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Problem with Perl bindings?

From: Roderich Schupp <roderich.schupp_at_gmail.com>
Date: Wed, 24 Jul 2013 13:29:33 +0200

Hi,

I'm investigating a problem with the Perl bindings and it looks as if an
APR hash gets
corrupted when it's marshalled to/from Perl.

Specifically I'm looking at
/subversion/bindings/swig/perl/libsvn_swig_perl/swigutil_pl.c (from trunk)
and the function svn_swig_pl_to_hash. This is the universal converter from
"Perl hash of somethings"
to "APR hash of somethings (else)". The guts of this function is (comments
are mine):

    apr_hash_t *hash;
    HV *h;
    char *key;
    I32 cnt, retlen;

    // create the APR hash that we're going to return
    hash = apr_hash_make(pool);

    // prepare to iterate over the Perl hash "source" (both keys and
values, like "each %hash" in Perl)
    h = (HV *)SvRV(source);
    cnt = hv_iterinit(h);

     while (cnt--) {
        // get the next key (into "key") and value (into "item")
        SV* item = hv_iternextsv(h, &key, &retlen);

        // convert value from Perl to SVN using the supplied callback cv
        void *val = cv(item, ctx, pool);

        // store converted value under key in APR hash
        svn_hash_sets(hash, key, val);
    }

IMHO the last statement is problematic: The Perl API call hv_iternextsv
just
stores a pointer to the Perl internal key string into "key". And we use this
internal pointer to set the APR hash key. Shouldn't we make a copy
of the string (in some pool) and use that to set the APR hash key?

Note: if this is indeed a problem it may have gone unrecognized for a long
time.
The reason is that the keys for all Perl hashes in a program are stored in
a central location, i.e. if we have hashes %foo and %bar that both
have a key "fubar", then this "fubar" is stored only once. And "fubar"
will only be garbage collected (and the bytes at its address recycled)
if no hash anywhere contains a key "fubar" anymore.

Cheers, Roderich
Received on 2013-07-24 13:30:20 CEST

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