// MT-optimized allocator -*- C++ -*- // Copyright (C) 2003-2017 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 // . /** @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 #include #include #include #include #if __cplusplus >= 201103L #include #endif namespace __gnu_cxx _GLIBCXX_VISIBILITY(default) { _GLIBCXX_BEGIN_NAMESPACE_VERSION using std::size_t; using std::ptrdiff_t; 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; // 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 class __pool; /// Specialization for single thread. template<> class __pool : 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 : 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 _GLIBCXX_CONST 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