/usr/include/simgear/structure/singleton.hpp is in libsimgear-dev 3.0.0-6+b2.
This file is owned by root:root, with mode 0o644.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 | // 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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