org.apache.druid.frame.processor

Interface FrameProcessor<T>

All Known Implementing Classes:

FrameChannelBatcher, FrameChannelHashPartitioner, FrameChannelMerger, FrameChannelMixer

public interface FrameProcessor<T>

A FrameProcessor is like an incremental version of Runnable that operates on ReadableFrameChannel and WritableFrameChannel. It is designed to enable interleaved non-blocking work on a fixed-size thread pool. Typically, this is done using an instance of FrameProcessorExecutor.

Method Summary

Modifier and Type	Method and Description
void	cleanup() Closes resources used by this worker.
List<ReadableFrameChannel>	inputChannels() List of input channels.
List<WritableFrameChannel>	outputChannels() List of output channels.
ReturnOrAwait<T>	runIncrementally(it.unimi.dsi.fastutil.ints.IntSet readableInputs) Runs some of the algorithm, without blocking, and either returns a value or a set of input channels to wait for.

Method Detail

inputChannels

List<ReadableFrameChannel> inputChannels()

List of input channels. The positions of channels in this list are used to build the readableInputs set provided to runIncrementally(it.unimi.dsi.fastutil.ints.IntSet).

outputChannels

List<WritableFrameChannel> outputChannels()

List of output channels.

runIncrementally

ReturnOrAwait<T> runIncrementally(it.unimi.dsi.fastutil.ints.IntSet readableInputs)
                           throws InterruptedException,
                                  IOException

Runs some of the algorithm, without blocking, and either returns a value or a set of input channels to wait for. This method is called by FrameProcessorExecutor.runFully(org.apache.druid.frame.processor.FrameProcessor<T>, java.lang.String) when all output channels are writable. Therefore, it is guaranteed that each output channel can accept at least one frame. This method must not read more than one frame from each readable input channel, and must not write more than one frame to each output channel.

Parameters:

readableInputs - channels from inputChannels() that are either finished or ready to read. That is: either ReadableFrameChannel.isFinished() or ReadableFrameChannel.canRead() are true.

Returns:

either a final return value or a set of input channels to wait for. Must be nonnull.

Throws:

InterruptedException

IOException

cleanup

void cleanup()
      throws IOException

Closes resources used by this worker. Exact same concept as Closeable.close(). This interface does not extend Closeable, in order to make it easier to find all places where cleanup happens. (Static analysis tools can lose the thread when Closeables are closed in generic ways.) Implementations typically call ReadableFrameChannel.close() and WritableFrameChannel.close() on all input and output channels, as well as releasing any additional resources that may be held, such as FrameWriter. In cases of cancellation, this method may be called even if runIncrementally(it.unimi.dsi.fastutil.ints.IntSet) has not yet returned a result via ReturnOrAwait.returnObject(T).

Throws:

IOException