org.apache.flink.streaming.api.functions.source

Class ContinuousFileMonitoringFunction<OUT>

java.lang.Object

org.apache.flink.api.common.functions.AbstractRichFunction

org.apache.flink.streaming.api.functions.source.RichSourceFunction<TimestampedFileInputSplit>

org.apache.flink.streaming.api.functions.source.ContinuousFileMonitoringFunction<OUT>

All Implemented Interfaces:

Serializable, org.apache.flink.api.common.functions.Function, org.apache.flink.api.common.functions.RichFunction, CheckpointedFunction, SourceFunction<TimestampedFileInputSplit>

@Internal
public class ContinuousFileMonitoringFunction<OUT>
extends RichSourceFunction<TimestampedFileInputSplit>
implements CheckpointedFunction

This is the single (non-parallel) monitoring task which takes a FileInputFormat and, depending on the FileProcessingMode and the FilePathFilter, it is responsible for:

1. Monitoring a user-provided path.
2. Deciding which files should be further read and processed.
3. Creating the splits corresponding to those files.
4. Assigning them to downstream tasks for further processing.

The splits to be read are forwarded to the downstream ContinuousFileReaderOperator which can have parallelism greater than one.

IMPORTANT NOTE: Splits are forwarded downstream for reading in ascending modification time order, based on the modification time of the files they belong to.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.flink.streaming.api.functions.source.SourceFunction

SourceFunction.SourceContext<T>

Field Summary

Fields

Modifier and Type	Field and Description
static long	MIN_MONITORING_INTERVAL The minimum interval allowed between consecutive path scans.

Constructor Summary

Constructors

Constructor and Description
ContinuousFileMonitoringFunction(org.apache.flink.api.common.io.FileInputFormat<OUT> format, FileProcessingMode watchType, int readerParallelism, long interval)

Method Summary

Modifier and Type	Method and Description
void	cancel() Cancels the source.
void	close()
long	getGlobalModificationTime()
void	initializeState(org.apache.flink.runtime.state.FunctionInitializationContext context) This method is called when the parallel function instance is created during distributed execution.
void	open(org.apache.flink.configuration.Configuration parameters)
void	run(SourceFunction.SourceContext<TimestampedFileInputSplit> context) Starts the source.
void	snapshotState(org.apache.flink.runtime.state.FunctionSnapshotContext context) This method is called when a snapshot for a checkpoint is requested.

Methods inherited from class org.apache.flink.api.common.functions.AbstractRichFunction

getIterationRuntimeContext, getRuntimeContext, setRuntimeContext

Methods inherited from class java.lang.Object

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

Field Detail

MIN_MONITORING_INTERVAL

public static final long MIN_MONITORING_INTERVAL

The minimum interval allowed between consecutive path scans.

NOTE: Only applicable to the PROCESS_CONTINUOUSLY mode.

See Also:

Constant Field Values

Constructor Detail

ContinuousFileMonitoringFunction

public ContinuousFileMonitoringFunction(org.apache.flink.api.common.io.FileInputFormat<OUT> format,
                                        FileProcessingMode watchType,
                                        int readerParallelism,
                                        long interval)

Method Detail

getGlobalModificationTime

@VisibleForTesting
public long getGlobalModificationTime()

initializeState

public void initializeState(org.apache.flink.runtime.state.FunctionInitializationContext context)
                     throws Exception

Description copied from interface: CheckpointedFunction

This method is called when the parallel function instance is created during distributed execution. Functions typically set up their state storing data structures in this method.

Specified by:

initializeState in interface CheckpointedFunction

Parameters:

context - the context for initializing the operator

Throws:

Exception

open

public void open(org.apache.flink.configuration.Configuration parameters)
          throws Exception

Specified by:

open in interface org.apache.flink.api.common.functions.RichFunction

Overrides:

open in class org.apache.flink.api.common.functions.AbstractRichFunction

Throws:

Exception

run

public void run(SourceFunction.SourceContext<TimestampedFileInputSplit> context)
         throws Exception

Description copied from interface: SourceFunction

Starts the source. Implementations can use the SourceFunction.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);
      }
 }
 

Specified by:

run in interface SourceFunction<TimestampedFileInputSplit>

Parameters:

context - The context to emit elements to and for accessing locks.

Throws:

Exception

close

public void close()
           throws Exception

Specified by:

close in interface org.apache.flink.api.common.functions.RichFunction

Overrides:

close in class org.apache.flink.api.common.functions.AbstractRichFunction

Throws:

Exception

cancel

public void cancel()

Description copied from interface: SourceFunction

Cancels the source. Most sources will have a while loop inside the 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.

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.

Specified by:

cancel in interface SourceFunction<TimestampedFileInputSplit>

snapshotState

public void snapshotState(org.apache.flink.runtime.state.FunctionSnapshotContext context)
                   throws Exception

Description copied from interface: CheckpointedFunction

This method is called when a snapshot for a checkpoint is requested. This acts as a hook to the function to ensure that all state is exposed by means previously offered through FunctionInitializationContext when the Function was initialized, or offered now by FunctionSnapshotContext itself.

Specified by:

snapshotState in interface CheckpointedFunction

Parameters:

context - the context for drawing a snapshot of the operator

Throws:

Exception