Examples of ProcessingElement

• eu.admire.dispel.core.ProcessingElement
  A representation of the model object 'Processing Element'.

  The following features are supported:

  • {@link eu.admire.dispel.core.ProcessingElement#getProcessingElementParameters Processing Element Parameters}

  @see eu.admire.dispel.core.CorePackage#getProcessingElement() @model abstract="true" @generated
• eu.admire.gateway.engine.ogsadai.ProcessingElement
  Represents a generic activity. The resource ID must be provided as a literal. Only the last value in an input sequence is used, all other values are ignored. Resource inputs cannot be connected to activity outputs. @author Amy Krause
• eu.admire.registry.ogsadai.rdfactivity.server.update.admire.ProcessingElement
• org.apache.s4.core.ProcessingElement

  Base class for implementing processing in S4. All instances are organized as follows:

  • A PE prototype is a special type of instance that, along with {@link Stream} defines the topology of theapplication graph.
  • PE prototypes manage the creation and destruction of PE instances.
  • All PE instances are clones of a PE prototype.
  • PE instances are associated with a unique key.
  • PE instances do the actual work by processing any number of input events of various types and emit output events of various types.
  • To process events, {@code ProcessingElement} dynamically matches an event type to a processing method. See{@link org.apache.s4.core.gen.OverloadDispatcher} . There are two types of processing methods:
    • {@code onEvent(SomeEvent event)} When implemented, input events of type {@code SomeEvent} will be dispatched tothis method.
    • {@code onTrigger(AnotherEvent event)} When implemented, input events of type {@code AnotherEvent} will bedispatched to this method when certain conditions are met. See {@link #setTrigger(Class,int,long,TimeUnit)}.
  • A PE implementation must not create threads. A periodic task can be implemented by overloading the {@link #onTime()}method. See {@link #setTimerInterval(long,TimeUnit)}
  • If a reference in the PE prototype shared by the PE instances, the object must be thread safe.
  • The code in a PE instance is synchronized by the framework to avoid concurrency problems.
  • In some special cases, it may be desirable to allow concurrency in the PE instance. For example, there may be several event processing methods that can safely run concurrently. To enable concurrency, annotate the implementation of {@code ProcessingElement} with {@link ThreadSafe}.
  • PE instances never use the constructor. They must be initialized by implementing the {@link #onCreate()} method.
  • PE class fields are cloned from the prototype. References are also copied which means that if the prototype creates a collection object, all instances will be sharing the same collection object which is usually NOT what the programmer intended . The application developer is responsible for initializing objects in the {@link #onCreate()} method. For example, if each instance requires aList object the PE should implement the following:

     public class MyPE extends ProcessingElement { private Map wordCount; ... onCreate() { wordCount = new HashMap; logger.trace("Created a map for instance PE with id {}, getId()); } }