Package org.apache.beam.sdk.io

Class BlockBasedSource.BlockBasedReader<T>

java.lang.Object

org.apache.beam.sdk.io.Source.Reader<T>

org.apache.beam.sdk.io.BoundedSource.BoundedReader<T>

org.apache.beam.sdk.io.OffsetBasedSource.OffsetBasedReader<T>

org.apache.beam.sdk.io.FileBasedSource.FileBasedReader<T>

org.apache.beam.sdk.io.BlockBasedSource.BlockBasedReader<T>

All Implemented Interfaces:

AutoCloseable

Direct Known Subclasses:

AvroSource.AvroReader

Enclosing class:

BlockBasedSource<T>

public abstract static class BlockBasedSource.BlockBasedReader<T>
extends FileBasedSource.FileBasedReader<T>

A Reader that reads records from a BlockBasedSource. If the source is a subrange of a file, the blocks that will be read by this reader are those such that the first byte of the block is within the range [start, end).

Field Summary

Fields inherited from class org.apache.beam.sdk.io.BoundedSource.BoundedReader

SPLIT_POINTS_UNKNOWN

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	BlockBasedReader(BlockBasedSource<T> source)

Method Summary

Modifier and Type	Method	Description
final T	getCurrent()	Returns the value of the data item that was read by the last Source.Reader.start() or Source.Reader.advance() call.
abstract @Nullable BlockBasedSource.Block<T>	getCurrentBlock()	Returns the current block (the block that was read by the last successful call to readNextBlock()).
abstract long	getCurrentBlockOffset()	Returns the largest offset such that starting to read from that offset includes the current block.
abstract long	getCurrentBlockSize()	Returns the size of the current block in bytes as it is represented in the underlying file, if possible.
protected long	getCurrentOffset()	Returns the starting offset of the current record, which has been read by the last successful Source.Reader.start() or Source.Reader.advance() call.
@Nullable Double	getFractionConsumed()	Returns a value in [0, 1] representing approximately what fraction of the current source this reader has read so far, or null if such an estimate is not available.
boolean	isAtSplitPoint()	Returns true if the reader is at a split point.
abstract boolean	readNextBlock()	Read the next block from the input.
protected final boolean	readNextRecord()	Reads the next record from the current block if possible.

Methods inherited from class org.apache.beam.sdk.io.FileBasedSource.FileBasedReader

advanceImpl, allowsDynamicSplitting, close, getCurrentSource, startImpl, startReading

Methods inherited from class org.apache.beam.sdk.io.OffsetBasedSource.OffsetBasedReader

advance, getSplitPointsConsumed, getSplitPointsRemaining, isDone, isStarted, splitAtFraction, start

Methods inherited from class org.apache.beam.sdk.io.BoundedSource.BoundedReader

getCurrentTimestamp

Methods inherited from class java.lang.Object

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

Constructor Details

BlockBasedReader

protected BlockBasedReader(BlockBasedSource<T> source)

Method Details

readNextBlock

public abstract boolean readNextBlock()
                               throws IOException

Read the next block from the input.

Throws:

IOException

getCurrentBlock

public abstract @Nullable BlockBasedSource.Block<T> getCurrentBlock()

Returns the current block (the block that was read by the last successful call to readNextBlock()). May return null initially, or if no block has been successfully read.

getCurrentBlockSize

public abstract long getCurrentBlockSize()

Returns the size of the current block in bytes as it is represented in the underlying file, if possible. This method may return 0 if the size of the current block is unknown.

The size returned by this method must be such that for two successive blocks A and B, offset(A) + size(A) <= offset(B). If this is not satisfied, the progress reported by the BlockBasedReader will be non-monotonic and will interfere with the quality (but not correctness) of dynamic work rebalancing.

This method and BlockBasedSource.Block.getFractionOfBlockConsumed() are used to provide an estimate of progress within a block (getCurrentBlock().getFractionOfBlockConsumed() * getCurrentBlockSize()). It is acceptable for the result of this computation to be 0, but progress estimation will be inaccurate.

getCurrentBlockOffset

public abstract long getCurrentBlockOffset()

Returns the largest offset such that starting to read from that offset includes the current block.

getCurrent

public final T getCurrent()
                   throws NoSuchElementException

Description copied from class: Source.Reader

Returns the value of the data item that was read by the last Source.Reader.start() or Source.Reader.advance() call. The returned value must be effectively immutable and remain valid indefinitely.

Multiple calls to this method without an intervening call to Source.Reader.advance() should return the same result.

Specified by:

getCurrent in class Source.Reader<T>

Throws:

NoSuchElementException - if Source.Reader.start() was never called, or if the last Source.Reader.start() or Source.Reader.advance() returned false.

isAtSplitPoint

public boolean isAtSplitPoint()

Returns true if the reader is at a split point. A BlockBasedReader is at a split point if the current record is the first record in a block. In other words, split points are block boundaries.

Overrides:

isAtSplitPoint in class OffsetBasedSource.OffsetBasedReader<T>

readNextRecord

protected final boolean readNextRecord()
                                throws IOException

Reads the next record from the current block if possible. Will call readNextBlock() to advance to the next block if not.

The first record read from a block is treated as a split point.

Specified by:

readNextRecord in class FileBasedSource.FileBasedReader<T>

Returns:

true if a record was successfully read, false if the end of the channel was reached before successfully reading a new record.

Throws:

IOException

getFractionConsumed

public @Nullable Double getFractionConsumed()

Description copied from class: BoundedSource.BoundedReader

Returns a value in [0, 1] representing approximately what fraction of the current source this reader has read so far, or null if such an estimate is not available.

It is recommended that this method should satisfy the following properties:

• Should return 0 before the Source.Reader.start() call.
• Should return 1 after a Source.Reader.start() or Source.Reader.advance() call that returns false.
• The returned values should be non-decreasing (though they don't have to be unique).

By default, returns null to indicate that this cannot be estimated.

Thread safety

If BoundedSource.BoundedReader.splitAtFraction(double) is implemented, this method can be called concurrently to other methods (including itself), and it is therefore critical for it to be implemented in a thread-safe way.

Overrides:

getFractionConsumed in class OffsetBasedSource.OffsetBasedReader<T>

getCurrentOffset

protected long getCurrentOffset()

Description copied from class: OffsetBasedSource.OffsetBasedReader

Returns the starting offset of the current record, which has been read by the last successful Source.Reader.start() or Source.Reader.advance() call.

If no such call has been made yet, the return value is unspecified.

See RangeTracker for description of offset semantics.

Specified by:

getCurrentOffset in class OffsetBasedSource.OffsetBasedReader<T>