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From "Bill Mitchell (JIRA)" <>
Subject [jira] Commented: (AXIS2C-884) Seg fault in libxml when svc client torn down in a multithreaded client
Date Fri, 08 Feb 2008 12:54:07 GMT


Bill Mitchell commented on AXIS2C-884:

You're very welcome.  

By the way, to implement a call to initialize libxml in my main thread, I did not have to
include all the libxml includes which caused some conflicts with other xml related includes
I had.  Instead I excerpted just the fragment of the header file for initialization and encapsulated
it under an ifdef in my app:

// If libxml2 is used, instead of guththila, then we need to explicitly initialize outside
of Axis2c
// Define libxml entry points directly, to avoid conflicts with Xerces
#ifdef __cplusplus
extern "C" {

#include <libxml/xmlexports.h>

    xmlInitParser    (void);
    xmlCleanupParser    (void);

#ifdef __cplusplus

Then I added a call to xmlInitParser() in my main thread, again under ifdef, and worked around
the problem.  I may have had another issue to make sure that libxml2 and its friends are built
with the VS debug C runtime included in the manifest, but I had already solved that issue
in order to debug libxml2.  

The other, simpler workaround is to rebuild Axis to use the guththila parser.  I only went
back to libxml2 as I was encountering guththila problems that I thought would take some time
to resolve.  All the ones I encountered in my app have been fixed in 1.3 and it works fine
for me. There are a couple of other minor ones that are preventing the guththila parser becoming
the default parser today.  I think the general direction is to move to guththila as soon as
practicable.  For your app, like mine, it may be there already.  

> Seg fault in libxml when svc client torn down in a multithreaded client
> -----------------------------------------------------------------------
>                 Key: AXIS2C-884
>                 URL:
>             Project: Axis2-C
>          Issue Type: Bug
>          Components: core/deployment
>    Affects Versions: Current (Nightly)
>         Environment: Windows XP, Visual Studio 2005, libxml 2.6.25 and libxml 2.6.30,
>            Reporter: Bill Mitchell
>         Attachments: axis2.trace, desc_builder_diff.txt
> In a multithreaded application, if the stub/svc client is freed in a thread different
from that used when the svc client was built, libxml crashes.  The trace below shows the information
available from a release build with debug information embedded.  
> I have verified this is not an effect of combining debug and release C runtimes, or different
versions of the C runtime.  Rebuilding all the libxml related dlls with the same runtime as
is used for Axis and the client app does not solve the problem.  
> Interestingly, rebuilding libxml with threads disabled does make the crash go away. 
But the default build of libxml commonly available has native threads enabled, and building
without thread support may make the library not thread safe.  
> By adding debug trace statements in the axis2.trace file, I have verified that the xml_reader
being torn down when the crash happens is the one used to read the axis2.xml file when the
configuration was first read.  (axis2.trace file attached.)
> Looking at the code in libxml, it appears that libxml decides to close the reader using
an internal close routine intended for closing compressed channels through zlib.  Apparently
the C runtime library returns a -1 EOF status when closing a file opened for read.  The close
routine, gzio.c in zlib, treats this as an error, and when libxml attempts to report the error
and determines that it is in a different thread, things really go downhill fast.  I have not
isolated why the EnterCriticalSection call crashes in the system, but it does.  
> One way to avoid the problem would be to guarantee that the stub/svc client is freed
in the same thread as created it.  In my multithreaded client application, though, I work
hard to share the stub across threads deliberately to reduce the number of distinct service
clients and the associated demand on the server.  
> Windows call traceback at time of crash:
>  	ntdll.dll!7c918fea() 	
>  	[Frames below may be incorrect and/or missing, no symbols loaded for ntdll.dll]	
>  	msvcr80.dll!78134d09() 	
>  	ntdll.dll!7c910e91() 	
>  	ntdll.dll!7c9106eb() 	
>  	msvcr80.dll!78134d83() 	
>  	ntdll.dll!7c90104b() 	
> >	libxml2.dll!xmlGetGlobalState()  Line 570	C
>  	libxml2.dll!__xmlLastError()  Line 709 + 0x5 bytes	C
>  	libxml2.dll!__xmlRaiseError(void (void *, _xmlError *)* schannel=0x00000000, void (void
*, const char *, <no type>)* channel=0x00000000, void * data=0x00000000, void * ctx=0x00000000,
void * nod=0x00000000, int domain=8, int code=0, xmlErrorLevel level=XML_ERR_ERROR, const
char * file=0x00000000, int line=0, const char * str1=0x00c5d420, const char * str2=0x00000000,
const char * str3=0x00000000, int int1=0, int col=0, const char * msg=0x00c5d360, ...)  Line
452 + 0x5 bytes	C
>  	libxml2.dll!__xmlSimpleError(int domain=8, int code=0, _xmlNode * node=0x00000000,
const char * msg=0x00c5d360, const char * extra=0x00c5d420)  Line 657 + 0x2d bytes	C
>  	libxml2.dll!__xmlIOErr(int domain=8, int code=0, const char * extra=0x00c5d420)  Line
417 + 0x1a bytes	C
>  	libxml2.dll!xmlGzfileClose(void * context=0x03301f80)  Line 1155 + 0x10 bytes	C
>  	libxml2.dll!xmlFreeParserInputBuffer(_xmlParserInputBuffer * in=0x03304578)  Line 2207
+ 0x5 bytes	C
>  	libxml2.dll!xmlTextReaderClose(_xmlTextReader * reader=0x03304760)  Line 2244 + 0x6
bytes	C
>  	axis2_parser.dll!axis2_libxml2_reader_wrapper_free(axiom_xml_reader * parser=0x03301e00,
const axutil_env * env=0x031aa150)  Line 510	C
>  	axiom.dll!axiom_stax_builder_free(axiom_stax_builder * om_builder=0x03271aa8, const
axutil_env * env=0x031aa150)  Line 886	C
>  	axis2_engine.dll!axis2_desc_builder_free(axis2_desc_builder * desc_builder=0x03301d58,
const axutil_env * env=0x031aa150)  Line 141	C
>  	axis2_engine.dll!axis2_conf_builder_free(axis2_conf_builder * conf_builder=0x03301d70,
const axutil_env * env=0x031aa150)  Line 128	C
>  	axis2_engine.dll!axis2_dep_engine_free(axis2_dep_engine * dep_engine=0x031aa2e8, const
axutil_env * env=0x031aa150)  Line 380	C
>  	axis2_engine.dll!axis2_conf_free(axis2_conf * conf=0x0330cad8, const axutil_env * env=0x031aa150)
 Line 328	C
>  	axis2_engine.dll!axis2_conf_ctx_free(axis2_conf_ctx * conf_ctx=0x00000000, const axutil_env
* env=0x031aa150)  Line 439	C
>  	axis2_engine.dll!axis2_svc_client_free(axis2_svc_client * svc_client=0x031aa1a8, const
axutil_env * env=0x031aa150)  Line 1303	C
>  	axis2_engine.dll!axis2_stub_free(axis2_stub * stub=0x031aa198, const axutil_env * env=0x031aa150)
 Line 131	C

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