cascading.flow
Class FlowProcess

java.lang.Object
  cascading.flow.FlowProcess

Direct Known Subclasses:

HadoopFlowProcess

public abstract class FlowProcess
extends Object

FlowProcess implementations provide a call-back interface into the current computing system. Each Operation is given a reference to a particluar implemenation, allowing it to get configuration properties, send a "keep alive" ping, or to set a counter value.

Depending on the underlying system, FlowProcess instances are not continuous across all operations in a Flow. Thus, a call to increment(Enum, int) may start incrementing from zero if the operation making the call belongs to a subsquent 'job' or 'step' from any previous operations calling increment.

A FlowProcess is roughly a child of FlowSession. FlowSession is roughly one to one with a particular Flow. And every FlowSession will have one or more FlowProcesses.

See Also:

FlowSession

Field Summary

static FlowProcess

NULL Field NULL is a noop implemenation of FlowSession.

Constructor Summary

protected	FlowProcess()
protected	FlowProcess(FlowSession currentSession)

Method Summary

FlowSession	getCurrentSession() Method getCurrentSession returns the currentSession of this FlowProcess object.
abstract Object	getProperty(String key) Method getProperty should be used to return configuration parameters from the underlying system.
abstract void	increment(Enum counter, int amount) Method increement is used to increment a custom counter.
abstract void	keepAlive() Method keepAlive notifies the system that the current process is still alive.
abstract TupleEntryIterator	openTapForRead(Tap tap) Method openTapForRead return a TupleIterator for the given Tap instance.
abstract TupleEntryCollector	openTapForWrite(Tap tap) Method openTapForWrite returns a (@link TupleCollector} for the given Tap instance.
void	setCurrentSession(FlowSession currentSession) Method setCurrentSession sets the currentSession of this FlowProcess object.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

NULL

public static FlowProcess NULL

Field NULL is a noop implemenation of FlowSession.

Constructor Detail

FlowProcess

protected FlowProcess()

FlowProcess

protected FlowProcess(FlowSession currentSession)

Method Detail

getCurrentSession

public FlowSession getCurrentSession()

Method getCurrentSession returns the currentSession of this FlowProcess object.

Returns:

the currentSession (type FlowSession) of this FlowProcess object.

setCurrentSession

public void setCurrentSession(FlowSession currentSession)

Method setCurrentSession sets the currentSession of this FlowProcess object.

Parameters:

currentSession - the currentSession of this FlowProcess object.

getProperty

public abstract Object getProperty(String key)

Method getProperty should be used to return configuration parameters from the underlying system.

In the case of Hadoop, the current JobConf will be queried.

Parameters:

key - of type String

Returns:

an Object

keepAlive

public abstract void keepAlive()

Method keepAlive notifies the system that the current process is still alive. Use this method if a particular Operation takes some moments to complete. Each system is different, so calling ping every few seconds to every minute or so would be best.

increment

public abstract void increment(Enum counter,
                               int amount)

Method increement is used to increment a custom counter. Counters must be of type Enum. The amount to increment must be a positive integer value.

Parameters:

counter - of type Enum

amount - of type int

openTapForRead

public abstract TupleEntryIterator openTapForRead(Tap tap)
                                           throws IOException

Method openTapForRead return a TupleIterator for the given Tap instance.

Parameters:

tap - of type Tap

Returns:

TupleIterator

Throws:

IOException - when there is a failure opening the resource

openTapForWrite

public abstract TupleEntryCollector openTapForWrite(Tap tap)
                                             throws IOException

Method openTapForWrite returns a (@link TupleCollector} for the given Tap instance.

Parameters:

tap - of type Tap

Returns:

TupleCollector

Throws:

IOException - when there is a failure opening the resource