--- /dev/null
+// Copyright (C) 2000 Stephen Cleary
+//
+// Distributed under the Boost Software License, Version 1.0.
+// Boost Software License - Version 1.0 - August 17th, 2003
+
+// Permission is hereby granted, free of charge, to any person or organization
+// obtaining a copy of the software and accompanying documentation covered by
+// this license (the "Software") to use, reproduce, display, distribute,
+// execute, and transmit the Software, and to prepare derivative works of the
+// Software, and to permit third-parties to whom the Software is furnished to
+// do so, all subject to the following:
+
+// The copyright notices in the Software and this entire statement, including
+// the above license grant, this restriction and the following disclaimer,
+// must be included in all copies of the Software, in whole or in part, and
+// all derivative works of the Software, unless such copies or derivative
+// works are solely in the form of machine-executable object code generated by
+// a source language processor.
+
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+//
+// See http://www.boost.org for updates, documentation, and revision history.
+
+#ifndef BOOST_POOL_SINGLETON_HPP
+#define BOOST_POOL_SINGLETON_HPP
+
+// The following code might be put into some Boost.Config header in a later revision
+#ifdef __BORLANDC__
+# pragma option push -w-inl
+#endif
+
+//
+// The following helper classes are placeholders for a generic "singleton"
+// class. The classes below support usage of singletons, including use in
+// program startup/shutdown code, AS LONG AS there is only one thread
+// running before main() begins, and only one thread running after main()
+// exits.
+//
+// This class is also limited in that it can only provide singleton usage for
+// classes with default constructors.
+//
+
+// The design of this class is somewhat twisted, but can be followed by the
+// calling inheritance. Let us assume that there is some user code that
+// calls "singleton_default<T>::instance()". The following (convoluted)
+// sequence ensures that the same function will be called before main():
+// instance() contains a call to create_object.do_nothing()
+// Thus, object_creator is implicitly instantiated, and create_object
+// must exist.
+// Since create_object is a static member, its constructor must be
+// called before main().
+// The constructor contains a call to instance(), thus ensuring that
+// instance() will be called before main().
+// The first time instance() is called (i.e., before main()) is the
+// latest point in program execution where the object of type T
+// can be created.
+// Thus, any call to instance() will auto-magically result in a call to
+// instance() before main(), unless already present.
+// Furthermore, since the instance() function contains the object, instead
+// of the singleton_default class containing a static instance of the
+// object, that object is guaranteed to be constructed (at the latest) in
+// the first call to instance(). This permits calls to instance() from
+// static code, even if that code is called before the file-scope objects
+// in this file have been initialized.
+
+namespace boost {
+
+namespace details {
+namespace pool {
+
+// T must be: no-throw default constructible and no-throw destructible
+template <typename T>
+struct singleton_default
+{
+ private:
+ struct object_creator
+ {
+ // This constructor does nothing more than ensure that instance()
+ // is called before main() begins, thus creating the static
+ // T object before multithreading race issues can come up.
+ object_creator() { singleton_default<T>::instance(); }
+ inline void do_nothing() const { }
+ };
+ static object_creator create_object;
+
+ singleton_default();
+
+ public:
+ typedef T object_type;
+
+ // If, at any point (in user code), singleton_default<T>::instance()
+ // is called, then the following function is instantiated.
+ static object_type & instance()
+ {
+ // This is the object that we return a reference to.
+ // It is guaranteed to be created before main() begins because of
+ // the next line.
+ static object_type obj;
+
+ // The following line does nothing else than force the instantiation
+ // of singleton_default<T>::create_object, whose constructor is
+ // called before main() begins.
+ create_object.do_nothing();
+
+ return obj;
+ }
+};
+template <typename T>
+typename singleton_default<T>::object_creator
+singleton_default<T>::create_object;
+
+} // namespace pool
+} // namespace details
+
+} // namespace boost
+
+// The following code might be put into some Boost.Config header in a later revision
+#ifdef __BORLANDC__
+# pragma option pop
+#endif
+
+#endif
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