T - The type of elements returned by this function.@PublicEvolving public class FromElementsFunction<T> extends Object implements SourceFunction<T>, CheckpointedAsynchronously<Integer>
Upon construction, this source function serializes the elements using Flink's type information. That way, any object transport using Java serialization will not be affected by the serializability of the elements.
SourceFunction.SourceContext<T>| Constructor and Description |
|---|
FromElementsFunction(TypeSerializer<T> serializer,
Iterable<T> elements) |
FromElementsFunction(TypeSerializer<T> serializer,
T... elements) |
| Modifier and Type | Method and Description |
|---|---|
void |
cancel()
Cancels the source.
|
static <OUT> void |
checkCollection(Collection<OUT> elements,
Class<OUT> viewedAs)
Verifies that all elements in the collection are non-null, and are of the given class, or
a subclass thereof.
|
int |
getNumElements()
Gets the number of elements produced in total by this function.
|
int |
getNumElementsEmitted()
Gets the number of elements emitted so far.
|
void |
restoreState(Integer state)
Restores the state of the function or operator to that of a previous checkpoint.
|
void |
run(SourceFunction.SourceContext<T> ctx)
Starts the source.
|
Integer |
snapshotState(long checkpointId,
long checkpointTimestamp)
Gets the current state of the function of operator.
|
public FromElementsFunction(TypeSerializer<T> serializer, T... elements) throws IOException
IOExceptionpublic FromElementsFunction(TypeSerializer<T> serializer, Iterable<T> elements) throws IOException
IOExceptionpublic void run(SourceFunction.SourceContext<T> ctx) throws Exception
SourceFunctionSourceFunction.SourceContext emit
elements.
Sources that implement Checkpointed
must lock on the checkpoint lock (using a synchronized block) before updating internal
state and emitting elements, to make both an atomic operation:
public class ExampleSource<T> implements SourceFunction<T>, Checkpointed<Long> {
private long count = 0L;
private volatile boolean isRunning = true;
public void run(SourceContext<T> ctx) {
while (isRunning && count < 1000) {
synchronized (ctx.getCheckpointLock()) {
ctx.collect(count);
count++;
}
}
}
public void cancel() {
isRunning = false;
}
public Long snapshotState(long checkpointId, long checkpointTimestamp) { return count; }
public void restoreState(Long state) { this.count = state; }
}
run in interface SourceFunction<T>ctx - The context to emit elements to and for accessing locks.Exceptionpublic void cancel()
SourceFunctionSourceFunction.run(SourceContext) method. The implementation needs to ensure that the
source will break out of that loop after this method is called.
A typical pattern is to have an "volatile boolean isRunning" flag that is set to
false in this method. That flag is checked in the loop condition.
When a source is canceled, the executing thread will also be interrupted
(via Thread.interrupt()). The interruption happens strictly after this
method has been called, so any interruption handler can rely on the fact that
this method has completed. It is good practice to make any flags altered by
this method "volatile", in order to guarantee the visibility of the effects of
this method to any interruption handler.
cancel in interface SourceFunction<T>public int getNumElements()
public int getNumElementsEmitted()
public Integer snapshotState(long checkpointId, long checkpointTimestamp)
CheckpointedsnapshotState in interface Checkpointed<Integer>checkpointId - The ID of the checkpoint.checkpointTimestamp - The timestamp of the checkpoint, as derived by
System.currentTimeMillis() on the JobManager.public void restoreState(Integer state)
CheckpointedrestoreState in interface Checkpointed<Integer>state - The state to be restored.public static <OUT> void checkCollection(Collection<OUT> elements, Class<OUT> viewedAs)
OUT - The generic type of the collection to be checked.elements - The collection to check.viewedAs - The class to which the elements must be assignable to.Copyright © 2014–2017 The Apache Software Foundation. All rights reserved.