cascading.operation
Interface Buffer<C>

All Superinterfaces:

Operation<C>

public interface Buffer<C>
extends Operation<C>

A Buffer is similiar to an Aggregator by the fact that it operates on unique groups of values. It differs by the fact that an Iterator is provided and it is the responsibility of the operate(cascading.flow.FlowProcess, BufferCall) method to iterate overall all the input arguments returned by this Iterator.

Buffer is very useful when header or footer values need to be inserted into a grouping, or if values need to be inserted into the middle of the group values. For example, consider a stream of timestamps. A Buffer could be used to add missing entries, or to calculate running or moving averages over a smaller "window" within the grouping.

There may be only one Buffer after a GroupBy or CoGroup. And there may not be any additional Every pipes before or after the buffers Every pipe instance. A PlannerException will be thrown if these rules are violated.

Buffer implementations should be reentrant. There is no guarantee an Buffer instance will be executed in a unique vm, or by a single thread. Also, note the Iterator will return the same TupleEntry instance, but with new values in its child Tuple.

Field Summary

Fields inherited from interface cascading.operation.Operation

ANY

Method Summary

void	operate(FlowProcess flowProcess, BufferCall<C> bufferCall) Method operate is called once for each grouping.

Methods inherited from interface cascading.operation.Operation

cleanup, getFieldDeclaration, getNumArgs, prepare

Method Detail

operate

void operate(FlowProcess flowProcess,
             BufferCall<C> bufferCall)

Method operate is called once for each grouping. BufferCall passes in an Iterator that returns an argument TupleEntry for each value in the grouping defined by the argument selector on the parent Every pipe instance.

TupleEntry entry, or entry.getTuple() should not be stored directly in a collection or modified. A copy of the tuple should be made via the new Tuple( entry.getTuple() ) copy constructor.

Parameters:

flowProcess - of type FlowProcess

bufferCall - of type BufferCall