In a sense, perl (the C program) is a good example of embedding Perl
(the language), so I'll demonstrate embedding with I<miniperlmain.c>,
-included in the source distribution. Here's a bastardized, nonportable
+included in the source distribution. Here's a bastardized, non-portable
version of I<miniperlmain.c> containing the essentials of embedding:
#include <EXTERN.h> /* from the Perl distribution */
main (int argc, char **argv, char **env)
{
- STRLEN n_a;
char *embedding[] = { "", "-e", "0" };
PERL_SYS_INIT3(&argc,&argv,&env);
/** Treat $a as a string **/
eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
- printf("a = %s\n", SvPV(get_sv("a", FALSE), n_a));
+ printf("a = %s\n", SvPV_nolen(get_sv("a", FALSE)));
perl_destruct(my_perl);
perl_free(my_perl);
a = Just Another Perl Hacker
In the example above, we've created a global variable to temporarily
-store the computed value of our eval'd expression. It is also
+store the computed value of our eval'ed expression. It is also
possible and in most cases a better strategy to fetch the return value
from I<eval_pv()> instead. Example:
...
- STRLEN n_a;
SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
- printf("%s\n", SvPV(val,n_a));
+ printf("%s\n", SvPV_nolen(val));
...
This way, we avoid namespace pollution by not creating global
{
dSP;
SV* retval;
- STRLEN n_a;
+
PUSHMARK(SP);
eval_sv(sv, G_SCALAR);
PUTBACK;
if (croak_on_error && SvTRUE(ERRSV))
- croak(SvPVx(ERRSV, n_a));
+ croak(SvPVx_nolen(ERRSV));
return retval;
}
I32 match(SV *string, char *pattern)
{
- SV *command = NEWSV(1099, 0), *retval;
- STRLEN n_a;
+ SV *command = newSV(0), *retval;
sv_setpvf(command, "my $string = '%s'; $string =~ %s",
- SvPV(string,n_a), pattern);
+ SvPV_nolen(string), pattern);
retval = my_eval_sv(command, TRUE);
SvREFCNT_dec(command);
I32 substitute(SV **string, char *pattern)
{
- SV *command = NEWSV(1099, 0), *retval;
- STRLEN n_a;
+ SV *command = newSV(0), *retval;
sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
- SvPV(*string,n_a), pattern);
+ SvPV_nolen(*string), pattern);
retval = my_eval_sv(command, TRUE);
SvREFCNT_dec(command);
I32 matches(SV *string, char *pattern, AV **match_list)
{
- SV *command = NEWSV(1099, 0);
+ SV *command = newSV(0);
I32 num_matches;
- STRLEN n_a;
sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
- SvPV(string,n_a), pattern);
+ SvPV_nolen(string), pattern);
my_eval_sv(command, TRUE);
SvREFCNT_dec(command);
AV *match_list;
I32 num_matches, i;
SV *text;
- STRLEN n_a;
PERL_SYS_INIT3(&argc,&argv,&env);
my_perl = perl_alloc();
perl_parse(my_perl, NULL, 3, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
- text = NEWSV(1099,0);
+ text = newSV(0);
sv_setpv(text, "When he is at a convenience store and the "
"bill comes to some amount like 76 cents, Maynard is "
"aware that there is something he *should* do, something "
printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
for (i = 0; i < num_matches; i++)
- printf("match: %s\n", SvPV(*av_fetch(match_list, i, FALSE),n_a));
+ printf("match: %s\n", SvPV_nolen(*av_fetch(match_list, i, FALSE)));
printf("\n");
/** Remove all vowels from text **/
if (num_matches) {
printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
num_matches);
- printf("Now text is: %s\n\n", SvPV(text,n_a));
+ printf("Now text is: %s\n\n", SvPV_nolen(text));
}
/** Attempt a substitution **/
char *args[] = { "", DO_CLEAN, NULL };
char filename[BUFFER_SIZE];
int exitstatus = 0;
- STRLEN n_a;
PERL_SYS_INIT3(&argc,&argv,&env);
if((my_perl = perl_alloc()) == NULL) {
}
perl_construct(my_perl);
+ PL_origalen = 1; /* don't let $0 assignment update the proctitle or embedding[0] */
exitstatus = perl_parse(my_perl, NULL, 2, embedding, NULL);
PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
if(!exitstatus) {
/* check $@ */
if(SvTRUE(ERRSV))
- fprintf(stderr, "eval error: %s\n", SvPV(ERRSV,n_a));
+ fprintf(stderr, "eval error: %s\n", SvPV_nolen(ERRSV));
}
}
to get the new behaviour. This also enables the running of END blocks if
the perl_parse fails and C<perl_destruct> will return the exit value.
+=head2 $0 assignments
+
+When a perl script assigns a value to $0 then the perl runtime will
+try to make this value show up as the program name reported by "ps" by
+updating the memory pointed to by the argv passed to perl_parse() and
+also calling API functions like setproctitle() where available. This
+behaviour might not be appropriate when embedding perl and can be
+disabled by assigning the value C<1> to the variable C<PL_origalen>
+before perl_parse() is called.
+
+The F<persistent.c> example above is for instance likely to segfault
+when $0 is assigned to if the C<PL_origalen = 1;> assignment is
+removed. This because perl will try to write to the read only memory
+of the C<embedding[]> strings.
+
=head2 Maintaining multiple interpreter instances
Some rare applications will need to create more than one interpreter
not be initialized correctly between consecutive runs and your
application may crash.
+See also L<perlxs/Thread-aware system interfaces>.
+
Using C<-Dusethreads -Duseithreads> rather than C<-Dusemultiplicity>
is more appropriate if you intend to run multiple interpreters
concurrently in different threads, because it enables support for