// Allocators -*- C++ -*- // Copyright (C) 2001, 2002, 2003, 2004 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 2, 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. // You should have received a copy of the GNU General Public License along // with this library; see the file COPYING. If not, write to the Free // Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, // USA. // As a special exception, you may use this file as part of a free software // library without restriction. Specifically, if other files instantiate // templates or use macros or inline functions from this file, or you compile // this file and link it with other files to produce an executable, this // file does not by itself cause the resulting executable to be covered by // the GNU General Public License. This exception does not however // invalidate any other reasons why the executable file might be covered by // the GNU General Public License. /* * Copyright (c) 1996-1997 * Silicon Graphics Computer Systems, Inc. * * Permission to use, copy, modify, distribute and sell this software * and its documentation for any purpose is hereby granted without fee, * provided that the above copyright notice appear in all copies and * that both that copyright notice and this permission notice appear * in supporting documentation. Silicon Graphics makes no * representations about the suitability of this software for any * purpose. It is provided "as is" without express or implied warranty. */ /** @file ext/pool_allocator.h * This file is a GNU extension to the Standard C++ Library. * You should only include this header if you are using GCC 3 or later. */ #ifndef _POOL_ALLOCATOR_H #define _POOL_ALLOCATOR_H 1 #include #include #include #include #include namespace __gnu_cxx { using std::__throw_bad_alloc; /** * @if maint * Default node allocator. "SGI" style. Uses various allocators to * fulfill underlying requests (and makes as few requests as possible * when in default high-speed pool mode). * * Important implementation properties: * 0. If globally mandated, then allocate objects from new * 1. If the clients request an object of size > _S_max_bytes, the resulting * object will be obtained directly from new * 2. In all other cases, we allocate an object of size exactly * _S_round_up(requested_size). Thus the client has enough size * information that we can return the object to the proper free list * without permanently losing part of the object. * * The first template parameter specifies whether more than one thread may * use this allocator. It is safe to allocate an object from one instance * of a default_alloc and deallocate it with another one. This effectively * transfers its ownership to the second one. This may have undesirable * effects on reference locality. * * The second parameter is unused and serves only to allow the * creation of multiple default_alloc instances. Note that * containers built on different allocator instances have different * types, limiting the utility of this approach. If you do not * wish to share the free lists with the main default_alloc * instance, instantiate this with a non-zero __inst. * * @endif * (See @link Allocators allocators info @endlink for more.) */ template class __pool_alloc { private: enum {_S_align = 8}; enum {_S_max_bytes = 128}; enum {_S_freelists = _S_max_bytes / _S_align}; union _Obj { union _Obj* _M_free_list_link; char _M_client_data[1]; // The client sees this. }; static _Obj* volatile _S_free_list[_S_freelists]; // Chunk allocation state. static char* _S_start_free; static char* _S_end_free; static size_t _S_heap_size; static _STL_mutex_lock _S_lock; static _Atomic_word _S_force_new; static size_t _S_round_up(size_t __bytes) { return ((__bytes + (size_t)_S_align - 1) & ~((size_t)_S_align - 1)); } static size_t _S_freelist_index(size_t __bytes) { return ((__bytes + (size_t)_S_align - 1)/(size_t)_S_align - 1); } // Returns an object of size __n, and optionally adds to size __n // free list. static void* _S_refill(size_t __n); // Allocates a chunk for nobjs of size size. nobjs may be reduced // if it is inconvenient to allocate the requested number. static char* _S_chunk_alloc(size_t __n, int& __nobjs); // It would be nice to use _STL_auto_lock here. But we need a // test whether threads are in use. struct _Lock { _Lock() { if (__threads) _S_lock._M_acquire_lock(); } ~_Lock() { if (__threads) _S_lock._M_release_lock(); } } __attribute__ ((__unused__)); friend struct _Lock; public: // __n must be > 0 static void* allocate(size_t __n); // __p may not be 0 static void deallocate(void* __p, size_t __n); }; template inline bool operator==(const __pool_alloc<__threads,__inst>&, const __pool_alloc<__threads,__inst>&) { return true; } template inline bool operator!=(const __pool_alloc<__threads,__inst>&, const __pool_alloc<__threads,__inst>&) { return false; } // Allocate memory in large chunks in order to avoid fragmenting the // heap too much. Assume that __n is properly aligned. We hold // the allocation lock. template char* __pool_alloc<__threads, __inst>::_S_chunk_alloc(size_t __n, int& __nobjs) { char* __result; size_t __total_bytes = __n * __nobjs; size_t __bytes_left = _S_end_free - _S_start_free; if (__bytes_left >= __total_bytes) { __result = _S_start_free; _S_start_free += __total_bytes; return __result ; } else if (__bytes_left >= __n) { __nobjs = (int)(__bytes_left/__n); __total_bytes = __n * __nobjs; __result = _S_start_free; _S_start_free += __total_bytes; return __result; } else { size_t __bytes_to_get = 2 * __total_bytes + _S_round_up(_S_heap_size >> 4); // Try to make use of the left-over piece. if (__bytes_left > 0) { _Obj* volatile* __free_list = _S_free_list + _S_freelist_index(__bytes_left); ((_Obj*)(void*)_S_start_free)->_M_free_list_link = *__free_list; *__free_list = (_Obj*)(void*)_S_start_free; } _S_start_free = static_cast(::operator new(__bytes_to_get)); if (_S_start_free == 0) { size_t __i; _Obj* volatile* __free_list; _Obj* __p; // Try to make do with what we have. That can't hurt. We // do not try smaller requests, since that tends to result // in disaster on multi-process machines. __i = __n; for (; __i <= (size_t) _S_max_bytes; __i += (size_t) _S_align) { __free_list = _S_free_list + _S_freelist_index(__i); __p = *__free_list; if (__p != 0) { *__free_list = __p -> _M_free_list_link; _S_start_free = (char*)__p; _S_end_free = _S_start_free + __i; return _S_chunk_alloc(__n, __nobjs); // Any leftover piece will eventually make it to the // right free list. } } _S_end_free = 0; // In case of exception. _S_start_free = static_cast(::operator new(__bytes_to_get)); // This should either throw an exception or remedy the situation. // Thus we assume it succeeded. } _S_heap_size += __bytes_to_get; _S_end_free = _S_start_free + __bytes_to_get; return _S_chunk_alloc(__n, __nobjs); } } // Returns an object of size __n, and optionally adds to "size // __n"'s free list. We assume that __n is properly aligned. We // hold the allocation lock. template void* __pool_alloc<__threads, __inst>::_S_refill(size_t __n) { int __nobjs = 20; char* __chunk = _S_chunk_alloc(__n, __nobjs); _Obj* volatile* __free_list; _Obj* __result; _Obj* __current_obj; _Obj* __next_obj; int __i; if (1 == __nobjs) return __chunk; __free_list = _S_free_list + _S_freelist_index(__n); // Build free list in chunk. __result = (_Obj*)(void*)__chunk; *__free_list = __next_obj = (_Obj*)(void*)(__chunk + __n); for (__i = 1; ; __i++) { __current_obj = __next_obj; __next_obj = (_Obj*)(void*)((char*)__next_obj + __n); if (__nobjs - 1 == __i) { __current_obj -> _M_free_list_link = 0; break; } else __current_obj -> _M_free_list_link = __next_obj; } return __result; } template void* __pool_alloc<__threads, __inst>::allocate(size_t __n) { void* __ret = 0; // If there is a race through here, assume answer from getenv // will resolve in same direction. Inspired by techniques // to efficiently support threading found in basic_string.h. if (_S_force_new == 0) { if (getenv("GLIBCXX_FORCE_NEW")) __atomic_add(&_S_force_new, 1); else __atomic_add(&_S_force_new, -1); } if ((__n > (size_t) _S_max_bytes) || (_S_force_new > 0)) __ret = ::operator new(__n); else { _Obj* volatile* __free_list = _S_free_list + _S_freelist_index(__n); // Acquire the lock here with a constructor call. This // ensures that it is released in exit or during stack // unwinding. _Lock __lock_instance; _Obj* __restrict__ __result = *__free_list; if (__builtin_expect(__result == 0, 0)) __ret = _S_refill(_S_round_up(__n)); else { *__free_list = __result -> _M_free_list_link; __ret = __result; } if (__builtin_expect(__ret == 0, 0)) __throw_bad_alloc(); } return __ret; } template void __pool_alloc<__threads, __inst>::deallocate(void* __p, size_t __n) { if ((__n > (size_t) _S_max_bytes) || (_S_force_new > 0)) ::operator delete(__p); else { _Obj* volatile* __free_list = _S_free_list + _S_freelist_index(__n); _Obj* __q = (_Obj*)__p; // Acquire the lock here with a constructor call. This // ensures that it is released in exit or during stack // unwinding. _Lock __lock_instance; __q -> _M_free_list_link = *__free_list; *__free_list = __q; } } template typename __pool_alloc<__threads, __inst>::_Obj* volatile __pool_alloc<__threads, __inst>::_S_free_list[_S_freelists]; template char* __pool_alloc<__threads, __inst>::_S_start_free = 0; template char* __pool_alloc<__threads, __inst>::_S_end_free = 0; template size_t __pool_alloc<__threads, __inst>::_S_heap_size = 0; template _STL_mutex_lock __pool_alloc<__threads, __inst>::_S_lock __STL_MUTEX_INITIALIZER; template _Atomic_word __pool_alloc<__threads, __inst>::_S_force_new = 0; // Inhibit implicit instantiations for required instantiations, // which are defined via explicit instantiations elsewhere. // NB: This syntax is a GNU extension. #if _GLIBCXX_EXTERN_TEMPLATE extern template class __pool_alloc; #endif } // namespace __gnu_cxx #endif