Activity (constellation 2.0.0 API)

java.lang.Object
- ibis.constellation.Activity

All Implemented Interfaces:

java.io.Serializable

Direct Known Subclasses:

FlexibleEventCollector, MultiEventCollector, SimpleActivity, SingleEventCollector
```
public abstract class Activity
extends java.lang.Object
implements java.io.Serializable
```
In Constellation, a program consists of a collection of loosely coupled activities, which may communicate using Events. Each Activity represents an action that is to be performed by the application, i.e. run a task or process some Events. This class is the base class for all application activities. Applications should extend this class and implement the initialize, process and cleanup methods. After creating an Activity, it can be submitted to Constellation using Constellation.submit(ibis.constellation.Activity). During this submit, a globally unique ActivityIdentifier will be assigned to the Activity. Using setIdentifier this identifier will be stored in the Activity. Use the identifier method to retrieve it. The Activity will be scheduled to run on a Constellation that matches the Context. When it starts running, initialize will be invoked once. This method may perform any processing that is needed, but should not block indefinitely as this may result in deadlocks. When finished, the method should either return FINISH of SUSPEND. By returning FINISH the Activity indicates it no further processing is needed. By returning SUSPEND the Activity indicates it expects an Event. The Activity is then suspend by Constellation, until the Event arrives. Upon arrival of the Event, the process method will be invoked. After processing the event, process can indicate if more events are expected (by returning SUSPEND or if the Activity is done (by returning FINISH. After FINISH is returned by either initialize of process, the cleanup method is invoked. After this method returns, the Activity is finished and will nore receive any more processingtime.

See Also:

Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`static int`	`FINISH` Value to be returned by `initialize(ibis.constellation.Constellation)` or `process(ibis.constellation.Constellation, ibis.constellation.Event)` when no further processing is needed.
`static int`	`SUSPEND` Value to be returned by `initialize(ibis.constellation.Constellation)` or `process(ibis.constellation.Constellation, ibis.constellation.Event)` when (further) events are expected.

Constructor Summary

Constructors
Constructor and Description
`Activity(AbstractContext context, boolean expectsEvents)` Create an Activity with a specified context, and specify if it expects to receive Events.
`Activity(AbstractContext context, boolean mayBeStolen, boolean expectsEvents)` Create an Activity with a specified context, and indicate if this Activity may be stolen by other Constellations, and if it expects to receive Events.

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`abstract void`	`cleanup(Constellation constellation)` The implementation of this method is called when the activity is finished.
`boolean`	`expectsEvents()` Returns if this Activity expects `Event`s.
`AbstractContext`	`getContext()` Returns the `AbstractContext` of this Activity.
`ActivityIdentifier`	`identifier()` Returns the globally unique `ActivityIdentifier` assigned to this Activity, or `null` if this Activity has not been submitted yet.
`abstract int`	`initialize(Constellation constellation)` The implementation of this method should perform the initial processing when the activity is first activated.
`boolean`	`mayBeStolen()` Returns if this Activity may be stolen by another `Constellation`.
`abstract int`	`process(Constellation constellation, Event event)` The implementation of this method is called when an event is received for this activity.
`void`	`setIdentifier(ActivityIdentifier identifier)` This is a callback method used by the Constellation to assign a globally unique `ActivityIdentifier` to this Activity.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - FINISH
```
public static final int FINISH
```
    Value to be returned by initialize(ibis.constellation.Constellation) or process(ibis.constellation.Constellation, ibis.constellation.Event) when no further processing is needed.
    
    See Also:
    
    Constant Field Values
  - SUSPEND
```
public static final int SUSPEND
```
    Value to be returned by initialize(ibis.constellation.Constellation) or process(ibis.constellation.Constellation, ibis.constellation.Event) when (further) events are expected.
    
    See Also:
    
    Constant Field Values
- Constructor Detail
  - Activity
```
public Activity(AbstractContext context,
                boolean mayBeStolen,
                boolean expectsEvents)
```
    Create an Activity with a specified context, and indicate if this Activity may be stolen by other Constellations, and if it expects to receive Events.
    
    Parameters:
    
    context - the context in which this activity should be run.
    
    mayBeStolen - if this activity may be stolen by other Constellations
    
    expectsEvents - if this Activity expects events
  - Activity
```
public Activity(AbstractContext context,
                boolean expectsEvents)
```
    Create an Activity with a specified context, and specify if it expects to receive Events. When using this constructor, it is assumed that this Activity is allowed to be stolen by other Constellations.
    
    Parameters:
    
    context - the context in which this activity should be run.
    
    expectsEvents - if this Activity expects events
- Method Detail
  - setIdentifier
```
public void setIdentifier(ActivityIdentifier identifier)
```
    This is a callback method used by the Constellation to assign a globally unique ActivityIdentifier to this Activity. This method may only be invoked once, since the identifier may not change once set. Any subsequent invocation will result in an IllegalStateException.
    
    Parameters:
    
    identifier - the globally unique ActivityIdentifier
  - identifier
```
public ActivityIdentifier identifier()
```
    Returns the globally unique ActivityIdentifier assigned to this Activity, or null if this Activity has not been submitted yet.
    
    Returns:
    
    the globally unique ActivityIdentifier of this Activity or null.
  - getContext
```
public AbstractContext getContext()
```
    Returns the AbstractContext of this Activity.
    
    Returns:
    
    the AbstractContext of this Activity.
  - mayBeStolen
```
public boolean mayBeStolen()
```
    Returns if this Activity may be stolen by another Constellation.
    
    Returns:
    
    if this Activity may be stolen by another Constellation.
  - expectsEvents
```
public boolean expectsEvents()
```
    Returns if this Activity expects Events.
    
    Returns:
    
    if this Activity expects Events.
  - initialize
```
public abstract int initialize(Constellation constellation)
```
    The implementation of this method should perform the initial processing when the activity is first activated. It may perform as much processing as needed, but should not block for a prolonged period, as this may result in deadlocks. When finished, it should return either SUSPEND or FINISH, depending on what the activity is to do next: SUSPEND when it wants to wait for events, and FINISH when it is done. Note that this method does not throw checked exceptions. It can, however, throw runtime exceptions or errors, and the Constellation running this Activity will deal with that.
    
    Parameters:
    
    constellation - the Constellation on which the Activity is running
    
    Returns:
    
    either FINISH if this Activity is done or SUSPEND if this Activity expects events.
  - process
```
public abstract int process(Constellation constellation,
                            Event event)
```
    The implementation of this method is called when an event is received for this activity. After the event is processed it must return SUSPEND or FINISH, depending on what the activity is to do next: SUSPEND when it expects other events, and FINISH when it is done. This method is invoked once at a time, even if more events arrive more or less simultaneously. Note that this method does not throw checked exceptions. It can, however, throw runtime exceptions or errors, and the Constellation running this Activity will deal with that.
    
    Parameters:
    
    constellation - the Constellation on which the Activity is running
    
    event - the Event to process.
    
    Returns:
    
    either FINISH if this Activity is done or SUSPEND if this Activity expects events.
  - cleanup
```
public abstract void cleanup(Constellation constellation)
```
    The implementation of this method is called when the activity is finished. It allows the activity to perform cleanup, and, for example, send events to its parent activity. Note that this method does not throw checked exceptions. It can, however, throw runtime exceptions or errors, and the Constellation running this Activity will deal with that.
    
    Parameters:
    
    constellation - the Constellation on which the Activity is running

Class Activity

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

FINISH

SUSPEND

Constructor Detail

Activity

Activity

Method Detail

setIdentifier

identifier

getContext

mayBeStolen

expectsEvents

initialize

process

cleanup