The operator[] method on hash_map will unnecessarily resize the container when used to access an existing element when the container size is at any of the values in the __stl_prime_list table (ext/hashtable.h). This unnecessarily causes the container capacity to double in size and the elements to be rehashed.
There is also a more serious consequence when using operator[] access in a multithreaded environment which I think adds further justification for the change. This caused some controversy on the libstdc++ which I won't repeat here. See the following messages (and follow-ups) for details: http://gcc.gnu.org/ml/libstdc++/2004-11/msg00132.html http://gcc.gnu.org/ml/libstdc++/2004-11/msg00150.html http://gcc.gnu.org/ml/libstdc++/2004-11/msg00156.html The problem could be fixed in ext/hashtable.h by moving the call to resize() to be after the first return statement: template <class _Val, class _Key, class _HF, class _Ex, class _Eq, class _All> typename hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::reference hashtable<_Val,_Key,_HF,_Ex,_Eq,_All>::find_or_insert(const value_type& __obj) { resize(_M_num_elements + 1); // <- FROM HERE size_type __n = _M_bkt_num(__obj); _Node* __first = _M_buckets[__n]; for (_Node* __cur = __first; __cur; __cur = __cur->_M_next) if (_M_equals(_M_get_key(__cur->_M_val), _M_get_key(__obj))) return __cur->_M_val; // <-- TO HERE _Node* __tmp = _M_new_node(__obj); __tmp->_M_next = __first; _M_buckets[__n] = __tmp; ++_M_num_elements; return __tmp->_M_val; } -- Summary: resource allocation problem with __gnu_cxx::hash_map Product: gcc Version: 3.4.3 Status: UNCONFIRMED Severity: normal Priority: P2 Component: libstdc++ AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: work at paul dot dubuc dot org CC: gcc-bugs at gcc dot gnu dot org GCC host triplet: sparc-sun-solaris2.8 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18633
