PullingAsyncDataInput (Flink : 2.0-preview1 API)

All Superinterfaces:

AvailabilityProvider

All Known Implementing Classes:

CheckpointedInputGate, IndexedInputGate, InputGate, InputGateWithMetrics, SingleInputGate, UnionInputGate
```
@Internal
public interface PullingAsyncDataInput<T>
extends AvailabilityProvider
```
Interface defining couple of essential methods for asynchronous and non blocking data polling.
For the most efficient usage, user of this class is supposed to call pollNext() until it returns that no more elements are available. If that happens, he should check if input isFinished(). If not, he should wait for AvailabilityProvider.getAvailableFuture() CompletableFuture to be completed. For example:
```
 AsyncDataInput<T> input = ...;
 while (!input.isFinished()) {
 	Optional<T> next;

 	while (true) {
 		next = input.pollNext();
 		if (!next.isPresent()) {
 			break;
 		}
 		// do something with next
 	}

 	input.getAvailableFuture().get();
 }
 
```

Nested Class Summary

Nested Classes
Modifier and Type Interface Description

static class PullingAsyncDataInput.EndOfDataStatus
Status for describing if we have reached the end of data.
- Nested classes/interfaces inherited from interface org.apache.flink.runtime.io.AvailabilityProvider
  AvailabilityProvider.AvailabilityHelper

Field Summary
- Fields inherited from interface org.apache.flink.runtime.io.AvailabilityProvider
  AVAILABLE

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`PullingAsyncDataInput.EndOfDataStatus`	`hasReceivedEndOfData()`	Tells if we consumed all available data.
`boolean`	`isFinished()`
`Optional<T>`	`pollNext()`	Poll the next element.

Methods inherited from interface org.apache.flink.runtime.io.AvailabilityProvider
getAvailableFuture, isApproximatelyAvailable, isAvailable

- Method Detail
  - pollNext
```
Optional<T> pollNext()
              throws Exception
```
    Poll the next element. This method should be non blocking.
    
    Returns:
    
    Optional.empty() will be returned if there is no data to return or if isFinished() returns true. Otherwise Optional.of(element).
    
    Throws:
    
    Exception
  - isFinished
```
boolean isFinished()
```
    Returns:
    
    true if is finished and for example end of input was reached, false otherwise.
  - hasReceivedEndOfData
```
PullingAsyncDataInput.EndOfDataStatus hasReceivedEndOfData()
```
    Tells if we consumed all available data.
    Moreover it tells us the reason why there is no more data incoming. If any of the upstream subtasks finished because of the stop-with-savepoint --no-drain, we should not drain the input. See also StopMode.