public static final class StreamingFileSinkProgram.Generator extends Object implements SourceFunction<Tuple2<Integer,Integer>>, ListCheckpointed<Integer>
SourceFunction.SourceContext<T>| Modifier and Type | Method and Description |
|---|---|
void |
cancel()
Cancels the source.
|
void |
restoreState(List<Integer> states)
Restores the state of the function or operator to that of a previous checkpoint.
|
void |
run(SourceFunction.SourceContext<Tuple2<Integer,Integer>> ctx)
Starts the source.
|
List<Integer> |
snapshotState(long checkpointId,
long timestamp)
Gets the current state of the function.
|
public void run(SourceFunction.SourceContext<Tuple2<Integer,Integer>> ctx) throws Exception
SourceFunctionSourceFunction.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);
}
}
public 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<Tuple2<Integer,Integer>>public List<Integer> snapshotState(long checkpointId, long timestamp)
ListCheckpointedThe returned list should contain one entry for redistributable unit of state. See
the class docs for an illustration how list-style state
redistribution works.
As special case, the returned list may be null or empty (if the operator has no state) or it may contain a single element (if the operator state is indivisible).
snapshotState in interface ListCheckpointed<Integer>checkpointId - The ID of the checkpoint - a unique and monotonously increasing value.timestamp - The wall clock timestamp when the checkpoint was triggered by the master.public void restoreState(List<Integer> states)
ListCheckpointedThe given state list will contain all the sub states that this parallel
instance of the function needs to handle. Refer to the class docs
for an illustration how list-style state redistribution works.
Important: When implementing this interface together with RichFunction,
then the restoreState() method is called before RichFunction.open(Configuration).
restoreState in interface ListCheckpointed<Integer>states - The state to be restored as a list of atomic sub-states.Copyright © 2014–2020 The Apache Software Foundation. All rights reserved.