Fix issue ReactiveX#1187

language-adaptors/rxjava-scala/src/examples/scala/rx/lang/scala/examples/RxScalaDemo.scala

@@ -16,6 +16,8 @@
 package rx.lang.scala.examples
 
 import java.io.IOException
+import java.util.concurrent.CountDownLatch
+import java.util.concurrent.TimeUnit
 
 import scala.concurrent.duration.Duration
 import scala.concurrent.duration.DurationInt
@@ -790,4 +792,50 @@ class RxScalaDemo extends JUnitSuite {
     assertEquals(List(1, 2, 3, 4), o.toBlockingObservable.toList)
   }
 
+  @Test def schedulerExample1(): Unit = {
+    val latch = new CountDownLatch(1)
+    val worker = IOScheduler().createWorker
+    worker.schedule {
+      println("Hello from Scheduler")
+      latch.countDown()
+    }
+    latch.await(5, TimeUnit.SECONDS)
+  }
+
+  @Test def schedulerExample2(): Unit = {
+    val latch = new CountDownLatch(1)
+    val worker = IOScheduler().createWorker
+    worker.schedule(
+      {
+        println("Hello from Scheduler after 1 second")
+        latch.countDown()
+      }, 1 seconds)
+    latch.await(5, TimeUnit.SECONDS)
+  }
+
+  @Test def schedulerExample3(): Unit = {
+    val worker = IOScheduler().createWorker
+    var no = 1
+    val subscription = worker.schedulePeriodically(
+      {
+        println(s"Hello(${no}) from Scheduler")
+        no += 1
+      }, initialDelay = 1 seconds, period = 100 millis)
+    TimeUnit.SECONDS.sleep(2)
+    subscription.unsubscribe()
+  }
+
+  @Test def schedulerExample4(): Unit = {
+    val worker = IOScheduler().createWorker
+    var no = 1
+    def hello: Unit = {
+      println(s"Hello(${no}) from Scheduler")
+      no += 1
+      worker.schedule(hello, 100 millis)
+    }
+    val subscription = worker.schedule(hello, 1 seconds)
+    TimeUnit.SECONDS.sleep(2)
+    subscription.unsubscribe()
+  }
+
 }

language-adaptors/rxjava-scala/src/main/scala/rx/lang/scala/Scheduler.scala

@@ -31,7 +31,7 @@ trait Scheduler {
   /**
    * Parallelism available to a Scheduler.
    *
-   * This defaults to {@code Runtime.getRuntime().availableProcessors()} but can be overridden for use cases such as scheduling work on a computer cluster.
+   * This defaults to `Runtime.getRuntime().availableProcessors()` but can be overridden for use cases such as scheduling work on a computer cluster.
    *
    * @return the scheduler's available degree of parallelism.
    */
@@ -42,6 +42,15 @@ trait Scheduler {
    */
   def now: Long = this.asJavaScheduler.now()
 
+  /**
+   * Retrieve or create a new [[rx.lang.scala.Worker]] that represents serial execution of actions.
+   * <p>
+   * When work is completed it should be unsubscribed using [[rx.lang.scala.Worker unsubscribe]].
+   * <p>
+   * Work on a [[rx.lang.scala.Worker]] is guaranteed to be sequential.
+   *
+   * @return Inner representing a serial queue of actions to be executed
+   */
   def createWorker: Worker = this.asJavaScheduler.createWorker()
 
 }
@@ -54,24 +63,55 @@ trait Worker extends Subscription {
   private [scala] val asJavaWorker: rx.Scheduler.Worker
 
   /**
-   * Schedules a cancelable action to be executed in delayTime.
+   * Schedules an Action for execution at some point in the future.
+   *
+   * @param action the Action to schedule
+   * @param delay time to wait before executing the action
+   * @return a subscription to be able to unsubscribe the action (unschedule it if not executed)
    */
-  def schedule(action: Unit => Unit, delayTime: Duration): Subscription =
+  def schedule(action: => Unit, delay: Duration): Subscription = {
     this.asJavaWorker.schedule(
       new Action0 {
-        override def call(): Unit = action()
+        override def call(): Unit = action
       },
-      delayTime.length,
-      delayTime.unit)
+      delay.length,
+      delay.unit)
+  }
+
+  /**
+   * Schedules an Action for execution.
+   *
+   * @param action the Action to schedule
+   * @return a subscription to be able to unsubscribe the action (unschedule it if not executed)
+   */
+  def schedule(action: => Unit): Subscription = {
+    this.asJavaWorker.schedule(
+      new Action0 {
+        override def call(): Unit = action
+      }
+    )
+  }
 
   /**
-   * Schedules a cancelable action to be executed immediately.
+   * Schedules a cancelable action to be executed periodically. This default implementation schedules
+   * recursively and waits for actions to complete (instead of potentially executing long-running actions
+   * concurrently). Each scheduler that can do periodic scheduling in a better way should override this.
+   *
+   * @param action the Action to execute periodically
+   * @param initialDelay  time to wait before executing the action for the first time
+   * @param period the time interval to wait each time in between executing the action
+   * @return a subscription to be able to unsubscribe the action (unschedule it if not executed)
    */
-  def schedule(action: Unit => Unit): Subscription = this.asJavaWorker.schedule(
-    new Action0 {
-      override def call(): Unit = action()
-    }
-  )
+  def schedulePeriodically(action: => Unit, initialDelay: Duration, period: Duration): Subscription = {
+    this.asJavaWorker.schedulePeriodically(
+      new Action0 {
+        override def call(): Unit = action
+      },
+      initialDelay.toNanos,
+      period.toNanos,
+      duration.NANOSECONDS
+    )
+  }
 
   /**
    * @return the scheduler's notion of current absolute time in milliseconds.