Daniel Spangenberg said: > Hello, Boosters! > > Today I stumbled across an unspecified behaviour which can be caused by > the example class "counter" of the Boost thread FAQ. > The errounous lines are inside the copy assignment operator of the > class: > > boost::mutex::scoped_lock lock1(&m_mutex < &other.m_mutex ? > m_mutex : other.m_mutex); > boost::mutex::scoped_lock lock2(&m_mutex > &other.m_mutex ? > m_mutex : other.m_mutex); > > Reasoning: Both the m_mutex member of *this as well as the m_mutex > member of the argument > other are not elements of the same object, so according to 5.9/p.2: > "[..] the results > of p<q, p>q, p<=q, and p>=q are unspecified.". > On the first sight this does not mean so much for the first line (We > just don't know, which one of the > mutexes is chosen), but it can result in an errounous program combined > with the same unspecified > behaviour of the 2nd line. A valid implementation could in both cases > return true (or false) and thus > could lead to two successive trials to lock the same mutex, which would > lead to an lock exception.
You're correct, and the solution is simply to replace the < operator with std::less calls. -- William E. Kempf _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
