Hi James,
So sorry to take so long to get back to you, but I was out of town. I'll grab the changes and do some testing. Thanks for your time!
I'll let you know how it goes... -Chris
On Feb 11, 2005, at 4:47 PM, James Berry wrote:
Chris,
I just checked in a code revision that implements (2b). Could you please review, when you get a chance, to see if this resolves the problem you reported?
James.
On Jan 19, 2005, at 2:42 PM, Chris Cates wrote:
Hey James,
Thanks very much for the response. I'm definitely in favor of option (2b).
First of all, I'm out of my league in this part of the code, so I'll have to leave the writing to you. I'm more than happy to help test whatever you'd like, tho. Second, the problem isn't very reliably reproducible right now (thanks to the timing of the threads, no doubt). I'm going to spend some time seeing if I can get it to happen more predictably to make any testing more reliable.
Thanks, and just drop me a note on what I can do to help.
-Chris
On Jan 19, 2005, at 3:42 PM, James Berry wrote:Hi Chris,
Oops. I don't have any confirmation that UCCompareTextDefault is thread safe, although my general impression through the years is that the UnicodeConverter, in general, is...within certain guidelines.
But it sounds (and looks) like you've come up with a case where it isn't. It looks like there's a race condition in the code having to do with deallocation of the collator used internally by UCCompareTextDefault...which wouldn't really be optimal anyway.
You've got two choices:
(1) Switch to using the icu transcoder (it's interesting that the UC routine is actually failing in a call to icu... ;)
(2) Work with me to fix this problem in the MacOSUnicodeConverter.
(3) Or both.
To fix MacOSUnicodeConverter, we've got several choices:
(a) Rewrite those comparison routines to use CFString functions for the comparisons (similar to implementation of MacOSUnicodeConverter::upperCase). This pays the penalty of a malloc/dealloc per call, which isn't too nice. But this should be thread-safe otherwise.
(b) Rewrite those comparison routines to use a fixed instance of a UCCreateCollator that we allocate ourselves during construction of the MacOSUnicodeConverter.. At least we'll be able to control the lifetime of the collator this way. Since we'll have a single instance of this collator for Xerces, we'll hope that it's re-entrant...which I believe it to be. We'll then use UCCompareText instead of UCCompareTextDefault. This should get around the fact that UCCompareTextDefault is apparently not properly protecting the collator that it uses internally. If we had to, we could put a mutex around the use of our collator.
(c) Some other choice.
Since you've got a somewhat reproducible test, I'd love it if you'd help me write and/or test 2b.
-jdb
On Jan 19, 2005, at 11:40 AM, Chris Cates wrote:I have an odd problem that I was wondering if anyone has seen before or could maybe offer some input on.
I'm using xerces 2.6.0 on MacOS 10.3.7, and my application is multi-threaded. There are two threads using xerces, each with its own parser and associated data. I have seen a seg fault a couple times now from these threads with identical stack traces on both of the xerces threads. (Both threads stacks are included at the bottom from a single crash.)
The only guess I've been able to come up with for what's going on is that the Apple Carbon routine UCCompareTextDefault() is not thread-safe. I was wondering if anyone has run into anything like this before, or knows whether indeed, it may be a threading issue related to the Apple routines.
Help? Thanks very much in advance.
-Chris
------------------------------
Thread 2 Crashed:
0 libicucore.A.dylib 0x968d2208 ures_close + 0x18
1 libicucore.A.dylib 0x968e9fe8 ucol_close + 0xa8
2 ...ple.CoreServices.CarbonCore 0x902ce4c4 SetICUCollator + 0x30
3 ...ple.CoreServices.CarbonCore 0x902a4e58 UCCompareTextDefault + 0x98
4 libxerces-c.26.0.dylib 0x014f0e5c xercesc_2_6::MacOSUnicodeConverter::compareIString(unsigned short const*, unsigned short const*) + 0xc0
5 libxerces-c.26.0.dylib 0x01567174 xercesc_2_6::XMLString::compareIString(unsigned short const*, unsigned short const*) + 0x40
6 libxerces-c.26.0.dylib 0x01569c48 xercesc_2_6::XMLURL::lookupByName(unsigned short const*) + 0x3c
7 libxerces-c.26.0.dylib 0x0156c4dc xercesc_2_6::XMLURL::parse(unsigned short const*) + 0x284
8 libxerces-c.26.0.dylib 0x0156adc0 xercesc_2_6::XMLURL::setURL(unsigned short const*) + 0x28
9 libxerces-c.26.0.dylib 0x0156a314 _ZN11xercesc_2_66XMLURLC4EPKcPNS_13MemoryManagerE + 0x8c
10 libxerces-c.26.0.dylib 0x0156a278 xercesc_2_6::XMLURL::XMLURL(char const*, xercesc_2_6::MemoryManager*) + 0x10
11 intercomd 0x0003250c xml::DomParser::ParseURL(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) + 0x310
12 intercomd 0x000cb384 weather::Parser::Update() + 0x3c4
13 intercomd 0x00098abc weather::Implementation::DoUpdate(bool, bool, bool) + 0x354
14 intercomd 0x000d3bdc weather::Thread::execute() + 0x69c
15 intercomd 0x00029054 util::Thread::run() + 0x38
16 intercomd 0x0002909c util::Thread::threadFunction(void*) + 0x34
17 libSystem.B.dylib 0x900246e8 _pthread_body + 0x28
Thread 3 Crashed:
0 libicucore.A.dylib 0x968d2208 ures_close + 0x18
1 libicucore.A.dylib 0x968e9fe8 ucol_close + 0xa8
2 ...ple.CoreServices.CarbonCore 0x902ce4c4 SetICUCollator + 0x30
3 ...ple.CoreServices.CarbonCore 0x902a4e58 UCCompareTextDefault + 0x98
4 libxerces-c.26.0.dylib 0x014f0e5c xercesc_2_6::MacOSUnicodeConverter::compareIString(unsigned short const*, unsigned short const*) + 0xc0
5 libxerces-c.26.0.dylib 0x01567174 xercesc_2_6::XMLString::compareIString(unsigned short const*, unsigned short const*) + 0x40
6 libxerces-c.26.0.dylib 0x01569c48 xercesc_2_6::XMLURL::lookupByName(unsigned short const*) + 0x3c
7 libxerces-c.26.0.dylib 0x0156c4dc xercesc_2_6::XMLURL::parse(unsigned short const*) + 0x284
8 libxerces-c.26.0.dylib 0x0156adc0 xercesc_2_6::XMLURL::setURL(unsigned short const*) + 0x28
9 libxerces-c.26.0.dylib 0x0156a314 _ZN11xercesc_2_66XMLURLC4EPKcPNS_13MemoryManagerE + 0x8c
10 libxerces-c.26.0.dylib 0x0156a278 xercesc_2_6::XMLURL::XMLURL(char const*, xercesc_2_6::MemoryManager*) + 0x10
11 intercomd 0x0003250c xml::DomParser::ParseURL(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) + 0x310
12 intercomd 0x000b7838 rss::Parser::Parse(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) + 0x314
13 intercomd 0x0008a834 rss::Implementation::DoUpdate() + 0x2d8
14 intercomd 0x000b9b48 rss::Thread::execute() + 0x5cc
15 intercomd 0x00029054 util::Thread::run() + 0x38
16 intercomd 0x0002909c util::Thread::threadFunction(void*) + 0x34
17 libSystem.B.dylib 0x900246e8 _pthread_body + 0x28
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