Question

I am working actually on a data processing code using libxml2. I am stuck on a memory leak impossible to remove . Here is a minimal code to generate it :

#include <stdlib.h>
#include <stdio.h>
#include <libxml/parser.h>
#include <libxml/tree.h>
#include <omp.h>

int main(void)
{
    xmlDoc *doc;
    int tn;
    char fname[32];

    omp_set_num_threads(2);
    xmlInitParser();
    #pragma omp parallel private(doc,tn,fname)
    {
        tn  = omp_get_thread_num();
        sprintf(fname,"testdoc%d.xml",tn);
        doc = xmlReadFile(fname,NULL,0);
        printf("document %s parsed on thread %d (%p)\n",fname,tn,doc);
        xmlFreeDoc(doc);
    }
    xmlCleanupParser();

    return EXIT_SUCCESS;
}

At runtime, output is :

document testdoc0.xml parsed on thread 0 (0x1005413a0)
document testdoc1.xml parsed on thread 1 (0x1005543c0)

confirming that we really have multi-threading and that doc is really private in the parallel region. One can notice that I applied correctly the thread safety instructions for using libxml2 (http://xmlsoft.org/threads.html). Valgrind reports :

HEAP SUMMARY:
    in use at exit: 9,000 bytes in 8 blocks
  total heap usage: 956 allocs, 948 frees, 184,464 bytes allocated

968 bytes in 1 blocks are definitely lost in loss record 6 of 8
   at 0x1000107AF: malloc (vg_replace_malloc.c:236)
   by 0x1000B2590: xmlGetGlobalState (in /opt/local/lib/libxml2.2.dylib)
   by 0x1000B1A18: __xmlDefaultSAXHandler (in /opt/local/lib/libxml2.2.dylib)
   by 0x100106D18: xmlDefaultSAXHandlerInit (in /opt/local/lib/libxml2.2.dylib)
   by 0x100041BE7: xmlInitParserCtxt (in /opt/local/lib/libxml2.2.dylib)
   by 0x100042145: xmlNewParserCtxt (in /opt/local/lib/libxml2.2.dylib)
   by 0x10004615E: xmlCreateURLParserCtxt (in /opt/local/lib/libxml2.2.dylib)
   by 0x10005B56B: xmlReadFile (in /opt/local/lib/libxml2.2.dylib)
   by 0x100000E03: main.omp_fn.0 (in ./xtest)
   by 0x100028FA3: gomp_thread_start (in /opt/local/lib/gcc44/libgomp.1.dylib)
   by 0x1001E8535: _pthread_start (in /usr/lib/libSystem.B.dylib)
   by 0x1001E83E8: thread_start (in /usr/lib/libSystem.B.dylib)

LEAK SUMMARY:
   definitely lost: 968 bytes in 1 blocks
   indirectly lost: 0 bytes in 0 blocks
     possibly lost: 0 bytes in 0 blocks
   still reachable: 8,032 bytes in 7 blocks
        suppressed: 0 bytes in 0 blocks
Reachable blocks (those to which a pointer was found) are not shown.
To see them, rerun with: --leak-check=full --show-reachable=yes

This is working for me whatever the XML document used. I am using libxml 2.7.8, on Mac OS X 10.6.5 with gcc 4.4.5.

Is someone able to reproduce this bug ?

Thanks,

Antonin

Answer 1

You should probably bring this up on the libxml2 mailing list.

http://mail.gnome.org/mailman/listinfo/xml