1 // MT-optimized allocator -*- C++ -*- 2 3 // Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 4 // Free Software Foundation, Inc. 5 // 6 // This file is part of the GNU ISO C++ Library. This library is free 7 // software; you can redistribute it and/or modify it under the 8 // terms of the GNU General Public License as published by the 9 // Free Software Foundation; either version 3, or (at your option) 10 // any later version. 11 12 // This library is distributed in the hope that it will be useful, 13 // but WITHOUT ANY WARRANTY; without even the implied warranty of 14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 // GNU General Public License for more details. 16 17 // Under Section 7 of GPL version 3, you are granted additional 18 // permissions described in the GCC Runtime Library Exception, version 19 // 3.1, as published by the Free Software Foundation. 20 21 // You should have received a copy of the GNU General Public License and 22 // a copy of the GCC Runtime Library Exception along with this program; 23 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 24 // <http://www.gnu.org/licenses/>. 25 26 /** @file ext/mt_allocator.h 27 * This file is a GNU extension to the Standard C++ Library. 28 */ 29 30 #ifndef _MT_ALLOCATOR_H 31 #define _MT_ALLOCATOR_H 1 32 33 #include <new> 34 #include <cstdlib> 35 #include <bits/functexcept.h> 36 #include <ext/atomicity.h> 37 #include <bits/move.h> 38 39 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx) 40 41 using std::size_t; 42 using std::ptrdiff_t; 43 44 typedef void (*__destroy_handler)(void*); 45 46 /// Base class for pool object. 47 struct __pool_base 48 { 49 // Using short int as type for the binmap implies we are never 50 // caching blocks larger than 32768 with this allocator. 51 typedef unsigned short int _Binmap_type; 52 53 // Variables used to configure the behavior of the allocator, 54 // assigned and explained in detail below. 55 struct _Tune 56 { 57 // Compile time constants for the default _Tune values. 58 enum { _S_align = 8 }; 59 enum { _S_max_bytes = 128 }; 60 enum { _S_min_bin = 8 }; 61 enum { _S_chunk_size = 4096 - 4 * sizeof(void*) }; 62 enum { _S_max_threads = 4096 }; 63 enum { _S_freelist_headroom = 10 }; 64 65 // Alignment needed. 66 // NB: In any case must be >= sizeof(_Block_record), that 67 // is 4 on 32 bit machines and 8 on 64 bit machines. 68 size_t _M_align; 69 70 // Allocation requests (after round-up to power of 2) below 71 // this value will be handled by the allocator. A raw new/ 72 // call will be used for requests larger than this value. 73 // NB: Must be much smaller than _M_chunk_size and in any 74 // case <= 32768. 75 size_t _M_max_bytes; 76 77 // Size in bytes of the smallest bin. 78 // NB: Must be a power of 2 and >= _M_align (and of course 79 // much smaller than _M_max_bytes). 80 size_t _M_min_bin; 81 82 // In order to avoid fragmenting and minimize the number of 83 // new() calls we always request new memory using this 84 // value. Based on previous discussions on the libstdc++ 85 // mailing list we have chosen the value below. 86 // See http://gcc.gnu.org/ml/libstdc++/2001-07/msg00077.html 87 // NB: At least one order of magnitude > _M_max_bytes. 88 size_t _M_chunk_size; 89 90 // The maximum number of supported threads. For 91 // single-threaded operation, use one. Maximum values will 92 // vary depending on details of the underlying system. (For 93 // instance, Linux 2.4.18 reports 4070 in 94 // /proc/sys/kernel/threads-max, while Linux 2.6.6 reports 95 // 65534) 96 size_t _M_max_threads; 97 98 // Each time a deallocation occurs in a threaded application 99 // we make sure that there are no more than 100 // _M_freelist_headroom % of used memory on the freelist. If 101 // the number of additional records is more than 102 // _M_freelist_headroom % of the freelist, we move these 103 // records back to the global pool. 104 size_t _M_freelist_headroom; 105 106 // Set to true forces all allocations to use new(). 107 bool _M_force_new; 108 109 explicit 110 _Tune() 111 : _M_align(_S_align), _M_max_bytes(_S_max_bytes), _M_min_bin(_S_min_bin), 112 _M_chunk_size(_S_chunk_size), _M_max_threads(_S_max_threads), 113 _M_freelist_headroom(_S_freelist_headroom), 114 _M_force_new(std::getenv("GLIBCXX_FORCE_NEW") ? true : false) 115 { } 116 117 explicit 118 _Tune(size_t __align, size_t __maxb, size_t __minbin, size_t __chunk, 119 size_t __maxthreads, size_t __headroom, bool __force) 120 : _M_align(__align), _M_max_bytes(__maxb), _M_min_bin(__minbin), 121 _M_chunk_size(__chunk), _M_max_threads(__maxthreads), 122 _M_freelist_headroom(__headroom), _M_force_new(__force) 123 { } 124 }; 125 126 struct _Block_address 127 { 128 void* _M_initial; 129 _Block_address* _M_next; 130 }; 131 132 const _Tune& 133 _M_get_options() const 134 { return _M_options; } 135 136 void 137 _M_set_options(_Tune __t) 138 { 139 if (!_M_init) 140 _M_options = __t; 141 } 142 143 bool 144 _M_check_threshold(size_t __bytes) 145 { return __bytes > _M_options._M_max_bytes || _M_options._M_force_new; } 146 147 size_t 148 _M_get_binmap(size_t __bytes) 149 { return _M_binmap[__bytes]; } 150 151 size_t 152 _M_get_align() 153 { return _M_options._M_align; } 154 155 explicit 156 __pool_base() 157 : _M_options(_Tune()), _M_binmap(NULL), _M_init(false) { } 158 159 explicit 160 __pool_base(const _Tune& __options) 161 : _M_options(__options), _M_binmap(NULL), _M_init(false) { } 162 163 private: 164 explicit 165 __pool_base(const __pool_base&); 166 167 __pool_base& 168 operator=(const __pool_base&); 169 170 protected: 171 // Configuration options. 172 _Tune _M_options; 173 174 _Binmap_type* _M_binmap; 175 176 // Configuration of the pool object via _M_options can happen 177 // after construction but before initialization. After 178 // initialization is complete, this variable is set to true. 179 bool _M_init; 180 }; 181 182 183 /** 184 * @brief Data describing the underlying memory pool, parameterized on 185 * threading support. 186 */ 187 template<bool _Thread> 188 class __pool; 189 190 /// Specialization for single thread. 191 template<> 192 class __pool<false> : public __pool_base 193 { 194 public: 195 union _Block_record 196 { 197 // Points to the block_record of the next free block. 198 _Block_record* _M_next; 199 }; 200 201 struct _Bin_record 202 { 203 // An "array" of pointers to the first free block. 204 _Block_record** _M_first; 205 206 // A list of the initial addresses of all allocated blocks. 207 _Block_address* _M_address; 208 }; 209 210 void 211 _M_initialize_once() 212 { 213 if (__builtin_expect(_M_init == false, false)) 214 _M_initialize(); 215 } 216 217 void 218 _M_destroy() throw(); 219 220 char* 221 _M_reserve_block(size_t __bytes, const size_t __thread_id); 222 223 void 224 _M_reclaim_block(char* __p, size_t __bytes) throw (); 225 226 size_t 227 _M_get_thread_id() { return 0; } 228 229 const _Bin_record& 230 _M_get_bin(size_t __which) 231 { return _M_bin[__which]; } 232 233 void 234 _M_adjust_freelist(const _Bin_record&, _Block_record*, size_t) 235 { } 236 237 explicit __pool() 238 : _M_bin(NULL), _M_bin_size(1) { } 239 240 explicit __pool(const __pool_base::_Tune& __tune) 241 : __pool_base(__tune), _M_bin(NULL), _M_bin_size(1) { } 242 243 private: 244 // An "array" of bin_records each of which represents a specific 245 // power of 2 size. Memory to this "array" is allocated in 246 // _M_initialize(). 247 _Bin_record* _M_bin; 248 249 // Actual value calculated in _M_initialize(). 250 size_t _M_bin_size; 251 252 void 253 _M_initialize(); 254 }; 255 256 #ifdef __GTHREADS 257 /// Specialization for thread enabled, via gthreads.h. 258 template<> 259 class __pool<true> : public __pool_base 260 { 261 public: 262 // Each requesting thread is assigned an id ranging from 1 to 263 // _S_max_threads. Thread id 0 is used as a global memory pool. 264 // In order to get constant performance on the thread assignment 265 // routine, we keep a list of free ids. When a thread first 266 // requests memory we remove the first record in this list and 267 // stores the address in a __gthread_key. When initializing the 268 // __gthread_key we specify a destructor. When this destructor 269 // (i.e. the thread dies) is called, we return the thread id to 270 // the front of this list. 271 struct _Thread_record 272 { 273 // Points to next free thread id record. NULL if last record in list. 274 _Thread_record* _M_next; 275 276 // Thread id ranging from 1 to _S_max_threads. 277 size_t _M_id; 278 }; 279 280 union _Block_record 281 { 282 // Points to the block_record of the next free block. 283 _Block_record* _M_next; 284 285 // The thread id of the thread which has requested this block. 286 size_t _M_thread_id; 287 }; 288 289 struct _Bin_record 290 { 291 // An "array" of pointers to the first free block for each 292 // thread id. Memory to this "array" is allocated in 293 // _S_initialize() for _S_max_threads + global pool 0. 294 _Block_record** _M_first; 295 296 // A list of the initial addresses of all allocated blocks. 297 _Block_address* _M_address; 298 299 // An "array" of counters used to keep track of the amount of 300 // blocks that are on the freelist/used for each thread id. 301 // - Note that the second part of the allocated _M_used "array" 302 // actually hosts (atomic) counters of reclaimed blocks: in 303 // _M_reserve_block and in _M_reclaim_block those numbers are 304 // subtracted from the first ones to obtain the actual size 305 // of the "working set" of the given thread. 306 // - Memory to these "arrays" is allocated in _S_initialize() 307 // for _S_max_threads + global pool 0. 308 size_t* _M_free; 309 size_t* _M_used; 310 311 // Each bin has its own mutex which is used to ensure data 312 // integrity while changing "ownership" on a block. The mutex 313 // is initialized in _S_initialize(). 314 __gthread_mutex_t* _M_mutex; 315 }; 316 317 // XXX GLIBCXX_ABI Deprecated 318 void 319 _M_initialize(__destroy_handler); 320 321 void 322 _M_initialize_once() 323 { 324 if (__builtin_expect(_M_init == false, false)) 325 _M_initialize(); 326 } 327 328 void 329 _M_destroy() throw(); 330 331 char* 332 _M_reserve_block(size_t __bytes, const size_t __thread_id); 333 334 void 335 _M_reclaim_block(char* __p, size_t __bytes) throw (); 336 337 const _Bin_record& 338 _M_get_bin(size_t __which) 339 { return _M_bin[__which]; } 340 341 void 342 _M_adjust_freelist(const _Bin_record& __bin, _Block_record* __block, 343 size_t __thread_id) 344 { 345 if (__gthread_active_p()) 346 { 347 __block->_M_thread_id = __thread_id; 348 --__bin._M_free[__thread_id]; 349 ++__bin._M_used[__thread_id]; 350 } 351 } 352 353 // XXX GLIBCXX_ABI Deprecated 354 _GLIBCXX_CONST void 355 _M_destroy_thread_key(void*) throw (); 356 357 size_t 358 _M_get_thread_id(); 359 360 explicit __pool() 361 : _M_bin(NULL), _M_bin_size(1), _M_thread_freelist(NULL) 362 { } 363 364 explicit __pool(const __pool_base::_Tune& __tune) 365 : __pool_base(__tune), _M_bin(NULL), _M_bin_size(1), 366 _M_thread_freelist(NULL) 367 { } 368 369 private: 370 // An "array" of bin_records each of which represents a specific 371 // power of 2 size. Memory to this "array" is allocated in 372 // _M_initialize(). 373 _Bin_record* _M_bin; 374 375 // Actual value calculated in _M_initialize(). 376 size_t _M_bin_size; 377 378 _Thread_record* _M_thread_freelist; 379 void* _M_thread_freelist_initial; 380 381 void 382 _M_initialize(); 383 }; 384 #endif 385 386 template<template <bool> class _PoolTp, bool _Thread> 387 struct __common_pool 388 { 389 typedef _PoolTp<_Thread> pool_type; 390 391 static pool_type& 392 _S_get_pool() 393 { 394 static pool_type _S_pool; 395 return _S_pool; 396 } 397 }; 398 399 template<template <bool> class _PoolTp, bool _Thread> 400 struct __common_pool_base; 401 402 template<template <bool> class _PoolTp> 403 struct __common_pool_base<_PoolTp, false> 404 : public __common_pool<_PoolTp, false> 405 { 406 using __common_pool<_PoolTp, false>::_S_get_pool; 407 408 static void 409 _S_initialize_once() 410 { 411 static bool __init; 412 if (__builtin_expect(__init == false, false)) 413 { 414 _S_get_pool()._M_initialize_once(); 415 __init = true; 416 } 417 } 418 }; 419 420 #ifdef __GTHREADS 421 template<template <bool> class _PoolTp> 422 struct __common_pool_base<_PoolTp, true> 423 : public __common_pool<_PoolTp, true> 424 { 425 using __common_pool<_PoolTp, true>::_S_get_pool; 426 427 static void 428 _S_initialize() 429 { _S_get_pool()._M_initialize_once(); } 430 431 static void 432 _S_initialize_once() 433 { 434 static bool __init; 435 if (__builtin_expect(__init == false, false)) 436 { 437 if (__gthread_active_p()) 438 { 439 // On some platforms, __gthread_once_t is an aggregate. 440 static __gthread_once_t __once = __GTHREAD_ONCE_INIT; 441 __gthread_once(&__once, _S_initialize); 442 } 443 444 // Double check initialization. May be necessary on some 445 // systems for proper construction when not compiling with 446 // thread flags. 447 _S_get_pool()._M_initialize_once(); 448 __init = true; 449 } 450 } 451 }; 452 #endif 453 454 /// Policy for shared __pool objects. 455 template<template <bool> class _PoolTp, bool _Thread> 456 struct __common_pool_policy : public __common_pool_base<_PoolTp, _Thread> 457 { 458 template<typename _Tp1, template <bool> class _PoolTp1 = _PoolTp, 459 bool _Thread1 = _Thread> 460 struct _M_rebind 461 { typedef __common_pool_policy<_PoolTp1, _Thread1> other; }; 462 463 using __common_pool_base<_PoolTp, _Thread>::_S_get_pool; 464 using __common_pool_base<_PoolTp, _Thread>::_S_initialize_once; 465 }; 466 467 468 template<typename _Tp, template <bool> class _PoolTp, bool _Thread> 469 struct __per_type_pool 470 { 471 typedef _Tp value_type; 472 typedef _PoolTp<_Thread> pool_type; 473 474 static pool_type& 475 _S_get_pool() 476 { 477 // Sane defaults for the _PoolTp. 478 typedef typename pool_type::_Block_record _Block_record; 479 const static size_t __a = (__alignof__(_Tp) >= sizeof(_Block_record) 480 ? __alignof__(_Tp) : sizeof(_Block_record)); 481 482 typedef typename __pool_base::_Tune _Tune; 483 static _Tune _S_tune(__a, sizeof(_Tp) * 64, 484 sizeof(_Tp) * 2 >= __a ? sizeof(_Tp) * 2 : __a, 485 sizeof(_Tp) * size_t(_Tune::_S_chunk_size), 486 _Tune::_S_max_threads, 487 _Tune::_S_freelist_headroom, 488 std::getenv("GLIBCXX_FORCE_NEW") ? true : false); 489 static pool_type _S_pool(_S_tune); 490 return _S_pool; 491 } 492 }; 493 494 template<typename _Tp, template <bool> class _PoolTp, bool _Thread> 495 struct __per_type_pool_base; 496 497 template<typename _Tp, template <bool> class _PoolTp> 498 struct __per_type_pool_base<_Tp, _PoolTp, false> 499 : public __per_type_pool<_Tp, _PoolTp, false> 500 { 501 using __per_type_pool<_Tp, _PoolTp, false>::_S_get_pool; 502 503 static void 504 _S_initialize_once() 505 { 506 static bool __init; 507 if (__builtin_expect(__init == false, false)) 508 { 509 _S_get_pool()._M_initialize_once(); 510 __init = true; 511 } 512 } 513 }; 514 515 #ifdef __GTHREADS 516 template<typename _Tp, template <bool> class _PoolTp> 517 struct __per_type_pool_base<_Tp, _PoolTp, true> 518 : public __per_type_pool<_Tp, _PoolTp, true> 519 { 520 using __per_type_pool<_Tp, _PoolTp, true>::_S_get_pool; 521 522 static void 523 _S_initialize() 524 { _S_get_pool()._M_initialize_once(); } 525 526 static void 527 _S_initialize_once() 528 { 529 static bool __init; 530 if (__builtin_expect(__init == false, false)) 531 { 532 if (__gthread_active_p()) 533 { 534 // On some platforms, __gthread_once_t is an aggregate. 535 static __gthread_once_t __once = __GTHREAD_ONCE_INIT; 536 __gthread_once(&__once, _S_initialize); 537 } 538 539 // Double check initialization. May be necessary on some 540 // systems for proper construction when not compiling with 541 // thread flags. 542 _S_get_pool()._M_initialize_once(); 543 __init = true; 544 } 545 } 546 }; 547 #endif 548 549 /// Policy for individual __pool objects. 550 template<typename _Tp, template <bool> class _PoolTp, bool _Thread> 551 struct __per_type_pool_policy 552 : public __per_type_pool_base<_Tp, _PoolTp, _Thread> 553 { 554 template<typename _Tp1, template <bool> class _PoolTp1 = _PoolTp, 555 bool _Thread1 = _Thread> 556 struct _M_rebind 557 { typedef __per_type_pool_policy<_Tp1, _PoolTp1, _Thread1> other; }; 558 559 using __per_type_pool_base<_Tp, _PoolTp, _Thread>::_S_get_pool; 560 using __per_type_pool_base<_Tp, _PoolTp, _Thread>::_S_initialize_once; 561 }; 562 563 564 /// Base class for _Tp dependent member functions. 565 template<typename _Tp> 566 class __mt_alloc_base 567 { 568 public: 569 typedef size_t size_type; 570 typedef ptrdiff_t difference_type; 571 typedef _Tp* pointer; 572 typedef const _Tp* const_pointer; 573 typedef _Tp& reference; 574 typedef const _Tp& const_reference; 575 typedef _Tp value_type; 576 577 pointer 578 address(reference __x) const 579 { return &__x; } 580 581 const_pointer 582 address(const_reference __x) const 583 { return &__x; } 584 585 size_type 586 max_size() const throw() 587 { return size_t(-1) / sizeof(_Tp); } 588 589 // _GLIBCXX_RESOLVE_LIB_DEFECTS 590 // 402. wrong new expression in [some_] allocator::construct 591 void 592 construct(pointer __p, const _Tp& __val) 593 { ::new((void *)__p) _Tp(__val); } 594 595 #ifdef __GXX_EXPERIMENTAL_CXX0X__ 596 template<typename... _Args> 597 void 598 construct(pointer __p, _Args&&... __args) 599 { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); } 600 #endif 601 602 void 603 destroy(pointer __p) { __p->~_Tp(); } 604 }; 605 606 #ifdef __GTHREADS 607 #define __thread_default true 608 #else 609 #define __thread_default false 610 #endif 611 612 /** 613 * @brief This is a fixed size (power of 2) allocator which - when 614 * compiled with thread support - will maintain one freelist per 615 * size per thread plus a @a global one. Steps are taken to limit 616 * the per thread freelist sizes (by returning excess back to 617 * the @a global list). 618 * @ingroup allocators 619 * 620 * Further details: 621 * http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt12ch32.html 622 */ 623 template<typename _Tp, 624 typename _Poolp = __common_pool_policy<__pool, __thread_default> > 625 class __mt_alloc : public __mt_alloc_base<_Tp> 626 { 627 public: 628 typedef size_t size_type; 629 typedef ptrdiff_t difference_type; 630 typedef _Tp* pointer; 631 typedef const _Tp* const_pointer; 632 typedef _Tp& reference; 633 typedef const _Tp& const_reference; 634 typedef _Tp value_type; 635 typedef _Poolp __policy_type; 636 typedef typename _Poolp::pool_type __pool_type; 637 638 template<typename _Tp1, typename _Poolp1 = _Poolp> 639 struct rebind 640 { 641 typedef typename _Poolp1::template _M_rebind<_Tp1>::other pol_type; 642 typedef __mt_alloc<_Tp1, pol_type> other; 643 }; 644 645 __mt_alloc() throw() { } 646 647 __mt_alloc(const __mt_alloc&) throw() { } 648 649 template<typename _Tp1, typename _Poolp1> 650 __mt_alloc(const __mt_alloc<_Tp1, _Poolp1>&) throw() { } 651 652 ~__mt_alloc() throw() { } 653 654 pointer 655 allocate(size_type __n, const void* = 0); 656 657 void 658 deallocate(pointer __p, size_type __n); 659 660 const __pool_base::_Tune 661 _M_get_options() 662 { 663 // Return a copy, not a reference, for external consumption. 664 return __policy_type::_S_get_pool()._M_get_options(); 665 } 666 667 void 668 _M_set_options(__pool_base::_Tune __t) 669 { __policy_type::_S_get_pool()._M_set_options(__t); } 670 }; 671 672 template<typename _Tp, typename _Poolp> 673 typename __mt_alloc<_Tp, _Poolp>::pointer 674 __mt_alloc<_Tp, _Poolp>:: 675 allocate(size_type __n, const void*) 676 { 677 if (__n > this->max_size()) 678 std::__throw_bad_alloc(); 679 680 __policy_type::_S_initialize_once(); 681 682 // Requests larger than _M_max_bytes are handled by operator 683 // new/delete directly. 684 __pool_type& __pool = __policy_type::_S_get_pool(); 685 const size_t __bytes = __n * sizeof(_Tp); 686 if (__pool._M_check_threshold(__bytes)) 687 { 688 void* __ret = ::operator new(__bytes); 689 return static_cast<_Tp*>(__ret); 690 } 691 692 // Round up to power of 2 and figure out which bin to use. 693 const size_t __which = __pool._M_get_binmap(__bytes); 694 const size_t __thread_id = __pool._M_get_thread_id(); 695 696 // Find out if we have blocks on our freelist. If so, go ahead 697 // and use them directly without having to lock anything. 698 char* __c; 699 typedef typename __pool_type::_Bin_record _Bin_record; 700 const _Bin_record& __bin = __pool._M_get_bin(__which); 701 if (__bin._M_first[__thread_id]) 702 { 703 // Already reserved. 704 typedef typename __pool_type::_Block_record _Block_record; 705 _Block_record* __block = __bin._M_first[__thread_id]; 706 __bin._M_first[__thread_id] = __block->_M_next; 707 708 __pool._M_adjust_freelist(__bin, __block, __thread_id); 709 __c = reinterpret_cast<char*>(__block) + __pool._M_get_align(); 710 } 711 else 712 { 713 // Null, reserve. 714 __c = __pool._M_reserve_block(__bytes, __thread_id); 715 } 716 return static_cast<_Tp*>(static_cast<void*>(__c)); 717 } 718 719 template<typename _Tp, typename _Poolp> 720 void 721 __mt_alloc<_Tp, _Poolp>:: 722 deallocate(pointer __p, size_type __n) 723 { 724 if (__builtin_expect(__p != 0, true)) 725 { 726 // Requests larger than _M_max_bytes are handled by 727 // operators new/delete directly. 728 __pool_type& __pool = __policy_type::_S_get_pool(); 729 const size_t __bytes = __n * sizeof(_Tp); 730 if (__pool._M_check_threshold(__bytes)) 731 ::operator delete(__p); 732 else 733 __pool._M_reclaim_block(reinterpret_cast<char*>(__p), __bytes); 734 } 735 } 736 737 template<typename _Tp, typename _Poolp> 738 inline bool 739 operator==(const __mt_alloc<_Tp, _Poolp>&, const __mt_alloc<_Tp, _Poolp>&) 740 { return true; } 741 742 template<typename _Tp, typename _Poolp> 743 inline bool 744 operator!=(const __mt_alloc<_Tp, _Poolp>&, const __mt_alloc<_Tp, _Poolp>&) 745 { return false; } 746 747 #undef __thread_default 748 749 _GLIBCXX_END_NAMESPACE 750 751 #endif 752