public class SequenceGeneratorSource extends RichParallelSourceFunction<Event> implements CheckpointedFunction
SourceFunction.SourceContext<T>| Modifier and Type | Method and Description |
|---|---|
void |
cancel()
Cancels the source.
|
void |
initializeState(FunctionInitializationContext context)
This method is called when the parallel function instance is created during distributed
execution.
|
void |
run(SourceFunction.SourceContext<Event> ctx)
Starts the source.
|
void |
snapshotState(FunctionSnapshotContext context)
This method is called when a snapshot for a checkpoint is requested.
|
close, getIterationRuntimeContext, getRuntimeContext, open, setRuntimeContextpublic void run(SourceFunction.SourceContext<Event> 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);
}
}
run in interface SourceFunction<Event>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<Event>public void snapshotState(FunctionSnapshotContext context) throws Exception
CheckpointedFunctionFunctionInitializationContext when
the Function was initialized, or offered now by FunctionSnapshotContext itself.snapshotState in interface CheckpointedFunctioncontext - the context for drawing a snapshot of the operatorExceptionpublic void initializeState(FunctionInitializationContext context) throws Exception
CheckpointedFunctioninitializeState in interface CheckpointedFunctioncontext - the context for initializing the operatorExceptionCopyright © 2014–2020 The Apache Software Foundation. All rights reserved.