include/rtl/instance.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
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   8  *
   9  * This file incorporates work covered by the following license notice:
  10  *
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  12  *   contributor license agreements. See the NOTICE file distributed
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  14  *   ownership. The ASF licenses this file to you under the Apache
  15  *   License, Version 2.0 (the "License"); you may not use this file
  16  *   except in compliance with the License. You may obtain a copy of
  17  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  18  */
  19
  20 /*
  21  * This file is part of LibreOffice published API.
  22  */
  23
  24 #ifndef INCLUDED_RTL_INSTANCE_HXX
  25 #define INCLUDED_RTL_INSTANCE_HXX
  26
  27 #include "sal/config.h"
  28
  29 #include <cstddef>
  30
  31 #include "osl/doublecheckedlocking.h"
  32 #include "osl/getglobalmutex.hxx"
  33
  34 namespace {
  35
  36 /** A non-broken version of the double-checked locking pattern.
  37
  38     See
  39     <http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html>
  40     for a description of double-checked locking, why it is broken, and how it
  41     can be fixed.  Always use this template instead of spelling out the
  42     double-checked locking pattern explicitly, and only in those rare cases
  43     where that is not possible and you have to spell it out explicitly, at
  44     least call OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER() at the right
  45     places.  That way, all platform-dependent code to make double-checked
  46     locking work can be kept in one place.
  47
  48     Usage scenarios:
  49
  50     1  Static instance (most common case)
  51
  52     Pattern:
  53
  54       T * getInstance()
  55       {
  56           static T * pInstance = 0;
  57           if (!pInstance)
  58           {
  59               ::osl::MutexGuard aGuard(::osl::Mutex::getGlobalMutex());
  60               if (!pInstance)
  61               {
  62                   static T aInstance;
  63                   pInstance = &aInstance;
  64               }
  65           }
  66           return pInstance;
  67       }
  68
  69     Code:
  70
  71       #include <rtl/instance.hxx>
  72       #include <osl/getglobalmutex.hxx>
  73
  74       namespace {
  75           struct Init
  76           {
  77               T * operator()()
  78               {
  79                   static T aInstance;
  80                   return &aInstance;
  81               }
  82           };
  83       }
  84
  85       T * getInstance()
  86       {
  87           return rtl_Instance< T, Init, ::osl::MutexGuard,
  88                                ::osl::GetGlobalMutex >::create(
  89               Init(), ::osl::GetGlobalMutex());
  90       }
  91
  92     2  Dynamic instance
  93
  94     Pattern:
  95
  96       T * getInstance()
  97       {
  98           static T * pInstance = 0;
  99           if (!pInstance)
 100           {
 101               ::osl::MutexGuard aGuard(::osl::Mutex::getGlobalMutex());
 102               if (!pInstance)
 103                   pInstance = new T;
 104           }
 105           return pInstance;
 106       }
 107
 108     Code:
 109
 110       #include <rtl/instance.hxx>
 111       #include <osl/getglobalmutex.hxx>
 112
 113       namespace {
 114           struct Init
 115           {
 116               T * operator()()
 117               {
 118                   return new T;
 119               }
 120           };
 121       }
 122
 123       T * getInstance()
 124       {
 125           return rtl_Instance< T, Init, ::osl::MutexGuard,
 126                                ::osl::GetGlobalMutex >::create(
 127               Init(), ::osl::GetGlobalMutex());
 128       }
 129
 130     3  Other guard/mutex
 131
 132     Pattern:
 133
 134       T * getInstance()
 135       {
 136           static T * pInstance = 0;
 137           if (!pInstance)
 138           {
 139               SomeGuard aGuard(pSomeMutex);
 140               if (!pInstance)
 141               {
 142                   static T aInstance;
 143                   pInstance = &aInstance;
 144               }
 145           }
 146           return pInstance;
 147       }
 148
 149     Code:
 150
 151       #include <rtl/instance.hxx>
 152
 153       namespace {
 154           struct InitInstance
 155           {
 156               T * operator()()
 157               {
 158                   static T aInstance;
 159                   return &aInstance;
 160               }
 161           };
 162
 163           struct InitGuard
 164           {
 165               SomeMutex * operator()()
 166               {
 167                   return pSomeMutex;
 168               }
 169           };
 170       }
 171
 172       T * getInstance()
 173       {
 174           return rtl_Instance< T, InitInstance,
 175                                SomeGuard, InitGuard >::create(
 176               InitInstance(), InitMutex());
 177       }
 178
 179     4  Calculate extra data
 180
 181     Pattern:
 182
 183       T * getInstance()
 184       {
 185           static T * pInstance = 0;
 186           if (!pInstance)
 187           {
 188               Data aData(...);
 189               ::osl::MutexGuard aGuard(::osl::Mutex::getGlobalMutex());
 190               if (!pInstance)
 191               {
 192                   static T aInstance(aData);
 193                   pInstance = &aInstance;
 194               }
 195           }
 196           return pInstance;
 197       }
 198
 199     Code:
 200
 201       #include <rtl/instance.hxx>
 202       #include <osl/getglobalmutex.hxx>
 203
 204       namespace {
 205           struct InitInstance
 206           {
 207               T * operator()()
 208               {
 209                   static T aInstance;
 210                   return &aInstance;
 211               }
 212           }
 213
 214           struct InitData
 215           {
 216               Data const & operator()()
 217               {
 218                   return ...;
 219               }
 220           }
 221       }
 222
 223       T * getInstance()
 224       {
 225           return rtl_Instance< T, InitInstance,
 226                                ::osl::MutexGuard, ::osl::GetGlobalMutex,
 227                                Data, InitData >::create(
 228               InitInstance(), ::osl::GetGlobalMutex(), InitData());
 229       }
 230
 231     Some comments:
 232
 233     For any instantiation of rtl_Instance, at most one call to a create method
 234     may occur in the program code:  Each occurrence of a create method within
 235     the program code is supposed to return a fresh object instance on the
 236     first call, and that same object instance on subsequent calls; but
 237     independent occurrences of create methods are supposed to return
 238     independent object instances.  Since there is a one-to-one correspondence
 239     between object instances and instantiations of rtl_Instance, the
 240     requirement should be clear.  One measure to enforce the requirement is
 241     that rtl_Instance lives in an unnamed namespace, so that instantiations of
 242     rtl_Instance in different translation units will definitely be different
 243     instantiations.  A drawback of that measure is that the name of the class
 244     needs a funny "hand coded" prefix "rtl_" instead of a proper namespace
 245     prefix like "::rtl::".
 246
 247     A known problem with this template is when two occurrences of calls to
 248     create methods with identical template arguments appear in one translation
 249     unit.  Those two places will share a single object instance.  This can be
 250     avoided by using different Init structs (see the above code samples) in
 251     the two places.
 252
 253     There is no need to make m_pInstance volatile, in order to avoid usage of
 254     stale copies of m_pInstance:  At the first check, a thread will see that
 255     m_pInstance contains either 0 or a valid pointer.  If it contains a valid
 256     pointer, it cannot be stale, and that pointer is used.  If it contains 0,
 257     acquiring the mutex will ensure that the second check sees a non-stale
 258     value in all cases.
 259
 260     On some compilers, the create methods would not be inlined if they
 261     contained any static variables, so m_pInstance is made a class member
 262     instead (and the create methods are inlined).  But on MSC, the definition
 263     of the class member m_pInstance would cause compilation to fail with an
 264     internal compiler error.  Since MSC is able to inline methods containing
 265     static variables, m_pInstance is moved into the methods there.  Note that
 266     this only works well because for any instantiation of rtl_Instance at most
 267     one call to a create method should be present, anyway.
 268  */
 269 template< typename Inst, typename InstCtor,
 270           typename Guard, typename GuardCtor,
 271           typename Data = int, typename DataCtor = int >
 272 class rtl_Instance
 273 {
 274 public:
 275     static Inst * create(InstCtor aInstCtor, GuardCtor aGuardCtor)
 276     {
 277 #if defined _MSC_VER
 278         static Inst * m_pInstance = 0;
 279 #endif // _MSC_VER
 280         Inst * p = m_pInstance;
 281         if (!p)
 282         {
 283             Guard aGuard(aGuardCtor());
 284             p = m_pInstance;
 285             if (!p)
 286             {
 287                 p = aInstCtor();
 288                 OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
 289                 m_pInstance = p;
 290             }
 291         }
 292         else
 293         {
 294             OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
 295         }
 296         return p;
 297     }
 298
 299     static Inst * create(InstCtor aInstCtor, GuardCtor aGuardCtor,
 300                                 DataCtor aDataCtor)
 301     {
 302 #if defined _MSC_VER
 303         static Inst * m_pInstance = 0;
 304 #endif // _MSC_VER
 305         Inst * p = m_pInstance;
 306         if (!p)
 307         {
 308             Data aData(aDataCtor());
 309             Guard aGuard(aGuardCtor());
 310             p = m_pInstance;
 311             if (!p)
 312             {
 313                 p = aInstCtor(aData);
 314                 OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
 315                 m_pInstance = p;
 316             }
 317         }
 318         else
 319         {
 320             OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
 321         }
 322         return p;
 323     }
 324
 325     static Inst * create(InstCtor aInstCtor, GuardCtor aGuardCtor,
 326                                 const Data &rData)
 327     {
 328 #if defined _MSC_VER
 329         static Inst * m_pInstance = 0;
 330 #endif // _MSC_VER
 331         Inst * p = m_pInstance;
 332         if (!p)
 333         {
 334             Guard aGuard(aGuardCtor());
 335             p = m_pInstance;
 336             if (!p)
 337             {
 338                 p = aInstCtor(rData);
 339                 OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
 340                 m_pInstance = p;
 341             }
 342         }
 343         else
 344         {
 345             OSL_DOUBLE_CHECKED_LOCKING_MEMORY_BARRIER();
 346         }
 347         return p;
 348     }
 349
 350 private:
 351 #if !defined _MSC_VER
 352     static Inst * m_pInstance;
 353 #endif // _MSC_VER
 354 };
 355
 356 #if !defined _MSC_VER
 357 template< typename Inst, typename InstCtor,
 358           typename Guard, typename GuardCtor,
 359           typename Data, typename DataCtor >
 360 Inst *
 361 rtl_Instance< Inst, InstCtor, Guard, GuardCtor, Data, DataCtor >::m_pInstance
 362 = NULL;
 363 #endif // _MSC_VER
 364
 365 }
 366
 367 namespace rtl {
 368
 369 /** Helper base class for a late-initialized (default-constructed)
 370     static variable, implementing the double-checked locking pattern correctly.
 371
 372     @derive
 373     Derive from this class (common practice), e.g.
 374     <pre>
 375     struct MyStatic : public rtl::Static<MyType, MyStatic> {};
 376     ...
 377     MyType & rStatic = MyStatic::get();
 378     ...
 379     </pre>
 380
 381     @tparam T
 382               variable's type
 383     @tparam Unique
 384               Implementation trick to make the inner static holder unique,
 385               using the outer class
 386               (the one that derives from this base class)
 387 */
 388 #if defined LIBO_INTERNAL_ONLY
 389 template<typename T, typename Unique>
 390 class Static {
 391 public:
 392     /** Gets the static.  Mutual exclusion is implied by a functional
 393         -fthreadsafe-statics
 394
 395         @return
 396                 static variable
 397     */
 398     static T & get() {
 399         static T instance;
 400         return instance;
 401     }
 402 };
 403 #else
 404 template<typename T, typename Unique>
 405 class Static {
 406 public:
 407     /** Gets the static.  Mutual exclusion is performed using the
 408         osl global mutex.
 409
 410         @return
 411                 static variable
 412     */
 413     static T & get() {
 414         return *rtl_Instance<
 415             T, StaticInstance,
 416             ::osl::MutexGuard, ::osl::GetGlobalMutex >::create(
 417                 StaticInstance(), ::osl::GetGlobalMutex() );
 418     }
 419 private:
 420     struct StaticInstance {
 421         T * operator () () {
 422             static T instance;
 423             return &instance;
 424         }
 425     };
 426 };
 427 #endif
 428
 429 /** Helper base class for a late-initialized (default-constructed)
 430     static variable, implementing the double-checked locking pattern correctly.
 431
 432     @derive
 433     Derive from this class (common practice), e.g.
 434     <pre>
 435     struct MyStatic : public rtl::Static<MyType, MyStatic> {};
 436     ...
 437     MyType & rStatic = MyStatic::get();
 438     ...
 439     </pre>
 440
 441     @tparam T
 442               variable's type
 443     @tparam Unique
 444               Implementation trick to make the inner static holder unique,
 445               using the outer class
 446               (the one that derives from this base class)
 447 */
 448 #if defined LIBO_INTERNAL_ONLY
 449 template<typename T, typename Data, typename Unique>
 450 class StaticWithArg {
 451 public:
 452     /** Gets the static.  Mutual exclusion is implied by a functional
 453         -fthreadsafe-statics
 454
 455         @return
 456                 static variable
 457     */
 458     static T & get(const Data& rData) {
 459         static T instance(rData);
 460         return instance;
 461     }
 462
 463     /** Gets the static.  Mutual exclusion is implied by a functional
 464         -fthreadsafe-statics
 465
 466         @return
 467                 static variable
 468     */
 469     static T & get(Data& rData) {
 470         static T instance(rData);
 471         return instance;
 472     }
 473 };
 474 #else
 475 template<typename T, typename Data, typename Unique>
 476 class StaticWithArg {
 477 public:
 478     /** Gets the static.  Mutual exclusion is performed using the
 479         osl global mutex.
 480
 481         @return
 482                 static variable
 483     */
 484     static T & get(const Data& rData) {
 485         return *rtl_Instance<
 486             T, StaticInstanceWithArg,
 487             ::osl::MutexGuard, ::osl::GetGlobalMutex,
 488             Data >::create( StaticInstanceWithArg(),
 489                                       ::osl::GetGlobalMutex(),
 490                                       rData );
 491     }
 492
 493     /** Gets the static.  Mutual exclusion is performed using the
 494         osl global mutex.
 495
 496         @return
 497                 static variable
 498     */
 499     static T & get(Data& rData) {
 500         return *rtl_Instance<
 501             T, StaticInstanceWithArg,
 502             ::osl::MutexGuard, ::osl::GetGlobalMutex,
 503             Data >::create( StaticInstanceWithArg(),
 504                                       ::osl::GetGlobalMutex(),
 505                                       rData );
 506     }
 507 private:
 508     struct StaticInstanceWithArg {
 509         T * operator () (const Data& rData) {
 510             static T instance(rData);
 511             return &instance;
 512         }
 513
 514         T * operator () (Data& rData) {
 515             static T instance(rData);
 516             return &instance;
 517          }
 518     };
 519 };
 520 #endif
 521
 522 /** Helper class for a late-initialized static aggregate, e.g. an array,
 523     implementing the double-checked locking pattern correctly.
 524
 525     @tparam T
 526               aggregate's element type
 527     @tparam InitAggregate
 528               initializer functor class
 529 */
 530 #if defined LIBO_INTERNAL_ONLY
 531 template<typename T, typename InitAggregate>
 532 class StaticAggregate {
 533 public:
 534     /** Gets the static aggregate, late-initializing.
 535         Mutual exclusion is implied by a functional
 536         -fthreadsafe-statics
 537
 538         @return
 539                 aggregate
 540     */
 541     static T * get() {
 542         static T *instance = InitAggregate()();
 543         return instance;
 544     }
 545 };
 546 #else
 547 template<typename T, typename InitAggregate>
 548 class StaticAggregate {
 549 public:
 550     /** Gets the static aggregate, late-initializing.
 551         Mutual exclusion is performed using the osl global mutex.
 552
 553         @return
 554                 aggregate
 555     */
 556     static T * get() {
 557         return rtl_Instance<
 558             T, InitAggregate,
 559             ::osl::MutexGuard, ::osl::GetGlobalMutex >::create(
 560                 InitAggregate(), ::osl::GetGlobalMutex() );
 561     }
 562 };
 563 #endif
 564 /** Helper base class for a late-initialized static variable,
 565     implementing the double-checked locking pattern correctly.
 566
 567     @derive
 568     Derive from this class (common practice),
 569     providing an initializer functor class, e.g.
 570     <pre>
 571     struct MyStatic : public rtl::StaticWithInit<MyType, MyStatic> {
 572         MyType operator () () {
 573             ...
 574             return MyType( ... );
 575         }
 576     };
 577     ...
 578     MyType & rStatic = MyStatic::get();
 579     ...
 580     </pre>
 581
 582     @tparam T
 583               variable's type
 584     @tparam InitData
 585               initializer functor class
 586     @tparam Unique
 587               Implementation trick to make the inner static holder unique,
 588               using the outer class
 589               (the one that derives from this base class).
 590               Default is InitData (common practice).
 591     @tparam Data
 592               Initializer functor's return type.
 593               Default is T (common practice).
 594 */
 595 #if defined LIBO_INTERNAL_ONLY
 596 template<typename T, typename InitData,
 597          typename Unique = InitData, typename Data = T>
 598 class StaticWithInit {
 599 public:
 600     /** Gets the static.  Mutual exclusion is implied by a functional
 601         -fthreadsafe-statics
 602
 603         @return
 604                 static variable
 605     */
 606     static T & get() {
 607         static T instance = InitData()();
 608         return instance;
 609     }
 610 };
 611 #else
 612 template<typename T, typename InitData,
 613          typename Unique = InitData, typename Data = T>
 614 class StaticWithInit {
 615 public:
 616     /** Gets the static.  Mutual exclusion is performed using the
 617         osl global mutex.
 618
 619         @return
 620                 static variable
 621     */
 622     static T & get() {
 623         return *rtl_Instance<
 624             T, StaticInstanceWithInit,
 625             ::osl::MutexGuard, ::osl::GetGlobalMutex,
 626             Data, InitData >::create( StaticInstanceWithInit(),
 627                                       ::osl::GetGlobalMutex(),
 628                                       InitData() );
 629     }
 630 private:
 631     struct StaticInstanceWithInit {
 632         T * operator () ( Data d ) {
 633             static T instance(d);
 634             return &instance;
 635         }
 636     };
 637 };
 638 #endif
 639 } // namespace rtl
 640
 641 #endif // INCLUDED_RTL_INSTANCE_HXX
 642
 643 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */