[gmime-devel] GObject unref hell

[Mario Theodoridis <mario theodoridis regify com>]

Hello,

i'm currently in the process of using GMime for a mail process 
application. First of all i'd like to thank Jeffrey and potential other 
contributors to GMime for writing this wonderful library, as MIME 
parsing and generating is everything but fun.

I find myself with a problem that i can't seem to wrap my head around.
The following code snippet deterministically works in some instances, 
but not in others.

#define rfunref(obj) if (obj) { if G_IS_OBJECT(obj) { \
    g_debug("[%s:%d] unref "#obj, __FILE__, __LINE__); \
    g_object_unref(obj); obj = NULL; \
    g_debug("[%s:%d] unrefed "#obj, __FILE__, __LINE__); }}

  GMimeDataWrapper *content = NULL;
  GMimeStream *mem = NULL;
  GMimePart *part = NULL;
  GMimeMultipart *multipart = NULL;
  char *fileName = NULL;
  char *type = NULL, *subtype = NULL, *param = NULL, *value = NULL;

  do{
    /* other stuff here */

    /* set type, subtype, filename, etc. */
    /* find type */
    getType(msg, res, resLen, &type, &subtype, &param, &value);
    part = g_mime_part_new_with_type(type, subtype);
    g_mime_part_set_filename(part, fileName);
    g_mime_object_set_content_type_parameter((GMimeObject*)part,
                                              param, value);
    if (g_ascii_strcasecmp(type, "text") == 0) {
        g_mime_part_set_content_encoding(
                part, GMIME_CONTENT_ENCODING_QUOTEDPRINTABLE);
    } else {
        g_mime_part_set_content_encoding (
                part, GMIME_CONTENT_ENCODING_BASE64);
    }
    g_mime_part_set_content_object (part, content);
    rfunref (content);

    g_mime_multipart_add (multipart, (GMimeObject *) part);
    rfunref (part);
  } while(attachments);

  g_mime_message_set_mime_part (message, (GMimeObject*) multipart);
  headerList = g_mime_object_get_header_list((GMimeObject*)multipart);
  rfunref (multipart);


A failed event looks like this

VERB: successfully extracted mime type: [application] subtype: 
[octet-stream] param: [charset] value: [binary]
VERB: [mime.c:270] unref content
VERB: [mime.c:270] unrefed content
VERB: [mime.c:273] unref part
VERB: [mime.c:273] unrefed part

(process:9549): GLib-GObject-CRITICAL **: g_object_unref: assertion 
`G_IS_OBJECT (object)' failed
VERB: [mime.c:280] unref multipart
VERB: [mime.c:280] unrefed multipart

while a good one looks like

VERB: successfully extracted mime type: [text] subtype: [plain] param: 
[charset] value: [utf-8]
VERB: [mime.c:270] unref content
VERB: [mime.c:270] unrefed content
VERB: [mime.c:273] unref part
VERB: [mime.c:273] unrefed part
VERB: [mime.c:280] unref multipart
VERB: [mime.c:280] unrefed multipart

The unref macro is a mere act of desperation.

I have 2 general questions here.
1. What is going on here. No code was skipped between unref part and 
multipart.
2. Is there a way to safely unref a GObject, i.e. unref it if it needs 
to be? This is mainly because it is not always clear to me when and when 
not due to issues like the current.

Clue sticks to either question would be greatly appreciated.

--
Mit Freundlichen Grüßen / Regards

Mario Theodoridis

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