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1 | =head1 NAME |
2 | |
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3 | perlembed - how to embed perl in your C program |
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4 | |
5 | =head1 DESCRIPTION |
6 | |
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7 | =head2 PREAMBLE |
8 | |
9 | Do you want to: |
10 | |
11 | =over 5 |
12 | |
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13 | =item B<Use C from Perl?> |
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14 | |
15 | Read L<perlcall> and L<perlxs>. |
16 | |
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17 | =item B<Use a Unix program from Perl?> |
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18 | |
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19 | Read about back-quotes and about C<system> and C<exec> in L<perlfunc>. |
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20 | |
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21 | =item B<Use Perl from Perl?> |
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22 | |
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23 | Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlfunc/require> |
24 | and L<perlfunc/use>. |
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25 | |
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26 | =item B<Use C from C?> |
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27 | |
28 | Rethink your design. |
29 | |
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30 | =item B<Use Perl from C?> |
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31 | |
32 | Read on... |
33 | |
34 | =back |
35 | |
36 | =head2 ROADMAP |
37 | |
38 | L<Compiling your C program> |
39 | |
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40 | There's one example in each of the eight sections: |
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41 | |
42 | L<Adding a Perl interpreter to your C program> |
43 | |
44 | L<Calling a Perl subroutine from your C program> |
45 | |
46 | L<Evaluating a Perl statement from your C program> |
47 | |
48 | L<Performing Perl pattern matches and substitutions from your C program> |
49 | |
50 | L<Fiddling with the Perl stack from your C program> |
51 | |
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52 | L<Maintaining a persistent interpreter> |
53 | |
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54 | L<Maintaining multiple interpreter instances> |
55 | |
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56 | L<Using Perl modules, which themselves use C libraries, from your C program> |
57 | |
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58 | This documentation is Unix specific; if you have information about how |
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59 | to embed Perl on other platforms, please send e-mail to <F<orwant@tpj.com>>. |
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60 | |
61 | =head2 Compiling your C program |
62 | |
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63 | If you have trouble compiling the scripts in this documentation, |
64 | you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY |
65 | THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.) |
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66 | |
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67 | Also, every C program that uses Perl must link in the I<perl library>. |
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68 | What's that, you ask? Perl is itself written in C; the perl library |
69 | is the collection of compiled C programs that were used to create your |
70 | perl executable (I</usr/bin/perl> or equivalent). (Corollary: you |
71 | can't use Perl from your C program unless Perl has been compiled on |
72 | your machine, or installed properly--that's why you shouldn't blithely |
73 | copy Perl executables from machine to machine without also copying the |
74 | I<lib> directory.) |
75 | |
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76 | When you use Perl from C, your C program will--usually--allocate, |
77 | "run", and deallocate a I<PerlInterpreter> object, which is defined by |
78 | the perl library. |
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79 | |
80 | If your copy of Perl is recent enough to contain this documentation |
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81 | (version 5.002 or later), then the perl library (and I<EXTERN.h> and |
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82 | I<perl.h>, which you'll also need) will reside in a directory |
83 | that looks like this: |
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84 | |
85 | /usr/local/lib/perl5/your_architecture_here/CORE |
86 | |
87 | or perhaps just |
88 | |
89 | /usr/local/lib/perl5/CORE |
90 | |
91 | or maybe something like |
92 | |
93 | /usr/opt/perl5/CORE |
94 | |
95 | Execute this statement for a hint about where to find CORE: |
96 | |
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97 | perl -MConfig -e 'print $Config{archlib}' |
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98 | |
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99 | Here's how you'd compile the example in the next section, |
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100 | L<Adding a Perl interpreter to your C program>, on my Linux box: |
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101 | |
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102 | % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include |
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103 | -I/usr/local/lib/perl5/i586-linux/5.003/CORE |
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104 | -L/usr/local/lib/perl5/i586-linux/5.003/CORE |
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105 | -o interp interp.c -lperl -lm |
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106 | |
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107 | (That's all one line.) On my DEC Alpha running 5.003_05, the incantation |
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108 | is a bit different: |
109 | |
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110 | % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include |
111 | -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE |
112 | -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib |
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113 | -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm |
114 | |
115 | How can you figure out what to add? Assuming your Perl is post-5.001, |
116 | execute a C<perl -V> command and pay special attention to the "cc" and |
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117 | "ccflags" information. |
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118 | |
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119 | You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for |
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120 | your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what |
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121 | to use. |
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122 | |
123 | You'll also have to choose the appropriate library directory |
124 | (I</usr/local/lib/...>) for your machine. If your compiler complains |
125 | that certain functions are undefined, or that it can't locate |
126 | I<-lperl>, then you need to change the path following the C<-L>. If it |
127 | complains that it can't find I<EXTERN.h> and I<perl.h>, you need to |
128 | change the path following the C<-I>. |
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129 | |
130 | You may have to add extra libraries as well. Which ones? |
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131 | Perhaps those printed by |
132 | |
133 | perl -MConfig -e 'print $Config{libs}' |
134 | |
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135 | Provided your perl binary was properly configured and installed the |
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136 | B<ExtUtils::Embed> module will determine all of this information for |
137 | you: |
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138 | |
139 | % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
140 | |
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141 | If the B<ExtUtils::Embed> module isn't part of your Perl distribution, |
142 | you can retrieve it from |
143 | http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils::Embed. (If |
144 | this documentation came from your Perl distribution, then you're |
145 | running 5.004 or better and you already have it.) |
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146 | |
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147 | The B<ExtUtils::Embed> kit on CPAN also contains all source code for |
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148 | the examples in this document, tests, additional examples and other |
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149 | information you may find useful. |
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150 | |
151 | =head2 Adding a Perl interpreter to your C program |
152 | |
153 | In a sense, perl (the C program) is a good example of embedding Perl |
154 | (the language), so I'll demonstrate embedding with I<miniperlmain.c>, |
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155 | from the source distribution. Here's a bastardized, nonportable |
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156 | version of I<miniperlmain.c> containing the essentials of embedding: |
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157 | |
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158 | #include <EXTERN.h> /* from the Perl distribution */ |
159 | #include <perl.h> /* from the Perl distribution */ |
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160 | |
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161 | static PerlInterpreter *my_perl; /*** The Perl interpreter ***/ |
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162 | |
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163 | int main(int argc, char **argv, char **env) |
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164 | { |
165 | my_perl = perl_alloc(); |
166 | perl_construct(my_perl); |
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167 | perl_parse(my_perl, NULL, argc, argv, (char **)NULL); |
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168 | perl_run(my_perl); |
169 | perl_destruct(my_perl); |
170 | perl_free(my_perl); |
171 | } |
172 | |
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173 | Notice that we don't use the C<env> pointer. Normally handed to |
174 | C<perl_parse> as its final argument, C<env> here is replaced by |
175 | C<NULL>, which means that the current environment will be used. |
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176 | |
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177 | Now compile this program (I'll call it I<interp.c>) into an executable: |
178 | |
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179 | % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
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180 | |
181 | After a successful compilation, you'll be able to use I<interp> just |
182 | like perl itself: |
183 | |
184 | % interp |
185 | print "Pretty Good Perl \n"; |
186 | print "10890 - 9801 is ", 10890 - 9801; |
187 | <CTRL-D> |
188 | Pretty Good Perl |
189 | 10890 - 9801 is 1089 |
190 | |
191 | or |
192 | |
193 | % interp -e 'printf("%x", 3735928559)' |
194 | deadbeef |
195 | |
196 | You can also read and execute Perl statements from a file while in the |
197 | midst of your C program, by placing the filename in I<argv[1]> before |
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198 | calling I<perl_run()>. |
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199 | |
200 | =head2 Calling a Perl subroutine from your C program |
201 | |
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202 | To call individual Perl subroutines, you can use any of the B<perl_call_*> |
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203 | functions documented in the L<perlcall> manpage. |
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204 | In this example we'll use I<perl_call_argv>. |
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205 | |
206 | That's shown below, in a program I'll call I<showtime.c>. |
207 | |
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208 | #include <EXTERN.h> |
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209 | #include <perl.h> |
210 | |
211 | static PerlInterpreter *my_perl; |
212 | |
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213 | int main(int argc, char **argv, char **env) |
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214 | { |
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215 | char *args[] = { NULL }; |
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216 | my_perl = perl_alloc(); |
217 | perl_construct(my_perl); |
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218 | |
219 | perl_parse(my_perl, NULL, argc, argv, NULL); |
220 | |
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221 | /*** skipping perl_run() ***/ |
222 | |
223 | perl_call_argv("showtime", G_DISCARD | G_NOARGS, args); |
224 | |
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225 | perl_destruct(my_perl); |
226 | perl_free(my_perl); |
227 | } |
228 | |
229 | where I<showtime> is a Perl subroutine that takes no arguments (that's the |
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230 | I<G_NOARGS>) and for which I'll ignore the return value (that's the |
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231 | I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>. |
232 | |
233 | I'll define the I<showtime> subroutine in a file called I<showtime.pl>: |
234 | |
235 | print "I shan't be printed."; |
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236 | |
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237 | sub showtime { |
238 | print time; |
239 | } |
240 | |
241 | Simple enough. Now compile and run: |
242 | |
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243 | % cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
244 | |
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245 | % showtime showtime.pl |
246 | 818284590 |
247 | |
248 | yielding the number of seconds that elapsed between January 1, 1970 |
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249 | (the beginning of the Unix epoch), and the moment I began writing this |
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250 | sentence. |
251 | |
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252 | In this particular case we don't have to call I<perl_run>, but in |
253 | general it's considered good practice to ensure proper initialization |
254 | of library code, including execution of all object C<DESTROY> methods |
255 | and package C<END {}> blocks. |
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256 | |
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257 | If you want to pass arguments to the Perl subroutine, you can add |
258 | strings to the C<NULL>-terminated C<args> list passed to |
259 | I<perl_call_argv>. For other data types, or to examine return values, |
260 | you'll need to manipulate the Perl stack. That's demonstrated in the |
261 | last section of this document: L<Fiddling with the Perl stack from |
262 | your C program>. |
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263 | |
264 | =head2 Evaluating a Perl statement from your C program |
265 | |
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266 | One way to evaluate pieces of Perl code is to use |
267 | L<perlguts/perl_eval_sv()>. We've wrapped this inside our own |
268 | I<perl_eval()> function, which converts a command string to an SV, |
269 | passing this and the L<perlcall/G_DISCARD> flag to |
270 | L<perlguts/perl_eval_sv()>. |
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271 | |
272 | Arguably, this is the only routine you'll ever need to execute |
273 | snippets of Perl code from within your C program. Your string can be |
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274 | as long as you wish; it can contain multiple statements; it can employ |
275 | L<perlfunc/use>, L<perlfunc/require> and L<perlfunc/do> to include |
276 | external Perl files. |
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277 | |
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278 | Our I<perl_eval()> lets us evaluate individual Perl strings, and then |
279 | extract variables for coercion into C types. The following program, |
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280 | I<string.c>, executes three Perl strings, extracting an C<int> from |
281 | the first, a C<float> from the second, and a C<char *> from the third. |
282 | |
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283 | #include <EXTERN.h> |
284 | #include <perl.h> |
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285 | |
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286 | static PerlInterpreter *my_perl; |
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287 | |
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288 | I32 perl_eval(char *string) |
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289 | { |
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290 | return perl_eval_sv(newSVpv(string,0), G_DISCARD); |
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291 | } |
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292 | |
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293 | main (int argc, char **argv, char **env) |
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294 | { |
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295 | char *embedding[] = { "", "-e", "0" }; |
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296 | STRLEN length; |
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297 | |
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298 | my_perl = perl_alloc(); |
299 | perl_construct( my_perl ); |
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300 | |
301 | perl_parse(my_perl, NULL, 3, embedding, NULL); |
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302 | perl_run(my_perl); |
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303 | /** Treat $a as an integer **/ |
304 | perl_eval("$a = 3; $a **= 2"); |
305 | printf("a = %d\n", SvIV(perl_get_sv("a", FALSE))); |
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306 | |
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307 | /** Treat $a as a float **/ |
308 | perl_eval("$a = 3.14; $a **= 2"); |
309 | printf("a = %f\n", SvNV(perl_get_sv("a", FALSE))); |
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310 | |
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311 | /** Treat $a as a string **/ |
312 | perl_eval("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a); "); |
313 | printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), length)); |
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314 | |
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315 | perl_destruct(my_perl); |
316 | perl_free(my_perl); |
317 | } |
318 | |
319 | All of those strange functions with I<sv> in their names help convert Perl scalars to C types. They're described in L<perlguts>. |
320 | |
321 | If you compile and run I<string.c>, you'll see the results of using |
322 | I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and |
323 | I<SvPV()> to create a string: |
324 | |
325 | a = 9 |
326 | a = 9.859600 |
327 | a = Just Another Perl Hacker |
328 | |
8f183262 |
329 | In the example above, we've created a global variable to temporarily |
330 | store the computed value of our eval'd expression. It is also |
331 | possible and in most cases a better strategy to fetch the return value |
332 | from L<perl_eval_sv> instead. Example: |
333 | |
334 | SV *perl_eval(char *string, int croak_on_error) |
335 | { |
336 | dSP; |
337 | SV *sv = newSVpv(string,0); |
338 | |
339 | PUSHMARK(sp); |
340 | perl_eval_sv(sv, G_SCALAR); |
341 | SvREFCNT_dec(sv); |
342 | |
343 | SPAGAIN; |
344 | sv = POPs; |
345 | PUTBACK; |
346 | |
347 | if (croak_on_error && SvTRUE(GvSV(errgv))) |
348 | croak(SvPV(GvSV(errgv),na)); |
349 | |
350 | return sv; |
351 | } |
352 | ... |
353 | SV *val = perl_eval("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE); |
354 | printf("%s\n", SvPV(val,na)); |
355 | ... |
356 | |
357 | This way, we avoid namespace pollution by not creating global |
358 | variables and we've simplified our code as well. |
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359 | |
360 | =head2 Performing Perl pattern matches and substitutions from your C program |
361 | |
362 | Our I<perl_eval()> lets us evaluate strings of Perl code, so we can |
363 | define some functions that use it to "specialize" in matches and |
364 | substitutions: I<match()>, I<substitute()>, and I<matches()>. |
365 | |
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366 | char match(char *string, char *pattern); |
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367 | |
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368 | Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which |
369 | in your C program might appear as "/\\b\\w*\\b/"), match() |
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370 | returns 1 if the string matches the pattern and 0 otherwise. |
371 | |
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372 | int substitute(char *string[], char *pattern); |
373 | |
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374 | Given a pointer to a string and an C<=~> operation (e.g., |
375 | C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string |
376 | according to the operation, returning the number of substitutions |
377 | made. |
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378 | |
379 | int matches(char *string, char *pattern, char **matches[]); |
380 | |
381 | Given a string, a pattern, and a pointer to an empty array of strings, |
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382 | matches() evaluates C<$string =~ $pattern> in an array context, and |
383 | fills in I<matches> with the array elements (allocating memory as it |
384 | does so), returning the number of matches found. |
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385 | |
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386 | Here's a sample program, I<match.c>, that uses all three (long lines have |
387 | been wrapped here): |
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388 | |
cb1a09d0 |
389 | #include <EXTERN.h> |
390 | #include <perl.h> |
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391 | |
cb1a09d0 |
392 | static PerlInterpreter *my_perl; |
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393 | I32 perl_eval(char *string) |
cb1a09d0 |
394 | { |
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395 | return perl_eval_sv(newSVpv(string,0), G_DISCARD); |
cb1a09d0 |
396 | } |
cb1a09d0 |
397 | /** match(string, pattern) |
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398 | ** |
399 | ** Used for matches in a scalar context. |
400 | ** |
401 | ** Returns 1 if the match was successful; 0 otherwise. |
402 | **/ |
403 | char match(char *string, char *pattern) |
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404 | { |
405 | char *command; |
406 | command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37); |
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407 | sprintf(command, "$string = '%s'; $return = $string =~ %s", |
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408 | string, pattern); |
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409 | perl_eval(command); |
410 | free(command); |
411 | return SvIV(perl_get_sv("return", FALSE)); |
412 | } |
cb1a09d0 |
413 | /** substitute(string, pattern) |
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414 | ** |
415 | ** Used for =~ operations that modify their left-hand side (s/// and tr///) |
416 | ** |
417 | ** Returns the number of successful matches, and |
418 | ** modifies the input string if there were any. |
419 | **/ |
420 | int substitute(char *string[], char *pattern) |
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421 | { |
422 | char *command; |
423 | STRLEN length; |
424 | command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35); |
96dbc785 |
425 | sprintf(command, "$string = '%s'; $ret = ($string =~ %s)", |
8ebc5c01 |
426 | *string, pattern); |
427 | perl_eval(command); |
428 | free(command); |
429 | *string = SvPV(perl_get_sv("string", FALSE), length); |
430 | return SvIV(perl_get_sv("ret", FALSE)); |
cb1a09d0 |
431 | } |
cb1a09d0 |
432 | /** matches(string, pattern, matches) |
96dbc785 |
433 | ** |
434 | ** Used for matches in an array context. |
435 | ** |
436 | ** Returns the number of matches, |
437 | ** and fills in **matches with the matching substrings (allocates memory!) |
438 | **/ |
439 | int matches(char *string, char *pattern, char **match_list[]) |
cb1a09d0 |
440 | { |
441 | char *command; |
442 | SV *current_match; |
443 | AV *array; |
444 | I32 num_matches; |
445 | STRLEN length; |
446 | int i; |
cb1a09d0 |
447 | command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 38); |
96dbc785 |
448 | sprintf(command, "$string = '%s'; @array = ($string =~ %s)", |
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449 | string, pattern); |
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450 | perl_eval(command); |
451 | free(command); |
452 | array = perl_get_av("array", FALSE); |
453 | num_matches = av_len(array) + 1; /** assume $[ is 0 **/ |
96dbc785 |
454 | *match_list = (char **) malloc(sizeof(char *) * num_matches); |
455 | for (i = 0; i <= num_matches; i++) { |
cb1a09d0 |
456 | current_match = av_shift(array); |
96dbc785 |
457 | (*match_list)[i] = SvPV(current_match, length); |
cb1a09d0 |
458 | } |
459 | return num_matches; |
460 | } |
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461 | main (int argc, char **argv, char **env) |
cb1a09d0 |
462 | { |
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463 | char *embedding[] = { "", "-e", "0" }; |
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464 | char *text, **match_list; |
cb1a09d0 |
465 | int num_matches, i; |
466 | int j; |
cb1a09d0 |
467 | my_perl = perl_alloc(); |
468 | perl_construct( my_perl ); |
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469 | perl_parse(my_perl, NULL, 3, embedding, NULL); |
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470 | perl_run(my_perl); |
471 | |
cb1a09d0 |
472 | text = (char *) malloc(sizeof(char) * 486); /** A long string follows! **/ |
96dbc785 |
473 | sprintf(text, "%s", "When he is at a convenience store and the bill \ |
474 | comes to some amount like 76 cents, Maynard is aware that there is \ |
475 | something he *should* do, something that will enable him to get back \ |
476 | a quarter, but he has no idea *what*. He fumbles through his red \ |
477 | squeezey changepurse and gives the boy three extra pennies with his \ |
478 | dollar, hoping that he might luck into the correct amount. The boy \ |
479 | gives him back two of his own pennies and then the big shiny quarter \ |
480 | that is his prize. -RICHH"); |
481 | if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/ |
482 | printf("match: Text contains the word 'quarter'.\n\n"); |
483 | else |
484 | printf("match: Text doesn't contain the word 'quarter'.\n\n"); |
485 | if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/ |
486 | printf("match: Text contains the word 'eighth'.\n\n"); |
487 | else |
488 | printf("match: Text doesn't contain the word 'eighth'.\n\n"); |
489 | /** Match all occurrences of /wi../ **/ |
490 | num_matches = matches(text, "m/(wi..)/g", &match_list); |
491 | printf("matches: m/(wi..)/g found %d matches...\n", num_matches); |
492 | for (i = 0; i < num_matches; i++) |
493 | printf("match: %s\n", match_list[i]); |
cb1a09d0 |
494 | printf("\n"); |
495 | for (i = 0; i < num_matches; i++) { |
96dbc785 |
496 | free(match_list[i]); |
cb1a09d0 |
497 | } |
96dbc785 |
498 | free(match_list); |
499 | /** Remove all vowels from text **/ |
500 | num_matches = substitute(&text, "s/[aeiou]//gi"); |
cb1a09d0 |
501 | if (num_matches) { |
96dbc785 |
502 | printf("substitute: s/[aeiou]//gi...%d substitutions made.\n", |
8ebc5c01 |
503 | num_matches); |
cb1a09d0 |
504 | printf("Now text is: %s\n\n", text); |
505 | } |
96dbc785 |
506 | /** Attempt a substitution **/ |
507 | if (!substitute(&text, "s/Perl/C/")) { |
508 | printf("substitute: s/Perl/C...No substitution made.\n\n"); |
cb1a09d0 |
509 | } |
cb1a09d0 |
510 | free(text); |
cb1a09d0 |
511 | perl_destruct(my_perl); |
512 | perl_free(my_perl); |
513 | } |
514 | |
96dbc785 |
515 | which produces the output (again, long lines have been wrapped here) |
cb1a09d0 |
516 | |
8a7dc658 |
517 | match: Text contains the word 'quarter'. |
96dbc785 |
518 | |
8a7dc658 |
519 | match: Text doesn't contain the word 'eighth'. |
96dbc785 |
520 | |
8a7dc658 |
521 | matches: m/(wi..)/g found 2 matches... |
cb1a09d0 |
522 | match: will |
523 | match: with |
96dbc785 |
524 | |
8a7dc658 |
525 | substitute: s/[aeiou]//gi...139 substitutions made. |
54310121 |
526 | Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts, |
96dbc785 |
527 | Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck |
528 | qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by |
529 | thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs |
530 | hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH |
531 | |
8a7dc658 |
532 | substitute: s/Perl/C...No substitution made. |
96dbc785 |
533 | |
cb1a09d0 |
534 | =head2 Fiddling with the Perl stack from your C program |
535 | |
536 | When trying to explain stacks, most computer science textbooks mumble |
537 | something about spring-loaded columns of cafeteria plates: the last |
538 | thing you pushed on the stack is the first thing you pop off. That'll |
539 | do for our purposes: your C program will push some arguments onto "the Perl |
540 | stack", shut its eyes while some magic happens, and then pop the |
541 | results--the return value of your Perl subroutine--off the stack. |
96dbc785 |
542 | |
cb1a09d0 |
543 | First you'll need to know how to convert between C types and Perl |
544 | types, with newSViv() and sv_setnv() and newAV() and all their |
545 | friends. They're described in L<perlguts>. |
546 | |
547 | Then you'll need to know how to manipulate the Perl stack. That's |
548 | described in L<perlcall>. |
549 | |
96dbc785 |
550 | Once you've understood those, embedding Perl in C is easy. |
cb1a09d0 |
551 | |
54310121 |
552 | Because C has no builtin function for integer exponentiation, let's |
cb1a09d0 |
553 | make Perl's ** operator available to it (this is less useful than it |
5f05dabc |
554 | sounds, because Perl implements ** with C's I<pow()> function). First |
cb1a09d0 |
555 | I'll create a stub exponentiation function in I<power.pl>: |
556 | |
557 | sub expo { |
558 | my ($a, $b) = @_; |
559 | return $a ** $b; |
560 | } |
561 | |
562 | Now I'll create a C program, I<power.c>, with a function |
563 | I<PerlPower()> that contains all the perlguts necessary to push the |
564 | two arguments into I<expo()> and to pop the return value out. Take a |
565 | deep breath... |
566 | |
cb1a09d0 |
567 | #include <EXTERN.h> |
568 | #include <perl.h> |
96dbc785 |
569 | |
cb1a09d0 |
570 | static PerlInterpreter *my_perl; |
96dbc785 |
571 | |
cb1a09d0 |
572 | static void |
573 | PerlPower(int a, int b) |
574 | { |
575 | dSP; /* initialize stack pointer */ |
576 | ENTER; /* everything created after here */ |
577 | SAVETMPS; /* ...is a temporary variable. */ |
578 | PUSHMARK(sp); /* remember the stack pointer */ |
579 | XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */ |
580 | XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */ |
581 | PUTBACK; /* make local stack pointer global */ |
582 | perl_call_pv("expo", G_SCALAR); /* call the function */ |
583 | SPAGAIN; /* refresh stack pointer */ |
584 | /* pop the return value from stack */ |
585 | printf ("%d to the %dth power is %d.\n", a, b, POPi); |
96dbc785 |
586 | PUTBACK; |
cb1a09d0 |
587 | FREETMPS; /* free that return value */ |
588 | LEAVE; /* ...and the XPUSHed "mortal" args.*/ |
589 | } |
96dbc785 |
590 | |
591 | int main (int argc, char **argv, char **env) |
cb1a09d0 |
592 | { |
593 | char *my_argv[2]; |
96dbc785 |
594 | |
cb1a09d0 |
595 | my_perl = perl_alloc(); |
596 | perl_construct( my_perl ); |
96dbc785 |
597 | |
cb1a09d0 |
598 | my_argv[1] = (char *) malloc(10); |
599 | sprintf(my_argv[1], "power.pl"); |
96dbc785 |
600 | |
601 | perl_parse(my_perl, NULL, argc, my_argv, NULL); |
8ebc5c01 |
602 | perl_run(my_perl); |
96dbc785 |
603 | |
cb1a09d0 |
604 | PerlPower(3, 4); /*** Compute 3 ** 4 ***/ |
96dbc785 |
605 | |
cb1a09d0 |
606 | perl_destruct(my_perl); |
607 | perl_free(my_perl); |
608 | } |
96dbc785 |
609 | |
cb1a09d0 |
610 | |
611 | |
612 | Compile and run: |
613 | |
96dbc785 |
614 | % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
615 | |
616 | % power |
cb1a09d0 |
617 | 3 to the 4th power is 81. |
618 | |
a6006777 |
619 | =head2 Maintaining a persistent interpreter |
620 | |
8a7dc658 |
621 | When developing interactive and/or potentially long-running |
622 | applications, it's a good idea to maintain a persistent interpreter |
623 | rather than allocating and constructing a new interpreter multiple |
624 | times. The major reason is speed: since Perl will only be loaded into |
54310121 |
625 | memory once. |
8a7dc658 |
626 | |
627 | However, you have to be more cautious with namespace and variable |
628 | scoping when using a persistent interpreter. In previous examples |
629 | we've been using global variables in the default package C<main>. We |
630 | knew exactly what code would be run, and assumed we could avoid |
631 | variable collisions and outrageous symbol table growth. |
632 | |
633 | Let's say your application is a server that will occasionally run Perl |
634 | code from some arbitrary file. Your server has no way of knowing what |
635 | code it's going to run. Very dangerous. |
636 | |
637 | If the file is pulled in by C<perl_parse()>, compiled into a newly |
638 | constructed interpreter, and subsequently cleaned out with |
639 | C<perl_destruct()> afterwards, you're shielded from most namespace |
640 | troubles. |
641 | |
642 | One way to avoid namespace collisions in this scenario is to translate |
643 | the filename into a guaranteed-unique package name, and then compile |
644 | the code into that package using L<perlfunc/eval>. In the example |
645 | below, each file will only be compiled once. Or, the application |
646 | might choose to clean out the symbol table associated with the file |
647 | after it's no longer needed. Using L<perlcall/perl_call_argv>, We'll |
648 | call the subroutine C<Embed::Persistent::eval_file> which lives in the |
649 | file C<persistent.pl> and pass the filename and boolean cleanup/cache |
a6006777 |
650 | flag as arguments. |
651 | |
8a7dc658 |
652 | Note that the process will continue to grow for each file that it |
653 | uses. In addition, there might be C<AUTOLOAD>ed subroutines and other |
654 | conditions that cause Perl's symbol table to grow. You might want to |
655 | add some logic that keeps track of the process size, or restarts |
656 | itself after a certain number of requests, to ensure that memory |
657 | consumption is minimized. You'll also want to scope your variables |
658 | with L<perlfunc/my> whenever possible. |
a6006777 |
659 | |
54310121 |
660 | |
a6006777 |
661 | package Embed::Persistent; |
662 | #persistent.pl |
54310121 |
663 | |
a6006777 |
664 | use strict; |
665 | use vars '%Cache'; |
54310121 |
666 | |
a6006777 |
667 | sub valid_package_name { |
668 | my($string) = @_; |
669 | $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg; |
670 | # second pass only for words starting with a digit |
671 | $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg; |
54310121 |
672 | |
a6006777 |
673 | # Dress it up as a real package name |
674 | $string =~ s|/|::|g; |
675 | return "Embed" . $string; |
676 | } |
54310121 |
677 | |
a6006777 |
678 | #borrowed from Safe.pm |
679 | sub delete_package { |
680 | my $pkg = shift; |
681 | my ($stem, $leaf); |
54310121 |
682 | |
a6006777 |
683 | no strict 'refs'; |
8ebc5c01 |
684 | $pkg = "main::$pkg\::"; # expand to full symbol table name |
a6006777 |
685 | ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/; |
54310121 |
686 | |
a6006777 |
687 | my $stem_symtab = *{$stem}{HASH}; |
54310121 |
688 | |
a6006777 |
689 | delete $stem_symtab->{$leaf}; |
690 | } |
54310121 |
691 | |
a6006777 |
692 | sub eval_file { |
693 | my($filename, $delete) = @_; |
694 | my $package = valid_package_name($filename); |
695 | my $mtime = -M $filename; |
696 | if(defined $Cache{$package}{mtime} |
697 | && |
54310121 |
698 | $Cache{$package}{mtime} <= $mtime) |
a6006777 |
699 | { |
54310121 |
700 | # we have compiled this subroutine already, |
8ebc5c01 |
701 | # it has not been updated on disk, nothing left to do |
702 | print STDERR "already compiled $package->handler\n"; |
a6006777 |
703 | } |
704 | else { |
8ebc5c01 |
705 | local *FH; |
706 | open FH, $filename or die "open '$filename' $!"; |
707 | local($/) = undef; |
708 | my $sub = <FH>; |
709 | close FH; |
54310121 |
710 | |
8ebc5c01 |
711 | #wrap the code into a subroutine inside our unique package |
712 | my $eval = qq{package $package; sub handler { $sub; }}; |
713 | { |
714 | # hide our variables within this block |
715 | my($filename,$mtime,$package,$sub); |
716 | eval $eval; |
717 | } |
718 | die $@ if $@; |
54310121 |
719 | |
8ebc5c01 |
720 | #cache it unless we're cleaning out each time |
721 | $Cache{$package}{mtime} = $mtime unless $delete; |
a6006777 |
722 | } |
54310121 |
723 | |
a6006777 |
724 | eval {$package->handler;}; |
725 | die $@ if $@; |
54310121 |
726 | |
a6006777 |
727 | delete_package($package) if $delete; |
54310121 |
728 | |
a6006777 |
729 | #take a look if you want |
730 | #print Devel::Symdump->rnew($package)->as_string, $/; |
731 | } |
54310121 |
732 | |
a6006777 |
733 | 1; |
54310121 |
734 | |
a6006777 |
735 | __END__ |
736 | |
737 | /* persistent.c */ |
54310121 |
738 | #include <EXTERN.h> |
739 | #include <perl.h> |
740 | |
a6006777 |
741 | /* 1 = clean out filename's symbol table after each request, 0 = don't */ |
742 | #ifndef DO_CLEAN |
743 | #define DO_CLEAN 0 |
744 | #endif |
54310121 |
745 | |
a6006777 |
746 | static PerlInterpreter *perl = NULL; |
54310121 |
747 | |
a6006777 |
748 | int |
749 | main(int argc, char **argv, char **env) |
750 | { |
751 | char *embedding[] = { "", "persistent.pl" }; |
752 | char *args[] = { "", DO_CLEAN, NULL }; |
753 | char filename [1024]; |
754 | int exitstatus = 0; |
54310121 |
755 | |
a6006777 |
756 | if((perl = perl_alloc()) == NULL) { |
8ebc5c01 |
757 | fprintf(stderr, "no memory!"); |
758 | exit(1); |
a6006777 |
759 | } |
54310121 |
760 | perl_construct(perl); |
761 | |
a6006777 |
762 | exitstatus = perl_parse(perl, NULL, 2, embedding, NULL); |
54310121 |
763 | |
764 | if(!exitstatus) { |
8ebc5c01 |
765 | exitstatus = perl_run(perl); |
54310121 |
766 | |
8ebc5c01 |
767 | while(printf("Enter file name: ") && gets(filename)) { |
54310121 |
768 | |
8ebc5c01 |
769 | /* call the subroutine, passing it the filename as an argument */ |
770 | args[0] = filename; |
54310121 |
771 | perl_call_argv("Embed::Persistent::eval_file", |
8ebc5c01 |
772 | G_DISCARD | G_EVAL, args); |
54310121 |
773 | |
8ebc5c01 |
774 | /* check $@ */ |
54310121 |
775 | if(SvTRUE(GvSV(errgv))) |
8ebc5c01 |
776 | fprintf(stderr, "eval error: %s\n", SvPV(GvSV(errgv),na)); |
777 | } |
a6006777 |
778 | } |
54310121 |
779 | |
a6006777 |
780 | perl_destruct_level = 0; |
54310121 |
781 | perl_destruct(perl); |
782 | perl_free(perl); |
a6006777 |
783 | exit(exitstatus); |
784 | } |
785 | |
a6006777 |
786 | Now compile: |
787 | |
54310121 |
788 | % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
a6006777 |
789 | |
790 | Here's a example script file: |
791 | |
792 | #test.pl |
793 | my $string = "hello"; |
794 | foo($string); |
795 | |
796 | sub foo { |
797 | print "foo says: @_\n"; |
798 | } |
799 | |
800 | Now run: |
801 | |
802 | % persistent |
803 | Enter file name: test.pl |
804 | foo says: hello |
805 | Enter file name: test.pl |
806 | already compiled Embed::test_2epl->handler |
807 | foo says: hello |
808 | Enter file name: ^C |
809 | |
8ebc5c01 |
810 | =head2 Maintaining multiple interpreter instances |
811 | |
8a7dc658 |
812 | Some rare applications will need to create more than one interpreter |
813 | during a session. Such an application might sporadically decide to |
54310121 |
814 | release any resources associated with the interpreter. |
8a7dc658 |
815 | |
816 | The program must take care to ensure that this takes place I<before> |
817 | the next interpreter is constructed. By default, the global variable |
818 | C<perl_destruct_level> is set to C<0>, since extra cleaning isn't |
819 | needed when a program has only one interpreter. |
820 | |
821 | Setting C<perl_destruct_level> to C<1> makes everything squeaky clean: |
822 | |
54310121 |
823 | perl_destruct_level = 1; |
8ebc5c01 |
824 | |
8ebc5c01 |
825 | while(1) { |
826 | ... |
827 | /* reset global variables here with perl_destruct_level = 1 */ |
54310121 |
828 | perl_construct(my_perl); |
8ebc5c01 |
829 | ... |
830 | /* clean and reset _everything_ during perl_destruct */ |
54310121 |
831 | perl_destruct(my_perl); |
832 | perl_free(my_perl); |
8ebc5c01 |
833 | ... |
834 | /* let's go do it again! */ |
835 | } |
836 | |
54310121 |
837 | When I<perl_destruct()> is called, the interpreter's syntax parse tree |
838 | and symbol tables are cleaned up, and global variables are reset. |
8ebc5c01 |
839 | |
8a7dc658 |
840 | Now suppose we have more than one interpreter instance running at the |
841 | same time. This is feasible, but only if you used the |
842 | C<-DMULTIPLICITY> flag when building Perl. By default, that sets |
843 | C<perl_destruct_level> to C<1>. |
8ebc5c01 |
844 | |
845 | Let's give it a try: |
846 | |
847 | |
848 | #include <EXTERN.h> |
8a7dc658 |
849 | #include <perl.h> |
8ebc5c01 |
850 | |
851 | /* we're going to embed two interpreters */ |
852 | /* we're going to embed two interpreters */ |
853 | |
8ebc5c01 |
854 | #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)" |
855 | |
8ebc5c01 |
856 | int main(int argc, char **argv, char **env) |
857 | { |
54310121 |
858 | PerlInterpreter |
8ebc5c01 |
859 | *one_perl = perl_alloc(), |
54310121 |
860 | *two_perl = perl_alloc(); |
8ebc5c01 |
861 | char *one_args[] = { "one_perl", SAY_HELLO }; |
862 | char *two_args[] = { "two_perl", SAY_HELLO }; |
863 | |
864 | perl_construct(one_perl); |
865 | perl_construct(two_perl); |
866 | |
867 | perl_parse(one_perl, NULL, 3, one_args, (char **)NULL); |
868 | perl_parse(two_perl, NULL, 3, two_args, (char **)NULL); |
869 | |
870 | perl_run(one_perl); |
871 | perl_run(two_perl); |
872 | |
873 | perl_destruct(one_perl); |
874 | perl_destruct(two_perl); |
875 | |
876 | perl_free(one_perl); |
877 | perl_free(two_perl); |
878 | } |
879 | |
880 | |
881 | Compile as usual: |
882 | |
883 | % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
884 | |
885 | Run it, Run it: |
886 | |
887 | % multiplicity |
888 | Hi, I'm one_perl |
889 | Hi, I'm two_perl |
890 | |
96dbc785 |
891 | =head2 Using Perl modules, which themselves use C libraries, from your C program |
892 | |
893 | If you've played with the examples above and tried to embed a script |
894 | that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library, |
895 | this probably happened: |
896 | |
897 | |
898 | Can't load module Socket, dynamic loading not available in this perl. |
899 | (You may need to build a new perl executable which either supports |
900 | dynamic loading or has the Socket module statically linked into it.) |
901 | |
902 | |
903 | What's wrong? |
904 | |
905 | Your interpreter doesn't know how to communicate with these extensions |
906 | on its own. A little glue will help. Up until now you've been |
907 | calling I<perl_parse()>, handing it NULL for the second argument: |
908 | |
909 | perl_parse(my_perl, NULL, argc, my_argv, NULL); |
910 | |
911 | That's where the glue code can be inserted to create the initial contact between |
912 | Perl and linked C/C++ routines. Let's take a look some pieces of I<perlmain.c> |
913 | to see how Perl does this: |
914 | |
915 | |
916 | #ifdef __cplusplus |
917 | # define EXTERN_C extern "C" |
918 | #else |
919 | # define EXTERN_C extern |
920 | #endif |
921 | |
922 | static void xs_init _((void)); |
923 | |
924 | EXTERN_C void boot_DynaLoader _((CV* cv)); |
925 | EXTERN_C void boot_Socket _((CV* cv)); |
926 | |
927 | |
928 | EXTERN_C void |
929 | xs_init() |
930 | { |
931 | char *file = __FILE__; |
932 | /* DynaLoader is a special case */ |
933 | newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file); |
934 | newXS("Socket::bootstrap", boot_Socket, file); |
935 | } |
936 | |
937 | Simply put: for each extension linked with your Perl executable |
938 | (determined during its initial configuration on your |
939 | computer or when adding a new extension), |
940 | a Perl subroutine is created to incorporate the extension's |
941 | routines. Normally, that subroutine is named |
942 | I<Module::bootstrap()> and is invoked when you say I<use Module>. In |
943 | turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl |
944 | counterpart for each of the extension's XSUBs. Don't worry about this |
945 | part; leave that to the I<xsubpp> and extension authors. If your |
946 | extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()> |
947 | for you on the fly. In fact, if you have a working DynaLoader then there |
5f05dabc |
948 | is rarely any need to link in any other extensions statically. |
96dbc785 |
949 | |
950 | |
951 | Once you have this code, slap it into the second argument of I<perl_parse()>: |
952 | |
953 | |
954 | perl_parse(my_perl, xs_init, argc, my_argv, NULL); |
955 | |
956 | |
957 | Then compile: |
958 | |
8a7dc658 |
959 | % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts` |
96dbc785 |
960 | |
961 | % interp |
962 | use Socket; |
963 | use SomeDynamicallyLoadedModule; |
964 | |
965 | print "Now I can use extensions!\n"' |
966 | |
967 | B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code. |
968 | |
8a7dc658 |
969 | % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c |
96dbc785 |
970 | % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts` |
971 | % cc -c interp.c `perl -MExtUtils::Embed -e ccopts` |
8a7dc658 |
972 | % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts` |
96dbc785 |
973 | |
974 | Consult L<perlxs> and L<perlguts> for more details. |
975 | |
976 | |
cb1a09d0 |
977 | =head1 MORAL |
978 | |
979 | You can sometimes I<write faster code> in C, but |
5f05dabc |
980 | you can always I<write code faster> in Perl. Because you can use |
cb1a09d0 |
981 | each from the other, combine them as you wish. |
982 | |
983 | |
984 | =head1 AUTHOR |
985 | |
9607fc9c |
986 | Jon Orwant and <F<orwant@tpj.com>> and Doug MacEachern <F<dougm@osf.org>>, |
987 | with small contributions from Tim Bunce, Tom Christiansen, Hallvard Furuseth, |
988 | Dov Grobgeld, and Ilya Zakharevich. |
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989 | |
990 | Check out Doug's article on embedding in Volume 1, Issue 4 of The Perl |
991 | Journal. Info about TPJ is available from http://tpj.com. |
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992 | |
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993 | February 1, 1997 |
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994 | |
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995 | Some of this material is excerpted from Jon Orwant's book: I<Perl 5 |
996 | Interactive>, Waite Group Press, 1996 (ISBN 1-57169-064-6) and appears |
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997 | courtesy of Waite Group Press. |
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998 | |
999 | =head1 COPYRIGHT |
1000 | |
1001 | Copyright (C) 1995, 1996, 1997 Doug MacEachern and Jon Orwant. All |
1002 | Rights Reserved. |
1003 | |
1004 | Although destined for release with the standard Perl distribution, |
1005 | this document is not public domain, nor is any of Perl and its |
1006 | documentation. Permission is granted to freely distribute verbatim |
1007 | copies of this document provided that no modifications outside of |
1008 | formatting be made, and that this notice remain intact. You are |
1009 | permitted and encouraged to use its code and derivatives thereof in |
1010 | your own source code for fun or for profit as you see fit. |