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Distributable Singleton

In a distributed system, a singleton class could mean two different semantics. One is that the class has only one instance on each node. The other semantic is to assume that there is only one instance of the object in the whole system. The developer can choose which semantic to be used for the singleton class. If a singleton class is also distributable, it means there should be only one instance of the class in the whole system and remotely accessible by other nodes. Otherwise, there can be one instance on every node.

The target runtime component of the singleton object is the name of the class by default. All of the getInstance() calls in the entire system will be redirected to a single object.

 SingletonClass.getInstance().getName(); 

 

Alternatively, a specific runtime component can be given as a parameter of the getInstance() method. In this case, there will be a single object on each node.

 SingletonClass.getInstance(UmpleRuntime.getComponent(“component1”)).getName();