same as C<__END__> does in | |
132 | package 'main', but for other modules data after C<__END__> is not | |
133 | automatically retreivable , whereas data after C<__DATA__> is. | |
134 | The C<__DATA__> token is not recognized in versions of perl prior to | |
f8881bd9 AD |
135 | 5.001m. |
136 | ||
463e8aa9 | 137 | Note that it is possible to have C<__DATA__> tokens in the same package |
138 | in multiple files, and that the last C<__DATA__> token in a given | |
f8881bd9 | 139 | package that is encountered by the compiler is the one accessible |
463e8aa9 | 140 | by the filehandle. This also applies to C<__END__> and main, i.e. if |
141 | the 'main' program has an C<__END__>, but a module 'require'd (_not_ 'use'd) | |
142 | by that program has a 'package main;' declaration followed by an 'C<__DATA__>', | |
143 | then the C<DATA> filehandle is set to access the data after the C<__DATA__> | |
144 | in the module, _not_ the data after the C<__END__> token in the 'main' | |
f8881bd9 AD |
145 | program, since the compiler encounters the 'require'd file later. |
146 | ||
147 | =head2 SelfLoader autoloading | |
148 | ||
463e8aa9 | 149 | The B<SelfLoader> works by the user placing the C<__DATA__> |
150 | token I<after> perl code which needs to be compiled and | |
151 | run at 'require' time, but I<before> subroutine declarations | |
f8881bd9 AD |
152 | that can be loaded in later - usually because they may never |
153 | be called. | |
154 | ||
463e8aa9 | 155 | The B<SelfLoader> will read from the FOOBAR::DATA filehandle to |
156 | load in the data after C<__DATA__>, and load in any subroutine | |
f8881bd9 | 157 | when it is called. The costs are the one-time parsing of the |
463e8aa9 | 158 | data after C<__DATA__>, and a load delay for the _first_ |
f8881bd9 AD |
159 | call of any autoloaded function. The benefits (hopefully) |
160 | are a speeded up compilation phase, with no need to load | |
161 | functions which are never used. | |
162 | ||
463e8aa9 | 163 | The B<SelfLoader> will stop reading from C<__DATA__> if |
164 | it encounters the C<__END__> token - just as you would expect. | |
165 | If the C<__END__> token is present, and is followed by the | |
166 | token DATA, then the B<SelfLoader> leaves the FOOBAR::DATA | |
f8881bd9 AD |
167 | filehandle open on the line after that token. |
168 | ||
463e8aa9 | 169 | The B<SelfLoader> exports the C<AUTOLOAD> subroutine to the |
170 | package using the B<SelfLoader>, and this loads the called | |
f8881bd9 AD |
171 | subroutine when it is first called. |
172 | ||
173 | There is no advantage to putting subroutines which will _always_ | |
463e8aa9 | 174 | be called after the C<__DATA__> token. |
f8881bd9 AD |
175 | |
176 | =head2 Autoloading and package lexicals | |
177 | ||
178 | A 'my $pack_lexical' statement makes the variable $pack_lexical | |
463e8aa9 | 179 | local _only_ to the file up to the C<__DATA__> token. Subroutines |
f8881bd9 AD |
180 | declared elsewhere _cannot_ see these types of variables, |
181 | just as if you declared subroutines in the package but in another | |
182 | file, they cannot see these variables. | |
183 | ||
184 | So specifically, autoloaded functions cannot see package | |
463e8aa9 | 185 | lexicals (this applies to both the B<SelfLoader> and the Autoloader). |
186 | The C<vars> pragma provides an alternative to defining package-level | |
187 | globals that will be visible to autoloaded routines. See the documentation | |
188 | on B<vars> in the pragma section of L<perlmod>. | |
f8881bd9 AD |
189 | |
190 | =head2 SelfLoader and AutoLoader | |
191 | ||
463e8aa9 | 192 | The B<SelfLoader> can replace the AutoLoader - just change 'use AutoLoader' |
193 | to 'use SelfLoader' (though note that the B<SelfLoader> exports | |
f8881bd9 AD |
194 | the AUTOLOAD function - but if you have your own AUTOLOAD and |
195 | are using the AutoLoader too, you probably know what you're doing), | |
463e8aa9 | 196 | and the C<__END__> token to C<__DATA__>. You will need perl version 5.001m |
f8881bd9 AD |
197 | or later to use this (version 5.001 with all patches up to patch m). |
198 | ||
463e8aa9 | 199 | There is no need to inherit from the B<SelfLoader>. |
f8881bd9 | 200 | |
463e8aa9 | 201 | The B<SelfLoader> works similarly to the AutoLoader, but picks up the |
202 | subs from after the C<__DATA__> instead of in the 'lib/auto' directory. | |
f8881bd9 AD |
203 | There is a maintainance gain in not needing to run AutoSplit on the module |
204 | at installation, and a runtime gain in not needing to keep opening and | |
205 | closing files to load subs. There is a runtime loss in needing | |
463e8aa9 | 206 | to parse the code after the C<__DATA__>. Details of the B<AutoLoader> and |
207 | another view of these distinctions can be found in that module's | |
208 | documentation. | |
f8881bd9 AD |
209 | |
210 | =head2 __DATA__, __END__, and the FOOBAR::DATA filehandle. | |
211 | ||
212 | This section is only relevant if you want to use | |
463e8aa9 | 213 | the C<FOOBAR::DATA> together with the B<SelfLoader>. |
214 | ||
215 | Data after the C<__DATA__> token in a module is read using the | |
216 | FOOBAR::DATA filehandle. C<__END__> can still be used to denote the end | |
217 | of the C<__DATA__> section if followed by the token DATA - this is supported | |
218 | by the B<SelfLoader>. The C<FOOBAR::DATA> filehandle is left open if an | |
219 | C<__END__> followed by a DATA is found, with the filehandle positioned at | |
220 | the start of the line after the C<__END__> token. If no C<__END__> token is | |
221 | present, or an C<__END__> token with no DATA token on the same line, then | |
222 | the filehandle is closed. | |
223 | ||
224 | The B<SelfLoader> reads from wherever the current | |
225 | position of the C<FOOBAR::DATA> filehandle is, until the | |
226 | EOF or C<__END__>. This means that if you want to use | |
f8881bd9 AD |
227 | that filehandle (and ONLY if you want to), you should either |
228 | ||
229 | 1. Put all your subroutine declarations immediately after | |
463e8aa9 | 230 | the C<__DATA__> token and put your own data after those |
231 | declarations, using the C<__END__> token to mark the end | |
232 | of subroutine declarations. You must also ensure that the B<SelfLoader> | |
1fef88e7 | 233 | reads first by calling 'SelfLoader-E<gt>load_stubs();', or by using a |
f8881bd9 AD |
234 | function which is selfloaded; |
235 | ||
236 | or | |
237 | ||
463e8aa9 | 238 | 2. You should read the C<FOOBAR::DATA> filehandle first, leaving |
f8881bd9 AD |
239 | the handle open and positioned at the first line of subroutine |
240 | declarations. | |
241 | ||
242 | You could conceivably do both. | |
243 | ||
244 | =head2 Classes and inherited methods. | |
245 | ||
246 | For modules which are not classes, this section is not relevant. | |
247 | This section is only relevant if you have methods which could | |
248 | be inherited. | |
249 | ||
250 | A subroutine stub (or forward declaration) looks like | |
251 | ||
252 | sub stub; | |
253 | ||
254 | i.e. it is a subroutine declaration without the body of the | |
255 | subroutine. For modules which are not classes, there is no real | |
256 | need for stubs as far as autoloading is concerned. | |
257 | ||
258 | For modules which ARE classes, and need to handle inherited methods, | |
259 | stubs are needed to ensure that the method inheritance mechanism works | |
260 | properly. You can load the stubs into the module at 'require' time, by | |
1fef88e7 | 261 | adding the statement 'SelfLoader-E<gt>load_stubs();' to the module to do |
f8881bd9 AD |
262 | this. |
263 | ||
463e8aa9 | 264 | The alternative is to put the stubs in before the C<__DATA__> token BEFORE |
265 | releasing the module, and for this purpose the C<Devel::SelfStubber> | |
f8881bd9 AD |
266 | module is available. However this does require the extra step of ensuring |
267 | that the stubs are in the module. If this is done I strongly recommend | |
268 | that this is done BEFORE releasing the module - it should NOT be done | |
269 | at install time in general. | |
270 | ||
271 | =head1 Multiple packages and fully qualified subroutine names | |
272 | ||
273 | Subroutines in multiple packages within the same file are supported - but you | |
463e8aa9 | 274 | should note that this requires exporting the C<SelfLoader::AUTOLOAD> to |
f8881bd9 | 275 | every package which requires it. This is done automatically by the |
463e8aa9 | 276 | B<SelfLoader> when it first loads the subs into the cache, but you should |
277 | really specify it in the initialization before the C<__DATA__> by putting | |
f8881bd9 AD |
278 | a 'use SelfLoader' statement in each package. |
279 | ||
280 | Fully qualified subroutine names are also supported. For example, | |
281 | ||
282 | __DATA__ | |
283 | sub foo::bar {23} | |
284 | package baz; | |
285 | sub dob {32} | |
286 | ||
463e8aa9 | 287 | will all be loaded correctly by the B<SelfLoader>, and the B<SelfLoader> |
f8881bd9 | 288 | will ensure that the packages 'foo' and 'baz' correctly have the |
463e8aa9 | 289 | B<SelfLoader> C<AUTOLOAD> method when the data after C<__DATA__> is first |
290 | parsed. | |
f8881bd9 AD |
291 | |
292 | =cut |