rc_string_base.h
Go to the documentation of this file.
// Reference-counted versatile string base -*- C++ -*-
// Copyright (C) 2005-2014 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file ext/rc_string_base.h
* This is an internal header file, included by other library headers.
* Do not attempt to use it directly. @headername{ext/vstring.h}
*/
#ifndef _RC_STRING_BASE_H
#define _RC_STRING_BASE_H 1
#include <ext/atomicity.h>
#include <bits/stl_iterator_base_funcs.h>
namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* Documentation? What's that?
* Nathan Myers <ncm@cantrip.org>.
*
* A string looks like this:
*
* @code
* [_Rep]
* _M_length
* [__rc_string_base<char_type>] _M_capacity
* _M_dataplus _M_refcount
* _M_p ----------------> unnamed array of char_type
* @endcode
*
* Where the _M_p points to the first character in the string, and
* you cast it to a pointer-to-_Rep and subtract 1 to get a
* pointer to the header.
*
* This approach has the enormous advantage that a string object
* requires only one allocation. All the ugliness is confined
* within a single pair of inline functions, which each compile to
* a single @a add instruction: _Rep::_M_refdata(), and
* __rc_string_base::_M_rep(); and the allocation function which gets a
* block of raw bytes and with room enough and constructs a _Rep
* object at the front.
*
* The reason you want _M_data pointing to the character array and
* not the _Rep is so that the debugger can see the string
* contents. (Probably we should add a non-inline member to get
* the _Rep for the debugger to use, so users can check the actual
* string length.)
*
* Note that the _Rep object is a POD so that you can have a
* static <em>empty string</em> _Rep object already @a constructed before
* static constructors have run. The reference-count encoding is
* chosen so that a 0 indicates one reference, so you never try to
* destroy the empty-string _Rep object.
*
* All but the last paragraph is considered pretty conventional
* for a C++ string implementation.
*/
template<typename _CharT, typename _Traits, typename _Alloc>
class __rc_string_base
: protected __vstring_utility<_CharT, _Traits, _Alloc>
{
public:
typedef _Traits traits_type;
typedef typename _Traits::char_type value_type;
typedef _Alloc allocator_type;
typedef __vstring_utility<_CharT, _Traits, _Alloc> _Util_Base;
typedef typename _Util_Base::_CharT_alloc_type _CharT_alloc_type;
typedef typename _CharT_alloc_type::size_type size_type;
private:
// _Rep: string representation
// Invariants:
// 1. String really contains _M_length + 1 characters: due to 21.3.4
// must be kept null-terminated.
// 2. _M_capacity >= _M_length
// Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
// 3. _M_refcount has three states:
// -1: leaked, one reference, no ref-copies allowed, non-const.
// 0: one reference, non-const.
// n>0: n + 1 references, operations require a lock, const.
// 4. All fields == 0 is an empty string, given the extra storage
// beyond-the-end for a null terminator; thus, the shared
// empty string representation needs no constructor.
struct _Rep
{
union
{
struct
{
size_type _M_length;
size_type _M_capacity;
_Atomic_word _M_refcount;
} _M_info;
// Only for alignment purposes.
_CharT _M_align;
};
typedef typename _Alloc::template rebind<_Rep>::other _Rep_alloc_type;
_CharT*
_M_refdata() throw()
{ return reinterpret_cast<_CharT*>(this + 1); }
_CharT*
_M_refcopy() throw()
{
__atomic_add_dispatch(&_M_info._M_refcount, 1);
return _M_refdata();
} // XXX MT
void
_M_set_length(size_type __n)
{
_M_info._M_refcount = 0; // One reference.
_M_info._M_length = __n;
// grrr. (per 21.3.4)
// You cannot leave those LWG people alone for a second.
traits_type::assign(_M_refdata()[__n], _CharT());
}
// Create & Destroy
static _Rep*
_S_create(size_type, size_type, const _Alloc&);
void
_M_destroy(const _Alloc&) throw();
_CharT*
_M_clone(const _Alloc&, size_type __res = 0);
};
struct _Rep_empty
: public _Rep
{
_CharT _M_terminal;
};
static _Rep_empty _S_empty_rep;
// The maximum number of individual char_type elements of an
// individual string is determined by _S_max_size. This is the
// value that will be returned by max_size(). (Whereas npos
// is the maximum number of bytes the allocator can allocate.)
// If one was to divvy up the theoretical largest size string,
// with a terminating character and m _CharT elements, it'd
// look like this:
// npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
// + sizeof(_Rep) - 1
// (NB: last two terms for rounding reasons, see _M_create below)
// Solving for m:
// m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
// In addition, this implementation halves this amount.
enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
+ 1) / sizeof(_CharT)) - 1) / 2 };
// Data Member (private):
mutable typename _Util_Base::template _Alloc_hider<_Alloc> _M_dataplus;
void
_M_data(_CharT* __p)
{ _M_dataplus._M_p = __p; }
_Rep*
_M_rep() const
{ return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
_CharT*
_M_grab(const _Alloc& __alloc) const
{
return (!_M_is_leaked() && _M_get_allocator() == __alloc)
? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
}
void
_M_dispose()
{
// Be race-detector-friendly. For more info see bits/c++config.
_GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&_M_rep()->_M_info.
_M_refcount);
if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
-1) <= 0)
{
_GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&_M_rep()->_M_info.
_M_refcount);
_M_rep()->_M_destroy(_M_get_allocator());
}
} // XXX MT
bool
_M_is_leaked() const
{ return _M_rep()->_M_info._M_refcount < 0; }
void
_M_set_sharable()
{ _M_rep()->_M_info._M_refcount = 0; }
void
_M_leak_hard();
// _S_construct_aux is used to implement the 21.3.1 para 15 which
// requires special behaviour if _InIterator is an integral type
template<typename _InIterator>
static _CharT*
_S_construct_aux(_InIterator __beg, _InIterator __end,
const _Alloc& __a, std::__false_type)
{
typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
return _S_construct(__beg, __end, __a, _Tag());
}
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 438. Ambiguity in the "do the right thing" clause
template<typename _Integer>
static _CharT*
_S_construct_aux(_Integer __beg, _Integer __end,
const _Alloc& __a, std::__true_type)
{ return _S_construct_aux_2(static_cast<size_type>(__beg),
__end, __a); }
static _CharT*
_S_construct_aux_2(size_type __req, _CharT __c, const _Alloc& __a)
{ return _S_construct(__req, __c, __a); }
template<typename _InIterator>
static _CharT*
_S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
{
typedef typename std::__is_integer<_InIterator>::__type _Integral;
return _S_construct_aux(__beg, __end, __a, _Integral());
}
// For Input Iterators, used in istreambuf_iterators, etc.
template<typename _InIterator>
static _CharT*
_S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
std::input_iterator_tag);
// For forward_iterators up to random_access_iterators, used for
// string::iterator, _CharT*, etc.
template<typename _FwdIterator>
static _CharT*
_S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
std::forward_iterator_tag);
static _CharT*
_S_construct(size_type __req, _CharT __c, const _Alloc& __a);
public:
size_type
_M_max_size() const
{ return size_type(_S_max_size); }
_CharT*
_M_data() const
{ return _M_dataplus._M_p; }
size_type
_M_length() const
{ return _M_rep()->_M_info._M_length; }
size_type
_M_capacity() const
{ return _M_rep()->_M_info._M_capacity; }
bool
_M_is_shared() const
{ return _M_rep()->_M_info._M_refcount > 0; }
void
_M_set_leaked()
{ _M_rep()->_M_info._M_refcount = -1; }
void
_M_leak() // for use in begin() & non-const op[]
{
if (!_M_is_leaked())
_M_leak_hard();
}
void
_M_set_length(size_type __n)
{ _M_rep()->_M_set_length(__n); }
__rc_string_base()
: _M_dataplus(_S_empty_rep._M_refcopy()) { }
__rc_string_base(const _Alloc& __a);
__rc_string_base(const __rc_string_base& __rcs);
#if __cplusplus >= 201103L
__rc_string_base(__rc_string_base&& __rcs)
: _M_dataplus(__rcs._M_dataplus)
{ __rcs._M_data(_S_empty_rep._M_refcopy()); }
#endif
__rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
template<typename _InputIterator>
__rc_string_base(_InputIterator __beg, _InputIterator __end,
const _Alloc& __a);
~__rc_string_base()
{ _M_dispose(); }
allocator_type&
_M_get_allocator()
{ return _M_dataplus; }
const allocator_type&
_M_get_allocator() const
{ return _M_dataplus; }
void
_M_swap(__rc_string_base& __rcs);
void
_M_assign(const __rc_string_base& __rcs);
void
_M_reserve(size_type __res);
void
_M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
size_type __len2);
void
_M_erase(size_type __pos, size_type __n);
void
_M_clear()
{ _M_erase(size_type(0), _M_length()); }
bool
_M_compare(const __rc_string_base&) const
{ return false; }
};
template<typename _CharT, typename _Traits, typename _Alloc>
typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty
__rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;
template<typename _CharT, typename _Traits, typename _Alloc>
typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*
__rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
_S_create(size_type __capacity, size_type __old_capacity,
const _Alloc& __alloc)
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 83. String::npos vs. string::max_size()
if (__capacity > size_type(_S_max_size))
std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
// The standard places no restriction on allocating more memory
// than is strictly needed within this layer at the moment or as
// requested by an explicit application call to reserve().
// Many malloc implementations perform quite poorly when an
// application attempts to allocate memory in a stepwise fashion
// growing each allocation size by only 1 char. Additionally,
// it makes little sense to allocate less linear memory than the
// natural blocking size of the malloc implementation.
// Unfortunately, we would need a somewhat low-level calculation
// with tuned parameters to get this perfect for any particular
// malloc implementation. Fortunately, generalizations about
// common features seen among implementations seems to suffice.
// __pagesize need not match the actual VM page size for good
// results in practice, thus we pick a common value on the low
// side. __malloc_header_size is an estimate of the amount of
// overhead per memory allocation (in practice seen N * sizeof
// (void*) where N is 0, 2 or 4). According to folklore,
// picking this value on the high side is better than
// low-balling it (especially when this algorithm is used with
// malloc implementations that allocate memory blocks rounded up
// to a size which is a power of 2).
const size_type __pagesize = 4096;
const size_type __malloc_header_size = 4 * sizeof(void*);
// The below implements an exponential growth policy, necessary to
// meet amortized linear time requirements of the library: see
// http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
{
__capacity = 2 * __old_capacity;
// Never allocate a string bigger than _S_max_size.
if (__capacity > size_type(_S_max_size))
__capacity = size_type(_S_max_size);
}
// NB: Need an array of char_type[__capacity], plus a terminating
// null char_type() element, plus enough for the _Rep data structure,
// plus sizeof(_Rep) - 1 to upper round to a size multiple of
// sizeof(_Rep).
// Whew. Seemingly so needy, yet so elemental.
size_type __size = ((__capacity + 1) * sizeof(_CharT)
+ 2 * sizeof(_Rep) - 1);
const size_type __adj_size = __size + __malloc_header_size;
if (__adj_size > __pagesize && __capacity > __old_capacity)
{
const size_type __extra = __pagesize - __adj_size % __pagesize;
__capacity += __extra / sizeof(_CharT);
if (__capacity > size_type(_S_max_size))
__capacity = size_type(_S_max_size);
__size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
}
// NB: Might throw, but no worries about a leak, mate: _Rep()
// does not throw.
_Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
_Rep* __p = new (__place) _Rep;
__p->_M_info._M_capacity = __capacity;
return __p;
}
template<typename _CharT, typename _Traits, typename _Alloc>
void
__rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
_M_destroy(const _Alloc& __a) throw ()
{
const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
+ 2 * sizeof(_Rep) - 1);
_Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
}
template<typename _CharT, typename _Traits, typename _Alloc>
_CharT*
__rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
_M_clone(const _Alloc& __alloc, size_type __res)
{
// Requested capacity of the clone.
const size_type __requested_cap = _M_info._M_length + __res;
_Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
__alloc);
if (_M_info._M_length)
__rc_string_base::_S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
__r->_M_set_length(_M_info._M_length);
return __r->_M_refdata();
}
template<typename _CharT, typename _Traits, typename _Alloc>
__rc_string_base<_CharT, _Traits, _Alloc>::
__rc_string_base(const _Alloc& __a)
: _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
template<typename _CharT, typename _Traits, typename _Alloc>
__rc_string_base<_CharT, _Traits, _Alloc>::
__rc_string_base(const __rc_string_base& __rcs)
: _M_dataplus(__rcs._M_get_allocator(),
__rcs._M_grab(__rcs._M_get_allocator())) { }
template<typename _CharT, typename _Traits, typename _Alloc>
__rc_string_base<_CharT, _Traits, _Alloc>::
__rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
: _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
template<typename _CharT, typename _Traits, typename _Alloc>
template<typename _InputIterator>
__rc_string_base<_CharT, _Traits, _Alloc>::
__rc_string_base(_InputIterator __beg, _InputIterator __end,
const _Alloc& __a)
: _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
template<typename _CharT, typename _Traits, typename _Alloc>
void
__rc_string_base<_CharT, _Traits, _Alloc>::
_M_leak_hard()
{
if (_M_is_shared())
_M_erase(0, 0);
_M_set_leaked();
}
// NB: This is the special case for Input Iterators, used in
// istreambuf_iterators, etc.
// Input Iterators have a cost structure very different from
// pointers, calling for a different coding style.
template<typename _CharT, typename _Traits, typename _Alloc>
template<typename _InIterator>
_CharT*
__rc_string_base<_CharT, _Traits, _Alloc>::
_S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
std::input_iterator_tag)
{
if (__beg == __end && __a == _Alloc())
return _S_empty_rep._M_refcopy();
// Avoid reallocation for common case.
_CharT __buf[128];
size_type __len = 0;
while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
{
__buf[__len++] = *__beg;
++__beg;
}
_Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
_S_copy(__r->_M_refdata(), __buf, __len);
__try
{
while (__beg != __end)
{
if (__len == __r->_M_info._M_capacity)
{
// Allocate more space.
_Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
_S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
__r->_M_destroy(__a);
__r = __another;
}
__r->_M_refdata()[__len++] = *__beg;
++__beg;
}
}
__catch(...)
{
__r->_M_destroy(__a);
__throw_exception_again;
}
__r->_M_set_length(__len);
return __r->_M_refdata();
}
template<typename _CharT, typename _Traits, typename _Alloc>
template<typename _InIterator>
_CharT*
__rc_string_base<_CharT, _Traits, _Alloc>::
_S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
std::forward_iterator_tag)
{
if (__beg == __end && __a == _Alloc())
return _S_empty_rep._M_refcopy();
// NB: Not required, but considered best practice.
if (__is_null_pointer(__beg) && __beg != __end)
std::__throw_logic_error(__N("__rc_string_base::"
"_S_construct null not valid"));
const size_type __dnew = static_cast<size_type>(std::distance(__beg,
__end));
// Check for out_of_range and length_error exceptions.
_Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
__try
{ __rc_string_base::_S_copy_chars(__r->_M_refdata(), __beg, __end); }
__catch(...)
{
__r->_M_destroy(__a);
__throw_exception_again;
}
__r->_M_set_length(__dnew);
return __r->_M_refdata();
}
template<typename _CharT, typename _Traits, typename _Alloc>
_CharT*
__rc_string_base<_CharT, _Traits, _Alloc>::
_S_construct(size_type __n, _CharT __c, const _Alloc& __a)
{
if (__n == 0 && __a == _Alloc())
return _S_empty_rep._M_refcopy();
// Check for out_of_range and length_error exceptions.
_Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
if (__n)
__rc_string_base::_S_assign(__r->_M_refdata(), __n, __c);
__r->_M_set_length(__n);
return __r->_M_refdata();
}
template<typename _CharT, typename _Traits, typename _Alloc>
void
__rc_string_base<_CharT, _Traits, _Alloc>::
_M_swap(__rc_string_base& __rcs)
{
if (_M_is_leaked())
_M_set_sharable();
if (__rcs._M_is_leaked())
__rcs._M_set_sharable();
_CharT* __tmp = _M_data();
_M_data(__rcs._M_data());
__rcs._M_data(__tmp);
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 431. Swapping containers with unequal allocators.
std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
__rcs._M_get_allocator());
}
template<typename _CharT, typename _Traits, typename _Alloc>
void
__rc_string_base<_CharT, _Traits, _Alloc>::
_M_assign(const __rc_string_base& __rcs)
{
if (_M_rep() != __rcs._M_rep())
{
_CharT* __tmp = __rcs._M_grab(_M_get_allocator());
_M_dispose();
_M_data(__tmp);
}
}
template<typename _CharT, typename _Traits, typename _Alloc>
void
__rc_string_base<_CharT, _Traits, _Alloc>::
_M_reserve(size_type __res)
{
// Make sure we don't shrink below the current size.
if (__res < _M_length())
__res = _M_length();
if (__res != _M_capacity() || _M_is_shared())
{
_CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
__res - _M_length());
_M_dispose();
_M_data(__tmp);
}
}
template<typename _CharT, typename _Traits, typename _Alloc>
void
__rc_string_base<_CharT, _Traits, _Alloc>::
_M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
size_type __len2)
{
const size_type __how_much = _M_length() - __pos - __len1;
_Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
_M_capacity(), _M_get_allocator());
if (__pos)
this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
if (__s && __len2)
this->_S_copy(__r->_M_refdata() + __pos, __s, __len2);
if (__how_much)
this->_S_copy(__r->_M_refdata() + __pos + __len2,
_M_data() + __pos + __len1, __how_much);
_M_dispose();
_M_data(__r->_M_refdata());
}
template<typename _CharT, typename _Traits, typename _Alloc>
void
__rc_string_base<_CharT, _Traits, _Alloc>::
_M_erase(size_type __pos, size_type __n)
{
const size_type __new_size = _M_length() - __n;
const size_type __how_much = _M_length() - __pos - __n;
if (_M_is_shared())
{
// Must reallocate.
_Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
_M_get_allocator());
if (__pos)
this->_S_copy(__r->_M_refdata(), _M_data(), __pos);
if (__how_much)
this->_S_copy(__r->_M_refdata() + __pos,
_M_data() + __pos + __n, __how_much);
_M_dispose();
_M_data(__r->_M_refdata());
}
else if (__how_much && __n)
{
// Work in-place.
this->_S_move(_M_data() + __pos,
_M_data() + __pos + __n, __how_much);
}
_M_rep()->_M_set_length(__new_size);
}
template<>
inline bool
__rc_string_base<char, std::char_traits<char>,
std::allocator<char> >::
_M_compare(const __rc_string_base& __rcs) const
{
if (_M_rep() == __rcs._M_rep())
return true;
return false;
}
#ifdef _GLIBCXX_USE_WCHAR_T
template<>
inline bool
__rc_string_base<wchar_t, std::char_traits<wchar_t>,
std::allocator<wchar_t> >::
_M_compare(const __rc_string_base& __rcs) const
{
if (_M_rep() == __rcs._M_rep())
return true;
return false;
}
#endif
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif /* _RC_STRING_BASE_H */
atomicity.h
stl_iterator_base_funcs.h
std::forward_iterator_tag
Forward iterators support a superset of input iterator operations.
Definition: stl_iterator_base_types.h:95
std::input_iterator_tag
Marking input iterators.
Definition: stl_iterator_base_types.h:89
std::allocator
The standard allocator, as per [20.4].
Definition: allocator.h:92
std::distance
iterator_traits< _InputIterator >::difference_type distance(_InputIterator __first, _InputIterator __last)
A generalization of pointer arithmetic.
Definition: stl_iterator_base_funcs.h:114
__gnu_cxx::__rc_string_base
Definition: rc_string_base.h:82