public class WikipediaEditsSource extends RichSourceFunction<WikipediaEditEvent>
WikipediaEditEvent
instances from the IRC
channel #en.wikipedia
.SourceFunction.SourceContext<T>
Modifier and Type | Field and Description |
---|---|
static String |
DEFAULT_CHANNEL
IRC channel to join.
|
static String |
DEFAULT_HOST
Hostname of the server to connect to.
|
static int |
DEFAULT_PORT
Port of the server to connect to.
|
Constructor and Description |
---|
WikipediaEditsSource()
Creates a source reading
WikipediaEditEvent instances from the IRC channel
#en.wikipedia . |
WikipediaEditsSource(String host,
int port,
String channel)
Creates a source reading
WikipediaEditEvent instances from the specified IRC channel. |
Modifier and Type | Method and Description |
---|---|
void |
cancel()
Cancels the source.
|
void |
run(SourceFunction.SourceContext<WikipediaEditEvent> ctx)
Starts the source.
|
close, getIterationRuntimeContext, getRuntimeContext, open, setRuntimeContext
public static final String DEFAULT_HOST
public static final int DEFAULT_PORT
public static final String DEFAULT_CHANNEL
public WikipediaEditsSource()
WikipediaEditEvent
instances from the IRC channel
#en.wikipedia
.
This creates a separate Thread for the IRC connection.
public WikipediaEditsSource(String host, int port, String channel)
WikipediaEditEvent
instances from the specified IRC channel.
In most cases, you want to use the default WikipediaEditsSource(java.lang.String, int, java.lang.String)
constructor. This
constructor is meant to be used only if there is a problem with the default constructor.
host
- The IRC server to connect to.port
- The port of the IRC server to connect to.channel
- The channel to join. Messages not matching the expected format will be
ignored.public void run(SourceFunction.SourceContext<WikipediaEditEvent> ctx) throws Exception
SourceFunction
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);
}
}
ctx
- The context to emit elements to and for accessing locks.Exception
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.
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