mt_allocator.h
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// MT-optimized allocator -*- C++ -*-
// Copyright (C) 2003-2022 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/mt_allocator.h
* This file is a GNU extension to the Standard C++ Library.
*/
#ifndef _MT_ALLOCATOR_H
#define _MT_ALLOCATOR_H 1
#include <new>
#include <cstdlib>
#include <bits/functexcept.h>
#include <ext/atomicity.h>
#include <bits/move.h>
#if __cplusplus >= 201103L
#include <type_traits>
#endif
namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
typedef void (*__destroy_handler)(void*);
/// Base class for pool object.
struct __pool_base
{
// Using short int as type for the binmap implies we are never
// caching blocks larger than 32768 with this allocator.
typedef unsigned short int _Binmap_type;
typedef std::size_t size_t;
// Variables used to configure the behavior of the allocator,
// assigned and explained in detail below.
struct _Tune
{
// Compile time constants for the default _Tune values.
enum { _S_align = 8 };
enum { _S_max_bytes = 128 };
enum { _S_min_bin = 8 };
enum { _S_chunk_size = 4096 - 4 * sizeof(void*) };
enum { _S_max_threads = 4096 };
enum { _S_freelist_headroom = 10 };
// Alignment needed.
// NB: In any case must be >= sizeof(_Block_record), that
// is 4 on 32 bit machines and 8 on 64 bit machines.
size_t _M_align;
// Allocation requests (after round-up to power of 2) below
// this value will be handled by the allocator. A raw new/
// call will be used for requests larger than this value.
// NB: Must be much smaller than _M_chunk_size and in any
// case <= 32768.
size_t _M_max_bytes;
// Size in bytes of the smallest bin.
// NB: Must be a power of 2 and >= _M_align (and of course
// much smaller than _M_max_bytes).
size_t _M_min_bin;
// In order to avoid fragmenting and minimize the number of
// new() calls we always request new memory using this
// value. Based on previous discussions on the libstdc++
// mailing list we have chosen the value below.
// See http://gcc.gnu.org/ml/libstdc++/2001-07/msg00077.html
// NB: At least one order of magnitude > _M_max_bytes.
size_t _M_chunk_size;
// The maximum number of supported threads. For
// single-threaded operation, use one. Maximum values will
// vary depending on details of the underlying system. (For
// instance, Linux 2.4.18 reports 4070 in
// /proc/sys/kernel/threads-max, while Linux 2.6.6 reports
// 65534)
size_t _M_max_threads;
// Each time a deallocation occurs in a threaded application
// we make sure that there are no more than
// _M_freelist_headroom % of used memory on the freelist. If
// the number of additional records is more than
// _M_freelist_headroom % of the freelist, we move these
// records back to the global pool.
size_t _M_freelist_headroom;
// Set to true forces all allocations to use new().
bool _M_force_new;
explicit
_Tune()
: _M_align(_S_align), _M_max_bytes(_S_max_bytes), _M_min_bin(_S_min_bin),
_M_chunk_size(_S_chunk_size), _M_max_threads(_S_max_threads),
_M_freelist_headroom(_S_freelist_headroom),
_M_force_new(std::getenv("GLIBCXX_FORCE_NEW") ? true : false)
{ }
explicit
_Tune(size_t __align, size_t __maxb, size_t __minbin, size_t __chunk,
size_t __maxthreads, size_t __headroom, bool __force)
: _M_align(__align), _M_max_bytes(__maxb), _M_min_bin(__minbin),
_M_chunk_size(__chunk), _M_max_threads(__maxthreads),
_M_freelist_headroom(__headroom), _M_force_new(__force)
{ }
};
struct _Block_address
{
void* _M_initial;
_Block_address* _M_next;
};
const _Tune&
_M_get_options() const
{ return _M_options; }
void
_M_set_options(_Tune __t)
{
if (!_M_init)
_M_options = __t;
}
bool
_M_check_threshold(size_t __bytes)
{ return __bytes > _M_options._M_max_bytes || _M_options._M_force_new; }
size_t
_M_get_binmap(size_t __bytes)
{ return _M_binmap[__bytes]; }
size_t
_M_get_align()
{ return _M_options._M_align; }
explicit
__pool_base()
: _M_options(_Tune()), _M_binmap(0), _M_init(false) { }
explicit
__pool_base(const _Tune& __options)
: _M_options(__options), _M_binmap(0), _M_init(false) { }
private:
explicit
__pool_base(const __pool_base&);
__pool_base&
operator=(const __pool_base&);
protected:
// Configuration options.
_Tune _M_options;
_Binmap_type* _M_binmap;
// Configuration of the pool object via _M_options can happen
// after construction but before initialization. After
// initialization is complete, this variable is set to true.
bool _M_init;
};
/**
* @brief Data describing the underlying memory pool, parameterized on
* threading support.
*/
template<bool _Thread>
class __pool;
/// Specialization for single thread.
template<>
class __pool<false> : public __pool_base
{
public:
union _Block_record
{
// Points to the block_record of the next free block.
_Block_record* _M_next;
};
struct _Bin_record
{
// An "array" of pointers to the first free block.
_Block_record** _M_first;
// A list of the initial addresses of all allocated blocks.
_Block_address* _M_address;
};
void
_M_initialize_once()
{
if (__builtin_expect(_M_init == false, false))
_M_initialize();
}
void
_M_destroy() throw();
char*
_M_reserve_block(size_t __bytes, const size_t __thread_id);
void
_M_reclaim_block(char* __p, size_t __bytes) throw ();
size_t
_M_get_thread_id() { return 0; }
const _Bin_record&
_M_get_bin(size_t __which)
{ return _M_bin[__which]; }
void
_M_adjust_freelist(const _Bin_record&, _Block_record*, size_t)
{ }
explicit __pool()
: _M_bin(0), _M_bin_size(1) { }
explicit __pool(const __pool_base::_Tune& __tune)
: __pool_base(__tune), _M_bin(0), _M_bin_size(1) { }
private:
// An "array" of bin_records each of which represents a specific
// power of 2 size. Memory to this "array" is allocated in
// _M_initialize().
_Bin_record* _M_bin;
// Actual value calculated in _M_initialize().
size_t _M_bin_size;
void
_M_initialize();
};
#ifdef __GTHREADS
/// Specialization for thread enabled, via gthreads.h.
template<>
class __pool<true> : public __pool_base
{
public:
// Each requesting thread is assigned an id ranging from 1 to
// _S_max_threads. Thread id 0 is used as a global memory pool.
// In order to get constant performance on the thread assignment
// routine, we keep a list of free ids. When a thread first
// requests memory we remove the first record in this list and
// stores the address in a __gthread_key. When initializing the
// __gthread_key we specify a destructor. When this destructor
// (i.e. the thread dies) is called, we return the thread id to
// the front of this list.
struct _Thread_record
{
// Points to next free thread id record. NULL if last record in list.
_Thread_record* _M_next;
// Thread id ranging from 1 to _S_max_threads.
size_t _M_id;
};
union _Block_record
{
// Points to the block_record of the next free block.
_Block_record* _M_next;
// The thread id of the thread which has requested this block.
size_t _M_thread_id;
};
struct _Bin_record
{
// An "array" of pointers to the first free block for each
// thread id. Memory to this "array" is allocated in
// _S_initialize() for _S_max_threads + global pool 0.
_Block_record** _M_first;
// A list of the initial addresses of all allocated blocks.
_Block_address* _M_address;
// An "array" of counters used to keep track of the amount of
// blocks that are on the freelist/used for each thread id.
// - Note that the second part of the allocated _M_used "array"
// actually hosts (atomic) counters of reclaimed blocks: in
// _M_reserve_block and in _M_reclaim_block those numbers are
// subtracted from the first ones to obtain the actual size
// of the "working set" of the given thread.
// - Memory to these "arrays" is allocated in _S_initialize()
// for _S_max_threads + global pool 0.
size_t* _M_free;
size_t* _M_used;
// Each bin has its own mutex which is used to ensure data
// integrity while changing "ownership" on a block. The mutex
// is initialized in _S_initialize().
__gthread_mutex_t* _M_mutex;
};
// XXX GLIBCXX_ABI Deprecated
void
_M_initialize(__destroy_handler);
void
_M_initialize_once()
{
if (__builtin_expect(_M_init == false, false))
_M_initialize();
}
void
_M_destroy() throw();
char*
_M_reserve_block(size_t __bytes, const size_t __thread_id);
void
_M_reclaim_block(char* __p, size_t __bytes) throw ();
const _Bin_record&
_M_get_bin(size_t __which)
{ return _M_bin[__which]; }
void
_M_adjust_freelist(const _Bin_record& __bin, _Block_record* __block,
size_t __thread_id)
{
if (__gthread_active_p())
{
__block->_M_thread_id = __thread_id;
--__bin._M_free[__thread_id];
++__bin._M_used[__thread_id];
}
}
// XXX GLIBCXX_ABI Deprecated
void
_M_destroy_thread_key(void*) throw ();
size_t
_M_get_thread_id();
explicit __pool()
: _M_bin(0), _M_bin_size(1), _M_thread_freelist(0)
{ }
explicit __pool(const __pool_base::_Tune& __tune)
: __pool_base(__tune), _M_bin(0), _M_bin_size(1),
_M_thread_freelist(0)
{ }
private:
// An "array" of bin_records each of which represents a specific
// power of 2 size. Memory to this "array" is allocated in
// _M_initialize().
_Bin_record* _M_bin;
// Actual value calculated in _M_initialize().
size_t _M_bin_size;
_Thread_record* _M_thread_freelist;
void* _M_thread_freelist_initial;
void
_M_initialize();
};
#endif
template<template <bool> class _PoolTp, bool _Thread>
struct __common_pool
{
typedef _PoolTp<_Thread> pool_type;
static pool_type&
_S_get_pool()
{
static pool_type _S_pool;
return _S_pool;
}
};
template<template <bool> class _PoolTp, bool _Thread>
struct __common_pool_base;
template<template <bool> class _PoolTp>
struct __common_pool_base<_PoolTp, false>
: public __common_pool<_PoolTp, false>
{
using __common_pool<_PoolTp, false>::_S_get_pool;
static void
_S_initialize_once()
{
static bool __init;
if (__builtin_expect(__init == false, false))
{
_S_get_pool()._M_initialize_once();
__init = true;
}
}
};
#ifdef __GTHREADS
template<template <bool> class _PoolTp>
struct __common_pool_base<_PoolTp, true>
: public __common_pool<_PoolTp, true>
{
using __common_pool<_PoolTp, true>::_S_get_pool;
static void
_S_initialize()
{ _S_get_pool()._M_initialize_once(); }
static void
_S_initialize_once()
{
static bool __init;
if (__builtin_expect(__init == false, false))
{
if (__gthread_active_p())
{
// On some platforms, __gthread_once_t is an aggregate.
static __gthread_once_t __once = __GTHREAD_ONCE_INIT;
__gthread_once(&__once, _S_initialize);
}
// Double check initialization. May be necessary on some
// systems for proper construction when not compiling with
// thread flags.
_S_get_pool()._M_initialize_once();
__init = true;
}
}
};
#endif
/// Policy for shared __pool objects.
template<template <bool> class _PoolTp, bool _Thread>
struct __common_pool_policy : public __common_pool_base<_PoolTp, _Thread>
{
template<typename _Tp1, template <bool> class _PoolTp1 = _PoolTp,
bool _Thread1 = _Thread>
struct _M_rebind
{ typedef __common_pool_policy<_PoolTp1, _Thread1> other; };
using __common_pool_base<_PoolTp, _Thread>::_S_get_pool;
using __common_pool_base<_PoolTp, _Thread>::_S_initialize_once;
};
template<typename _Tp, template <bool> class _PoolTp, bool _Thread>
struct __per_type_pool
{
typedef _Tp value_type;
typedef _PoolTp<_Thread> pool_type;
static pool_type&
_S_get_pool()
{
using std::size_t;
// Sane defaults for the _PoolTp.
typedef typename pool_type::_Block_record _Block_record;
const static size_t __a = (__alignof__(_Tp) >= sizeof(_Block_record)
? __alignof__(_Tp) : sizeof(_Block_record));
typedef typename __pool_base::_Tune _Tune;
static _Tune _S_tune(__a, sizeof(_Tp) * 64,
sizeof(_Tp) * 2 >= __a ? sizeof(_Tp) * 2 : __a,
sizeof(_Tp) * size_t(_Tune::_S_chunk_size),
_Tune::_S_max_threads,
_Tune::_S_freelist_headroom,
std::getenv("GLIBCXX_FORCE_NEW") ? true : false);
static pool_type _S_pool(_S_tune);
return _S_pool;
}
};
template<typename _Tp, template <bool> class _PoolTp, bool _Thread>
struct __per_type_pool_base;
template<typename _Tp, template <bool> class _PoolTp>
struct __per_type_pool_base<_Tp, _PoolTp, false>
: public __per_type_pool<_Tp, _PoolTp, false>
{
using __per_type_pool<_Tp, _PoolTp, false>::_S_get_pool;
static void
_S_initialize_once()
{
static bool __init;
if (__builtin_expect(__init == false, false))
{
_S_get_pool()._M_initialize_once();
__init = true;
}
}
};
#ifdef __GTHREADS
template<typename _Tp, template <bool> class _PoolTp>
struct __per_type_pool_base<_Tp, _PoolTp, true>
: public __per_type_pool<_Tp, _PoolTp, true>
{
using __per_type_pool<_Tp, _PoolTp, true>::_S_get_pool;
static void
_S_initialize()
{ _S_get_pool()._M_initialize_once(); }
static void
_S_initialize_once()
{
static bool __init;
if (__builtin_expect(__init == false, false))
{
if (__gthread_active_p())
{
// On some platforms, __gthread_once_t is an aggregate.
static __gthread_once_t __once = __GTHREAD_ONCE_INIT;
__gthread_once(&__once, _S_initialize);
}
// Double check initialization. May be necessary on some
// systems for proper construction when not compiling with
// thread flags.
_S_get_pool()._M_initialize_once();
__init = true;
}
}
};
#endif
/// Policy for individual __pool objects.
template<typename _Tp, template <bool> class _PoolTp, bool _Thread>
struct __per_type_pool_policy
: public __per_type_pool_base<_Tp, _PoolTp, _Thread>
{
template<typename _Tp1, template <bool> class _PoolTp1 = _PoolTp,
bool _Thread1 = _Thread>
struct _M_rebind
{ typedef __per_type_pool_policy<_Tp1, _PoolTp1, _Thread1> other; };
using __per_type_pool_base<_Tp, _PoolTp, _Thread>::_S_get_pool;
using __per_type_pool_base<_Tp, _PoolTp, _Thread>::_S_initialize_once;
};
/// Base class for _Tp dependent member functions.
template<typename _Tp>
class __mt_alloc_base
{
public:
typedef std::size_t size_type;
typedef std::ptrdiff_t difference_type;
typedef _Tp* pointer;
typedef const _Tp* const_pointer;
typedef _Tp& reference;
typedef const _Tp& const_reference;
typedef _Tp value_type;
#if __cplusplus >= 201103L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2103. propagate_on_container_move_assignment
typedef std::true_type propagate_on_container_move_assignment;
#endif
pointer
address(reference __x) const _GLIBCXX_NOEXCEPT
{ return std::__addressof(__x); }
const_pointer
address(const_reference __x) const _GLIBCXX_NOEXCEPT
{ return std::__addressof(__x); }
size_type
max_size() const _GLIBCXX_USE_NOEXCEPT
{ return size_type(-1) / sizeof(_Tp); }
#if __cplusplus >= 201103L
template<typename _Up, typename... _Args>
void
construct(_Up* __p, _Args&&... __args)
{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
template<typename _Up>
void
destroy(_Up* __p) { __p->~_Up(); }
#else
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 402. wrong new expression in [some_] allocator::construct
void
construct(pointer __p, const _Tp& __val)
{ ::new((void *)__p) _Tp(__val); }
void
destroy(pointer __p) { __p->~_Tp(); }
#endif
};
#ifdef __GTHREADS
#define __thread_default true
#else
#define __thread_default false
#endif
/**
* @brief This is a fixed size (power of 2) allocator which - when
* compiled with thread support - will maintain one freelist per
* size per thread plus a @a global one. Steps are taken to limit
* the per thread freelist sizes (by returning excess back to
* the @a global list).
* @ingroup allocators
*
* Further details:
* https://gcc.gnu.org/onlinedocs/libstdc++/manual/mt_allocator.html
*/
template<typename _Tp,
typename _Poolp = __common_pool_policy<__pool, __thread_default> >
class __mt_alloc : public __mt_alloc_base<_Tp>
{
public:
typedef std::size_t size_type;
typedef std::ptrdiff_t difference_type;
typedef _Tp* pointer;
typedef const _Tp* const_pointer;
typedef _Tp& reference;
typedef const _Tp& const_reference;
typedef _Tp value_type;
typedef _Poolp __policy_type;
typedef typename _Poolp::pool_type __pool_type;
template<typename _Tp1, typename _Poolp1 = _Poolp>
struct rebind
{
typedef typename _Poolp1::template _M_rebind<_Tp1>::other pol_type;
typedef __mt_alloc<_Tp1, pol_type> other;
};
__mt_alloc() _GLIBCXX_USE_NOEXCEPT { }
__mt_alloc(const __mt_alloc&) _GLIBCXX_USE_NOEXCEPT { }
template<typename _Tp1, typename _Poolp1>
__mt_alloc(const __mt_alloc<_Tp1, _Poolp1>&) _GLIBCXX_USE_NOEXCEPT { }
~__mt_alloc() _GLIBCXX_USE_NOEXCEPT { }
_GLIBCXX_NODISCARD pointer
allocate(size_type __n, const void* = 0);
void
deallocate(pointer __p, size_type __n);
const __pool_base::_Tune
_M_get_options()
{
// Return a copy, not a reference, for external consumption.
return __policy_type::_S_get_pool()._M_get_options();
}
void
_M_set_options(__pool_base::_Tune __t)
{ __policy_type::_S_get_pool()._M_set_options(__t); }
};
template<typename _Tp, typename _Poolp>
_GLIBCXX_NODISCARD typename __mt_alloc<_Tp, _Poolp>::pointer
__mt_alloc<_Tp, _Poolp>::
allocate(size_type __n, const void*)
{
if (__n > this->max_size())
std::__throw_bad_alloc();
#if __cpp_aligned_new
// Types with extended alignment are handled by operator new/delete.
if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
{
std::align_val_t __al = std::align_val_t(alignof(_Tp));
return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), __al));
}
#endif
__policy_type::_S_initialize_once();
// Requests larger than _M_max_bytes are handled by operator
// new/delete directly.
__pool_type& __pool = __policy_type::_S_get_pool();
const size_type __bytes = __n * sizeof(_Tp);
if (__pool._M_check_threshold(__bytes))
{
void* __ret = ::operator new(__bytes);
return static_cast<_Tp*>(__ret);
}
// Round up to power of 2 and figure out which bin to use.
const size_type __which = __pool._M_get_binmap(__bytes);
const size_type __thread_id = __pool._M_get_thread_id();
// Find out if we have blocks on our freelist. If so, go ahead
// and use them directly without having to lock anything.
char* __c;
typedef typename __pool_type::_Bin_record _Bin_record;
const _Bin_record& __bin = __pool._M_get_bin(__which);
if (__bin._M_first[__thread_id])
{
// Already reserved.
typedef typename __pool_type::_Block_record _Block_record;
_Block_record* __block = __bin._M_first[__thread_id];
__bin._M_first[__thread_id] = __block->_M_next;
__pool._M_adjust_freelist(__bin, __block, __thread_id);
__c = reinterpret_cast<char*>(__block) + __pool._M_get_align();
}
else
{
// Null, reserve.
__c = __pool._M_reserve_block(__bytes, __thread_id);
}
return static_cast<_Tp*>(static_cast<void*>(__c));
}
template<typename _Tp, typename _Poolp>
void
__mt_alloc<_Tp, _Poolp>::
deallocate(pointer __p, size_type __n)
{
if (__builtin_expect(__p != 0, true))
{
#if __cpp_aligned_new
// Types with extended alignment are handled by operator new/delete.
if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
{
::operator delete(__p, std::align_val_t(alignof(_Tp)));
return;
}
#endif
// Requests larger than _M_max_bytes are handled by
// operators new/delete directly.
__pool_type& __pool = __policy_type::_S_get_pool();
const size_type __bytes = __n * sizeof(_Tp);
if (__pool._M_check_threshold(__bytes))
::operator delete(__p);
else
__pool._M_reclaim_block(reinterpret_cast<char*>(__p), __bytes);
}
}
template<typename _Tp, typename _Poolp>
inline bool
operator==(const __mt_alloc<_Tp, _Poolp>&, const __mt_alloc<_Tp, _Poolp>&)
{ return true; }
#if __cpp_impl_three_way_comparison < 201907L
template<typename _Tp, typename _Poolp>
inline bool
operator!=(const __mt_alloc<_Tp, _Poolp>&, const __mt_alloc<_Tp, _Poolp>&)
{ return false; }
#endif
#undef __thread_default
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif
new
functexcept.h
move.h
atomicity.h
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:49
__gnu_cxx
GNU extensions for public use.
std::integral_constant
integral_constant
Definition: type_traits:63
__gnu_cxx::__pool_base
Base class for pool object.
Definition: mt_allocator.h:50
__gnu_cxx::__pool
Data describing the underlying memory pool, parameterized on threading support.
Definition: mt_allocator.h:191
__gnu_cxx::__common_pool_policy
Policy for shared __pool objects.
Definition: mt_allocator.h:460
__gnu_cxx::__per_type_pool_policy
Policy for individual __pool objects.
Definition: mt_allocator.h:557
__gnu_cxx::__mt_alloc_base
Base class for _Tp dependent member functions.
Definition: mt_allocator.h:571
__gnu_cxx::__mt_alloc
This is a fixed size (power of 2) allocator which - when compiled with thread support - will maintain...
Definition: mt_allocator.h:640
cstdlib
type_traits