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:

AsyncExceptionHandler

Direct Known Subclasses:

AbstractTwoInputStreamTask, MultipleInputStreamTask, OneInputStreamTask, SourceOperatorStreamTask, SourceStreamTask

@Internal
public abstract class StreamTask<OUT,OP extends StreamOperator<OUT>>
extends AbstractInvokable
implements 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 StreamConfig	configuration The configuration of this streaming task.
protected StreamInputProcessor	inputProcessor The input processor.
protected static org.slf4j.Logger	LOG The logger used by the StreamTask and its subclasses.
protected MailboxProcessor	mailboxProcessor
protected OP	mainOperator the main operator that consumes the input streams of this task.
protected OperatorChain<OUT,OP>	operatorChain The chain of operators executed by this task.
protected StateBackend	stateBackend Our state backend.
protected TimerService	timerService The internal TimerService used to define the current processing time (default = System.currentTimeMillis()) and register timers for tasks to be executed in the future.
static ThreadGroup	TRIGGER_THREAD_GROUP The thread group that holds all trigger timer threads.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	StreamTask(Environment env) Constructor for initialization, possibly with initial state (recovery / savepoint / etc).
protected	StreamTask(Environment env, TimerService timerService) Constructor for initialization, possibly with initial state (recovery / savepoint / etc).
protected	StreamTask(Environment environment, TimerService timerService, Thread.UncaughtExceptionHandler uncaughtExceptionHandler)
protected	StreamTask(Environment environment, TimerService timerService, Thread.UncaughtExceptionHandler uncaughtExceptionHandler, StreamTaskActionExecutor actionExecutor) Constructor for initialization, possibly with initial state (recovery / savepoint / etc).
protected	StreamTask(Environment environment, TimerService timerService, Thread.UncaughtExceptionHandler uncaughtExceptionHandler, StreamTaskActionExecutor actionExecutor, TaskMailbox mailbox)

Method Summary

Modifier and Type	Method and Description
void	abortCheckpointOnBarrier(long checkpointId, Throwable cause) Aborts a checkpoint as the result of receiving possibly some checkpoint barriers, but at least one CancelCheckpointMarker.
protected void	advanceToEndOfEventTime() Emits the MAX_WATERMARK so that all registered timers are fired.
protected void	afterInvoke()
protected void	beforeInvoke()
Future<Void>	cancel() This method is called when a task is canceled either as a result of a user abort or an execution failure.
protected void	cancelTask()
protected void	cleanup()
protected void	cleanUpInvoke()
static <OUT> RecordWriterDelegate<SerializationDelegate<StreamRecord<OUT>>>	createRecordWriterDelegate(StreamConfig configuration, Environment environment)
StreamTaskStateInitializer	createStreamTaskStateInitializer()
protected void	declineCheckpoint(long checkpointId)
void	dispatchOperatorEvent(OperatorID operator, SerializedValue<OperatorEvent> event)
protected void	finalize() The finalize method shuts down the timer.
protected void	finishTask() Instructs the task to go through its normal termination routine, i.e.
protected long	getAsyncCheckpointStartDelayNanos()
ExecutorService	getAsyncOperationsThreadPool()
CloseableRegistry	getCancelables()
CheckpointStorageWorkerView	getCheckpointStorage()
protected CompletableFuture<Void>	getCompletionFuture()
StreamConfig	getConfiguration()
MailboxExecutorFactory	getMailboxExecutorFactory()
String	getName() Gets the name of the task, in the form "taskname (2/5)".
ProcessingTimeServiceFactory	getProcessingTimeServiceFactory()
StreamStatusMaintainer	getStreamStatusMaintainer()
void	handleAsyncException(String message, Throwable exception) Handles an exception thrown by another thread (e.g.
protected abstract void	init()
void	invoke() Starts the execution.
boolean	isCanceled()
boolean	isFailing()
boolean	isMailboxLoopRunning()
boolean	isRunning()
Future<Void>	notifyCheckpointAbortAsync(long checkpointId) Invoked when a checkpoint has been aborted, i.e., when the checkpoint coordinator has received a decline message from one task and try to abort the targeted checkpoint by notification.
Future<Void>	notifyCheckpointCompleteAsync(long checkpointId) Invoked when a checkpoint has been completed, i.e., when the checkpoint coordinator has received the notification from all participating tasks.
protected void	processInput(MailboxDefaultAction.Controller controller) This method implements the default action of the task (e.g.
void	runMailboxLoop()
boolean	runMailboxStep()
protected Counter	setupNumRecordsInCounter(StreamOperator streamOperator)
String	toString()
Future<Boolean>	triggerCheckpointAsync(CheckpointMetaData checkpointMetaData, CheckpointOptions checkpointOptions) This method is called to trigger a checkpoint, asynchronously by the checkpoint coordinator.
void	triggerCheckpointOnBarrier(CheckpointMetaData checkpointMetaData, CheckpointOptions checkpointOptions, CheckpointMetricsBuilder checkpointMetrics) This method is called when a checkpoint is triggered as a result of receiving checkpoint barriers on all input streams.

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

getCurrentNumberOfSubtasks, getEnvironment, getExecutionConfig, getIndexInSubtaskGroup, getJobConfiguration, getTaskConfiguration, getUserCodeClassLoader, setShouldInterruptOnCancel, shouldInterruptOnCancel

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.

LOG

protected static final org.slf4j.Logger LOG

The logger used by the StreamTask and its subclasses.

inputProcessor

@Nullable
protected StreamInputProcessor inputProcessor

The input processor. Initialized in init() method.

mainOperator

protected OP extends StreamOperator<OUT> mainOperator

the main operator that consumes the input streams of this task.

operatorChain

protected OperatorChain<OUT,OP extends StreamOperator<OUT>> operatorChain

The chain of operators executed by this task.

configuration

protected final StreamConfig configuration

The configuration of this streaming task.

stateBackend

protected final StateBackend stateBackend

Our state backend. We use this to create checkpoint streams and a keyed state backend.

timerService

protected final TimerService timerService

The internal TimerService used to define the current processing time (default = System.currentTimeMillis()) and register timers for tasks to be executed in the future.

mailboxProcessor

protected final MailboxProcessor mailboxProcessor

Constructor Detail

StreamTask

protected StreamTask(Environment env)
              throws Exception

Constructor for initialization, possibly with initial state (recovery / savepoint / etc).

Parameters:

env - The task environment for this task.

Throws:

Exception

StreamTask

protected StreamTask(Environment env,
                     @Nullable
                     TimerService timerService)
              throws Exception

Constructor for initialization, possibly with initial state (recovery / savepoint / etc).

Parameters:

env - The task environment for this task.

timerService - Optionally, a specific timer service to use.

Throws:

Exception

StreamTask

protected StreamTask(Environment environment,
                     @Nullable
                     TimerService timerService,
                     Thread.UncaughtExceptionHandler uncaughtExceptionHandler)
              throws Exception

Throws:

Exception

StreamTask

protected StreamTask(Environment environment,
                     @Nullable
                     TimerService timerService,
                     Thread.UncaughtExceptionHandler uncaughtExceptionHandler,
                     StreamTaskActionExecutor actionExecutor)
              throws Exception

Constructor for initialization, possibly with initial state (recovery / savepoint / etc).

This constructor accepts a special TimerService. By default (and if null is passes for the timer service) a DefaultTimerService will be used.

Parameters:

environment - The task environment for this task.

timerService - Optionally, a specific timer service to use.

uncaughtExceptionHandler - to handle uncaught exceptions in the async operations thread pool

actionExecutor - a mean to wrap all actions performed by this task thread. Currently, only SynchronizedActionExecutor can be used to preserve locking semantics.

Throws:

Exception

StreamTask

protected StreamTask(Environment environment,
                     @Nullable
                     TimerService timerService,
                     Thread.UncaughtExceptionHandler uncaughtExceptionHandler,
                     StreamTaskActionExecutor actionExecutor,
                     TaskMailbox mailbox)
              throws Exception

Throws:

Exception

Method Detail

init

protected abstract void init()
                      throws Exception

Throws:

Exception

cancelTask

protected void cancelTask()
                   throws Exception

Throws:

Exception

cleanup

protected void cleanup()
                throws Exception

Throws:

Exception

processInput

protected void processInput(MailboxDefaultAction.Controller controller)
                     throws Exception

This method implements the default action of the task (e.g. processing one event from the input). Implementations should (in general) be non-blocking.

Parameters:

controller - controller object for collaborative interaction between the action and the stream task.

Throws:

Exception - on any problems in the action.

advanceToEndOfEventTime

protected void advanceToEndOfEventTime()
                                throws Exception

Emits the MAX_WATERMARK so that all registered timers are fired.

This is used by the source task when the job is TERMINATED. In the case, we want all the timers registered throughout the pipeline to fire and the related state (e.g. windows) to be flushed.

For tasks other than the source task, this method does nothing.

Throws:

Exception

finishTask

protected void finishTask()
                   throws Exception

Instructs the task to go through its normal termination routine, i.e. exit the run-loop and call StreamOperator.close() and StreamOperator.dispose() on its operators.

This is used by the source task to get out of the run-loop when the job is stopped with a savepoint.

For tasks other than the source task, this method does nothing.

Throws:

Exception

createStreamTaskStateInitializer

public StreamTaskStateInitializer createStreamTaskStateInitializer()

setupNumRecordsInCounter

protected Counter setupNumRecordsInCounter(StreamOperator streamOperator)

beforeInvoke

protected void beforeInvoke()
                     throws Exception

Throws:

Exception

invoke

public final void invoke()
                  throws Exception

Description copied from class: AbstractInvokable

Starts the execution.

Must be overwritten by the concrete task implementation. This method is called by the task manager when the actual execution of the task starts.

All resources should be cleaned up when the method returns. Make sure to guard the code with try-finally blocks where necessary.

Specified by:

invoke in class AbstractInvokable

Throws:

Exception - Tasks may forward their exceptions for the TaskManager to handle through failure/recovery.

runMailboxStep

@VisibleForTesting
public boolean runMailboxStep()
                                          throws Exception

Throws:

Exception

isMailboxLoopRunning

@VisibleForTesting
public boolean isMailboxLoopRunning()

runMailboxLoop

public void runMailboxLoop()
                    throws Exception

Throws:

Exception

afterInvoke

protected void afterInvoke()
                    throws Exception

Throws:

Exception

cleanUpInvoke

protected void cleanUpInvoke()
                      throws Exception

Throws:

Exception

getCompletionFuture

protected CompletableFuture<Void> getCompletionFuture()

cancel

public final Future<Void> cancel()
                          throws Exception

Description copied from class: AbstractInvokable

This method is called when a task is canceled either as a result of a user abort or an execution failure. It can be overwritten to respond to shut down the user code properly.

Overrides:

cancel in class AbstractInvokable

Returns:

a future that is completed when this AbstractInvokable is fully terminated. Note that it may never complete if the invokable is stuck.

Throws:

Exception - thrown if any exception occurs during the execution of the user code

getMailboxExecutorFactory

public MailboxExecutorFactory getMailboxExecutorFactory()

isRunning

public final boolean isRunning()

isCanceled

public final boolean isCanceled()

isFailing

public final boolean isFailing()

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 final String getName()

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

Returns:

The name of the task.

getCheckpointStorage

public CheckpointStorageWorkerView getCheckpointStorage()

getConfiguration

public StreamConfig getConfiguration()

getStreamStatusMaintainer

public StreamStatusMaintainer getStreamStatusMaintainer()

triggerCheckpointAsync

public Future<Boolean> triggerCheckpointAsync(CheckpointMetaData checkpointMetaData,
                                              CheckpointOptions checkpointOptions)

Description copied from class: AbstractInvokable

This method is called to trigger a checkpoint, asynchronously by the checkpoint coordinator.

This method is called for tasks that start the checkpoints by injecting the initial barriers, i.e., the source tasks. In contrast, checkpoints on downstream operators, which are the result of receiving checkpoint barriers, invoke the AbstractInvokable.triggerCheckpointOnBarrier(CheckpointMetaData, CheckpointOptions, CheckpointMetricsBuilder) method.

Overrides:

triggerCheckpointAsync in class AbstractInvokable

Parameters:

checkpointMetaData - Meta data for about this checkpoint

checkpointOptions - Options for performing this checkpoint

Returns:

future with value of false if the checkpoint was not carried out, true otherwise

triggerCheckpointOnBarrier

public void triggerCheckpointOnBarrier(CheckpointMetaData checkpointMetaData,
                                       CheckpointOptions checkpointOptions,
                                       CheckpointMetricsBuilder checkpointMetrics)
                                throws IOException

Description copied from class: AbstractInvokable

This method is called when a checkpoint is triggered as a result of receiving checkpoint barriers on all input streams.

Overrides:

triggerCheckpointOnBarrier in class AbstractInvokable

Parameters:

checkpointMetaData - Meta data for about this checkpoint

checkpointOptions - Options for performing this checkpoint

checkpointMetrics - Metrics about this checkpoint

Throws:

IOException

abortCheckpointOnBarrier

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

Description copied from class: AbstractInvokable

Aborts a checkpoint as the result of receiving possibly some checkpoint barriers, but at least one CancelCheckpointMarker.

This requires implementing tasks to forward a CancelCheckpointMarker to their outputs.

Overrides:

abortCheckpointOnBarrier in class AbstractInvokable

Parameters:

checkpointId - The ID of the checkpoint to be aborted.

cause - The reason why the checkpoint was aborted during alignment

Throws:

IOException

declineCheckpoint

protected void declineCheckpoint(long checkpointId)

getAsyncOperationsThreadPool

public final ExecutorService getAsyncOperationsThreadPool()

notifyCheckpointCompleteAsync

public Future<Void> notifyCheckpointCompleteAsync(long checkpointId)

Description copied from class: AbstractInvokable

Invoked when a checkpoint has been completed, i.e., when the checkpoint coordinator has received the notification from all participating tasks.

Overrides:

notifyCheckpointCompleteAsync in class AbstractInvokable

Parameters:

checkpointId - The ID of the checkpoint that is complete.

Returns:

future that completes when the notification has been processed by the task.

notifyCheckpointAbortAsync

public Future<Void> notifyCheckpointAbortAsync(long checkpointId)

Description copied from class: AbstractInvokable

Invoked when a checkpoint has been aborted, i.e., when the checkpoint coordinator has received a decline message from one task and try to abort the targeted checkpoint by notification.

Overrides:

notifyCheckpointAbortAsync in class AbstractInvokable

Parameters:

checkpointId - The ID of the checkpoint that is aborted.

Returns:

future that completes when the notification has been processed by the task.

dispatchOperatorEvent

public void dispatchOperatorEvent(OperatorID operator,
                                  SerializedValue<OperatorEvent> event)
                           throws FlinkException

Overrides:

dispatchOperatorEvent in class AbstractInvokable

Throws:

FlinkException

getProcessingTimeServiceFactory

public ProcessingTimeServiceFactory getProcessingTimeServiceFactory()

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 final CloseableRegistry getCancelables()

createRecordWriterDelegate

@VisibleForTesting
public static <OUT> RecordWriterDelegate<SerializationDelegate<StreamRecord<OUT>>> createRecordWriterDelegate(StreamConfig configuration,
                                                                                                                                 Environment environment)

getAsyncCheckpointStartDelayNanos

protected long getAsyncCheckpointStartDelayNanos()