org.eigenbase.runtime
Class CompoundParallelTupleIter

java.lang.Object
  org.eigenbase.runtime.AbstractTupleIter
      org.eigenbase.runtime.CompoundParallelTupleIter

All Implemented Interfaces:

TupleIter, ClosableAllocation

public class CompoundParallelTupleIter
extends AbstractTupleIter

CompoundParallelTupleIter creates one TupleIter out of several. Unlike its serial counterpart CompoundTupleIter, it runs all its inputs in parallel, in separate threads that it spawns. It outputs the next element available from any of its inputs. Note that the order of output rows is indeterminate, since it is unpredictable which input will arrive next.

The compound TupleIter is finished when all of its inputs are finished. The set of input iterators is fixed at construction.

This variant is needed when an input is infinite, since CompoundTupleIter would hang. Extending this class to preserve order is problematic, given its low level:

• items Are now synthetic Objects.
• Items would have to become things that expose a Comparable key value.
• Even if one input lags behind the other provding a Iterator.next() value, that missing value might sort before its available counterparts from the other inputs. There is no basis to decide to wait for it or not.

Version:

$Id: //open/dev/farrago/src/org/eigenbase/runtime/CompoundParallelTupleIter.java#8 $

Author:

Marc Berkowitz

Nested Class Summary

static class

CompoundParallelTupleIter.Test

Nested classes/interfaces inherited from interface org.eigenbase.runtime.TupleIter

TupleIter.NoDataReason, TupleIter.TimeoutException

Field Summary

private boolean[]	endOfData
private int	i
private TupleIter[]	in

Fields inherited from interface org.eigenbase.runtime.TupleIter

EMPTY_ITERATOR

Constructor Summary

CompoundParallelTupleIter(TupleIter[] tupleIters)

Method Summary

void	closeAllocation() Closes this object.
Object	fetchNext() Returns the next element in the iteration.
void	restart() Restarts this iterator, so that a subsequent call to TupleIter.fetchNext() returns the first element in the collection being iterated.

Methods inherited from class org.eigenbase.runtime.AbstractTupleIter

setTimeout

Methods inherited from class java.lang.Object

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

Field Detail

in

private final TupleIter[] in

endOfData

private final boolean[] endOfData

i

private int i

Constructor Detail

CompoundParallelTupleIter

public CompoundParallelTupleIter(TupleIter[] tupleIters)

Method Detail

fetchNext

public Object fetchNext()

Description copied from interface: TupleIter

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 TupleIter.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.

restart

public void restart()

Description copied from interface: TupleIter

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

Specified by:

restart in interface TupleIter

Overrides:

restart in class AbstractTupleIter

closeAllocation

public void closeAllocation()

Description copied from interface: ClosableAllocation

Closes this object.