Hmmm, this is a very well thought out and clearly explained post. And you know, we've been surprised by some problems with gcc 4.1+ related to export, which depends on serialization of a string which identifies the class. Hmmmmmmmmmmm. And I can appreciate what a huge amount of effort you had to expend to find this. I would like to a) see if someone can confirm this issue and its cause. b) see if this is the best solution. Since this string serialization is a very common operation, the method should be as fast as possible (lol - which seems to be the exact reason we find ourselves with this predicament). Somehow I think just pulling /pushing the characters from/to the input/output directly to to the string will be faster than creating a temporary string. c) after a/b above, it can be decided which version of boost the fix should be rolled into. Robert Ramey Chuck Bear wrote:
Folks,
We were recently tracking down some weirdness in our application, and think it may interest other users of boost archives. In essence, we are using the std::string library that comes with gcc 4.x, which reference counts the underlying characters. The iarchive loads seem to corrupt these characters if they are shared with other std::string instances. Here is a paraphrased example of what we were doing.
// First, we have a string instance static std::string defaultStringValue = "defaultValue";
// Next we make a class that uses this default to initialize a member in its base constructor class A { public: std::string member; A() : member(defaultStringValue); template<class Archive> void serialize(Archive & ar, const unsigned int serializer_version) { ar & member; } }
What we find happening is that if you deserialize an instance of A, the defaultStringValue *can* get clobbered (this has a bit to do with the length of the underlying value, as to whether the characters get clobbered or not). The scenario goes something like this: 1. Create an instance of A, this member will get a reference to the underlying "defaultValue" characters. 2. Load the instance of A from an archive that has a different value of member (the same length, or maybe shorter. If you test this, try something like "eefaultValue"). 3. This seems to mess up the value of defaultStringValue, you can print it out and see.
Inspection of the code reveals the following is happening (both in 1.34 and HEAD): text_iarchive_impl<Archive>::load(std::string &s) { std::size_t size; * this->This() >> size; // skip separating space is.get(); // borland de-allocator fixup #if BOOST_WORKAROUND(_RWSTD_VER, BOOST_TESTED_AT(20101)) if(NULL != s.data()) #endif s.resize(size); is.read(const_cast<char *>(s.data()), size); // <== This looks suspect }
Basically, data() is const because of the reference counting. Doing this const_cast and modification causes other strings that share the ref counted characters to be corrupted.
We have been applying the following patch to our production version of boost (1.34.0), to work around this issue. Basically, it makes its own temp string and then does the assignment.
diff -du -r boost_1_34_0/boost/archive/impl/basic_binary_iprimitive.ipp boost_1_34_0.my/boost/archive/impl/basic_binary_iprimitive.ipp --- boost_1_34_0/boost/archive/impl/basic_binary_iprimitive.ipp 2006-02-09 01:58:07.000000000 -0500 +++ boost_1_34_0.my/boost/archive/impl/basic_binary_iprimitive.ipp 2007-12-03 18:05:43.000000000 -0500 @@ -85,8 +85,9 @@
template<class Archive, class Elem, class Tr> BOOST_ARCHIVE_OR_WARCHIVE_DECL(void) -basic_binary_iprimitive<Archive, Elem, Tr>::load(std::string & s) +basic_binary_iprimitive<Archive, Elem, Tr>::load(std::string & res_s) { + std::string s; std::size_t l; this->This()->load(l); // borland de-allocator fixup @@ -96,6 +97,9 @@ s.resize(l); // note breaking a rule here - could be a problem on some platform load_binary(const_cast<char *>(s.data()), l); + + // Respect other references to the chars by assigning result string + res_s = s; }
#ifndef BOOST_NO_CWCHAR @@ -113,8 +117,9 @@ #ifndef BOOST_NO_STD_WSTRING template<class Archive, class Elem, class Tr> BOOST_ARCHIVE_OR_WARCHIVE_DECL(void) -basic_binary_iprimitive<Archive, Elem, Tr>::load(std::wstring & ws) +basic_binary_iprimitive<Archive, Elem, Tr>::load(std::wstring & res_ws) { + std::wstring ws; std::size_t l; this->This()->load(l); // borland de-allocator fixup @@ -124,6 +129,9 @@ ws.resize(l); // note breaking a rule here - is could be a problem on some platform load_binary(const_cast<wchar_t *>(ws.data()), l * sizeof(wchar_t) / sizeof(char)); + + // Respect other references to the chars by assigning result string + res_ws = ws; } #endif
diff -du -r boost_1_34_0/boost/archive/impl/text_iarchive_impl.ipp boost_1_34_0.my/boost/archive/impl/text_iarchive_impl.ipp --- boost_1_34_0/boost/archive/impl/text_iarchive_impl.ipp 2005-12-11 01:12:52.000000000 -0500 +++ boost_1_34_0.my/boost/archive/impl/text_iarchive_impl.ipp 2007-12-03 17:56:04.000000000 -0500 @@ -42,8 +42,9 @@
template<class Archive> BOOST_ARCHIVE_DECL(void) -text_iarchive_impl<Archive>::load(std::string &s) +text_iarchive_impl<Archive>::load(std::string &res_s) { + std::string s; std::size_t size; * this->This() >> size; // skip separating space @@ -54,6 +55,9 @@ #endif s.resize(size); is.read(const_cast<char *>(s.data()), size); + + // Respect other references to the chars by assigning result string + res_s = s; }
#ifndef BOOST_NO_CWCHAR @@ -74,8 +78,9 @@ #ifndef BOOST_NO_STD_WSTRING template<class Archive> BOOST_ARCHIVE_DECL(void) -text_iarchive_impl<Archive>::load(std::wstring &ws) +text_iarchive_impl<Archive>::load(std::wstring &res_ws) { + std::wstring ws; std::size_t size; * this->This() >> size; // borland de-allocator fixup @@ -86,6 +91,9 @@ // skip separating space is.get(); is.read((char *)ws.data(), size * sizeof(wchar_t)/sizeof(char)); + + // Respect other references to the chars by assigning result string + res_ws = ws; }
#endif // BOOST_NO_STD_WSTRING diff -du -r boost_1_34_0/boost/archive/impl/text_wiarchive_impl.ipp boost_1_34_0.my/boost/archive/impl/text_wiarchive_impl.ipp --- boost_1_34_0/boost/archive/impl/text_wiarchive_impl.ipp 2005-07-02 01:52:14.000000000 -0400 +++ boost_1_34_0.my/boost/archive/impl/text_wiarchive_impl.ipp 2007-12-03 18:05:07.000000000 -0500 @@ -79,8 +79,10 @@ #ifndef BOOST_NO_STD_WSTRING template<class Archive> BOOST_WARCHIVE_DECL(void) -text_wiarchive_impl<Archive>::load(std::wstring &ws) +text_wiarchive_impl<Archive>::load(std::wstring &res_ws) { + std::wstring ws; + std::size_t size; * this->This() >> size; // skip separating space @@ -93,6 +95,9 @@ ws.resize(size); // note breaking a rule here - is this a problem on some platform is.read(const_cast<wchar_t *>(ws.data()), size); + + // Respect other references to the chars by assigning result string + res_ws = ws; } #endif
Curious if anyone has thoughts on the matter...
Regards, Chuck _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost