include/comphelper/doublecheckedinit.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
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   9  * This file incorporates work covered by the following license notice:
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  17  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  18  */
  19
  20 #ifndef INCLUDED_COMPHELPER_DOUBLECHECKEDINIT_HXX
  21 #define INCLUDED_COMPHELPER_DOUBLECHECKEDINIT_HXX
  22
  23 #include <osl/getglobalmutex.hxx>
  24
  25 #include <atomic>
  26 // HACK: <atomic> includes <stdbool.h>, which in some Clang versions does '#define bool bool',
  27 // which confuses clang plugins.
  28 #undef bool
  29 #include <functional>
  30
  31 namespace comphelper
  32 {
  33 /**
  34  * Thread-safe singleton creation.
  35  *
  36  * It is normally sufficient to create singletons using static variables in a function.
  37  * This function is only for use cases that have a more complex lifetime of the object,
  38  * such as when the object may require specific cleanup or may be created more times
  39  * (e.g. when there is a "singleton" per each instance of another object).
  40  */
  41 template <typename Type, typename Function = std::function<Type*()>,
  42           typename Guard = osl::MutexGuard, typename GuardCtor = osl::GetGlobalMutex>
  43 static inline Type* doubleCheckedInit(std::atomic<Type*>& pointer, Function function,
  44                                       GuardCtor guardCtor = osl::GetGlobalMutex())
  45 {
  46     Type* p = pointer.load(std::memory_order_acquire);
  47     if (!p)
  48     {
  49         Guard guard(guardCtor());
  50         p = pointer.load(std::memory_order_relaxed);
  51         if (!p)
  52         {
  53             p = function();
  54             pointer.store(p, std::memory_order_release);
  55         }
  56     }
  57     return p;
  58 }
  59
  60 } // namespace
  61
  62 #endif // INCLUDED_COMPHELPER_DOUBLECHECKEDINIT_HXX
  63
  64 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */