org.apache.flink.streaming.runtime.tasks

Class StreamTask<OUT,OP extends StreamOperator<OUT>>

java.lang.Object

org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable

org.apache.flink.streaming.runtime.tasks.StreamTask<OUT,OP>

Type Parameters:

OUT -

OP -

All Implemented Interfaces:

StatefulTask, AsyncExceptionHandler

Direct Known Subclasses:

OneInputStreamTask, SourceStreamTask, TwoInputStreamTask

@Internal
public abstract class StreamTask<OUT,OP extends StreamOperator<OUT>>
extends AbstractInvokable
implements StatefulTask, AsyncExceptionHandler

Base class for all streaming tasks. A task is the unit of local processing that is deployed and executed by the TaskManagers. Each task runs one or more StreamOperators which form the Task's operator chain. Operators that are chained together execute synchronously in the same thread and hence on the same stream partition. A common case for these chains are successive map/flatmap/filter tasks.

The task chain contains one "head" operator and multiple chained operators. The StreamTask is specialized for the type of the head operator: one-input and two-input tasks, as well as for sources, iteration heads and iteration tails.

The Task class deals with the setup of the streams read by the head operator, and the streams produced by the operators at the ends of the operator chain. Note that the chain may fork and thus have multiple ends. The life cycle of the task is set up as follows:

-- setInitialState -> provides state of all operators in the chain

  -- invoke()
        |
        +----> Create basic utils (config, etc) and load the chain of operators
        +----> operators.setup()
        +----> task specific init()
        +----> initialize-operator-states()
        +----> open-operators()
        +----> run()
        +----> close-operators()
        +----> dispose-operators()
        +----> common cleanup
        +----> task specific cleanup()
 

The StreamTask has a lock object called lock. All calls to methods on a StreamOperator must be synchronized on this lock object to ensure that no methods are called concurrently.

Field Summary

Fields

Modifier and Type	Field and Description
protected OP	headOperator the head operator that consumes the input streams of this task
static ThreadGroup	TRIGGER_THREAD_GROUP The thread group that holds all trigger timer threads

Constructor Summary

Constructors

Constructor and Description
StreamTask()

Method Summary

Methods

Modifier and Type	Method and Description
void	abortCheckpointOnBarrier(long checkpointId, Throwable cause)
void	cancel()
protected abstract void	cancelTask()
protected abstract void	cleanup()
CheckpointStreamFactory	createCheckpointStreamFactory(StreamOperator<?> operator) This is only visible because GenericWriteAheadSink uses the checkpoint stream factory to write write-ahead logs.
<K> AbstractKeyedStateBackend<K>	createKeyedStateBackend(TypeSerializer<K> keySerializer, int numberOfKeyGroups, KeyGroupRange keyGroupRange)
OperatorStateBackend	createOperatorStateBackend(StreamOperator<?> op, Collection<OperatorStateHandle> restoreStateHandles)
protected void	finalize() The finalize method shuts down the timer.
Map<String,Accumulator<?,?>>	getAccumulatorMap()
ExecutorService	getAsyncOperationsThreadPool()
CloseableRegistry	getCancelables()
Object	getCheckpointLock() Gets the lock object on which all operations that involve data and state mutation have to lock.
StreamConfig	getConfiguration()
String	getName() Gets the name of the task, in the form "taskname (2/5)".
ProcessingTimeService	getProcessingTimeService() Returns the ProcessingTimeService responsible for telling the current processing time and registering timers.
void	handleAsyncException(String message, Throwable exception) Handles an exception thrown by another thread (e.g.
protected abstract void	init()
void	invoke()
boolean	isCanceled()
boolean	isRunning()
void	notifyCheckpointComplete(long checkpointId)
protected abstract void	run()
void	setInitialState(TaskStateHandles taskStateHandles)
void	setProcessingTimeService(ProcessingTimeService timeProvider) Allows the user to specify his own TimerServiceProvider.
String	toString()
boolean	triggerCheckpoint(CheckpointMetaData checkpointMetaData)
void	triggerCheckpointOnBarrier(CheckpointMetaData checkpointMetaData)

Methods inherited from class org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable

getCurrentNumberOfSubtasks, getEnvironment, getExecutionConfig, getIndexInSubtaskGroup, getJobConfiguration, getTaskConfiguration, getUserCodeClassLoader, setEnvironment

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

TRIGGER_THREAD_GROUP

public static final ThreadGroup TRIGGER_THREAD_GROUP

The thread group that holds all trigger timer threads

headOperator

protected OP extends StreamOperator<OUT> headOperator

the head operator that consumes the input streams of this task

Constructor Detail

StreamTask

public StreamTask()

Method Detail

init

protected abstract void init()
                      throws Exception

Throws:

Exception

run

protected abstract void run()
                     throws Exception

Throws:

Exception

cleanup

protected abstract void cleanup()
                         throws Exception

Throws:

Exception

cancelTask

protected abstract void cancelTask()
                            throws Exception

Throws:

Exception

setProcessingTimeService

public void setProcessingTimeService(ProcessingTimeService timeProvider)

Allows the user to specify his own TimerServiceProvider. By default a DefaultTimerService is going to be provided. Changing it can be useful for testing processing time functionality, such as WindowAssigners and Triggers.

invoke

public final void invoke()
                  throws Exception

Specified by:

invoke in class AbstractInvokable

Throws:

Exception

cancel

public final void cancel()
                  throws Exception

Overrides:

cancel in class AbstractInvokable

Throws:

Exception

isRunning

public final boolean isRunning()

isCanceled

public final boolean isCanceled()

finalize

protected void finalize()
                 throws Throwable

The finalize method shuts down the timer. This is a fail-safe shutdown, in case the original shutdown method was never called.

This should not be relied upon! It will cause shutdown to happen much later than if manual shutdown is attempted, and cause threads to linger for longer than needed.

Overrides:

finalize in class Object

Throws:

Throwable

getName

public String getName()

Gets the name of the task, in the form "taskname (2/5)".

Returns:

The name of the task.

getCheckpointLock

public Object getCheckpointLock()

Gets the lock object on which all operations that involve data and state mutation have to lock.

Returns:

The checkpoint lock object.

getConfiguration

public StreamConfig getConfiguration()

getAccumulatorMap

public Map<String,Accumulator<?,?>> getAccumulatorMap()

setInitialState

public void setInitialState(TaskStateHandles taskStateHandles)

Specified by:

setInitialState in interface StatefulTask

triggerCheckpoint

public boolean triggerCheckpoint(CheckpointMetaData checkpointMetaData)
                          throws Exception

Specified by:

triggerCheckpoint in interface StatefulTask

Throws:

Exception

triggerCheckpointOnBarrier

public void triggerCheckpointOnBarrier(CheckpointMetaData checkpointMetaData)
                                throws Exception

Specified by:

triggerCheckpointOnBarrier in interface StatefulTask

Throws:

Exception

abortCheckpointOnBarrier

public void abortCheckpointOnBarrier(long checkpointId,
                            Throwable cause)
                              throws Exception

Specified by:

abortCheckpointOnBarrier in interface StatefulTask

Throws:

Exception

getAsyncOperationsThreadPool

public ExecutorService getAsyncOperationsThreadPool()

notifyCheckpointComplete

public void notifyCheckpointComplete(long checkpointId)
                              throws Exception

Specified by:

notifyCheckpointComplete in interface StatefulTask

Throws:

Exception

createOperatorStateBackend

public OperatorStateBackend createOperatorStateBackend(StreamOperator<?> op,
                                              Collection<OperatorStateHandle> restoreStateHandles)
                                                throws Exception

Throws:

Exception

createKeyedStateBackend

public <K> AbstractKeyedStateBackend<K> createKeyedStateBackend(TypeSerializer<K> keySerializer,
                                                       int numberOfKeyGroups,
                                                       KeyGroupRange keyGroupRange)
                                                     throws Exception

Throws:

Exception

createCheckpointStreamFactory

public CheckpointStreamFactory createCheckpointStreamFactory(StreamOperator<?> operator)
                                                      throws IOException

This is only visible because GenericWriteAheadSink uses the checkpoint stream factory to write write-ahead logs. This should not be used for anything else.

Throws:

IOException

getProcessingTimeService

public ProcessingTimeService getProcessingTimeService()

Returns the ProcessingTimeService responsible for telling the current processing time and registering timers.

handleAsyncException

public void handleAsyncException(String message,
                        Throwable exception)

Handles an exception thrown by another thread (e.g. a TriggerTask), other than the one executing the main task by failing the task entirely. In more detail, it marks task execution failed for an external reason (a reason other than the task code itself throwing an exception). If the task is already in a terminal state (such as FINISHED, CANCELED, FAILED), or if the task is already canceling this does nothing. Otherwise it sets the state to FAILED, and, if the invokable code is running, starts an asynchronous thread that aborts that code.

This method never blocks.

Specified by:

handleAsyncException in interface AsyncExceptionHandler

toString

public String toString()

Overrides:

toString in class Object

getCancelables

public CloseableRegistry getCancelables()