org.apache.drill.exec.physical.impl.scan.v3.lifecycle

Class BaseTestScanLifecycle.NoDataReader

java.lang.Object

org.apache.drill.exec.physical.impl.scan.v3.lifecycle.BaseTestScanLifecycle.BaseMockBatchReader

org.apache.drill.exec.physical.impl.scan.v3.lifecycle.BaseTestScanLifecycle.NoDataReader

All Implemented Interfaces:

ManagedReader

Enclosing class:

BaseTestScanLifecycle

protected static class BaseTestScanLifecycle.NoDataReader
extends BaseTestScanLifecycle.BaseMockBatchReader

Mock reader with no data or schema, indicated by an early EOF exception.

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.drill.exec.physical.impl.scan.v3.ManagedReader

ManagedReader.EarlyEofException

Field Summary

Fields inherited from class org.apache.drill.exec.physical.impl.scan.v3.lifecycle.BaseTestScanLifecycle.BaseMockBatchReader

batchCount, batchLimit, startIndex, tableLoader

Constructor Summary

Constructors

Constructor and Description
NoDataReader(SchemaNegotiator sn)

Method Summary

Modifier and Type	Method and Description
boolean	next() Read the next batch.

Methods inherited from class org.apache.drill.exec.physical.impl.scan.v3.lifecycle.BaseTestScanLifecycle.BaseMockBatchReader

close, makeBatch

Methods inherited from class java.lang.Object

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

Constructor Detail

NoDataReader

public NoDataReader(SchemaNegotiator sn)
             throws ManagedReader.EarlyEofException

Throws:

ManagedReader.EarlyEofException

Method Detail

next

public boolean next()

Description copied from interface: ManagedReader

Read the next batch. Reading continues until either EOF, or until the mutator indicates that the batch is full. The batch is considered valid if it is non-empty. Returning true with an empty batch is valid, and is helpful on the very first batch (returning schema only.) An empty batch with a false return code indicates EOF and the batch will be discarded. A non-empty batch along with a false return result indicates a final, valid batch, but that EOF was reached and no more data is available.

This somewhat complex protocol avoids the need to allocate a final batch just to find out that no more data is available; it allows EOF to be returned along with the final batch.

Specified by:

next in interface ManagedReader

Overrides:

next in class BaseTestScanLifecycle.BaseMockBatchReader

Returns:

true if more data may be available (and so next() should be called again, false to indicate that EOF was reached