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挺简单的一个类，只是维护了一个成员 shared_ptr<detail::trackable_pointee> _tracked_ptr; 这样看来的话，所谓的track还是基于智能指针，这里注意，track的对象需要从trackable_pointee继承，一个空类，主要还是为了用于标识。
#ifndef BOOST_SIGNALS2_TRACKABLE_HPP
#define BOOST_SIGNALS2_TRACKABLE_HPP
#include <boost/assert.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/weak_ptr.hpp>
namespace boost {
namespace signals2 {
namespace detail
{
class tracked_objects_visitor;
// trackable_pointee is used to identify the tracked shared_ptr
// originating from the signals2::trackable class. These tracked
// shared_ptr are special in that we shouldn‘t bother to
// increment their use count during signal invocation, since
// they don‘t actually control the lifetime of the
// signals2::trackable object they are associated with.
class trackable_pointee
{};
}
class trackable {
protected:
trackable(): _tracked_ptr(static_cast<detail::trackable_pointee*>(0)) {}
trackable(const trackable &): _tracked_ptr(static_cast<detail::trackable_pointee*>(0)) {}
trackable& operator=(const trackable &)
{
return *this;
}
~trackable() {}
private:
friend class detail::tracked_objects_visitor;
weak_ptr<detail::trackable_pointee> get_weak_ptr() const
{
return _tracked_ptr;
}
shared_ptr<detail::trackable_pointee> _tracked_ptr;
};
} // end namespace signals2
} // end namespace boost
#endif // BOOST_SIGNALS2_TRACKABLE_HPP
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原文地址：http://www.cnblogs.com/csxy/p/5456879.html
