T
- The type of elements returned by this function.@PublicEvolving public class FromElementsFunction<T> extends Object implements SourceFunction<T>, CheckpointedFunction, OutputTypeConfigurable<T>
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(Iterable<T> elements) |
FromElementsFunction(T... elements) |
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.
|
TypeSerializer<T> |
getSerializer() |
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 |
setOutputType(TypeInformation<T> outTypeInfo,
ExecutionConfig executionConfig)
Set element type and re-serialize element if required.
|
void |
snapshotState(FunctionSnapshotContext context)
This method is called when a snapshot for a checkpoint is requested.
|
@SafeVarargs public FromElementsFunction(TypeSerializer<T> serializer, T... elements) throws IOException
IOException
public FromElementsFunction(TypeSerializer<T> serializer, Iterable<T> elements) throws IOException
IOException
@SafeVarargs public FromElementsFunction(T... elements)
@VisibleForTesting @Nullable public TypeSerializer<T> getSerializer()
public void setOutputType(TypeInformation<T> outTypeInfo, ExecutionConfig executionConfig)
setOutputType
in interface OutputTypeConfigurable<T>
outTypeInfo
- Output type information of the StreamTask
executionConfig
- Execution configurationpublic void initializeState(FunctionInitializationContext context) throws Exception
CheckpointedFunction
initializeState
in interface CheckpointedFunction
context
- the context for initializing the operatorException
- Thrown, if state could not be created ot restored.public void run(SourceFunction.SourceContext<T> ctx) throws Exception
SourceFunction
SourceFunction.SourceContext
to emit elements. Sources
that checkpoint their state for fault tolerance should use the SourceFunction.SourceContext.getCheckpointLock()
checkpoint lock} to ensure consistency between the
bookkeeping and emitting the elements.
Sources that implement CheckpointedFunction
must lock on the SourceFunction.SourceContext.getCheckpointLock()
checkpoint lock} checkpoint lock (using a synchronized
block) before updating internal state and emitting elements, to make both an atomic
operation.
Refer to the top-level class docs
for an example.
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.
In case of an ungraceful shutdown (cancellation of the source operator, possibly for
failover), the thread that calls SourceFunction.run(SourceContext)
will also be interrupted
) by the Flink runtime, in order to speed up the cancellation
(to ensure threads exit blocking methods fast, like I/O, blocking queues, etc.). The
interruption happens strictly after this method has been called, so any interruption handler
can rely on the fact that this method has completed (for example to ignore exceptions that
happen after cancellation).
During graceful shutdown (for example stopping a job with a savepoint), the program must
cleanly exit the SourceFunction.run(SourceContext)
method soon after this method was called. The
Flink runtime will NOT interrupt the source thread during graceful shutdown. Source
implementors must ensure that no thread interruption happens on any thread that emits records
through the SourceContext
from the SourceFunction.run(SourceContext)
method; otherwise the
clean shutdown may fail when threads are interrupted while processing the final records.
Because the SourceFunction
cannot easily differentiate whether the shutdown should
be graceful or ungraceful, we recommend that implementors refrain from interrupting any
threads that interact with the SourceContext
at all. You can rely on the Flink
runtime to interrupt the source thread in case of ungraceful cancellation. Any additionally
spawned threads that directly emit records through the SourceContext
should use a
shutdown method that does not rely on thread interruption.
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
- Thrown, if state could not be created ot 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 © 2014–2022 The Apache Software Foundation. All rights reserved.