org.apache.druid.frame.processor

Class OutputChannel

java.lang.Object

org.apache.druid.frame.processor.OutputChannel

public class OutputChannel
extends Object

Represents an output channel for some frame processor. Composed of a pair of WritableFrameChannel, which the processor writes to, along with a supplier of a ReadableFrameChannel, which readers can read from. At the time an instance of this class is created, the writable channel is already open, but the readable channel has not yet been created. It is created upon the first call to getReadableChannel().

Method Summary

Modifier and Type	Method and Description
MemoryAllocator	getFrameMemoryAllocator() Returns the memory allocator for the writable channel.
int	getPartitionNumber()
ReadableFrameChannel	getReadableChannel() Returns the readable channel of this pair.
WritableFrameChannel	getWritableChannel() Returns the writable channel of this pair.
OutputChannel	mapWritableChannel(Function<WritableFrameChannel,WritableFrameChannel> mapFn)
static OutputChannel	nil(int partitionNumber) Create a nil output channel, representing a processor that writes nothing.
static OutputChannel	pair(WritableFrameChannel writableChannel, MemoryAllocator frameMemoryAllocator, Supplier<ReadableFrameChannel> readableChannelSupplier, int partitionNumber) Creates an output channel pair.
OutputChannel	readOnly() Returns a read-only version of this instance.

Methods inherited from class java.lang.Object

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

Method Detail

pair

public static OutputChannel pair(WritableFrameChannel writableChannel,
                                 MemoryAllocator frameMemoryAllocator,
                                 Supplier<ReadableFrameChannel> readableChannelSupplier,
                                 int partitionNumber)

Creates an output channel pair.

Parameters:

writableChannel - writable channel for producer

frameMemoryAllocator - memory allocator for producer to use while writing frames to the channel

readableChannelSupplier - readable channel for consumer. May be called multiple times, so you should wrap this in Suppliers.memoize(com.google.common.base.Supplier<T>) if needed.

partitionNumber - partition number, if any; may be FrameWithPartition.NO_PARTITION if unknown

nil

public static OutputChannel nil(int partitionNumber)

Create a nil output channel, representing a processor that writes nothing. It is not actually writable, but provides a way for downstream processors to read nothing.

getWritableChannel

public WritableFrameChannel getWritableChannel()

Returns the writable channel of this pair. The producer writes to this channel.

getFrameMemoryAllocator

public MemoryAllocator getFrameMemoryAllocator()

Returns the memory allocator for the writable channel. The producer uses this to generate frames for the channel.

getReadableChannel

public ReadableFrameChannel getReadableChannel()

Returns the readable channel of this pair. This readable channel may, or may not, be usable before the writable channel is closed. It depends on whether the channel pair was created in a stream-capable manner or not.

getPartitionNumber

public int getPartitionNumber()

mapWritableChannel

public OutputChannel mapWritableChannel(Function<WritableFrameChannel,WritableFrameChannel> mapFn)

readOnly

public OutputChannel readOnly()

Returns a read-only version of this instance. Read-only versions have neither getWritableChannel() nor getFrameMemoryAllocator(), and therefore require substantially less memory.