Using the RWTSingleton Class
Singletons ensure that a class has only one instance and provide a global point of access to it. The Threads Module singleton implementation is the
RWTSingleton class. Because
RWTSingleton is a template class, it can adapt existing classes to behave as singletons, as shown in the example below.
Threads Module solves the problem of deleting singleton instances by using an
WTCountingPointer smart pointer in the
RWTSingleton<T> interface. You can think of
RWTCountingPointer as a handle to the singleton instance. When no more handles are bound to the singleton instance and the program terminates, the singleton instance dies.
In the following example, suppose you want to create a singleton version of your existing class Foo.
Example 60 – Creating a singleton instance of an existing class
class Foo {
public:
void function();
};
To create a singleton instance of class Foo you write:
RWTCountingPointer<Foo> singleFooPtr =
RWTSingleton<Foo>::instance();
The first call to
instance() creates a
Foo instance on the heap, by calling
Foo’s default constructor, and returns it. The returned singleton is wrapped in an
RWTCountingPointer. Now you can use either of the
RWTCountingPointer dereferencing operations to call
function(). For example:
singleFooPtr->function();
or
(*singleFooPtr).function();
NOTE: The RWTCountingPointer operator->() may not be available on all platforms. For maximum portability, use operator*() as in the second example above.
