Re: [Log4cpp-devel] getAllAppenders fail on Win32 with log4cpp as DLL

[Aaron I. <ai...@ya...>]

No real standard but "-Naur" seems to be preferred.
-Aaron
 Dirk Luetjens <di...@no...> wrote:A question and an answer: As usual after finding the error, explaning it 
to others one also finds the right words to search the net for 
solutions. I found two MSDN articles describing the problem:

---
http://support.microsoft.com/default.aspx?scid=KB;en-us;q172396

SYMPTOMS
When accessing an STL object created in one DLL or EXE through a pointer 
or reference in a different DLL or EXE, you may experience an access 
violation or other serious program errors including the appearance of 
data corruption or data loss.

---
http://support.microsoft.com/default.aspx?scid=kb;EN-US;168958


SUMMARY
This article demonstrates how to:

* Export an instantiation of a Standard Template Library (STL) class.
* Export a class that contains a data member that is an STL object.

Note that you may not export a generalized template. The template must 
be instantiated; that is, all of the template parameters must be 
supplied and must be completely defined types at the point of 
instantiation. For instance "stack;" instantiates the STL stack 
class. The instantiation forces all members of class stack to be 
generated.

Also note that some STL containers (map, set, queue, list, deque) cannot 
be exported. Please refer to the More Information section to follow for 
a detailed explanation.

... a little later ...
The only STL container that can currently be exported is vector.
...

---

The bottom line is: getAllAppenders _must_ generate a std::vector from 
the std::set like getCurrentCategories() to safely export the list of 
appenders.

I would like to give provide you with a patch for this change. Do you 
prefer specific parameters for the diff command?

Dirk



Dirk Luetjens wrote:
> Hi,
> 
> today I had a strange problem with the Categroy::getAllAppenders () 
> function. I'm writing a small gui dialog to customize the logging during 
> the execution of the program. Right now I can edit the categories with 
> the vector returned from getCurrentCategories (). I wanted to display 
> also the list of attached appenders so I asked for the AppenderSet via 
> the function getAllAppenders (). But the returned set is not valid, 
> since the implementation of the _Tree used in the std::set contains a 
> static _Nil node, which is not the same in the process and in the DLL.
> As a result when I try to iterate the returned set I get an invalid 
> AppenderSet::end () iterator and the iteration continues until the 
> software crashes.
> 
> Perhaps as little longer description: the STL implementation of the 
> std::set in Microsoft uses a std::_Tree. The std::_Tree maintains one 
> static _Nil and one static _Nilrefs member, that is used to mark the 
> ends in the trees. This _Nil is used in within all _Trees with the same 
> template arguments. Compiling log4cpp as a DLL will result in having one 
> static instance of these to members within the DLL, that are not the 
> same static instances of theses members in the Application. So copying 
> the AppenderSet within the context of the DLL will use the DLLs instance 
> of the _Nil pointer to mark the ends in the _Tree. But iterating through 
> the std::set within the application context will result in the usage of 
> a different _Nil element. So the iteration through the _Tree will never 
> end, since the end of the _Tree will never match the _Nil element.
> 
> 
> Any ideas how to circumvent the problem?




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