Fix thread issues

[Gustavo Sverzut Barbieri-3]

While developing a Gdome application using threads, I found an issue with the
way it handles singletons, like dome-xml-domimpl.c and gdome-xpath-xpeval.c.

You first test if global instance is NULL, if not you allocate the new,
_EMPTY_ instance directly to the global instance, then goes to fill needed
fields, like "vtab".

Problem happens if you allocate and is preempted by system. Global pointer is
not NULL anymore, however you don't have any required field, like "vtab", and
can segfault your application.

This could be solved easily without any locks, just use a local variable while
the instance is not setup, just then make it global.

Attached patch fix this problem.

Thanks,

--
Gustavo Sverzut Barbieri
------------------------
INdT, Recife, Brazil

Jabber: barbieri@...
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[gdome2-cvs-threadsafe.patch]

---

diff -ur gdome2-fix/libgdome/gdomecore/gdome-xml-domimpl.c gdome2-orig/libgdome/gdomecore/gdome-xml-domimpl.c
--- gdome2-fix/libgdome/gdomecore/gdome-xml-domimpl.c 2006-05-18 15:02:22.000000000 -0300
+++ gdome2-orig/libgdome/gdomecore/gdome-xml-domimpl.c 2005-05-13 04:05:56.000000000 -0300
@@ -70,11 +70,10 @@
 GdomeDOMImplementation *
 gdome_xml_di_mkref (void) {
  if (gdome_xml_DOMImplementation == NULL) {
- Gdome_xml_DOMImplementation *n;
- n = g_new0 (Gdome_xml_DOMImplementation, 1);
- n->refcnt = 1;
- n->vtab = &gdome_xml_di_vtab;
- gdome_xml_DOMImplementation = n;
+ gdome_xml_DOMImplementation = g_new (Gdome_xml_DOMImplementation, 1);
+ memset(gdome_xml_DOMImplementation, 0, sizeof(Gdome_xml_DOMImplementation));
+ gdome_xml_DOMImplementation->refcnt = 1;
+ gdome_xml_DOMImplementation->vtab = &gdome_xml_di_vtab;
  } else
  gdome_xml_DOMImplementation->refcnt++;
 
diff -ur gdome2-fix/libgdome/xpath/gdome-xpath-xpeval.c gdome2-orig/libgdome/xpath/gdome-xpath-xpeval.c
--- gdome2-fix/libgdome/xpath/gdome-xpath-xpeval.c 2006-05-18 15:01:55.000000000 -0300
+++ gdome2-orig/libgdome/xpath/gdome-xpath-xpeval.c 2006-05-18 15:11:48.000000000 -0300
@@ -53,11 +53,9 @@
 gdome_xpath_xpeval_mkref (void)
 {
   if (gdome_xpath_XPathEvaluator == NULL) {
- Gdome_xpath_XPathEvaluator *n;
- n = g_new0 (Gdome_xpath_XPathEvaluator, 1);
-    n->refcnt = 1;
-    n->vtab = &gdome_xpath_xpeval_vtab;
- gdome_xpath_XPathEvaluator = n;
+    gdome_xpath_XPathEvaluator = g_new (Gdome_xpath_XPathEvaluator, 1);
+    gdome_xpath_XPathEvaluator->refcnt = 1;
+    gdome_xpath_XPathEvaluator->vtab = &gdome_xpath_xpeval_vtab;
   } else
     gdome_xpath_XPathEvaluator->refcnt++;
 

---

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[Gustavo Sverzut Barbieri-3]

Sorry, but previous patch was wrong (it was a revert patch :-D).

Attached is the correct.

--
Gustavo Sverzut Barbieri
------------------------
INdT, Recife, Brazil

Jabber: barbieri@...
   MSN: barbieri@...
  ICQ#: 17249123
 Skype: gsbarbieri
Mobile: [phone]
 Phone:  [phone]@...
   GPG: 0xB640E1A2 @ wwwkeys.pgp.net

[gdome2-cvs-threadsafe.patch]

---

diff -ur gdome2-orig/libgdome/gdomecore/gdome-xml-domimpl.c gdome2-fix/libgdome/gdomecore/gdome-xml-domimpl.c
--- gdome2-orig/libgdome/gdomecore/gdome-xml-domimpl.c 2005-05-13 04:05:56.000000000 -0300
+++ gdome2-fix/libgdome/gdomecore/gdome-xml-domimpl.c 2006-05-18 15:02:22.000000000 -0300
@@ -70,10 +70,11 @@
 GdomeDOMImplementation *
 gdome_xml_di_mkref (void) {
  if (gdome_xml_DOMImplementation == NULL) {
- gdome_xml_DOMImplementation = g_new (Gdome_xml_DOMImplementation, 1);
- memset(gdome_xml_DOMImplementation, 0, sizeof(Gdome_xml_DOMImplementation));
- gdome_xml_DOMImplementation->refcnt = 1;
- gdome_xml_DOMImplementation->vtab = &gdome_xml_di_vtab;
+ Gdome_xml_DOMImplementation *n;
+ n = g_new0 (Gdome_xml_DOMImplementation, 1);
+ n->refcnt = 1;
+ n->vtab = &gdome_xml_di_vtab;
+ gdome_xml_DOMImplementation = n;
  } else
  gdome_xml_DOMImplementation->refcnt++;
 
diff -ur gdome2-orig/libgdome/xpath/gdome-xpath-xpeval.c gdome2-fix/libgdome/xpath/gdome-xpath-xpeval.c
--- gdome2-orig/libgdome/xpath/gdome-xpath-xpeval.c 2006-05-18 15:11:48.000000000 -0300
+++ gdome2-fix/libgdome/xpath/gdome-xpath-xpeval.c 2006-05-18 15:01:55.000000000 -0300
@@ -53,9 +53,11 @@
 gdome_xpath_xpeval_mkref (void)
 {
   if (gdome_xpath_XPathEvaluator == NULL) {
-    gdome_xpath_XPathEvaluator = g_new (Gdome_xpath_XPathEvaluator, 1);
-    gdome_xpath_XPathEvaluator->refcnt = 1;
-    gdome_xpath_XPathEvaluator->vtab = &gdome_xpath_xpeval_vtab;
+ Gdome_xpath_XPathEvaluator *n;
+ n = g_new0 (Gdome_xpath_XPathEvaluator, 1);
+    n->refcnt = 1;
+    n->vtab = &gdome_xpath_xpeval_vtab;
+ gdome_xpath_XPathEvaluator = n;
   } else
     gdome_xpath_XPathEvaluator->refcnt++;
 

---

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[Luca Padovani-2]

Thanks Gustavo, patch applied.

--luca

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