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https://issues.apache.org/jira/browse/AXIS2C-884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12556180#action_12556180
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Bill Mitchell commented on AXIS2C-884:
--------------------------------------
Much as I like the source fix in my recommendation, as it does fix one symptom
of the problem and frees resources, including files, sooner rather than later,
I must admit it is not a complete solution. The initial crash I reported is
remedied, but I still see other bizarre behavior from libxml when invoked from
multiple threads.
The libxml documentation indicates that it expects to be initialized once in
the "main" thread before multithreaded operation begins. Instead, Axis2 does
the initialization each time the op_client is created, which happens in my case
in one of the multiple threads after application initialization. I have tried
doing the initialization just once with a call to xmlInitParser() in the main
application thread before any call to the Axis2 routines, but this reintroduces
the crash in xmlGetGlobalState. So I can't honestly recommend that moving the
xmlInitParser call earlier, say when the first environment was created which
might happen in the application main thread, would alleviate any problem.
This suggests that libxml is not as thread-safe as we would like, and that each
thread must create and use its own set of svc clients, instead of sharing them
in a connection pool. Of course, the guththila parser does not suffer from
this particular thread problem.
> Seg fault in libxml when svc client torn down in a multithreaded client
> -----------------------------------------------------------------------
>
> Key: AXIS2C-884
> URL: https://issues.apache.org/jira/browse/AXIS2C-884
> 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, libcurl
> 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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