@Internal public class ContinuousFileMonitoringFunction<OUT> extends RichSourceFunction<FileInputSplit> implements Checkpointed<Long>
FileInputFormat
and is responsible for
i) monitoring a user-provided path, ii) deciding which files should be further read and processed,
iii) creating the FileInputSplits
corresponding to those files, and iv) assigning
them to downstream tasks for further reading and processing. Which splits will be further processed
depends on the user-provided FileProcessingMode
and the FilePathFilter
.
The splits of the files to be read are then forwarded to the downstream
ContinuousFileReaderOperator
which can have parallelism greater than one.SourceFunction.SourceContext<T>
Modifier and Type | Field and Description |
---|---|
static long |
MIN_MONITORING_INTERVAL
The minimum interval allowed between consecutive path scans.
|
Constructor and Description |
---|
ContinuousFileMonitoringFunction(FileInputFormat<OUT> format,
String path,
FilePathFilter filter,
FileProcessingMode watchType,
int readerParallelism,
long interval) |
Modifier and Type | Method and Description |
---|---|
void |
cancel()
Cancels the source.
|
void |
close()
Tear-down method for the user code.
|
void |
open(Configuration parameters)
Initialization method for the function.
|
void |
restoreState(Long state)
Restores the state of the function or operator to that of a previous checkpoint.
|
void |
run(SourceFunction.SourceContext<FileInputSplit> context)
Starts the source.
|
Long |
snapshotState(long checkpointId,
long checkpointTimestamp)
Gets the current state of the function of operator.
|
getIterationRuntimeContext, getRuntimeContext, setRuntimeContext
public static final long MIN_MONITORING_INTERVAL
watchType
is set to PROCESS_CONTINUOUSLY
.public ContinuousFileMonitoringFunction(FileInputFormat<OUT> format, String path, FilePathFilter filter, FileProcessingMode watchType, int readerParallelism, long interval)
public void open(Configuration parameters) throws Exception
RichFunction
The configuration object passed to the function can be used for configuration and initialization. The configuration contains all parameters that were configured on the function in the program composition.
public class MyMapper extends FilterFunction<String> {
private String searchString;
public void open(Configuration parameters) {
this.searchString = parameters.getString("foo");
}
public boolean filter(String value) {
return value.equals(searchString);
}
}
By default, this method does nothing.
open
in interface RichFunction
open
in class AbstractRichFunction
parameters
- The configuration containing the parameters attached to the contract.Exception
- Implementations may forward exceptions, which are caught by the runtime. When the
runtime catches an exception, it aborts the task and lets the fail-over logic
decide whether to retry the task execution.Configuration
public void run(SourceFunction.SourceContext<FileInputSplit> context) throws Exception
SourceFunction
SourceFunction.SourceContext
emit
elements.
Sources that implement Checkpointed
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 ExampleSource<T> implements SourceFunction<T>, Checkpointed<Long> {
private long count = 0L;
private volatile boolean isRunning = true;
public void run(SourceContext<T> ctx) {
while (isRunning && count < 1000) {
synchronized (ctx.getCheckpointLock()) {
ctx.collect(count);
count++;
}
}
}
public void cancel() {
isRunning = false;
}
public Long snapshotState(long checkpointId, long checkpointTimestamp) { return count; }
public void restoreState(Long state) { this.count = state; }
}
run
in interface SourceFunction<FileInputSplit>
context
- The context to emit elements to and for accessing locks.Exception
public void close() throws Exception
RichFunction
This method can be used for clean up work.
close
in interface RichFunction
close
in class AbstractRichFunction
Exception
- Implementations may forward exceptions, which are caught by the runtime. When the
runtime catches an exception, it aborts the task and lets the fail-over logic
decide whether to retry the task execution.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.
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.
cancel
in interface SourceFunction<FileInputSplit>
public Long snapshotState(long checkpointId, long checkpointTimestamp) throws Exception
Checkpointed
snapshotState
in interface Checkpointed<Long>
checkpointId
- The ID of the checkpoint.checkpointTimestamp
- The timestamp of the checkpoint, as derived by
System.currentTimeMillis() on the JobManager.Exception
- Thrown if the creation of the state object failed. This causes the
checkpoint to fail. The system may decide to fail the operation (and trigger
recovery), or to discard this checkpoint attempt and to continue running
and to try again with the next checkpoint attempt.public void restoreState(Long state) throws Exception
Checkpointed
restoreState
in interface Checkpointed<Long>
state
- The state to be restored.Exception
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