/usr/include/boost/serialization
Edit: /usr/include/boost/serialization/singleton.hpp (7603B)
#ifndef BOOST_SERIALIZATION_SINGLETON_HPP
#define BOOST_SERIALIZATION_SINGLETON_HPP
/////////1/////////2///////// 3/////////4/////////5/////////6/////////7/////////8
// singleton.hpp
//
// Copyright David Abrahams 2006. Original version
//
// Copyright Robert Ramey 2007. Changes made to permit
// application throughout the serialization library.
//
// Copyright Alexander Grund 2018. Corrections to singleton lifetime
//
// Distributed under the Boost
// Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// The intention here is to define a template which will convert
// any class into a singleton with the following features:
//
// a) initialized before first use.
// b) thread-safe for const access to the class
// c) non-locking
//
// In order to do this,
// a) Initialize dynamically when used.
// b) Require that all singletons be initialized before main
// is called or any entry point into the shared library is invoked.
// This guarentees no race condition for initialization.
// In debug mode, we assert that no non-const functions are called
// after main is invoked.
//
// MS compatible compilers support #pragma once
#if defined(_MSC_VER)
# pragma once
#endif
#include
#include
#include
#include
#include
#include
#include // must be the last header
#ifdef BOOST_MSVC
# pragma warning(push)
# pragma warning(disable : 4511 4512)
#endif
namespace boost {
namespace serialization {
//////////////////////////////////////////////////////////////////////
// Provides a dynamically-initialized (singleton) instance of T in a
// way that avoids LNK1179 on vc6. See http://tinyurl.com/ljdp8 or
// http://lists.boost.org/Archives/boost/2006/05/105286.php for
// details.
//
// Singletons created by this code are guaranteed to be unique
// within the executable or shared library which creates them.
// This is sufficient and in fact ideal for the serialization library.
// The singleton is created when the module is loaded and destroyed
// when the module is unloaded.
// This base class has two functions.
// First it provides a module handle for each singleton indicating
// the executable or shared library in which it was created. This
// turns out to be necessary and sufficient to implement the tables
// used by serialization library.
// Second, it provides a mechanism to detect when a non-const function
// is called after initialization.
// Make a singleton to lock/unlock all singletons for alteration.
// The intent is that all singletons created/used by this code
// are to be initialized before main is called. A test program
// can lock all the singletons when main is entered. Thus any
// attempt to retrieve a mutable instance while locked will
// generate an assertion if compiled for debug.
// The singleton template can be used in 2 ways:
// 1 (Recommended): Publicly inherit your type T from singleton,
// make its ctor protected and access it via T::get_const_instance()
// 2: Simply access singleton without changing T. Note that this only
// provides a global instance accesible by singleton::get_const_instance()
// or singleton::get_mutable_instance() to prevent using multiple instances
// of T make its ctor protected
// Note on usage of BOOST_DLLEXPORT: These functions are in danger of
// being eliminated by the optimizer when building an application in
// release mode. Usage of the macro is meant to signal the compiler/linker
// to avoid dropping these functions which seem to be unreferenced.
// This usage is not related to autolinking.
class BOOST_SYMBOL_VISIBLE singleton_module :
public boost::noncopyable
{
private:
BOOST_DLLEXPORT bool & get_lock() BOOST_USED {
static bool lock = false;
return lock;
}
public:
BOOST_DLLEXPORT void lock(){
get_lock() = true;
}
BOOST_DLLEXPORT void unlock(){
get_lock() = false;
}
BOOST_DLLEXPORT bool is_locked(){
return get_lock();
}
};
static inline singleton_module & get_singleton_module(){
static singleton_module m;
return m;
}
namespace detail {
// This is the class actually instantiated and hence the real singleton.
// So there will only be one instance of this class. This does not hold
// for singleton as a class derived from singleton could be
// instantiated multiple times.
// It also provides a flag `is_destroyed` which returns true, when the
// class was destructed. It is static and hence accesible even after
// destruction. This can be used to check, if the singleton is still
// accesible e.g. in destructors of other singletons.
template
class singleton_wrapper : public T
{
static bool & get_is_destroyed(){
// Prefer a static function member to avoid LNK1179.
// Note: As this is for a singleton (1 instance only) it must be set
// never be reset (to false)!
static bool is_destroyed_flag = false;
return is_destroyed_flag;
}
public:
singleton_wrapper(){
BOOST_ASSERT(! is_destroyed());
}
~singleton_wrapper(){
get_is_destroyed() = true;
}
static bool is_destroyed(){
return get_is_destroyed();
}
};
} // detail
template
class singleton {
private:
static T * m_instance;
// include this to provoke instantiation at pre-execution time
static void use(T const &) {}
static T & get_instance() {
BOOST_ASSERT(! is_destroyed());
// use a wrapper so that types T with protected constructors can be used
// Using a static function member avoids LNK1179
static detail::singleton_wrapper< T > t;
// note that the following is absolutely essential.
// commenting out this statement will cause compilers to fail to
// construct the instance at pre-execution time. This would prevent
// our usage/implementation of "locking" and introduce uncertainty into
// the sequence of object initialization.
// Unfortunately, this triggers detectors of undefine behavior
// and reports an error. But I've been unable to find a different
// of guarenteeing that the the singleton is created at pre-main time.
if (m_instance) use(* m_instance);
return static_cast(t);
}
protected:
// Do not allow instantiation of a singleton. But we want to allow
// `class T: public singleton` so we can't delete this ctor
BOOST_DLLEXPORT singleton(){}
public:
BOOST_DLLEXPORT static T & get_mutable_instance(){
BOOST_ASSERT(! get_singleton_module().is_locked());
return get_instance();
}
BOOST_DLLEXPORT static const T & get_const_instance(){
return get_instance();
}
BOOST_DLLEXPORT static bool is_destroyed(){
return detail::singleton_wrapper< T >::is_destroyed();
}
};
// Assigning the instance reference to a static member forces initialization
// at startup time as described in
// https://groups.google.com/forum/#!topic/microsoft.public.vc.language/kDVNLnIsfZk
template
T * singleton< T >::m_instance = & singleton< T >::get_instance();
} // namespace serialization
} // namespace boost
#include // pops abi_suffix.hpp pragmas
#ifdef BOOST_MSVC
#pragma warning(pop)
#endif
#endif // BOOST_SERIALIZATION_SINGLETON_HPP