public static class StatefulStreamingJob.MySource extends RichParallelSourceFunction<Integer>
SourceFunction.SourceContext<T>| Constructor and Description |
|---|
MySource() |
| Modifier and Type | Method and Description |
|---|---|
void |
cancel()
Cancels the source.
|
void |
run(SourceFunction.SourceContext<Integer> ctx)
Starts the source.
|
close, getIterationRuntimeContext, getRuntimeContext, open, setRuntimeContextpublic void run(SourceFunction.SourceContext<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);
}
}
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.
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