No subject

librdf_statement instance, with a usage count of 1.

The librdf_new_... function is therefore not a suitable function to use to make
a safe copy of the statement returned from librdf_stream_get_object.

Thus, either librdf_new_... is not implementing its documentation correctly (is
there perhaps a slippage between librdf_new_... and raptor_statement_copy which
means that the former can't reliably delegate to the latter), or else the
librdf_stream_get_object documentation needs to be more explicit about how this
safe copy is to be achieved.

Steps to Reproduce: 
This is perfectly reproducible in my usage of the library, but I haven't made a
separate reduction. 

In my usage of the library, I'm reading all of the statements from the stream in
turn, but these are being managed by the caller, as a group.  The program ends
up with all of the collected statements being identical.

Is the above explanation convincing alone?

My code:


    if ((statement = librdf_stream_get_object(stream)) == NULL) {
        return scheme_false;
    } else {
        librdf_statement* orig_statement;
        orig_statement = statement;
        if ((statement = librdf_new_statement_from_statement(orig_statement)) ==
NULL) {
            scheme_signal_error("Error copy-constructing statement");
        }
        fprintf(stderr, "get_stream_next: orig_statement=%p(%d)
statement=%p(%d)\n",
                orig_statement,
                ((raptor_statement*)orig_statement)->usage,
                statement,
                ((raptor_statement*)statement)->usage);
        fprintf(stderr, "get_stream_next: %s\n",
statement_to_string_internal(statement));
        librdf_stream_next(stream); /* move the stream up one */
        return statement;
    }

My debugging output:

hashes store:

get_stream_next: <http://nxg.me.uk/norman/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://xmlns.com/foaf/0.1/Person>
get_stream_next: orig_statement=0x1018160d0(2) statement=0x1018160d0(2)
get_stream_next: <http://nxg.me.uk/norman/> <http://purl.org/dc/terms/name>
"Norman"
get_stream_next: orig_statement=0x101817460(2) statement=0x101817460(2)
get_stream_next: _:r1319914503r13273r1
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://xmlns.com/foaf/0.1/Person>
get_stream_next: orig_statement=0x101820620(2) statement=0x101820620(2)
get_stream_next: _:r1319914503r13273r1 <http://xmlns.com/foaf/0.1/homepage>
<http://example.com/person>
get_stream_next: orig_statement=0x101816e90(2) statement=0x101816e90(2)
get_stream_next: <http://nxg.me.uk/norman/> <http://xmlns.com/foaf/0.1/knows>
_:r1319914503r13273r1
get_stream_next: orig_statement=0x10181b430(2) statement=0x10181b430(2)
get_stream_next: <http://nxg.me.uk/norman/> <http://xmlns.com/foaf/0.1/mbox>
<mailto:norman at astro.gla.ac.uk>

(note, problem is masked here, because the orig_statement is different each
time)

sqlite store:

get_stream_next: orig_statement=0x10181ebb0(2) statement=0x10181ebb0(2)
get_stream_next: <http://nxg.me.uk/norman/>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://xmlns.com/foaf/0.1/Person>
get_stream_next: orig_statement=0x10181ebb0(3) statement=0x10181ebb0(3)
get_stream_next: <http://nxg.me.uk/norman/> <http://purl.org/dc/terms/name>
"Norman"
get_stream_next: orig_statement=0x10181ebb0(4) statement=0x10181ebb0(4)
get_stream_next: _:r1319914503r13273r3
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://xmlns.com/foaf/0.1/Person>
get_stream_next: orig_statement=0x10181ebb0(5) statement=0x10181ebb0(5)
get_stream_next: _:r1319914503r13273r3 <http://xmlns.com/foaf/0.1/homepage>
<http://example.com/person>
get_stream_next: orig_statement=0x10181ebb0(6) statement=0x10181ebb0(6)
get_stream_next: <http://nxg.me.uk/norman/> <http://xmlns.com/foaf/0.1/knows>
_:r1319914503r13273r3
get_stream_next: orig_statement=0x10181ebb0(7) statement=0x10181ebb0(7)
get_stream_next: <http://nxg.me.uk/norman/> <http://xmlns.com/foaf/0.1/mbox>
<mailto:norman at astro.gla.ac.uk>

Note the same orig_statement and statement being used several times.  This _may_
happen only when using the sqlite store -- the in-memory and hashes stores seem
to produce different {orig_,}statement each time.

This 


Additional Information: 
I'm filing this as an API bug, rather than a documentation bug, but feel free to
change it.
====================================================================== 

Issue History 
Date Modified    Username       Field                    Change               
====================================================================== 
2011-10-29 19:30 normang        New Issue                                    
======================================================================