Avoid multi-processor bus contention on increment/decrement-and- test of the reference count in the empty-string object...
2003-06-13 Nathan C. Myers <ncm-nospam@cantrip.org>
Avoid multi-processor bus contention on increment/decrement-and-
test of the reference count in the empty-string object, by comparing
addresses first, and never touching the reference count of the empty-
string object.
* include/bits/basic_string.h:
(_S_empty_rep_storage): Move into basic_string<>::_Rep for use by its
members.
(_Rep::_S_empty_rep()): New accessor.
(_Rep::_M_length, _Rep::_M_capacity, _Rep::_M_references): Move to
a base class _Rep_base.
(_Rep::_M_dispose, _Rep::_M_refcopy): Check for the empty string.
(basic_string()): Change to use _M_refdata() in place of _M_refcopy(),
since no longer must increment its refcount.
* include/bits/basic_string.tcc:
(_Rep::_M_destroy, _M_leak_hard): Check for the empty string and
return immediately. The former might be unnecessary. The latter
prevents begin() and end() from cloning it unnecessarily.
(_S_construct(_InIterator, _InIterator, const _Alloc&,
input_iterator_tag), _S_construct(_InIterator, _InIterator,
const _Alloc&, forward_iterator_tag), _S_construct(size_type, _CharT,
const _Alloc&)): Change to use _M_refdata() in place of _M_refcopy().
(_M_mutate): Check for the empty string and treat it as shared.
This is necessary here because _M_mutate is sometimes called with
all-zero arguments; in all other uses of _M_is_shared, the test comes
out right anyhow.
From-SVN: r67912
