394 lines
14 KiB
C++
394 lines
14 KiB
C++
// Allocators -*- C++ -*-
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// Copyright (C) 2001, 2002, 2003 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 2, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING. If not, write to the Free
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// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
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// USA.
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// As a special exception, you may use this file as part of a free software
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// library without restriction. Specifically, if other files instantiate
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// templates or use macros or inline functions from this file, or you compile
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// this file and link it with other files to produce an executable, this
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// file does not by itself cause the resulting executable to be covered by
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// the GNU General Public License. This exception does not however
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// invalidate any other reasons why the executable file might be covered by
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// the GNU General Public License.
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/*
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* Copyright (c) 1996-1997
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* Silicon Graphics Computer Systems, Inc.
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*
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* Permission to use, copy, modify, distribute and sell this software
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* and its documentation for any purpose is hereby granted without fee,
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* provided that the above copyright notice appear in all copies and
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* that both that copyright notice and this permission notice appear
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* in supporting documentation. Silicon Graphics makes no
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* representations about the suitability of this software for any
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* purpose. It is provided "as is" without express or implied warranty.
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*/
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/** @file ext/debug_allocator.h
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* This file is a GNU extension to the Standard C++ Library.
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* You should only include this header if you are using GCC 3 or later.
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*/
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#ifndef _POOL_ALLOCATOR_H
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#define _POOL_ALLOCATOR_H 1
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#include <bits/functexcept.h>
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#include <bits/stl_threads.h>
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#include <bits/atomicity.h>
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#include <bits/allocator_traits.h>
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#include <ext/new_allocator.h>
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namespace __gnu_cxx
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{
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using std::_STL_mutex_lock;
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using std::__throw_bad_alloc;
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/**
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* @if maint
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* Default node allocator. "SGI" style. Uses various allocators to
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* fulfill underlying requests (and makes as few requests as possible
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* when in default high-speed pool mode).
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*
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* Important implementation properties:
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* 0. If globally mandated, then allocate objects from __new_alloc
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* 1. If the clients request an object of size > _S_max_bytes, the resulting
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* object will be obtained directly from __new_alloc
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* 2. In all other cases, we allocate an object of size exactly
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* _S_round_up(requested_size). Thus the client has enough size
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* information that we can return the object to the proper free list
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* without permanently losing part of the object.
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*
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* The first template parameter specifies whether more than one thread may
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* use this allocator. It is safe to allocate an object from one instance
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* of a default_alloc and deallocate it with another one. This effectively
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* transfers its ownership to the second one. This may have undesirable
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* effects on reference locality.
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*
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* The second parameter is unused and serves only to allow the creation of
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* multiple default_alloc instances. Note that containers built on different
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* allocator instances have different types, limiting the utility of this
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* approach. If you do not wish to share the free lists with the main
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* default_alloc instance, instantiate this with a non-zero __inst.
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*
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* @endif
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* (See @link Allocators allocators info @endlink for more.)
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*/
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template<bool __threads, int __inst>
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class __pool_alloc
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{
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private:
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enum {_S_align = 8};
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enum {_S_max_bytes = 128};
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enum {_S_freelists = _S_max_bytes / _S_align};
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union _Obj
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{
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union _Obj* _M_free_list_link;
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char _M_client_data[1]; // The client sees this.
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};
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static _Obj* volatile _S_free_list[_S_freelists];
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// Chunk allocation state.
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static char* _S_start_free;
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static char* _S_end_free;
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static size_t _S_heap_size;
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static _STL_mutex_lock _S_lock;
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static _Atomic_word _S_force_new;
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static size_t
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_S_round_up(size_t __bytes)
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{ return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); }
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static size_t
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_S_freelist_index(size_t __bytes)
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{ return ((__bytes + (size_t)_S_align - 1)/(size_t)_S_align - 1); }
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// Returns an object of size __n, and optionally adds to size __n
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// free list.
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static void*
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_S_refill(size_t __n);
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// Allocates a chunk for nobjs of size size. nobjs may be reduced
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// if it is inconvenient to allocate the requested number.
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static char*
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_S_chunk_alloc(size_t __n, int& __nobjs);
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// It would be nice to use _STL_auto_lock here. But we need a
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// test whether threads are in use.
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struct _Lock
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{
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_Lock() { if (__threads) _S_lock._M_acquire_lock(); }
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~_Lock() { if (__threads) _S_lock._M_release_lock(); }
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} __attribute__ ((__unused__));
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friend struct _Lock;
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public:
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// __n must be > 0
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static void*
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allocate(size_t __n);
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// __p may not be 0
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static void
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deallocate(void* __p, size_t __n);
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};
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template<bool __threads, int __inst>
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inline bool
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operator==(const __pool_alloc<__threads,__inst>&,
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const __pool_alloc<__threads,__inst>&)
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{ return true; }
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template<bool __threads, int __inst>
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inline bool
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operator!=(const __pool_alloc<__threads,__inst>&,
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const __pool_alloc<__threads,__inst>&)
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{ return false; }
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// Allocate memory in large chunks in order to avoid fragmenting the
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// heap too much. Assume that __n is properly aligned. We hold
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// the allocation lock.
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template<bool __threads, int __inst>
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char*
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__pool_alloc<__threads, __inst>::_S_chunk_alloc(size_t __n, int& __nobjs)
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{
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char* __result;
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size_t __total_bytes = __n * __nobjs;
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size_t __bytes_left = _S_end_free - _S_start_free;
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if (__bytes_left >= __total_bytes)
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{
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__result = _S_start_free;
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_S_start_free += __total_bytes;
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return __result ;
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}
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else if (__bytes_left >= __n)
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{
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__nobjs = (int)(__bytes_left/__n);
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__total_bytes = __n * __nobjs;
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__result = _S_start_free;
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_S_start_free += __total_bytes;
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return __result;
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}
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else
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{
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size_t __bytes_to_get =
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2 * __total_bytes + _S_round_up(_S_heap_size >> 4);
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// Try to make use of the left-over piece.
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if (__bytes_left > 0)
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{
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_Obj* volatile* __free_list =
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_S_free_list + _S_freelist_index(__bytes_left);
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((_Obj*)(void*)_S_start_free)->_M_free_list_link = *__free_list;
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*__free_list = (_Obj*)(void*)_S_start_free;
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}
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_S_start_free = (char*) __new_alloc::allocate(__bytes_to_get);
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if (_S_start_free == 0)
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{
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size_t __i;
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_Obj* volatile* __free_list;
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_Obj* __p;
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// Try to make do with what we have. That can't hurt. We
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// do not try smaller requests, since that tends to result
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// in disaster on multi-process machines.
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__i = __n;
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for (; __i <= (size_t) _S_max_bytes; __i += (size_t) _S_align)
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{
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__free_list = _S_free_list + _S_freelist_index(__i);
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__p = *__free_list;
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if (__p != 0)
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{
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*__free_list = __p -> _M_free_list_link;
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_S_start_free = (char*)__p;
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_S_end_free = _S_start_free + __i;
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return _S_chunk_alloc(__n, __nobjs);
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// Any leftover piece will eventually make it to the
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// right free list.
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}
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}
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_S_end_free = 0; // In case of exception.
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_S_start_free = (char*)__new_alloc::allocate(__bytes_to_get);
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// This should either throw an exception or remedy the situation.
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// Thus we assume it succeeded.
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}
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_S_heap_size += __bytes_to_get;
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_S_end_free = _S_start_free + __bytes_to_get;
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return _S_chunk_alloc(__n, __nobjs);
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}
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}
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// Returns an object of size __n, and optionally adds to "size
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// __n"'s free list. We assume that __n is properly aligned. We
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// hold the allocation lock.
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template<bool __threads, int __inst>
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void*
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__pool_alloc<__threads, __inst>::_S_refill(size_t __n)
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{
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int __nobjs = 20;
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char* __chunk = _S_chunk_alloc(__n, __nobjs);
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_Obj* volatile* __free_list;
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_Obj* __result;
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_Obj* __current_obj;
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_Obj* __next_obj;
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int __i;
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if (1 == __nobjs)
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return __chunk;
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__free_list = _S_free_list + _S_freelist_index(__n);
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// Build free list in chunk.
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__result = (_Obj*)(void*)__chunk;
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*__free_list = __next_obj = (_Obj*)(void*)(__chunk + __n);
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for (__i = 1; ; __i++)
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{
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__current_obj = __next_obj;
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__next_obj = (_Obj*)(void*)((char*)__next_obj + __n);
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if (__nobjs - 1 == __i)
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{
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__current_obj -> _M_free_list_link = 0;
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break;
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}
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else
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__current_obj -> _M_free_list_link = __next_obj;
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}
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return __result;
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}
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template<bool __threads, int __inst>
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void*
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__pool_alloc<__threads, __inst>::allocate(size_t __n)
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{
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void* __ret = 0;
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// If there is a race through here, assume answer from getenv
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// will resolve in same direction. Inspired by techniques
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// to efficiently support threading found in basic_string.h.
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if (_S_force_new == 0)
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{
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if (getenv("GLIBCXX_FORCE_NEW"))
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__atomic_add(&_S_force_new, 1);
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else
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__atomic_add(&_S_force_new, -1);
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}
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if ((__n > (size_t) _S_max_bytes) || (_S_force_new > 0))
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__ret = __new_alloc::allocate(__n);
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else
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{
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_Obj* volatile* __free_list = _S_free_list + _S_freelist_index(__n);
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// Acquire the lock here with a constructor call. This
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// ensures that it is released in exit or during stack
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// unwinding.
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_Lock __lock_instance;
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_Obj* __restrict__ __result = *__free_list;
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if (__builtin_expect(__result == 0, 0))
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__ret = _S_refill(_S_round_up(__n));
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else
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{
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*__free_list = __result -> _M_free_list_link;
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__ret = __result;
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}
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if (__builtin_expect(__ret == 0, 0))
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__throw_bad_alloc();
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}
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return __ret;
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}
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template<bool __threads, int __inst>
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void
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__pool_alloc<__threads, __inst>::deallocate(void* __p, size_t __n)
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{
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if ((__n > (size_t) _S_max_bytes) || (_S_force_new > 0))
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__new_alloc::deallocate(__p, __n);
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else
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{
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_Obj* volatile* __free_list = _S_free_list + _S_freelist_index(__n);
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_Obj* __q = (_Obj*)__p;
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// Acquire the lock here with a constructor call. This
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// ensures that it is released in exit or during stack
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// unwinding.
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_Lock __lock_instance;
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__q -> _M_free_list_link = *__free_list;
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*__free_list = __q;
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}
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}
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template<bool __threads, int __inst>
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typename __pool_alloc<__threads, __inst>::_Obj* volatile
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__pool_alloc<__threads, __inst>::_S_free_list[_S_freelists];
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template<bool __threads, int __inst>
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char* __pool_alloc<__threads, __inst>::_S_start_free = 0;
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template<bool __threads, int __inst>
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char* __pool_alloc<__threads, __inst>::_S_end_free = 0;
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template<bool __threads, int __inst>
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size_t __pool_alloc<__threads, __inst>::_S_heap_size = 0;
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template<bool __threads, int __inst>
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_STL_mutex_lock
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__pool_alloc<__threads, __inst>::_S_lock __STL_MUTEX_INITIALIZER;
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template<bool __threads, int __inst> _Atomic_word
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__pool_alloc<__threads, __inst>::_S_force_new = 0;
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// Inhibit implicit instantiations for required instantiations,
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// which are defined via explicit instantiations elsewhere.
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// NB: This syntax is a GNU extension.
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#if _GLIBCXX_EXTERN_TEMPLATE
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extern template class __pool_alloc<true, 0>;
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#endif
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} // namespace __gnu_cxx
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namespace std
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{
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//@{
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/// Versions for the predefined "SGI" style allocators.
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template<typename _Tp, bool __thr, int __inst>
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struct _Alloc_traits<_Tp, __gnu_cxx::__pool_alloc<__thr, __inst> >
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{
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static const bool _S_instanceless = true;
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typedef __gnu_cxx::__pool_alloc<__thr, __inst> base_alloc_type;
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typedef __simple_alloc<_Tp, base_alloc_type> _Alloc_type;
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typedef __allocator<_Tp, base_alloc_type> allocator_type;
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};
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//@}
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//@{
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/// Versions for the __allocator adaptor used with the predefined
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/// "SGI" style allocators.
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template<typename _Tp, typename _Tp1, bool __thr, int __inst>
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struct _Alloc_traits<_Tp, __allocator<_Tp1,
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__gnu_cxx::__pool_alloc<__thr, __inst> > >
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{
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static const bool _S_instanceless = true;
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typedef __gnu_cxx::__pool_alloc<__thr, __inst> base_alloc_type;
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typedef __simple_alloc<_Tp, base_alloc_type> _Alloc_type;
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typedef __allocator<_Tp, base_alloc_type> allocator_type;
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};
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//@}
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} // namespace std
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#endif
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