Re: [xml] LibXml2 Crash in MultiThreaded Windows

["Lav Mehrotra" <l mehrotra zensar com>]

Hi all,

Plz try to create 2 threads or more in a Windows VC++ 20005 Test exe /
Application. 
Put libxml2.dll , iconv.dll , zlib1.dll at runtime folder

Within the thread try to call xmlParseFile(const char* filename) or
xmlParseMemory() API if u intend to read any Xml within threads.
NOTE: These calls are in my Reader / Writer class Ctor

Or call xmlSaveFormatFile() / xmlSaveFile() APIs if u intend to save any
Xml within threads.

My crash occurs exactly when the 2nd thread is calling any of the above
APIs

CRASH Message : Unhandled Exception at XXX .Access Violation Writing
Location yyy

I have used Windows Mutex / Critical Sections & xmlMutex /xmlRMutex(
exposed in Threads.h) , within my ThreadProc but to no avail.

I have tried hard to play with all the possible switches /MT , /MTd ,
/MD , /MDd but could not resolve the crash.

I even made the same application in VC6 environment , but crash occurs
on 2nd Thread.

NOTE : Within my thread I create Reader / Writer object on Stack so it
goes out of scope when the thread fun exits , calls Dtor of Reader /
Writer object , which does 

xmlFreeDoc(m_ptrXMLDoc);
xmlCleanupParser();


I used Xml Memory APIs to check whether the crash is due to any FILE*
issues
In Parsing XML from memory there is no FILE* , but still it crashes on 
xmlParseMemory() when 2nd Thread calls it


Our application has a Server which sends some XML Data to clients using
Sockets , I have used xmlDocDumpFormatMemory() to get the Memory Buffer
& Size of a XML file , then send them  both to the client & use
xmlParseMemory() to parse the XmlBuf send by the Server


Regds,

Lav



-----Original Message-----
From: Daniel Veillard [mailto:veillard redhat com] 
Sent: Tuesday, June 10, 2008 5:28 PM
To: Rob Richards
Cc: Lav Mehrotra; xml gnome org; igor zlatkovic com
Subject: Re: [xml] LibXml2 Crash in MultiThreaded Windows

On Mon, Jun 09, 2008 at 07:56:42AM -0400, Rob Richards wrote:
> > Also it would be grt if u or Igor can spare some of ur valuable time
&
> > go thru this blog......
>
> http://blog.kowalczyk.info/archives/2006/08/07/the-missing-msvcr80dll-s
t
> > ory/

  But there isn't much we can do about this, this means the libc
interfaces
are not standardized on Windows.
> >  
>
> There is nothing strange about that. It also is a good reason why its 
> stressed not to mix where you allocate/de-allocate memory (same with 
> file descriptors) when working with dlls. If allocated in dll, make
sure 
> you de-allocate from within the dll. If you follow those guidelines,
you 
> can successfully use the library with a client compiled with a
different 
> run-time.

  Maybe one thing we can try do is minimize the reliance on FILE * . I
would
hope fd integers values might be more portable across implementations
(or at least not lead to crashes). Of course we can't just deprecate
FILE *
based APIs but making sure we don't use them too much internally and
maybe
document the associated problems. I think most of the FILE based APIs
are
about dump or debug output, and with the xmlSave module it should be as
convenient to use Fds .
  For internal use it's maybe the xmlIO.c which could be cleaned up 
a bit, but it's unclear this would really bring much benefits.

Daniel

-- 
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Daniel Veillard      | virtualization library  http://libvirt.org/
veillard redhat com  | libxml GNOME XML XSLT toolkit
http://xmlsoft.org/
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