org.eigenbase.runtime
Interface TupleIter

All Superinterfaces:

ClosableAllocation

All Known Implementing Classes:

AbstractTupleIter, CalcTupleIter, CompoundParallelTupleIter, CompoundTupleIter, CompoundTupleIter.Test.BoxTupleIter, FarragoJavaUdxIterator, FennelAbstractTupleIter, FennelPipeIterator, FennelPipeTupleIter, FennelTransformTupleIter, FennelTupleIter, MedMockTupleIter, NestedLoopCalcTupleIter, RestartableCollectionTupleIter, RestartableIteratorTupleIter, ResultSetTupleIter, TimeoutQueueTupleIterTest.TickIterator

public interface TupleIter
extends ClosableAllocation

TupleIter provides an Iterator-like interface for reading tuple data.

TupleIter replaces the combination of Iterator and RestartableIterator.

Note that calling closeAllocation() closes this iterator, allowing it to release its resources. No further calls to fetchNext() or restart() may be made once the iterator is closed.

Version:

$Id: //open/dev/farrago/src/org/eigenbase/runtime/TupleIter.java#9 $

Author:

Stephan Zuercher

Nested Class Summary

static class	TupleIter.NoDataReason NoDataReason provides a reason why no data was returned by a call to fetchNext().
static class	TupleIter.TimeoutException One way to indicate that fetchNext() timed-out.

Field Summary

static TupleIter

EMPTY_ITERATOR

Method Summary

Object	fetchNext() Returns the next element in the iteration.
void	restart() Restarts this iterator, so that a subsequent call to fetchNext() returns the first element in the collection being iterated.
boolean	setTimeout(long timeout, boolean asUnderflow) Sets a timeout for fetchNext(); (optional operation).

Methods inherited from interface org.eigenbase.util.ClosableAllocation

closeAllocation

Field Detail

EMPTY_ITERATOR

static final TupleIter EMPTY_ITERATOR

Method Detail

fetchNext

Object fetchNext()

Returns the next element in the iteration. If there is no next value, it returns a value from the TupleIter.NoDataReason enumeration indicating why no data was returned.

If this method returns TupleIter.NoDataReason.END_OF_DATA, no further data will be returned by this iterator unless restart() is called.

If this method returns TupleIter.NoDataReason.UNDERFLOW, no data is currently available, but may be come available in the future. It is possible for consecutive calls to return UNDERFLOW and then END_OF_DATA.

The object returned by this method may be re-used for each subsequent call to fetchNext(). In other words, callers must either make certain that the returned value is no longer needed or is copied before any subsequent calls to fetchNext().

Returns:

the next element in the iteration, or an instance of TupleIter.NoDataReason.

setTimeout

boolean setTimeout(long timeout,
                   boolean asUnderflow)

Sets a timeout for fetchNext(); (optional operation). Not all implementing classes support a timeout. For those that do, this method provides a common interface, For those that do not, the adapter TimeoutQueueTupleIter puts a timeout queue on top.

Parameters:

timeout - in milliseconds. 0 means poll, infinity means block.

asUnderflow - true means indicate timeout by returning TupleIter.NoDataReason.UNDERFLOW; false means throw TupleIter.TimeoutException on a timeout.

Returns:

true if the timeout was set, false if the implementing class does not support a timeout.

restart

void restart()

Restarts this iterator, so that a subsequent call to fetchNext() returns the first element in the collection being iterated.