libstdc++: mt_allocator.h Source File

libstdc++

mt_allocator.h
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1// MT-optimized allocator -*- C++ -*-
2
3// Copyright (C) 2003-2026 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file ext/mt_allocator.h
26 * This file is a GNU extension to the Standard C++ Library.
27 */
28
29#ifndef _MT_ALLOCATOR_H
30#define _MT_ALLOCATOR_H 1
31
32#include <bits/requires_hosted.h> // getenv
33
34#include <new>
35#include <cstdlib>
36#include <bits/new_throw.h>
37#include <ext/atomicity.h>
38#include <bits/move.h>
39#if __cplusplus >= 201103L
40#include <type_traits>
41#endif
42
43namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
44{
45_GLIBCXX_BEGIN_NAMESPACE_VERSION
46
47
48 typedef void (*__destroy_handler)(void*);
49
50 /// Base class for pool object.
51 struct __pool_base
52 {
53 // Using short int as type for the binmap implies we are never
54 // caching blocks larger than 32768 with this allocator.
55 typedef unsigned short int _Binmap_type;
56 typedef std::size_t size_t;
57
58 // Variables used to configure the behavior of the allocator,
59 // assigned and explained in detail below.
60 struct _Tune
61 {
62 // Compile time constants for the default _Tune values.
63 enum { _S_align = 8 };
64 enum { _S_max_bytes = 128 };
65 enum { _S_min_bin = 8 };
66 enum { _S_chunk_size = 4096 - 4 * sizeof(void*) };
67 enum { _S_max_threads = 4096 };
68 enum { _S_freelist_headroom = 10 };
69
70 // Alignment needed.
71 // NB: In any case must be >= sizeof(_Block_record), that
72 // is 4 on 32 bit machines and 8 on 64 bit machines.
73 size_t _M_align;
74
75 // Allocation requests (after round-up to power of 2) below
76 // this value will be handled by the allocator. A raw new/
77 // call will be used for requests larger than this value.
78 // NB: Must be much smaller than _M_chunk_size and in any
79 // case <= 32768.
80 size_t _M_max_bytes;
81
82 // Size in bytes of the smallest bin.
83 // NB: Must be a power of 2 and >= _M_align (and of course
84 // much smaller than _M_max_bytes).
85 size_t _M_min_bin;
86
87 // In order to avoid fragmenting and minimize the number of
88 // new() calls we always request new memory using this
89 // value. Based on previous discussions on the libstdc++
90 // mailing list we have chosen the value below.
91 // See http://gcc.gnu.org/ml/libstdc++/2001-07/msg00077.html
92 // NB: At least one order of magnitude > _M_max_bytes.
93 size_t _M_chunk_size;
94
95 // The maximum number of supported threads. For
96 // single-threaded operation, use one. Maximum values will
97 // vary depending on details of the underlying system. (For
98 // instance, Linux 2.4.18 reports 4070 in
99 // /proc/sys/kernel/threads-max, while Linux 2.6.6 reports
100 // 65534)
101 size_t _M_max_threads;
102
103 // Each time a deallocation occurs in a threaded application
104 // we make sure that there are no more than
105 // _M_freelist_headroom % of used memory on the freelist. If
106 // the number of additional records is more than
107 // _M_freelist_headroom % of the freelist, we move these
108 // records back to the global pool.
109 size_t _M_freelist_headroom;
110
111 // Set to true forces all allocations to use new().
112 bool _M_force_new;
113
114 explicit
115 _Tune()
116 : _M_align(_S_align), _M_max_bytes(_S_max_bytes), _M_min_bin(_S_min_bin),
117 _M_chunk_size(_S_chunk_size), _M_max_threads(_S_max_threads),
118 _M_freelist_headroom(_S_freelist_headroom),
119 _M_force_new(std::getenv("GLIBCXX_FORCE_NEW") ? true : false)
120 { }
121
122 explicit
123 _Tune(size_t __align, size_t __maxb, size_t __minbin, size_t __chunk,
124 size_t __maxthreads, size_t __headroom, bool __force)
125 : _M_align(__align), _M_max_bytes(__maxb), _M_min_bin(__minbin),
126 _M_chunk_size(__chunk), _M_max_threads(__maxthreads),
127 _M_freelist_headroom(__headroom), _M_force_new(__force)
128 { }
129 };
130
131 struct _Block_address
132 {
133 void* _M_initial;
134 _Block_address* _M_next;
135 };
136
137 const _Tune&
138 _M_get_options() const
139 { return _M_options; }
140
141 void
142 _M_set_options(_Tune __t)
143 {
144 if (!_M_init)
145 _M_options = __t;
146 }
147
148 bool
149 _M_check_threshold(size_t __bytes)
150 { return __bytes > _M_options._M_max_bytes || _M_options._M_force_new; }
151
152 size_t
153 _M_get_binmap(size_t __bytes)
154 { return _M_binmap[__bytes]; }
155
156 size_t
157 _M_get_align()
158 { return _M_options._M_align; }
159
160 explicit
161 __pool_base()
162 : _M_options(_Tune()), _M_binmap(0), _M_init(false) { }
163
164 explicit
165 __pool_base(const _Tune& __options)
166 : _M_options(__options), _M_binmap(0), _M_init(false) { }
167
168 private:
169 explicit
170 __pool_base(const __pool_base&);
171
172 __pool_base&
173 operator=(const __pool_base&);
174
175 protected:
176 // Configuration options.
177 _Tune _M_options;
178
179 _Binmap_type* _M_binmap;
180
181 // Configuration of the pool object via _M_options can happen
182 // after construction but before initialization. After
183 // initialization is complete, this variable is set to true.
184 bool _M_init;
185 };
186
187
188 /**
189 * @brief Data describing the underlying memory pool, parameterized on
190 * threading support.
191 */
192 template<bool _Thread>
193 class __pool;
194
195 /// Specialization for single thread.
196 template<>
197 class __pool<false> : public __pool_base
198 {
199 public:
200 union _Block_record
201 {
202 // Points to the block_record of the next free block.
203 _Block_record* _M_next;
204 };
205
206 struct _Bin_record
207 {
208 // An "array" of pointers to the first free block.
209 _Block_record** _M_first;
210
211 // A list of the initial addresses of all allocated blocks.
212 _Block_address* _M_address;
213 };
214
215 void
216 _M_initialize_once()
217 {
218 if (__builtin_expect(_M_init == false, false))
219 _M_initialize();
220 }
221
222 void
223 _M_destroy() throw();
224
225 char*
226 _M_reserve_block(size_t __bytes, const size_t __thread_id);
227
228 void
229 _M_reclaim_block(char* __p, size_t __bytes) throw ();
230
231 size_t
232 _M_get_thread_id() { return 0; }
233
234 const _Bin_record&
235 _M_get_bin(size_t __which)
236 { return _M_bin[__which]; }
237
238 void
239 _M_adjust_freelist(const _Bin_record&, _Block_record*, size_t)
240 { }
241
242 explicit __pool()
243 : _M_bin(0), _M_bin_size(1) { }
244
245 explicit __pool(const __pool_base::_Tune& __tune)
246 : __pool_base(__tune), _M_bin(0), _M_bin_size(1) { }
247
248 private:
249 // An "array" of bin_records each of which represents a specific
250 // power of 2 size. Memory to this "array" is allocated in
251 // _M_initialize().
252 _Bin_record* _M_bin;
253
254 // Actual value calculated in _M_initialize().
255 size_t _M_bin_size;
256
257 void
258 _M_initialize();
259 };
260
261#ifdef __GTHREADS
262 /// Specialization for thread enabled, via gthreads.h.
263 template<>
264 class __pool<true> : public __pool_base
265 {
266 public:
267 // Each requesting thread is assigned an id ranging from 1 to
268 // _S_max_threads. Thread id 0 is used as a global memory pool.
269 // In order to get constant performance on the thread assignment
270 // routine, we keep a list of free ids. When a thread first
271 // requests memory we remove the first record in this list and
272 // stores the address in a __gthread_key. When initializing the
273 // __gthread_key we specify a destructor. When this destructor
274 // (i.e. the thread dies) is called, we return the thread id to
275 // the front of this list.
276 struct _Thread_record
277 {
278 // Points to next free thread id record. NULL if last record in list.
279 _Thread_record* _M_next;
280
281 // Thread id ranging from 1 to _S_max_threads.
282 size_t _M_id;
283 };
284
285 union _Block_record
286 {
287 // Points to the block_record of the next free block.
288 _Block_record* _M_next;
289
290 // The thread id of the thread which has requested this block.
291 size_t _M_thread_id;
292 };
293
294 struct _Bin_record
295 {
296 // An "array" of pointers to the first free block for each
297 // thread id. Memory to this "array" is allocated in
298 // _S_initialize() for _S_max_threads + global pool 0.
299 _Block_record** _M_first;
300
301 // A list of the initial addresses of all allocated blocks.
302 _Block_address* _M_address;
303
304 // An "array" of counters used to keep track of the amount of
305 // blocks that are on the freelist/used for each thread id.
306 // - Note that the second part of the allocated _M_used "array"
307 // actually hosts (atomic) counters of reclaimed blocks: in
308 // _M_reserve_block and in _M_reclaim_block those numbers are
309 // subtracted from the first ones to obtain the actual size
310 // of the "working set" of the given thread.
311 // - Memory to these "arrays" is allocated in _S_initialize()
312 // for _S_max_threads + global pool 0.
313 size_t* _M_free;
314 size_t* _M_used;
315
316 // Each bin has its own mutex which is used to ensure data
317 // integrity while changing "ownership" on a block. The mutex
318 // is initialized in _S_initialize().
319 __gthread_mutex_t* _M_mutex;
320 };
321
322 // XXX GLIBCXX_ABI Deprecated
323 void
324 _M_initialize(__destroy_handler);
325
326 void
327 _M_initialize_once()
328 {
329 if (__builtin_expect(_M_init == false, false))
330 _M_initialize();
331 }
332
333 void
334 _M_destroy() throw();
335
336 char*
337 _M_reserve_block(size_t __bytes, const size_t __thread_id);
338
339 void
340 _M_reclaim_block(char* __p, size_t __bytes) throw ();
341
342 const _Bin_record&
343 _M_get_bin(size_t __which)
344 { return _M_bin[__which]; }
345
346 void
347 _M_adjust_freelist(const _Bin_record& __bin, _Block_record* __block,
348 size_t __thread_id)
349 {
350 if (__gthread_active_p())
351 {
352 __block->_M_thread_id = __thread_id;
353 --__bin._M_free[__thread_id];
354 ++__bin._M_used[__thread_id];
355 }
356 }
357
358 // XXX GLIBCXX_ABI Deprecated
359 void
360 _M_destroy_thread_key(void*) throw ();
361
362 size_t
363 _M_get_thread_id();
364
365 explicit __pool()
366 : _M_bin(0), _M_bin_size(1), _M_thread_freelist(0)
367 { }
368
369 explicit __pool(const __pool_base::_Tune& __tune)
370 : __pool_base(__tune), _M_bin(0), _M_bin_size(1),
371 _M_thread_freelist(0)
372 { }
373
374 private:
375 // An "array" of bin_records each of which represents a specific
376 // power of 2 size. Memory to this "array" is allocated in
377 // _M_initialize().
378 _Bin_record* _M_bin;
379
380 // Actual value calculated in _M_initialize().
381 size_t _M_bin_size;
382
383 _Thread_record* _M_thread_freelist;
384 void* _M_thread_freelist_initial;
385
386 void
387 _M_initialize();
388 };
389#endif
390
391 template<template <bool> class _PoolTp, bool _Thread>
392 struct __common_pool
393 {
394 typedef _PoolTp<_Thread> pool_type;
395
396 static pool_type&
397 _S_get_pool()
398 {
399 static pool_type _S_pool;
400 return _S_pool;
401 }
402 };
403
404 template<template <bool> class _PoolTp, bool _Thread>
405 struct __common_pool_base;
406
407 template<template <bool> class _PoolTp>
408 struct __common_pool_base<_PoolTp, false>
409 : public __common_pool<_PoolTp, false>
410 {
411 using __common_pool<_PoolTp, false>::_S_get_pool;
412
413 static void
414 _S_initialize_once()
415 {
416 static bool __init;
417 if (__builtin_expect(__init == false, false))
418 {
419 _S_get_pool()._M_initialize_once();
420 __init = true;
421 }
422 }
423 };
424
425#ifdef __GTHREADS
426 template<template <bool> class _PoolTp>
427 struct __common_pool_base<_PoolTp, true>
428 : public __common_pool<_PoolTp, true>
429 {
430 using __common_pool<_PoolTp, true>::_S_get_pool;
431
432 static void
433 _S_initialize()
434 { _S_get_pool()._M_initialize_once(); }
435
436 static void
437 _S_initialize_once()
438 {
439 static bool __init;
440 if (__builtin_expect(__init == false, false))
441 {
442 if (__gthread_active_p())
443 {
444 // On some platforms, __gthread_once_t is an aggregate.
445 static __gthread_once_t __once = __GTHREAD_ONCE_INIT;
446 __gthread_once(&__once, _S_initialize);
447 }
448
449 // Double check initialization. May be necessary on some
450 // systems for proper construction when not compiling with
451 // thread flags.
452 _S_get_pool()._M_initialize_once();
453 __init = true;
454 }
455 }
456 };
457#endif
458
459 /// Policy for shared __pool objects.
460 template<template <bool> class _PoolTp, bool _Thread>
461 struct __common_pool_policy : public __common_pool_base<_PoolTp, _Thread>
462 {
463 template<typename _Tp1, template <bool> class _PoolTp1 = _PoolTp,
464 bool _Thread1 = _Thread>
465 struct _M_rebind
466 { typedef __common_pool_policy<_PoolTp1, _Thread1> other; };
467
468 using __common_pool_base<_PoolTp, _Thread>::_S_get_pool;
469 using __common_pool_base<_PoolTp, _Thread>::_S_initialize_once;
470 };
471
472
473 template<typename _Tp, template <bool> class _PoolTp, bool _Thread>
474 struct __per_type_pool
475 {
476 typedef _Tp value_type;
477 typedef _PoolTp<_Thread> pool_type;
478
479 static pool_type&
480 _S_get_pool()
481 {
482 using std::size_t;
483 // Sane defaults for the _PoolTp.
484 typedef typename pool_type::_Block_record _Block_record;
485 const static size_t __a = (__alignof__(_Tp) >= sizeof(_Block_record)
486 ? __alignof__(_Tp) : sizeof(_Block_record));
487
488 typedef typename __pool_base::_Tune _Tune;
489 static _Tune _S_tune(__a, sizeof(_Tp) * 64,
490 sizeof(_Tp) * 2 >= __a ? sizeof(_Tp) * 2 : __a,
491 sizeof(_Tp) * size_t(_Tune::_S_chunk_size),
492 _Tune::_S_max_threads,
493 _Tune::_S_freelist_headroom,
494 std::getenv("GLIBCXX_FORCE_NEW") ? true : false);
495 static pool_type _S_pool(_S_tune);
496 return _S_pool;
497 }
498 };
499
500 template<typename _Tp, template <bool> class _PoolTp, bool _Thread>
501 struct __per_type_pool_base;
502
503 template<typename _Tp, template <bool> class _PoolTp>
504 struct __per_type_pool_base<_Tp, _PoolTp, false>
505 : public __per_type_pool<_Tp, _PoolTp, false>
506 {
507 using __per_type_pool<_Tp, _PoolTp, false>::_S_get_pool;
508
509 static void
510 _S_initialize_once()
511 {
512 static bool __init;
513 if (__builtin_expect(__init == false, false))
514 {
515 _S_get_pool()._M_initialize_once();
516 __init = true;
517 }
518 }
519 };
520
521 #ifdef __GTHREADS
522 template<typename _Tp, template <bool> class _PoolTp>
523 struct __per_type_pool_base<_Tp, _PoolTp, true>
524 : public __per_type_pool<_Tp, _PoolTp, true>
525 {
526 using __per_type_pool<_Tp, _PoolTp, true>::_S_get_pool;
527
528 static void
529 _S_initialize()
530 { _S_get_pool()._M_initialize_once(); }
531
532 static void
533 _S_initialize_once()
534 {
535 static bool __init;
536 if (__builtin_expect(__init == false, false))
537 {
538 if (__gthread_active_p())
539 {
540 // On some platforms, __gthread_once_t is an aggregate.
541 static __gthread_once_t __once = __GTHREAD_ONCE_INIT;
542 __gthread_once(&__once, _S_initialize);
543 }
544
545 // Double check initialization. May be necessary on some
546 // systems for proper construction when not compiling with
547 // thread flags.
548 _S_get_pool()._M_initialize_once();
549 __init = true;
550 }
551 }
552 };
553#endif
554
555 /// Policy for individual __pool objects.
556 template<typename _Tp, template <bool> class _PoolTp, bool _Thread>
557 struct __per_type_pool_policy
558 : public __per_type_pool_base<_Tp, _PoolTp, _Thread>
559 {
560 template<typename _Tp1, template <bool> class _PoolTp1 = _PoolTp,
561 bool _Thread1 = _Thread>
562 struct _M_rebind
563 { typedef __per_type_pool_policy<_Tp1, _PoolTp1, _Thread1> other; };
564
565 using __per_type_pool_base<_Tp, _PoolTp, _Thread>::_S_get_pool;
566 using __per_type_pool_base<_Tp, _PoolTp, _Thread>::_S_initialize_once;
567 };
568
569
570 /// Base class for _Tp dependent member functions.
571 template<typename _Tp>
572 class __mt_alloc_base
573 {
574 public:
575 typedef std::size_t size_type;
576 typedef std::ptrdiff_t difference_type;
577 typedef _Tp* pointer;
578 typedef const _Tp* const_pointer;
579 typedef _Tp& reference;
580 typedef const _Tp& const_reference;
581 typedef _Tp value_type;
582
583#if __cplusplus >= 201103L
584 // _GLIBCXX_RESOLVE_LIB_DEFECTS
585 // 2103. propagate_on_container_move_assignment
586 typedef std::true_type propagate_on_container_move_assignment;
587#endif
588
589 pointer
590 address(reference __x) const _GLIBCXX_NOEXCEPT
591 { return std::__addressof(__x); }
592
593 const_pointer
594 address(const_reference __x) const _GLIBCXX_NOEXCEPT
595 { return std::__addressof(__x); }
596
597 size_type
598 max_size() const _GLIBCXX_USE_NOEXCEPT
599 { return size_type(-1) / sizeof(_Tp); }
600
601#if __cplusplus >= 201103L
602 template<typename _Up, typename... _Args>
603 void
604 construct(_Up* __p, _Args&&... __args)
605 { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
606
607 template<typename _Up>
608 void
609 destroy(_Up* __p) { __p->~_Up(); }
610#else
611 // _GLIBCXX_RESOLVE_LIB_DEFECTS
612 // 402. wrong new expression in [some_] allocator::construct
613 void
614 construct(pointer __p, const _Tp& __val)
615 { ::new((void *)__p) _Tp(__val); }
616
617 void
618 destroy(pointer __p) { __p->~_Tp(); }
619#endif
620 };
621
622#ifdef __GTHREADS
623#define __thread_default true
624#else
625#define __thread_default false
626#endif
627
628 /**
629 * @brief This is a fixed size (power of 2) allocator which - when
630 * compiled with thread support - will maintain one freelist per
631 * size per thread plus a @a global one. Steps are taken to limit
632 * the per thread freelist sizes (by returning excess back to
633 * the @a global list).
634 * @ingroup allocators
635 *
636 * Further details:
637 * https://gcc.gnu.org/onlinedocs/libstdc++/manual/mt_allocator.html
638 */
639 template<typename _Tp,
640 typename _Poolp = __common_pool_policy<__pool, __thread_default> >
641 class __mt_alloc : public __mt_alloc_base<_Tp>
642 {
643 public:
644 typedef std::size_t size_type;
645 typedef std::ptrdiff_t difference_type;
646 typedef _Tp* pointer;
647 typedef const _Tp* const_pointer;
648 typedef _Tp& reference;
649 typedef const _Tp& const_reference;
650 typedef _Tp value_type;
651 typedef _Poolp __policy_type;
652 typedef typename _Poolp::pool_type __pool_type;
653
654 template<typename _Tp1, typename _Poolp1 = _Poolp>
655 struct rebind
656 {
657 typedef typename _Poolp1::template _M_rebind<_Tp1>::other pol_type;
658 typedef __mt_alloc<_Tp1, pol_type> other;
659 };
660
661 __mt_alloc() _GLIBCXX_USE_NOEXCEPT { }
662
663 __mt_alloc(const __mt_alloc&) _GLIBCXX_USE_NOEXCEPT { }
664
665 template<typename _Tp1, typename _Poolp1>
666 __mt_alloc(const __mt_alloc<_Tp1, _Poolp1>&) _GLIBCXX_USE_NOEXCEPT { }
667
668 ~__mt_alloc() _GLIBCXX_USE_NOEXCEPT { }
669
670 _GLIBCXX_NODISCARD pointer
671 allocate(size_type __n, const void* = 0);
672
673 void
674 deallocate(pointer __p, size_type __n);
675
676 const __pool_base::_Tune
677 _M_get_options()
678 {
679 // Return a copy, not a reference, for external consumption.
680 return __policy_type::_S_get_pool()._M_get_options();
681 }
682
683 void
684 _M_set_options(__pool_base::_Tune __t)
685 { __policy_type::_S_get_pool()._M_set_options(__t); }
686 };
687
688 template<typename _Tp, typename _Poolp>
689 _GLIBCXX_NODISCARD typename __mt_alloc<_Tp, _Poolp>::pointer
690 __mt_alloc<_Tp, _Poolp>::
691 allocate(size_type __n, const void*)
692 {
693 if (__n > this->max_size())
694 std::__throw_bad_alloc();
695
696#if __cpp_aligned_new && __cplusplus >= 201103L
697 // Types with extended alignment are handled by operator new/delete.
698 if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
699 {
700 std::align_val_t __al = std::align_val_t(alignof(_Tp));
701 return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), __al));
702 }
703#endif
704
705 __policy_type::_S_initialize_once();
706
707 // Requests larger than _M_max_bytes are handled by operator
708 // new/delete directly.
709 __pool_type& __pool = __policy_type::_S_get_pool();
710 const size_type __bytes = __n * sizeof(_Tp);
711 if (__pool._M_check_threshold(__bytes))
712 {
713 void* __ret = ::operator new(__bytes);
714 return static_cast<_Tp*>(__ret);
715 }
716
717 // Round up to power of 2 and figure out which bin to use.
718 const size_type __which = __pool._M_get_binmap(__bytes);
719 const size_type __thread_id = __pool._M_get_thread_id();
720
721 // Find out if we have blocks on our freelist. If so, go ahead
722 // and use them directly without having to lock anything.
723 char* __c;
724 typedef typename __pool_type::_Bin_record _Bin_record;
725 const _Bin_record& __bin = __pool._M_get_bin(__which);
726 if (__bin._M_first[__thread_id])
727 {
728 // Already reserved.
729 typedef typename __pool_type::_Block_record _Block_record;
730 _Block_record* __block = __bin._M_first[__thread_id];
731 __bin._M_first[__thread_id] = __block->_M_next;
732
733 __pool._M_adjust_freelist(__bin, __block, __thread_id);
734 __c = reinterpret_cast<char*>(__block) + __pool._M_get_align();
735 }
736 else
737 {
738 // Null, reserve.
739 __c = __pool._M_reserve_block(__bytes, __thread_id);
740 }
741 return static_cast<_Tp*>(static_cast<void*>(__c));
742 }
743
744 template<typename _Tp, typename _Poolp>
745 void
746 __mt_alloc<_Tp, _Poolp>::
747 deallocate(pointer __p, size_type __n)
748 {
749 if (__builtin_expect(__p != 0, true))
750 {
751#if __cpp_aligned_new && __cplusplus >= 201103L
752 // Types with extended alignment are handled by operator new/delete.
753 if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
754 {
755 ::operator delete(__p, std::align_val_t(alignof(_Tp)));
756 return;
757 }
758#endif
759
760 // Requests larger than _M_max_bytes are handled by
761 // operators new/delete directly.
762 __pool_type& __pool = __policy_type::_S_get_pool();
763 const size_type __bytes = __n * sizeof(_Tp);
764 if (__pool._M_check_threshold(__bytes))
765 ::operator delete(__p);
766 else
767 __pool._M_reclaim_block(reinterpret_cast<char*>(__p), __bytes);
768 }
769 }
770
771 template<typename _Tp, typename _Poolp>
772 inline bool
773 operator==(const __mt_alloc<_Tp, _Poolp>&, const __mt_alloc<_Tp, _Poolp>&)
774 { return true; }
775
776#if __cpp_impl_three_way_comparison < 201907L
777 template<typename _Tp, typename _Poolp>
778 inline bool
779 operator!=(const __mt_alloc<_Tp, _Poolp>&, const __mt_alloc<_Tp, _Poolp>&)
780 { return false; }
781#endif
782
783#undef __thread_default
784
785_GLIBCXX_END_NAMESPACE_VERSION
786} // namespace
787
788#endif
new
type_traits
cstdlib
new_throw.h
move.h
requires_hosted.h
atomicity.h
std::true_type
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition type_traits:119
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition move.h:52
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:72
__gnu_cxx
GNU extensions for public use.
__gnu_cxx::other
__gnu_cxx::__pool
Data describing the underlying memory pool, parameterized on threading support.
Definition mt_allocator.h:193
__gnu_cxx::__common_pool_policy
Policy for shared __pool objects.
Definition mt_allocator.h:462
__gnu_cxx::__per_type_pool_policy
Policy for individual __pool objects.
Definition mt_allocator.h:559
__gnu_cxx::__mt_alloc_base
Base class for _Tp dependent member functions.
Definition mt_allocator.h:573
__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:642