libstdc++
mt_allocator.h
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1 // MT-optimized allocator -*- C++ -*-
2 
3 // Copyright (C) 2003-2019 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 <new>
33 #include <cstdlib>
34 #include <bits/functexcept.h>
35 #include <ext/atomicity.h>
36 #include <bits/move.h>
37 #if __cplusplus >= 201103L
38 #include <type_traits>
39 #endif
40 
41 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
42 {
43 _GLIBCXX_BEGIN_NAMESPACE_VERSION
44 
45  using std::size_t;
46  using std::ptrdiff_t;
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 
57  // Variables used to configure the behavior of the allocator,
58  // assigned and explained in detail below.
59  struct _Tune
60  {
61  // Compile time constants for the default _Tune values.
62  enum { _S_align = 8 };
63  enum { _S_max_bytes = 128 };
64  enum { _S_min_bin = 8 };
65  enum { _S_chunk_size = 4096 - 4 * sizeof(void*) };
66  enum { _S_max_threads = 4096 };
67  enum { _S_freelist_headroom = 10 };
68 
69  // Alignment needed.
70  // NB: In any case must be >= sizeof(_Block_record), that
71  // is 4 on 32 bit machines and 8 on 64 bit machines.
72  size_t _M_align;
73 
74  // Allocation requests (after round-up to power of 2) below
75  // this value will be handled by the allocator. A raw new/
76  // call will be used for requests larger than this value.
77  // NB: Must be much smaller than _M_chunk_size and in any
78  // case <= 32768.
79  size_t _M_max_bytes;
80 
81  // Size in bytes of the smallest bin.
82  // NB: Must be a power of 2 and >= _M_align (and of course
83  // much smaller than _M_max_bytes).
84  size_t _M_min_bin;
85 
86  // In order to avoid fragmenting and minimize the number of
87  // new() calls we always request new memory using this
88  // value. Based on previous discussions on the libstdc++
89  // mailing list we have chosen the value below.
90  // See http://gcc.gnu.org/ml/libstdc++/2001-07/msg00077.html
91  // NB: At least one order of magnitude > _M_max_bytes.
92  size_t _M_chunk_size;
93 
94  // The maximum number of supported threads. For
95  // single-threaded operation, use one. Maximum values will
96  // vary depending on details of the underlying system. (For
97  // instance, Linux 2.4.18 reports 4070 in
98  // /proc/sys/kernel/threads-max, while Linux 2.6.6 reports
99  // 65534)
100  size_t _M_max_threads;
101 
102  // Each time a deallocation occurs in a threaded application
103  // we make sure that there are no more than
104  // _M_freelist_headroom % of used memory on the freelist. If
105  // the number of additional records is more than
106  // _M_freelist_headroom % of the freelist, we move these
107  // records back to the global pool.
108  size_t _M_freelist_headroom;
109 
110  // Set to true forces all allocations to use new().
111  bool _M_force_new;
112 
113  explicit
114  _Tune()
115  : _M_align(_S_align), _M_max_bytes(_S_max_bytes), _M_min_bin(_S_min_bin),
116  _M_chunk_size(_S_chunk_size), _M_max_threads(_S_max_threads),
117  _M_freelist_headroom(_S_freelist_headroom),
118  _M_force_new(std::getenv("GLIBCXX_FORCE_NEW") ? true : false)
119  { }
120 
121  explicit
122  _Tune(size_t __align, size_t __maxb, size_t __minbin, size_t __chunk,
123  size_t __maxthreads, size_t __headroom, bool __force)
124  : _M_align(__align), _M_max_bytes(__maxb), _M_min_bin(__minbin),
125  _M_chunk_size(__chunk), _M_max_threads(__maxthreads),
126  _M_freelist_headroom(__headroom), _M_force_new(__force)
127  { }
128  };
129 
130  struct _Block_address
131  {
132  void* _M_initial;
133  _Block_address* _M_next;
134  };
135 
136  const _Tune&
137  _M_get_options() const
138  { return _M_options; }
139 
140  void
141  _M_set_options(_Tune __t)
142  {
143  if (!_M_init)
144  _M_options = __t;
145  }
146 
147  bool
148  _M_check_threshold(size_t __bytes)
149  { return __bytes > _M_options._M_max_bytes || _M_options._M_force_new; }
150 
151  size_t
152  _M_get_binmap(size_t __bytes)
153  { return _M_binmap[__bytes]; }
154 
155  size_t
156  _M_get_align()
157  { return _M_options._M_align; }
158 
159  explicit
160  __pool_base()
161  : _M_options(_Tune()), _M_binmap(0), _M_init(false) { }
162 
163  explicit
164  __pool_base(const _Tune& __options)
165  : _M_options(__options), _M_binmap(0), _M_init(false) { }
166 
167  private:
168  explicit
169  __pool_base(const __pool_base&);
170 
171  __pool_base&
172  operator=(const __pool_base&);
173 
174  protected:
175  // Configuration options.
176  _Tune _M_options;
177 
178  _Binmap_type* _M_binmap;
179 
180  // Configuration of the pool object via _M_options can happen
181  // after construction but before initialization. After
182  // initialization is complete, this variable is set to true.
183  bool _M_init;
184  };
185 
186 
187  /**
188  * @brief Data describing the underlying memory pool, parameterized on
189  * threading support.
190  */
191  template<bool _Thread>
192  class __pool;
193 
194  /// Specialization for single thread.
195  template<>
196  class __pool<false> : public __pool_base
197  {
198  public:
199  union _Block_record
200  {
201  // Points to the block_record of the next free block.
202  _Block_record* _M_next;
203  };
204 
205  struct _Bin_record
206  {
207  // An "array" of pointers to the first free block.
208  _Block_record** _M_first;
209 
210  // A list of the initial addresses of all allocated blocks.
211  _Block_address* _M_address;
212  };
213 
214  void
215  _M_initialize_once()
216  {
217  if (__builtin_expect(_M_init == false, false))
218  _M_initialize();
219  }
220 
221  void
222  _M_destroy() throw();
223 
224  char*
225  _M_reserve_block(size_t __bytes, const size_t __thread_id);
226 
227  void
228  _M_reclaim_block(char* __p, size_t __bytes) throw ();
229 
230  size_t
231  _M_get_thread_id() { return 0; }
232 
233  const _Bin_record&
234  _M_get_bin(size_t __which)
235  { return _M_bin[__which]; }
236 
237  void
238  _M_adjust_freelist(const _Bin_record&, _Block_record*, size_t)
239  { }
240 
241  explicit __pool()
242  : _M_bin(0), _M_bin_size(1) { }
243 
244  explicit __pool(const __pool_base::_Tune& __tune)
245  : __pool_base(__tune), _M_bin(0), _M_bin_size(1) { }
246 
247  private:
248  // An "array" of bin_records each of which represents a specific
249  // power of 2 size. Memory to this "array" is allocated in
250  // _M_initialize().
251  _Bin_record* _M_bin;
252 
253  // Actual value calculated in _M_initialize().
254  size_t _M_bin_size;
255 
256  void
257  _M_initialize();
258  };
259 
260 #ifdef __GTHREADS
261  /// Specialization for thread enabled, via gthreads.h.
262  template<>
263  class __pool<true> : public __pool_base
264  {
265  public:
266  // Each requesting thread is assigned an id ranging from 1 to
267  // _S_max_threads. Thread id 0 is used as a global memory pool.
268  // In order to get constant performance on the thread assignment
269  // routine, we keep a list of free ids. When a thread first
270  // requests memory we remove the first record in this list and
271  // stores the address in a __gthread_key. When initializing the
272  // __gthread_key we specify a destructor. When this destructor
273  // (i.e. the thread dies) is called, we return the thread id to
274  // the front of this list.
275  struct _Thread_record
276  {
277  // Points to next free thread id record. NULL if last record in list.
278  _Thread_record* _M_next;
279 
280  // Thread id ranging from 1 to _S_max_threads.
281  size_t _M_id;
282  };
283 
284  union _Block_record
285  {
286  // Points to the block_record of the next free block.
287  _Block_record* _M_next;
288 
289  // The thread id of the thread which has requested this block.
290  size_t _M_thread_id;
291  };
292 
293  struct _Bin_record
294  {
295  // An "array" of pointers to the first free block for each
296  // thread id. Memory to this "array" is allocated in
297  // _S_initialize() for _S_max_threads + global pool 0.
298  _Block_record** _M_first;
299 
300  // A list of the initial addresses of all allocated blocks.
301  _Block_address* _M_address;
302 
303  // An "array" of counters used to keep track of the amount of
304  // blocks that are on the freelist/used for each thread id.
305  // - Note that the second part of the allocated _M_used "array"
306  // actually hosts (atomic) counters of reclaimed blocks: in
307  // _M_reserve_block and in _M_reclaim_block those numbers are
308  // subtracted from the first ones to obtain the actual size
309  // of the "working set" of the given thread.
310  // - Memory to these "arrays" is allocated in _S_initialize()
311  // for _S_max_threads + global pool 0.
312  size_t* _M_free;
313  size_t* _M_used;
314 
315  // Each bin has its own mutex which is used to ensure data
316  // integrity while changing "ownership" on a block. The mutex
317  // is initialized in _S_initialize().
318  __gthread_mutex_t* _M_mutex;
319  };
320 
321  // XXX GLIBCXX_ABI Deprecated
322  void
323  _M_initialize(__destroy_handler);
324 
325  void
326  _M_initialize_once()
327  {
328  if (__builtin_expect(_M_init == false, false))
329  _M_initialize();
330  }
331 
332  void
333  _M_destroy() throw();
334 
335  char*
336  _M_reserve_block(size_t __bytes, const size_t __thread_id);
337 
338  void
339  _M_reclaim_block(char* __p, size_t __bytes) throw ();
340 
341  const _Bin_record&
342  _M_get_bin(size_t __which)
343  { return _M_bin[__which]; }
344 
345  void
346  _M_adjust_freelist(const _Bin_record& __bin, _Block_record* __block,
347  size_t __thread_id)
348  {
349  if (__gthread_active_p())
350  {
351  __block->_M_thread_id = __thread_id;
352  --__bin._M_free[__thread_id];
353  ++__bin._M_used[__thread_id];
354  }
355  }
356 
357  // XXX GLIBCXX_ABI Deprecated
358  void
359  _M_destroy_thread_key(void*) throw ();
360 
361  size_t
362  _M_get_thread_id();
363 
364  explicit __pool()
365  : _M_bin(0), _M_bin_size(1), _M_thread_freelist(0)
366  { }
367 
368  explicit __pool(const __pool_base::_Tune& __tune)
369  : __pool_base(__tune), _M_bin(0), _M_bin_size(1),
370  _M_thread_freelist(0)
371  { }
372 
373  private:
374  // An "array" of bin_records each of which represents a specific
375  // power of 2 size. Memory to this "array" is allocated in
376  // _M_initialize().
377  _Bin_record* _M_bin;
378 
379  // Actual value calculated in _M_initialize().
380  size_t _M_bin_size;
381 
382  _Thread_record* _M_thread_freelist;
383  void* _M_thread_freelist_initial;
384 
385  void
386  _M_initialize();
387  };
388 #endif
389 
390  template<template <bool> class _PoolTp, bool _Thread>
391  struct __common_pool
392  {
393  typedef _PoolTp<_Thread> pool_type;
394 
395  static pool_type&
396  _S_get_pool()
397  {
398  static pool_type _S_pool;
399  return _S_pool;
400  }
401  };
402 
403  template<template <bool> class _PoolTp, bool _Thread>
404  struct __common_pool_base;
405 
406  template<template <bool> class _PoolTp>
407  struct __common_pool_base<_PoolTp, false>
408  : public __common_pool<_PoolTp, false>
409  {
410  using __common_pool<_PoolTp, false>::_S_get_pool;
411 
412  static void
413  _S_initialize_once()
414  {
415  static bool __init;
416  if (__builtin_expect(__init == false, false))
417  {
418  _S_get_pool()._M_initialize_once();
419  __init = true;
420  }
421  }
422  };
423 
424 #ifdef __GTHREADS
425  template<template <bool> class _PoolTp>
426  struct __common_pool_base<_PoolTp, true>
427  : public __common_pool<_PoolTp, true>
428  {
429  using __common_pool<_PoolTp, true>::_S_get_pool;
430 
431  static void
432  _S_initialize()
433  { _S_get_pool()._M_initialize_once(); }
434 
435  static void
436  _S_initialize_once()
437  {
438  static bool __init;
439  if (__builtin_expect(__init == false, false))
440  {
441  if (__gthread_active_p())
442  {
443  // On some platforms, __gthread_once_t is an aggregate.
444  static __gthread_once_t __once = __GTHREAD_ONCE_INIT;
445  __gthread_once(&__once, _S_initialize);
446  }
447 
448  // Double check initialization. May be necessary on some
449  // systems for proper construction when not compiling with
450  // thread flags.
451  _S_get_pool()._M_initialize_once();
452  __init = true;
453  }
454  }
455  };
456 #endif
457 
458  /// Policy for shared __pool objects.
459  template<template <bool> class _PoolTp, bool _Thread>
460  struct __common_pool_policy : public __common_pool_base<_PoolTp, _Thread>
461  {
462  template<typename _Tp1, template <bool> class _PoolTp1 = _PoolTp,
463  bool _Thread1 = _Thread>
464  struct _M_rebind
465  { typedef __common_pool_policy<_PoolTp1, _Thread1> other; };
466 
467  using __common_pool_base<_PoolTp, _Thread>::_S_get_pool;
468  using __common_pool_base<_PoolTp, _Thread>::_S_initialize_once;
469  };
470 
471 
472  template<typename _Tp, template <bool> class _PoolTp, bool _Thread>
473  struct __per_type_pool
474  {
475  typedef _Tp value_type;
476  typedef _PoolTp<_Thread> pool_type;
477 
478  static pool_type&
479  _S_get_pool()
480  {
481  // Sane defaults for the _PoolTp.
482  typedef typename pool_type::_Block_record _Block_record;
483  const static size_t __a = (__alignof__(_Tp) >= sizeof(_Block_record)
484  ? __alignof__(_Tp) : sizeof(_Block_record));
485 
486  typedef typename __pool_base::_Tune _Tune;
487  static _Tune _S_tune(__a, sizeof(_Tp) * 64,
488  sizeof(_Tp) * 2 >= __a ? sizeof(_Tp) * 2 : __a,
489  sizeof(_Tp) * size_t(_Tune::_S_chunk_size),
490  _Tune::_S_max_threads,
491  _Tune::_S_freelist_headroom,
492  std::getenv("GLIBCXX_FORCE_NEW") ? true : false);
493  static pool_type _S_pool(_S_tune);
494  return _S_pool;
495  }
496  };
497 
498  template<typename _Tp, template <bool> class _PoolTp, bool _Thread>
499  struct __per_type_pool_base;
500 
501  template<typename _Tp, template <bool> class _PoolTp>
502  struct __per_type_pool_base<_Tp, _PoolTp, false>
503  : public __per_type_pool<_Tp, _PoolTp, false>
504  {
505  using __per_type_pool<_Tp, _PoolTp, false>::_S_get_pool;
506 
507  static void
508  _S_initialize_once()
509  {
510  static bool __init;
511  if (__builtin_expect(__init == false, false))
512  {
513  _S_get_pool()._M_initialize_once();
514  __init = true;
515  }
516  }
517  };
518 
519  #ifdef __GTHREADS
520  template<typename _Tp, template <bool> class _PoolTp>
521  struct __per_type_pool_base<_Tp, _PoolTp, true>
522  : public __per_type_pool<_Tp, _PoolTp, true>
523  {
524  using __per_type_pool<_Tp, _PoolTp, true>::_S_get_pool;
525 
526  static void
527  _S_initialize()
528  { _S_get_pool()._M_initialize_once(); }
529 
530  static void
531  _S_initialize_once()
532  {
533  static bool __init;
534  if (__builtin_expect(__init == false, false))
535  {
536  if (__gthread_active_p())
537  {
538  // On some platforms, __gthread_once_t is an aggregate.
539  static __gthread_once_t __once = __GTHREAD_ONCE_INIT;
540  __gthread_once(&__once, _S_initialize);
541  }
542 
543  // Double check initialization. May be necessary on some
544  // systems for proper construction when not compiling with
545  // thread flags.
546  _S_get_pool()._M_initialize_once();
547  __init = true;
548  }
549  }
550  };
551 #endif
552 
553  /// Policy for individual __pool objects.
554  template<typename _Tp, template <bool> class _PoolTp, bool _Thread>
556  : public __per_type_pool_base<_Tp, _PoolTp, _Thread>
557  {
558  template<typename _Tp1, template <bool> class _PoolTp1 = _PoolTp,
559  bool _Thread1 = _Thread>
560  struct _M_rebind
562 
563  using __per_type_pool_base<_Tp, _PoolTp, _Thread>::_S_get_pool;
564  using __per_type_pool_base<_Tp, _PoolTp, _Thread>::_S_initialize_once;
565  };
566 
567 
568  /// Base class for _Tp dependent member functions.
569  template<typename _Tp>
571  {
572  public:
573  typedef size_t size_type;
574  typedef ptrdiff_t difference_type;
575  typedef _Tp* pointer;
576  typedef const _Tp* const_pointer;
577  typedef _Tp& reference;
578  typedef const _Tp& const_reference;
579  typedef _Tp value_type;
580 
581 #if __cplusplus >= 201103L
582  // _GLIBCXX_RESOLVE_LIB_DEFECTS
583  // 2103. propagate_on_container_move_assignment
585 #endif
586 
587  pointer
588  address(reference __x) const _GLIBCXX_NOEXCEPT
589  { return std::__addressof(__x); }
590 
591  const_pointer
592  address(const_reference __x) const _GLIBCXX_NOEXCEPT
593  { return std::__addressof(__x); }
594 
595  size_type
596  max_size() const _GLIBCXX_USE_NOEXCEPT
597  { return size_t(-1) / sizeof(_Tp); }
598 
599 #if __cplusplus >= 201103L
600  template<typename _Up, typename... _Args>
601  void
602  construct(_Up* __p, _Args&&... __args)
603  { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
604 
605  template<typename _Up>
606  void
607  destroy(_Up* __p) { __p->~_Up(); }
608 #else
609  // _GLIBCXX_RESOLVE_LIB_DEFECTS
610  // 402. wrong new expression in [some_] allocator::construct
611  void
612  construct(pointer __p, const _Tp& __val)
613  { ::new((void *)__p) _Tp(__val); }
614 
615  void
616  destroy(pointer __p) { __p->~_Tp(); }
617 #endif
618  };
619 
620 #ifdef __GTHREADS
621 #define __thread_default true
622 #else
623 #define __thread_default false
624 #endif
625 
626  /**
627  * @brief This is a fixed size (power of 2) allocator which - when
628  * compiled with thread support - will maintain one freelist per
629  * size per thread plus a @a global one. Steps are taken to limit
630  * the per thread freelist sizes (by returning excess back to
631  * the @a global list).
632  * @ingroup allocators
633  *
634  * Further details:
635  * https://gcc.gnu.org/onlinedocs/libstdc++/manual/mt_allocator.html
636  */
637  template<typename _Tp,
639  class __mt_alloc : public __mt_alloc_base<_Tp>
640  {
641  public:
642  typedef size_t size_type;
643  typedef ptrdiff_t difference_type;
644  typedef _Tp* pointer;
645  typedef const _Tp* const_pointer;
646  typedef _Tp& reference;
647  typedef const _Tp& const_reference;
648  typedef _Tp value_type;
649  typedef _Poolp __policy_type;
650  typedef typename _Poolp::pool_type __pool_type;
651 
652  template<typename _Tp1, typename _Poolp1 = _Poolp>
653  struct rebind
654  {
655  typedef typename _Poolp1::template _M_rebind<_Tp1>::other pol_type;
656  typedef __mt_alloc<_Tp1, pol_type> other;
657  };
658 
659  __mt_alloc() _GLIBCXX_USE_NOEXCEPT { }
660 
661  __mt_alloc(const __mt_alloc&) _GLIBCXX_USE_NOEXCEPT { }
662 
663  template<typename _Tp1, typename _Poolp1>
664  __mt_alloc(const __mt_alloc<_Tp1, _Poolp1>&) _GLIBCXX_USE_NOEXCEPT { }
665 
666  ~__mt_alloc() _GLIBCXX_USE_NOEXCEPT { }
667 
668  _GLIBCXX_NODISCARD pointer
669  allocate(size_type __n, const void* = 0);
670 
671  void
672  deallocate(pointer __p, size_type __n);
673 
674  const __pool_base::_Tune
675  _M_get_options()
676  {
677  // Return a copy, not a reference, for external consumption.
678  return __policy_type::_S_get_pool()._M_get_options();
679  }
680 
681  void
682  _M_set_options(__pool_base::_Tune __t)
683  { __policy_type::_S_get_pool()._M_set_options(__t); }
684  };
685 
686  template<typename _Tp, typename _Poolp>
687  _GLIBCXX_NODISCARD typename __mt_alloc<_Tp, _Poolp>::pointer
689  allocate(size_type __n, const void*)
690  {
691  if (__n > this->max_size())
692  std::__throw_bad_alloc();
693 
694 #if __cpp_aligned_new
695  // Types with extended alignment are handled by operator new/delete.
696  if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
697  {
698  std::align_val_t __al = std::align_val_t(alignof(_Tp));
699  return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), __al));
700  }
701 #endif
702 
703  __policy_type::_S_initialize_once();
704 
705  // Requests larger than _M_max_bytes are handled by operator
706  // new/delete directly.
707  __pool_type& __pool = __policy_type::_S_get_pool();
708  const size_t __bytes = __n * sizeof(_Tp);
709  if (__pool._M_check_threshold(__bytes))
710  {
711  void* __ret = ::operator new(__bytes);
712  return static_cast<_Tp*>(__ret);
713  }
714 
715  // Round up to power of 2 and figure out which bin to use.
716  const size_t __which = __pool._M_get_binmap(__bytes);
717  const size_t __thread_id = __pool._M_get_thread_id();
718 
719  // Find out if we have blocks on our freelist. If so, go ahead
720  // and use them directly without having to lock anything.
721  char* __c;
722  typedef typename __pool_type::_Bin_record _Bin_record;
723  const _Bin_record& __bin = __pool._M_get_bin(__which);
724  if (__bin._M_first[__thread_id])
725  {
726  // Already reserved.
727  typedef typename __pool_type::_Block_record _Block_record;
728  _Block_record* __block = __bin._M_first[__thread_id];
729  __bin._M_first[__thread_id] = __block->_M_next;
730 
731  __pool._M_adjust_freelist(__bin, __block, __thread_id);
732  __c = reinterpret_cast<char*>(__block) + __pool._M_get_align();
733  }
734  else
735  {
736  // Null, reserve.
737  __c = __pool._M_reserve_block(__bytes, __thread_id);
738  }
739  return static_cast<_Tp*>(static_cast<void*>(__c));
740  }
741 
742  template<typename _Tp, typename _Poolp>
743  void
744  __mt_alloc<_Tp, _Poolp>::
745  deallocate(pointer __p, size_type __n)
746  {
747  if (__builtin_expect(__p != 0, true))
748  {
749 #if __cpp_aligned_new
750  // Types with extended alignment are handled by operator new/delete.
751  if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
752  {
753  ::operator delete(__p, std::align_val_t(alignof(_Tp)));
754  return;
755  }
756 #endif
757 
758  // Requests larger than _M_max_bytes are handled by
759  // operators new/delete directly.
760  __pool_type& __pool = __policy_type::_S_get_pool();
761  const size_t __bytes = __n * sizeof(_Tp);
762  if (__pool._M_check_threshold(__bytes))
763  ::operator delete(__p);
764  else
765  __pool._M_reclaim_block(reinterpret_cast<char*>(__p), __bytes);
766  }
767  }
768 
769  template<typename _Tp, typename _Poolp>
770  inline bool
771  operator==(const __mt_alloc<_Tp, _Poolp>&, const __mt_alloc<_Tp, _Poolp>&)
772  { return true; }
773 
774  template<typename _Tp, typename _Poolp>
775  inline bool
776  operator!=(const __mt_alloc<_Tp, _Poolp>&, const __mt_alloc<_Tp, _Poolp>&)
777  { return false; }
778 
779 #undef __thread_default
780 
781 _GLIBCXX_END_NAMESPACE_VERSION
782 } // namespace
783 
784 #endif
integral_constant
Definition: type_traits:57
Data describing the underlying memory pool, parameterized on threading support.
Definition: mt_allocator.h:192
Base class for pool object.
Definition: mt_allocator.h:51
Policy for individual __pool objects.
Definition: mt_allocator.h:555
This is a fixed size (power of 2) allocator which - when compiled with thread support - will maintain...
Definition: mt_allocator.h:639
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:47
GNU extensions for public use.
Policy for shared __pool objects.
Definition: mt_allocator.h:460
Base class for _Tp dependent member functions.
Definition: mt_allocator.h:570