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, OneInputStreamTask, SourceStreamTask

@Internal
public abstract class StreamTask<OUT,OP extends StreamOperator<OUT>>
extends org.apache.flink.runtime.jobgraph.tasks.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.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	StreamTask.ActionContext The action context is passed as parameter into the default action method and holds control methods for feedback of from the default action to the mailbox.
protected static class	StreamTask.AsyncCheckpointRunnable This runnable executes the asynchronous parts of all involved backend snapshots for the subtask.

Field Summary

Fields

Modifier and Type	Field and Description
protected StreamConfig	configuration The configuration of this streaming task.
protected OP	headOperator the head operator that consumes the input streams of this task.
protected StreamInputProcessor	inputProcessor The input processor.
protected Mailbox	mailbox
protected OperatorChain<OUT,OP>	operatorChain The chain of operators executed by this task.
protected org.apache.flink.runtime.state.StateBackend	stateBackend Our state backend.
protected ProcessingTimeService	timerService The internal ProcessingTimeService 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(org.apache.flink.runtime.execution.Environment env) Constructor for initialization, possibly with initial state (recovery / savepoint / etc).
protected	StreamTask(org.apache.flink.runtime.execution.Environment env, ProcessingTimeService timeProvider) Constructor for initialization, possibly with initial state (recovery / savepoint / etc).
protected	StreamTask(org.apache.flink.runtime.execution.Environment environment, ProcessingTimeService timeProvider, Thread.UncaughtExceptionHandler uncaughtExceptionHandler) Constructor for initialization, possibly with initial state (recovery / savepoint / etc).

Method Summary

Modifier and Type	Method and Description
void	abortCheckpointOnBarrier(long checkpointId, Throwable cause)
protected void	advanceToEndOfEventTime() Emits the MAX_WATERMARK so that all registered timers are fired.
void	cancel()
protected void	cancelTask()
protected void	cleanup()
protected CheckpointExceptionHandlerFactory	createCheckpointExceptionHandlerFactory()
static <OUT> List<org.apache.flink.runtime.io.network.api.writer.RecordWriter<org.apache.flink.runtime.plugable.SerializationDelegate<StreamRecord<OUT>>>>	createRecordWriters(StreamConfig configuration, org.apache.flink.runtime.execution.Environment environment)
StreamTaskStateInitializer	createStreamTaskStateInitializer()
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.
Map<String,org.apache.flink.api.common.accumulators.Accumulator<?,?>>	getAccumulatorMap()
ExecutorService	getAsyncOperationsThreadPool()
org.apache.flink.core.fs.CloseableRegistry	getCancelables()
Object	getCheckpointLock() Gets the lock object on which all operations that involve data and state mutation have to lock.
org.apache.flink.runtime.state.CheckpointStorageWorkerView	getCheckpointStorage()
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.
StreamStatusMaintainer	getStreamStatusMaintainer()
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 void	processInput(StreamTask.ActionContext context) This method implements the default action of the task (e.g.
String	toString()
boolean	triggerCheckpoint(org.apache.flink.runtime.checkpoint.CheckpointMetaData checkpointMetaData, org.apache.flink.runtime.checkpoint.CheckpointOptions checkpointOptions, boolean advanceToEndOfEventTime)
void	triggerCheckpointOnBarrier(org.apache.flink.runtime.checkpoint.CheckpointMetaData checkpointMetaData, org.apache.flink.runtime.checkpoint.CheckpointOptions checkpointOptions, org.apache.flink.runtime.checkpoint.CheckpointMetrics checkpointMetrics)

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

getCurrentNumberOfSubtasks, getEnvironment, getExecutingThread, 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.

inputProcessor

@Nullable
protected StreamInputProcessor inputProcessor

The input processor. Initialized in init() method.

headOperator

protected OP extends StreamOperator<OUT> headOperator

the head 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 org.apache.flink.runtime.state.StateBackend stateBackend

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

timerService

protected ProcessingTimeService timerService

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

mailbox

protected final Mailbox mailbox

Constructor Detail

StreamTask

protected StreamTask(org.apache.flink.runtime.execution.Environment env)

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

Parameters:

env - The task environment for this task.

StreamTask

protected StreamTask(org.apache.flink.runtime.execution.Environment env,
                     @Nullable
                     ProcessingTimeService timeProvider)

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

Parameters:

env - The task environment for this task.

timeProvider - Optionally, a specific time provider to use.

StreamTask

protected StreamTask(org.apache.flink.runtime.execution.Environment environment,
                     @Nullable
                     ProcessingTimeService timeProvider,
                     Thread.UncaughtExceptionHandler uncaughtExceptionHandler)

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

This constructor accepts a special ProcessingTimeService. By default (and if null is passes for the time provider) a DefaultTimerService will be used.

Parameters:

environment - The task environment for this task.

timeProvider - Optionally, a specific time provider to use.

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

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(StreamTask.ActionContext context)
                     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:

context - context 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 stoppped with a savepoint.

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

Throws:

Exception

createStreamTaskStateInitializer

public StreamTaskStateInitializer createStreamTaskStateInitializer()

invoke

public final void invoke()
                  throws Exception

Specified by:

invoke in class org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable

Throws:

Exception

cancel

public final void cancel()
                  throws Exception

Overrides:

cancel in class org.apache.flink.runtime.jobgraph.tasks.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.

getCheckpointStorage

public org.apache.flink.runtime.state.CheckpointStorageWorkerView getCheckpointStorage()

getConfiguration

public StreamConfig getConfiguration()

getAccumulatorMap

public Map<String,org.apache.flink.api.common.accumulators.Accumulator<?,?>> getAccumulatorMap()

getStreamStatusMaintainer

public StreamStatusMaintainer getStreamStatusMaintainer()

triggerCheckpoint

public boolean triggerCheckpoint(org.apache.flink.runtime.checkpoint.CheckpointMetaData checkpointMetaData,
                                 org.apache.flink.runtime.checkpoint.CheckpointOptions checkpointOptions,
                                 boolean advanceToEndOfEventTime)
                          throws Exception

Overrides:

triggerCheckpoint in class org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable

Throws:

Exception

triggerCheckpointOnBarrier

public void triggerCheckpointOnBarrier(org.apache.flink.runtime.checkpoint.CheckpointMetaData checkpointMetaData,
                                       org.apache.flink.runtime.checkpoint.CheckpointOptions checkpointOptions,
                                       org.apache.flink.runtime.checkpoint.CheckpointMetrics checkpointMetrics)
                                throws Exception

Overrides:

triggerCheckpointOnBarrier in class org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable

Throws:

Exception

abortCheckpointOnBarrier

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

Overrides:

abortCheckpointOnBarrier in class org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable

Throws:

Exception

getAsyncOperationsThreadPool

public ExecutorService getAsyncOperationsThreadPool()

notifyCheckpointComplete

public void notifyCheckpointComplete(long checkpointId)
                              throws Exception

Overrides:

notifyCheckpointComplete in class org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable

Throws:

Exception

createCheckpointExceptionHandlerFactory

protected CheckpointExceptionHandlerFactory createCheckpointExceptionHandlerFactory()

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 org.apache.flink.core.fs.CloseableRegistry getCancelables()

createRecordWriters

@VisibleForTesting
public static <OUT> List<org.apache.flink.runtime.io.network.api.writer.RecordWriter<org.apache.flink.runtime.plugable.SerializationDelegate<StreamRecord<OUT>>>> createRecordWriters(StreamConfig configuration,
                                                                                                                                                                                                         org.apache.flink.runtime.execution.Environment environment)