T
- The type of elements returned by this function.@PublicEvolving public class FromElementsFunction<T> extends Object implements SourceFunction<T>, CheckpointedFunction
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.
NOTE: This source has a parallelism of 1.
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 |
initializeState(FunctionInitializationContext context)
This method is called when the parallel function instance is created during distributed
execution.
|
void |
run(SourceFunction.SourceContext<T> ctx)
Starts the source.
|
void |
snapshotState(FunctionSnapshotContext context)
This method is called when a snapshot for a checkpoint is requested.
|
public FromElementsFunction(TypeSerializer<T> serializer, T... elements) throws IOException
IOException
public FromElementsFunction(TypeSerializer<T> serializer, Iterable<T> elements) throws IOException
IOException
public void initializeState(FunctionInitializationContext context) throws Exception
CheckpointedFunction
initializeState
in interface CheckpointedFunction
context
- the context for initializing the operatorException
public void run(SourceFunction.SourceContext<T> ctx) throws Exception
SourceFunction
SourceFunction.SourceContext
emit
elements.
Sources that implement CheckpointedFunction
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 ExampleCountSource implements SourceFunction<Long>, CheckpointedFunction {
private long count = 0L;
private volatile boolean isRunning = true;
private transient ListState<Long> checkpointedCount;
public void run(SourceContext<T> ctx) {
while (isRunning && count < 1000) {
// this synchronized block ensures that state checkpointing,
// internal state updates and emission of elements are an atomic operation
synchronized (ctx.getCheckpointLock()) {
ctx.collect(count);
count++;
}
}
}
public void cancel() {
isRunning = false;
}
public void initializeState(FunctionInitializationContext context) {
this.checkpointedCount = context
.getOperatorStateStore()
.getListState(new ListStateDescriptor<>("count", Long.class));
if (context.isRestored()) {
for (Long count : this.checkpointedCount.get()) {
this.count = count;
}
}
}
public void snapshotState(FunctionSnapshotContext context) {
this.checkpointedCount.clear();
this.checkpointedCount.add(count);
}
}
run
in interface SourceFunction<T>
ctx
- The context to emit elements to and for accessing locks.Exception
public void cancel()
SourceFunction
SourceFunction.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 void snapshotState(FunctionSnapshotContext context) throws Exception
CheckpointedFunction
FunctionInitializationContext
when
the Function was initialized, or offered now by FunctionSnapshotContext
itself.snapshotState
in interface CheckpointedFunction
context
- the context for drawing a snapshot of the operatorException
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 © 2014–2020 The Apache Software Foundation. All rights reserved.