A factory creates objects of a certain type. The factory takes an ID of some sort as an argument and creates the object which has been registered with the factory with the respective ID.
This code sample shows one way to make a factory. All objects are stored in an interal (intrusive) list inside the factory together with their ID. To create an object given its ID, the factory searches the list for the ID and calls the copy constructor of the object to create a new object of the same type.
The memory pool is really fast in allocating and deallocating memory (O(1)). For real-time systems this is the right choice. It works by preallocating a pool of memory blocks. These memory blocks must all have the same size. So this is the downside to live with: This memory pool will only provide memory blocks of a certain size. If you need another size: Simply make another memory pool with that other size.
The very traditional way to implement the observer pattern is by using polymorphism. You have to derive the class which contains your callback function from an observer base class, and you have to overwrite the function notify(). This is done in the first code C++03 sample you see here. Create a ConcreteObserver, derived from Observer, and fill in your personal notify function. The subject stores all ConcreteObservers in a vector. When something changes in the Subject (e.
Mapping Signal IDs to function calls The state machine pattern assumes, that function calls are made by each incoming signal. But what if the signals exist only as a number or ID? How is the ID transformed into a function call? Of course, you could simply write a switch case, converting the integer ID into a function call. But switch cases “smell” (look into Martin Fowlers book on Refactoring).
This example uses the function process(Signal s) (line 61, lines 76 and 77) to process the signal which is given as an ID.
A singleton is a class which controls the number of objects to be created from this class. Most often there shall be just a single object from a certain type. The basic principle to reach this is to limit the access to the constructor, i.e. making it private. There is a static function which allowes a single point of access to the single object.
Controversial discussion There is a controversial discussion if a singleton is good design.
Hierarchical State Machines Hierarchical State Machines (D. Harel) [4] are a common way to model behaviour of a software modul. Bran Selic [5] has extended the ideas towards real time modeling, introducing actors, ports and other components. GoF [2] have first proposed an implementation. M. Samek [1] has elaborated on the implementation. Here, I propose an idea to implement the change of states using the placement new operator. Nico Manske has made experiments with this idea in his Bachelorthesis [3].
Introduction to Rodney Brooks Subsumption Architecture: The subsumption architecture is a layered methodology for robot control systems. It consists of coupled components and their hierarchical behaviours. One component is superimposed on the other as single layers. Each layer disposes of an arbitration scheme which empowers higher layered behaviours to manipulate the input and output of lower behaviours by suppressing the input or inhibiting the output (see fig. 01). Also visible in fig.
How to stop a thread. It is a nice idea to create a functor (overload operator()) and pass a functor object to a thread. The operator()() (line 9) should generally contain a while loop (event loop)(line 10). To be able to stop the while loop from the outside, one can use a member variable of the functor, e.g. bool IsStopped or bool IsRunning (line 15). The loop would then look like this