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Run Time Type Identification

To migrate an object from one thread to another, Graphcode needs to be able to create an object of the correct type in the destination address space. This is achieved by means of a run time type identification (RTTI) system. Given a type token t, an object of that type can be created by the call:

object *o=archetype[t]->lnew();

Instead of using C++'s built-in RTTI system, where tokens are compound objects of somewhat indeterminate size, Graphcode implements a simple RTTI system using template programming, in which a type token is a simple unsigned integer. This implies that each type of object to be used with Graph must be registered first, before use. This is taken care for you automatically if you use Graph::AddObject() to add your object to the Graph.

Adding the virtual type method to your class is also easy:

class foo: public object
{
 ...
 virtual int type() {return vtype(*this);}
};

The first vtype is called on an object, an object of that type is created (via its lcopy method), and added to the archetype vector. The index of that object within the archetype vector become the type token. It is vitally important that types are added to the archetype vector in the same order on all threads. Clearly this is a trivial requirement if only one type is used, but slightly more care needs to be taken in the case of multiple types of object.

If you have multiple object types, consider using the register_type template to ensure a consistent type registration across the different address spaces.


next up previous contents index
Next: Node and edge weights Up: Objects Previous: Virtual Constructors   Contents   Index
Russell Standish 2016-09-02