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https://issues.apache.org/jira/browse/AXIS2C-884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12556572#action_12556572
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Bill Mitchell commented on AXIS2C-884:
--------------------------------------
To handle the multithreaded case, clearly the libxml2 documentation means what
it says and there must be one initialize and one cleanup for the entire
application. This means creating new entry points, say axis2_initialize() and
axis2_cleanup, that the application client calls at the appropriate points.
But demanding that all clients call these as appropriate means changing all the
test cases, all the samples, all the documentation....
So, my suggestion is:
(1) Add new entry points, axis2_initialize() and axis2_cleanup() that the
client may call to manage the initialization and tear down itself. This would
be required for correct multi-thread operation with libxml.
(2) Add internal entry points, axis2_implicit_initialize, and
axis2_implicit_cleanup, that op_client.c could use to accomplish the
axiom_xml_reader_init() and cleanup. These routines would keep a use-count of
active users, and, when there was no explicit initialize, would perform the
underlying initialization only on the first use and the cleanup only when the
last use was complete.
Change (2) will fix the single-thread crash above by ensuring that no
xmlCleanupParser is issued while any structures are still in use. And libxml2
seems to tolerate serial reuse as long as it is in a single thread. Change (1)
gives the multithreaded client the chance to take control of the initialization
and termination.
> 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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