io.druid.data.input

Interface Firehose

All Superinterfaces:

AutoCloseable, Closeable

All Known Implementing Classes:

EventReceiverFirehoseFactory.EventReceiverFirehose, FileIteratingFirehose, IngestSegmentFirehose, PredicateFirehose

public interface Firehose
extends Closeable

This is an interface that holds onto the stream of incoming data. Realtime data ingestion is built around this abstraction. In order to add a new type of source for realtime data ingestion, all you need to do is implement one of these and register it with the Main. This object acts a lot like an Iterator, but it doesn't extend the Iterator interface because it extends Closeable and it is very important that the close() method doesn't get forgotten, which is easy to do if this gets passed around as an Iterator.

The implementation of this interface only needs to be minimally thread-safe. The three methods ##hasMore(), ##nextRow() and ##commit() are all called from the same thread. ##commit(), however, returns a callback which will be called on another thread, so the operations inside of that callback must be thread-safe.

Method Summary

Modifier and Type	Method and Description
Runnable	commit() Returns a runnable that will "commit" everything read up to the point at which commit() is called.
boolean	hasMore() Returns whether there are more rows to process.
InputRow	nextRow() The next row available.

Methods inherited from interface java.io.Closeable

close

Method Detail

hasMore

boolean hasMore()

Returns whether there are more rows to process. This is used to indicate that another item is immediately available via ##nextRow(). Thus, if the stream is still available but there are no new messages on it, this call should block until a new message is available. If something happens such that the stream is no longer available, this should return false.

Returns:

true if and when there is another row available, false if the stream has dried up

nextRow

@Nullable
InputRow nextRow()

The next row available. Should only be called if hasMore returns true. The return value can be null which means the caller must skip this row.

Returns:

The next row

commit

Runnable commit()

Returns a runnable that will "commit" everything read up to the point at which commit() is called. This is often equivalent to everything that has been read since the last commit() call (or instantiation of the object), but doesn't necessarily have to be. This method is called when the main processing loop starts to persist its current batch of things to process. The returned runnable will be run when the current batch has been successfully persisted, there is usually some time lag between when this method is called and when the runnable is run. The Runnable is also run on a separate thread so its operation should be thread-safe. The Runnable is essentially just a lambda/closure that is run() after data supplied by this instance has been committed on the writer side of this interface protocol.

A simple implementation of this interface might do nothing when run() is called (in which case the same do-nothing instance can be returned every time), or a more complex implementation might clean up temporary resources that are no longer needed because of InputRows delivered by prior calls to ##nextRow().