Periodic actions

[shikhar]

I am trying to have my job also run a periodic action by using a custom
source that emits a dummy element periodically and a sink that executes the
callback, as shown in the code below. However as soon as I start the job and
check the state in the JobManager UI this particular Sink->Source combo is
in state 'FINISHED' I know based on logging that the sink never received any
elements. What am I doing wrong?

```scala
    env
      .addSource(PeriodicSource(1.minutes))
      .addSink { _ => foo() }
```

```scala
import org.apache.flink.streaming.api.functions.source.SourceFunction
import
org.apache.flink.streaming.api.functions.source.SourceFunction.SourceContext

import scala.concurrent.duration.FiniteDuration

case class PeriodicSource(interval: FiniteDuration) extends
SourceFunction[Unit] {
  @volatile private var active = false

  override def run(ctx: SourceContext[Unit]): Unit = {
    while (active) {
      sleep()
      if (active) {
        ctx.getCheckpointLock
        ctx.collect(Unit)
      }
    }
  }

  override def cancel(): Unit = {
    active = false
  }

  private def sleep(): Unit = {
    val startTimeMs = System.currentTimeMillis()
    val desiredSleepMs = interval.toMillis
    do {
      Thread.sleep(math.min(desiredSleepMs, 100))
    } while (active && (System.currentTimeMillis() - startTimeMs) <
desiredSleepMs)
  }
}
```



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