libstdc++-v3/include/std/mutex

   1 // <mutex> -*- 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 include/mutex
  27  *  This is a Standard C++ Library header.
  28  */
  29
  30 #ifndef _GLIBCXX_MUTEX
  31 #define _GLIBCXX_MUTEX 1
  32
  33 #pragma GCC system_header
  34
  35 #ifndef __GXX_EXPERIMENTAL_CXX0X__
  36 # include <bits/c++0x_warning.h>
  37 #else
  38
  39 #include <tuple>
  40 #include <chrono>
  41 #include <exception>
  42 #include <type_traits>
  43 #include <functional>
  44 #include <system_error>
  45 #include <bits/functexcept.h>
  46 #include <bits/gthr.h>
  47 #include <bits/move.h> // for std::swap
  48
  49 #if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1)
  50
  51 _GLIBCXX_BEGIN_NAMESPACE(std)
  52
  53   /**
  54    * @defgroup mutexes Mutexes
  55    * @ingroup concurrency
  56    *
  57    * Classes for mutex support.
  58    * @{
  59    */
  60
  61   /// mutex
  62   class mutex
  63   {
  64     typedef __gthread_mutex_t                   __native_type;
  65     __native_type  _M_mutex;
  66
  67   public:
  68     typedef __native_type*                      native_handle_type;
  69
  70 #ifdef __GTHREAD_MUTEX_INIT
  71     constexpr mutex() : _M_mutex(__GTHREAD_MUTEX_INIT) { }
  72 #else
  73     mutex()
  74     {
  75       // XXX EAGAIN, ENOMEM, EPERM, EBUSY(may), EINVAL(may)
  76       __GTHREAD_MUTEX_INIT_FUNCTION(&_M_mutex);
  77     }
  78
  79     ~mutex() { __gthread_mutex_destroy(&_M_mutex); }
  80 #endif
  81
  82     mutex(const mutex&) = delete;
  83     mutex& operator=(const mutex&) = delete;
  84
  85     void
  86     lock()
  87     {
  88       int __e = __gthread_mutex_lock(&_M_mutex);
  89
  90       // EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)
  91       if (__e)
  92         __throw_system_error(__e);
  93     }
  94
  95     bool
  96     try_lock()
  97     {
  98       // XXX EINVAL, EAGAIN, EBUSY
  99       return !__gthread_mutex_trylock(&_M_mutex);
 100     }
 101
 102     void
 103     unlock()
 104     {
 105       // XXX EINVAL, EAGAIN, EPERM
 106       __gthread_mutex_unlock(&_M_mutex);
 107     }
 108
 109     native_handle_type
 110     native_handle()
 111     { return &_M_mutex; }
 112   };
 113
 114 #ifndef __GTHREAD_RECURSIVE_MUTEX_INIT
 115   // FIXME: gthreads doesn't define __gthread_recursive_mutex_destroy
 116   // so we need to obtain a __gthread_mutex_t to destroy
 117   class __destroy_recursive_mutex
 118   {
 119     template<typename _Mx, typename _Rm>
 120       static void
 121       _S_destroy_win32(_Mx* __mx, _Rm const* __rmx)
 122       {
 123         __mx->counter = __rmx->counter;
 124         __mx->sema = __rmx->sema;
 125         __gthread_mutex_destroy(__mx);
 126       }
 127
 128   public:
 129     // matches a gthr-win32.h recursive mutex
 130     template<typename _Rm>
 131       static typename enable_if<sizeof(&_Rm::sema), void>::type
 132       _S_destroy(_Rm* __mx)
 133       {
 134         __gthread_mutex_t __tmp;
 135         _S_destroy_win32(&__tmp, __mx);
 136       }
 137
 138     // matches a recursive mutex with a member 'actual'
 139     template<typename _Rm>
 140       static typename enable_if<sizeof(&_Rm::actual), void>::type
 141       _S_destroy(_Rm* __mx)
 142       { __gthread_mutex_destroy(&__mx->actual); }
 143
 144     // matches when there's only one mutex type
 145     template<typename _Rm>
 146       static
 147       typename enable_if<is_same<_Rm, __gthread_mutex_t>::value, void>::type
 148       _S_destroy(_Rm* __mx)
 149       { __gthread_mutex_destroy(__mx); }
 150   };
 151 #endif
 152
 153   /// recursive_mutex
 154   class recursive_mutex
 155   {
 156     typedef __gthread_recursive_mutex_t         __native_type;
 157     __native_type  _M_mutex;
 158
 159   public:
 160     typedef __native_type*                      native_handle_type;
 161
 162 #ifdef __GTHREAD_RECURSIVE_MUTEX_INIT
 163     recursive_mutex() : _M_mutex(__GTHREAD_RECURSIVE_MUTEX_INIT) { }
 164 #else
 165     recursive_mutex()
 166     {
 167       // XXX EAGAIN, ENOMEM, EPERM, EBUSY(may), EINVAL(may)
 168       __GTHREAD_RECURSIVE_MUTEX_INIT_FUNCTION(&_M_mutex);
 169     }
 170
 171     ~recursive_mutex()
 172     { __destroy_recursive_mutex::_S_destroy(&_M_mutex); }
 173 #endif
 174
 175     recursive_mutex(const recursive_mutex&) = delete;
 176     recursive_mutex& operator=(const recursive_mutex&) = delete;
 177
 178     void
 179     lock()
 180     {
 181       int __e = __gthread_recursive_mutex_lock(&_M_mutex);
 182
 183       // EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)
 184       if (__e)
 185         __throw_system_error(__e);
 186     }
 187
 188     bool
 189     try_lock()
 190     {
 191       // XXX EINVAL, EAGAIN, EBUSY
 192       return !__gthread_recursive_mutex_trylock(&_M_mutex);
 193     }
 194
 195     void
 196     unlock()
 197     {
 198       // XXX EINVAL, EAGAIN, EBUSY
 199       __gthread_recursive_mutex_unlock(&_M_mutex);
 200     }
 201
 202     native_handle_type
 203     native_handle()
 204     { return &_M_mutex; }
 205   };
 206
 207   /// timed_mutex
 208   class timed_mutex
 209   {
 210     typedef __gthread_mutex_t                   __native_type;
 211
 212 #ifdef _GLIBCXX_USE_CLOCK_MONOTONIC
 213     typedef chrono::monotonic_clock             __clock_t;
 214 #else
 215     typedef chrono::high_resolution_clock       __clock_t;
 216 #endif
 217
 218     __native_type  _M_mutex;
 219
 220   public:
 221     typedef __native_type*                      native_handle_type;
 222
 223 #ifdef __GTHREAD_MUTEX_INIT
 224     timed_mutex() : _M_mutex(__GTHREAD_MUTEX_INIT) { }
 225 #else
 226     timed_mutex()
 227     {
 228       __GTHREAD_MUTEX_INIT_FUNCTION(&_M_mutex);
 229     }
 230
 231     ~timed_mutex() { __gthread_mutex_destroy(&_M_mutex); }
 232 #endif
 233
 234     timed_mutex(const timed_mutex&) = delete;
 235     timed_mutex& operator=(const timed_mutex&) = delete;
 236
 237     void
 238     lock()
 239     {
 240       int __e = __gthread_mutex_lock(&_M_mutex);
 241
 242       // EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)
 243       if (__e)
 244         __throw_system_error(__e);
 245     }
 246
 247     bool
 248     try_lock()
 249     {
 250       // XXX EINVAL, EAGAIN, EBUSY
 251       return !__gthread_mutex_trylock(&_M_mutex);
 252     }
 253
 254     template <class _Rep, class _Period>
 255       bool
 256       try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
 257       { return __try_lock_for_impl(__rtime); }
 258
 259     template <class _Clock, class _Duration>
 260       bool
 261       try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
 262       {
 263         chrono::time_point<_Clock, chrono::seconds> __s =
 264           chrono::time_point_cast<chrono::seconds>(__atime);
 265
 266         chrono::nanoseconds __ns =
 267           chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
 268
 269         __gthread_time_t __ts = {
 270           static_cast<std::time_t>(__s.time_since_epoch().count()),
 271           static_cast<long>(__ns.count())
 272         };
 273
 274         return !__gthread_mutex_timedlock(&_M_mutex, &__ts);
 275       }
 276
 277     void
 278     unlock()
 279     {
 280       // XXX EINVAL, EAGAIN, EBUSY
 281       __gthread_mutex_unlock(&_M_mutex);
 282     }
 283
 284     native_handle_type
 285     native_handle()
 286     { return &_M_mutex; }
 287
 288   private:
 289     template<typename _Rep, typename _Period>
 290       typename enable_if<
 291         ratio_less_equal<__clock_t::period, _Period>::value, bool>::type
 292       __try_lock_for_impl(const chrono::duration<_Rep, _Period>& __rtime)
 293       {
 294         __clock_t::time_point __atime = __clock_t::now()
 295           + chrono::duration_cast<__clock_t::duration>(__rtime);
 296
 297         return try_lock_until(__atime);
 298       }
 299
 300     template <typename _Rep, typename _Period>
 301       typename enable_if<
 302         !ratio_less_equal<__clock_t::period, _Period>::value, bool>::type
 303       __try_lock_for_impl(const chrono::duration<_Rep, _Period>& __rtime)
 304       {
 305         __clock_t::time_point __atime = __clock_t::now()
 306           + ++chrono::duration_cast<__clock_t::duration>(__rtime);
 307
 308         return try_lock_until(__atime);
 309       }
 310   };
 311
 312   /// recursive_timed_mutex
 313   class recursive_timed_mutex
 314   {
 315     typedef __gthread_recursive_mutex_t         __native_type;
 316
 317 #ifdef _GLIBCXX_USE_CLOCK_MONOTONIC
 318     typedef chrono::monotonic_clock             __clock_t;
 319 #else
 320     typedef chrono::high_resolution_clock       __clock_t;
 321 #endif
 322
 323     __native_type  _M_mutex;
 324
 325   public:
 326     typedef __native_type*                      native_handle_type;
 327
 328 #ifdef __GTHREAD_RECURSIVE_MUTEX_INIT
 329     recursive_timed_mutex() : _M_mutex(__GTHREAD_RECURSIVE_MUTEX_INIT) { }
 330 #else
 331     recursive_timed_mutex()
 332     {
 333       // XXX EAGAIN, ENOMEM, EPERM, EBUSY(may), EINVAL(may)
 334       __GTHREAD_RECURSIVE_MUTEX_INIT_FUNCTION(&_M_mutex);
 335     }
 336
 337     ~recursive_timed_mutex()
 338     { __destroy_recursive_mutex::_S_destroy(&_M_mutex); }
 339 #endif
 340
 341     recursive_timed_mutex(const recursive_timed_mutex&) = delete;
 342     recursive_timed_mutex& operator=(const recursive_timed_mutex&) = delete;
 343
 344     void
 345     lock()
 346     {
 347       int __e = __gthread_recursive_mutex_lock(&_M_mutex);
 348
 349       // EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)
 350       if (__e)
 351         __throw_system_error(__e);
 352     }
 353
 354     bool
 355     try_lock()
 356     {
 357       // XXX EINVAL, EAGAIN, EBUSY
 358       return !__gthread_recursive_mutex_trylock(&_M_mutex);
 359     }
 360
 361     template <class _Rep, class _Period>
 362       bool
 363       try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
 364       { return __try_lock_for_impl(__rtime); }
 365
 366     template <class _Clock, class _Duration>
 367       bool
 368       try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
 369       {
 370         chrono::time_point<_Clock, chrono::seconds>  __s =
 371           chrono::time_point_cast<chrono::seconds>(__atime);
 372
 373         chrono::nanoseconds __ns =
 374           chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
 375
 376         __gthread_time_t __ts = {
 377           static_cast<std::time_t>(__s.time_since_epoch().count()),
 378           static_cast<long>(__ns.count())
 379         };
 380
 381         return !__gthread_recursive_mutex_timedlock(&_M_mutex, &__ts);
 382       }
 383
 384     void
 385     unlock()
 386     {
 387       // XXX EINVAL, EAGAIN, EBUSY
 388       __gthread_recursive_mutex_unlock(&_M_mutex);
 389     }
 390
 391     native_handle_type
 392     native_handle()
 393     { return &_M_mutex; }
 394
 395   private:
 396     template<typename _Rep, typename _Period>
 397       typename enable_if<
 398         ratio_less_equal<__clock_t::period, _Period>::value, bool>::type
 399       __try_lock_for_impl(const chrono::duration<_Rep, _Period>& __rtime)
 400       {
 401         __clock_t::time_point __atime = __clock_t::now()
 402           + chrono::duration_cast<__clock_t::duration>(__rtime);
 403
 404         return try_lock_until(__atime);
 405       }
 406
 407     template <typename _Rep, typename _Period>
 408       typename enable_if<
 409         !ratio_less_equal<__clock_t::period, _Period>::value, bool>::type
 410       __try_lock_for_impl(const chrono::duration<_Rep, _Period>& __rtime)
 411       {
 412         __clock_t::time_point __atime = __clock_t::now()
 413           + ++chrono::duration_cast<__clock_t::duration>(__rtime);
 414
 415         return try_lock_until(__atime);
 416       }
 417   };
 418
 419   /// Do not acquire ownership of the mutex.
 420   struct defer_lock_t { };
 421
 422   /// Try to acquire ownership of the mutex without blocking.
 423   struct try_to_lock_t { };
 424
 425   /// Assume the calling thread has already obtained mutex ownership
 426   /// and manage it.
 427   struct adopt_lock_t { };
 428
 429   constexpr defer_lock_t        defer_lock { };
 430   constexpr try_to_lock_t       try_to_lock { };
 431   constexpr adopt_lock_t        adopt_lock { };
 432
 433   /// @brief  Scoped lock idiom.
 434   // Acquire the mutex here with a constructor call, then release with
 435   // the destructor call in accordance with RAII style.
 436   template<typename _Mutex>
 437     class lock_guard
 438     {
 439     public:
 440       typedef _Mutex mutex_type;
 441
 442       explicit lock_guard(mutex_type& __m) : _M_device(__m)
 443       { _M_device.lock(); }
 444
 445       lock_guard(mutex_type& __m, adopt_lock_t) : _M_device(__m)
 446       { } // calling thread owns mutex
 447
 448       ~lock_guard()
 449       { _M_device.unlock(); }
 450
 451       lock_guard(const lock_guard&) = delete;
 452       lock_guard& operator=(const lock_guard&) = delete;
 453
 454     private:
 455       mutex_type&  _M_device;
 456     };
 457
 458   /// unique_lock
 459   template<typename _Mutex>
 460     class unique_lock
 461     {
 462     public:
 463       typedef _Mutex mutex_type;
 464
 465       unique_lock()
 466       : _M_device(0), _M_owns(false)
 467       { }
 468
 469       explicit unique_lock(mutex_type& __m)
 470       : _M_device(&__m), _M_owns(false)
 471       {
 472         lock();
 473         _M_owns = true;
 474       }
 475
 476       unique_lock(mutex_type& __m, defer_lock_t)
 477       : _M_device(&__m), _M_owns(false)
 478       { }
 479
 480       unique_lock(mutex_type& __m, try_to_lock_t)
 481       : _M_device(&__m), _M_owns(_M_device->try_lock())
 482       { }
 483
 484       unique_lock(mutex_type& __m, adopt_lock_t)
 485       : _M_device(&__m), _M_owns(true)
 486       {
 487         // XXX calling thread owns mutex
 488       }
 489
 490       template<typename _Clock, typename _Duration>
 491         unique_lock(mutex_type& __m,
 492                     const chrono::time_point<_Clock, _Duration>& __atime)
 493         : _M_device(&__m), _M_owns(_M_device->try_lock_until(__atime))
 494         { }
 495
 496       template<typename _Rep, typename _Period>
 497         unique_lock(mutex_type& __m,
 498                     const chrono::duration<_Rep, _Period>& __rtime)
 499         : _M_device(&__m), _M_owns(_M_device->try_lock_for(__rtime))
 500         { }
 501
 502       ~unique_lock()
 503       {
 504         if (_M_owns)
 505           unlock();
 506       }
 507
 508       unique_lock(const unique_lock&) = delete;
 509       unique_lock& operator=(const unique_lock&) = delete;
 510
 511       unique_lock(unique_lock&& __u)
 512       : _M_device(__u._M_device), _M_owns(__u._M_owns)
 513       {
 514         __u._M_device = 0;
 515         __u._M_owns = false;
 516       }
 517
 518       unique_lock& operator=(unique_lock&& __u)
 519       {
 520         if(_M_owns)
 521           unlock();
 522
 523         unique_lock(std::move(__u)).swap(*this);
 524
 525         __u._M_device = 0;
 526         __u._M_owns = false;
 527
 528         return *this;
 529       }
 530
 531       void
 532       lock()
 533       {
 534         if (!_M_device)
 535           __throw_system_error(int(errc::operation_not_permitted));
 536         else if (_M_owns)
 537           __throw_system_error(int(errc::resource_deadlock_would_occur));
 538         else
 539           {
 540             _M_device->lock();
 541             _M_owns = true;
 542           }
 543       }
 544
 545       bool
 546       try_lock()
 547       {
 548         if (!_M_device)
 549           __throw_system_error(int(errc::operation_not_permitted));
 550         else if (_M_owns)
 551           __throw_system_error(int(errc::resource_deadlock_would_occur));
 552         else
 553           {
 554             _M_owns = _M_device->try_lock();
 555             return _M_owns;
 556           }
 557       }
 558
 559       template<typename _Clock, typename _Duration>
 560         bool
 561         try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
 562         {
 563           if (!_M_device)
 564             __throw_system_error(int(errc::operation_not_permitted));
 565           else if (_M_owns)
 566             __throw_system_error(int(errc::resource_deadlock_would_occur));
 567           else
 568             {
 569               _M_owns = _M_device->try_lock_until(__atime);
 570               return _M_owns;
 571             }
 572         }
 573
 574       template<typename _Rep, typename _Period>
 575         bool
 576         try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
 577         {
 578           if (!_M_device)
 579             __throw_system_error(int(errc::operation_not_permitted));
 580           else if (_M_owns)
 581             __throw_system_error(int(errc::resource_deadlock_would_occur));
 582           else
 583             {
 584               _M_owns = _M_device->try_lock_for(__rtime);
 585               return _M_owns;
 586             }
 587          }
 588
 589       void
 590       unlock()
 591       {
 592         if (!_M_owns)
 593           __throw_system_error(int(errc::operation_not_permitted));
 594         else if (_M_device)
 595           {
 596             _M_device->unlock();
 597             _M_owns = false;
 598           }
 599       }
 600
 601       void
 602       swap(unique_lock& __u)
 603       {
 604         std::swap(_M_device, __u._M_device);
 605         std::swap(_M_owns, __u._M_owns);
 606       }
 607
 608       mutex_type*
 609       release()
 610       {
 611         mutex_type* __ret = _M_device;
 612         _M_device = 0;
 613         _M_owns = false;
 614         return __ret;
 615       }
 616
 617       bool
 618       owns_lock() const
 619       { return _M_owns; }
 620
 621       explicit operator bool() const
 622       { return owns_lock(); }
 623
 624       mutex_type*
 625       mutex() const
 626       { return _M_device; }
 627
 628     private:
 629       mutex_type*       _M_device;
 630       bool              _M_owns; // XXX use atomic_bool
 631     };
 632
 633   template<typename _Mutex>
 634     inline void
 635     swap(unique_lock<_Mutex>& __x, unique_lock<_Mutex>& __y)
 636     { __x.swap(__y); }
 637
 638   template<int _Idx>
 639     struct __unlock_impl
 640     {
 641       template<typename... _Lock>
 642         static void
 643         __do_unlock(tuple<_Lock&...>& __locks)
 644         {
 645           std::get<_Idx>(__locks).unlock();
 646           __unlock_impl<_Idx - 1>::__do_unlock(__locks);
 647         }
 648     };
 649
 650   template<>
 651     struct __unlock_impl<-1>
 652     {
 653       template<typename... _Lock>
 654         static void
 655         __do_unlock(tuple<_Lock&...>&)
 656         { }
 657     };
 658
 659   template<typename _Lock>
 660     unique_lock<_Lock>
 661     __try_to_lock(_Lock& __l)
 662     { return unique_lock<_Lock>(__l, try_to_lock); }
 663
 664   template<int _Idx, bool _Continue = true>
 665     struct __try_lock_impl
 666     {
 667       template<typename... _Lock>
 668         static void
 669         __do_try_lock(tuple<_Lock&...>& __locks, int& __idx)
 670         {
 671           __idx = _Idx;
 672           auto __lock = __try_to_lock(std::get<_Idx>(__locks));
 673           if (__lock.owns_lock())
 674             {
 675               __try_lock_impl<_Idx + 1, _Idx + 2 < sizeof...(_Lock)>::
 676                 __do_try_lock(__locks, __idx);
 677               if (__idx == -1)
 678                 __lock.release();
 679             }
 680         }
 681     };
 682
 683   template<int _Idx>
 684     struct __try_lock_impl<_Idx, false>
 685     {
 686       template<typename... _Lock>
 687         static void
 688         __do_try_lock(tuple<_Lock&...>& __locks, int& __idx)
 689         {
 690           __idx = _Idx;
 691           auto __lock = __try_to_lock(std::get<_Idx>(__locks));
 692           if (__lock.owns_lock())
 693             {
 694               __idx = -1;
 695               __lock.release();
 696             }
 697         }
 698     };
 699
 700   /** @brief Generic try_lock.
 701    *  @param __l1 Meets Mutex requirements (try_lock() may throw).
 702    *  @param __l2 Meets Mutex requirements (try_lock() may throw).
 703    *  @param __l3 Meets Mutex requirements (try_lock() may throw).
 704    *  @return Returns -1 if all try_lock() calls return true. Otherwise returns
 705    *          a 0-based index corresponding to the argument that returned false.
 706    *  @post Either all arguments are locked, or none will be.
 707    *
 708    *  Sequentially calls try_lock() on each argument.
 709    */
 710   template<typename _Lock1, typename _Lock2, typename... _Lock3>
 711     int
 712     try_lock(_Lock1& __l1, _Lock2& __l2, _Lock3&... __l3)
 713     {
 714       int __idx;
 715       auto __locks = std::tie(__l1, __l2, __l3...);
 716       __try
 717       { __try_lock_impl<0>::__do_try_lock(__locks, __idx); }
 718       __catch(...)
 719       { }
 720       return __idx;
 721     }
 722
 723   /** @brief Generic lock.
 724    *  @param __l1 Meets Mutex requirements (try_lock() may throw).
 725    *  @param __l2 Meets Mutex requirements (try_lock() may throw).
 726    *  @param __l3 Meets Mutex requirements (try_lock() may throw).
 727    *  @throw An exception thrown by an argument's lock() or try_lock() member.
 728    *  @post All arguments are locked.
 729    *
 730    *  All arguments are locked via a sequence of calls to lock(), try_lock()
 731    *  and unlock().  If the call exits via an exception any locks that were
 732    *  obtained will be released.
 733    */
 734   template<typename _L1, typename _L2, typename ..._L3>
 735     void
 736     lock(_L1& __l1, _L2& __l2, _L3&... __l3)
 737     {
 738       while (true)
 739         {
 740           unique_lock<_L1> __first(__l1);
 741           int __idx;
 742           auto __locks = std::tie(__l2, __l3...);
 743           __try_lock_impl<0, sizeof...(_L3)>::__do_try_lock(__locks, __idx);
 744           if (__idx == -1)
 745             {
 746               __first.release();
 747               return;
 748             }
 749         }
 750     }
 751
 752   /// once_flag
 753   struct once_flag
 754   {
 755   private:
 756     typedef __gthread_once_t __native_type;
 757     __native_type  _M_once;
 758
 759   public:
 760     constexpr once_flag() : _M_once(__GTHREAD_ONCE_INIT) { }
 761
 762     once_flag(const once_flag&) = delete;
 763     once_flag& operator=(const once_flag&) = delete;
 764
 765     template<typename _Callable, typename... _Args>
 766       friend void
 767       call_once(once_flag& __once, _Callable&& __f, _Args&&... __args);
 768   };
 769
 770 #ifdef _GLIBCXX_HAVE_TLS
 771   extern __thread void* __once_callable;
 772   extern __thread void (*__once_call)();
 773
 774   template<typename _Callable>
 775     inline void
 776     __once_call_impl()
 777     {
 778       (*(_Callable*)__once_callable)();
 779     }
 780 #else
 781   extern function<void()> __once_functor;
 782
 783   extern void
 784   __set_once_functor_lock_ptr(unique_lock<mutex>*);
 785
 786   extern mutex&
 787   __get_once_mutex();
 788 #endif
 789
 790   extern "C" void __once_proxy();
 791
 792   /// call_once
 793   template<typename _Callable, typename... _Args>
 794     void
 795     call_once(once_flag& __once, _Callable&& __f, _Args&&... __args)
 796     {
 797 #ifdef _GLIBCXX_HAVE_TLS
 798       auto __bound_functor = std::bind<void>(std::forward<_Callable>(__f),
 799           std::forward<_Args>(__args)...);
 800       __once_callable = &__bound_functor;
 801       __once_call = &__once_call_impl<decltype(__bound_functor)>;
 802 #else
 803       unique_lock<mutex> __functor_lock(__get_once_mutex());
 804       __once_functor = std::bind<void>(std::forward<_Callable>(__f),
 805           std::forward<_Args>(__args)...);
 806       __set_once_functor_lock_ptr(&__functor_lock);
 807 #endif
 808
 809       int __e = __gthread_once(&(__once._M_once), &__once_proxy);
 810
 811 #ifndef _GLIBCXX_HAVE_TLS
 812       if (__functor_lock)
 813         __set_once_functor_lock_ptr(0);
 814 #endif
 815
 816       if (__e)
 817         __throw_system_error(__e);
 818     }
 819
 820   // @} group mutexes
 821 _GLIBCXX_END_NAMESPACE
 822
 823 #endif // _GLIBCXX_HAS_GTHREADS && _GLIBCXX_USE_C99_STDINT_TR1
 824
 825 #endif // __GXX_EXPERIMENTAL_CXX0X__
 826
 827 #endif // _GLIBCXX_MUTEX