Improved scheduling and test reliability.

pom.xml

@@ -7,6 +7,33 @@
     <groupId>nl.andrewlalis</groupId>
     <artifactId>simply-scheduled</artifactId>
     <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <name>Simply Scheduled</name>
+    <description>Lightweight task scheduling library.</description>
+    <url>https://github.com/andrewlalis/SimplyScheduled</url>
+
+    <licenses>
+        <license>
+            <name>Apache License, Version 2.0</name>
+            <url>https://www.apache.org/licenses/LICENSE-2.0.txt</url>
+            <distribution>repo</distribution>
+        </license>
+    </licenses>
+
+    <developers>
+        <developer>
+            <name>Andrew Lalis</name>
+            <email>andrewlalisofficial@gmail.com</email>
+            <timezone>CEST</timezone>
+        </developer>
+    </developers>
+
+    <scm>
+        <connection>scm:git:git://github.com/andrewlalis/SimplyScheduled.git</connection>
+        <developerConnection>scm:git:ssh://github.com:andrewlalis/SimplyScheduled.git</developerConnection>
+        <url>https://github.com/andrewlalis/SimplyScheduled</url>
+    </scm>
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
@@ -20,7 +47,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
+                <version>3.0.0-M5</version>
             </plugin>
         </plugins>
     </build>
@@ -30,7 +57,7 @@
             <dependency>
                 <groupId>org.junit</groupId>
                 <artifactId>junit-bom</artifactId>
-                <version>5.7.1</version>
+                <version>5.7.2</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
@@ -42,7 +69,7 @@
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter</artifactId>
-            <version>5.7.1</version>
+            <version>5.7.2</version>
             <scope>test</scope>
         </dependency>
     </dependencies>

src/main/java/module-info.java

@@ -1,5 +1,6 @@
 module simply_scheduled {
 	exports nl.andrewlalis.simply_scheduled;
 	exports nl.andrewlalis.simply_scheduled.schedule;
+
 	opens nl.andrewlalis.simply_scheduled;
 }

src/main/java/nl/andrewlalis/simply_scheduled/BasicScheduler.java

@@ -8,6 +8,7 @@ import java.util.Optional;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.PriorityBlockingQueue;
+import java.util.concurrent.RejectedExecutionException;
 
 /**
  * A simple thread-based scheduler that sleeps until the next task, runs it
@@ -47,9 +48,9 @@ public class BasicScheduler extends Thread implements Scheduler {
 		this.running = true;
 		while (this.running) {
 			try {
-				Task nextTask = this.tasks.take();
+				final Task nextTask = this.tasks.take();
-				Instant now = this.clock.instant();
+				final Instant now = this.clock.instant();
-				Optional<Instant> optionalNextExecution = nextTask.getSchedule().getNextExecutionTime(now);
+				final Optional<Instant> optionalNextExecution = nextTask.getSchedule().getNextExecutionTime(now);
 				if (optionalNextExecution.isEmpty()) {
 					continue; // Skip if the schedule doesn't have a next execution planned.
 				}
@@ -57,10 +58,18 @@ public class BasicScheduler extends Thread implements Scheduler {
 				if (waitTime > 0) {
 					Thread.sleep(waitTime);
 				}
+				try {
 					this.executorService.execute(nextTask.getRunnable());
+				} catch (RejectedExecutionException e) {
+					if (!this.executorService.isShutdown()) {
+						// Only show the stack trace if the executor service is not being shut down.
+						// We expect the service to reject executions if it is shutting down.
+						e.printStackTrace();
+					}
+				}
 				nextTask.getSchedule().markExecuted(this.clock.instant());
 				if (nextTask.getSchedule().isRepeating()) {
-					this.tasks.put(nextTask); // Put the task back in the queue.
+					this.tasks.put(nextTask);
 				}
 			} catch (InterruptedException e) {
 				this.setRunning(false);

src/main/java/nl/andrewlalis/simply_scheduled/Demo.java

@@ -2,7 +2,6 @@ package nl.andrewlalis.simply_scheduled;
 
 import nl.andrewlalis.simply_scheduled.schedule.RepeatingSchedule;
 import nl.andrewlalis.simply_scheduled.schedule.Schedule;
-import nl.andrewlalis.simply_scheduled.schedule.Task;
 
 import java.time.Instant;
 import java.time.temporal.ChronoUnit;
@@ -10,9 +9,9 @@ import java.time.temporal.ChronoUnit;
 public class Demo {
 	public static void main(String[] args) {
 		Scheduler scheduler = new BasicScheduler();
-		Schedule schedule = new RepeatingSchedule(ChronoUnit.MILLIS, 250);
+		Schedule schedule = new RepeatingSchedule(ChronoUnit.SECONDS, 5, Instant.now().truncatedTo(ChronoUnit.SECONDS));
 		Runnable job = () -> System.out.println("Doing task: " + Instant.now().toString());
-		scheduler.addTask(Task.of(job, schedule));
+		scheduler.addTask(job, schedule);
 		scheduler.start();
 	}
 }

src/main/java/nl/andrewlalis/simply_scheduled/Scheduler.java

@@ -1,5 +1,6 @@
 package nl.andrewlalis.simply_scheduled;
 
+import nl.andrewlalis.simply_scheduled.schedule.Schedule;
 import nl.andrewlalis.simply_scheduled.schedule.Task;
 
 /**
@@ -14,6 +15,15 @@ public interface Scheduler {
 	 */
 	void addTask(Task task);
 
+	/**
+	 * Adds a task to this scheduler.
+	 * @param runnable The code to run.
+	 * @param schedule The schedule that dictates when the code should run.
+	 */
+	default void addTask(Runnable runnable, Schedule schedule) {
+		addTask(new Task(runnable, schedule));
+	}
+
 	/**
 	 * Starts the scheduler. A scheduler should only execute tasks once it has
 	 * started, and it is up to the implementation to determine whether new
@@ -27,4 +37,11 @@ public interface Scheduler {
 	 *              any currently-executing tasks are immediately shutdown.
 	 */
 	void stop(boolean force);
+
+	/**
+	 * Stops the scheduler, and waits for any currently-executing tasks to finish.
+	 */
+	default void stop() {
+		stop(false);
+	}
 }

src/main/java/nl/andrewlalis/simply_scheduled/schedule/MinutelySchedule.java

@@ -1,32 +0,0 @@
-package nl.andrewlalis.simply_scheduled.schedule;
-
-import java.time.Instant;
-import java.time.ZoneId;
-import java.time.ZonedDateTime;
-import java.time.temporal.ChronoUnit;
-import java.util.Optional;
-
-public class MinutelySchedule implements Schedule {
-
-	private final int second;
-	private final ZoneId zoneId;
-
-	public MinutelySchedule(int second, ZoneId zoneId) {
-		this.second = second;
-		this.zoneId = zoneId;
-	}
-
-	public MinutelySchedule(int second) {
-		this(second, ZoneId.systemDefault());
-	}
-
-	@Override
-	public Optional<Instant> getNextExecutionTime(Instant referenceInstant) {
-		ZonedDateTime currentTime = referenceInstant.atZone(this.zoneId);
-		int currentSecond = currentTime.getSecond();
-		if (currentSecond >= this.second) {
-			return Optional.of(currentTime.plusMinutes(1).withSecond(this.second).truncatedTo(ChronoUnit.SECONDS).toInstant());
-		}
-		return Optional.of(currentTime.withSecond(this.second).truncatedTo(ChronoUnit.SECONDS).toInstant());
-	}
-}

src/main/java/nl/andrewlalis/simply_scheduled/schedule/RepeatingSchedule.java

@@ -11,17 +11,29 @@ import java.util.Optional;
 public class RepeatingSchedule implements Schedule {
 	private final ChronoUnit unit;
 	private final long multiple;
-	private Instant lastExecution;
+	private long elapsedIntervals = 0;
+	private final Instant start;
 
 	/**
 	 * Constructs a new repeating schedule.
 	 * @param unit The unit of time that the interval consists of.
-	 * @param multiple The
+	 * @param multiple The number of units of time that each interval consists of.
+	 * @param start The starting point for this schedule.
 	 */
-	public RepeatingSchedule(ChronoUnit unit, long multiple) {
+	public RepeatingSchedule(ChronoUnit unit, long multiple, Instant start) {
 		this.unit = unit;
 		this.multiple = multiple;
-		this.lastExecution = null;
+		this.start = start;
+	}
+
+	/**
+	 * Constructs a new repeating schedule, using {@link Instant#now()} as the
+	 * starting point.
+	 * @param unit The unit of time that the interval consists of.
+	 * @param multiple The number of units of time that each interval consists of.
+	 */
+	public RepeatingSchedule(ChronoUnit unit, long multiple) {
+		this(unit, multiple, Instant.now());
 	}
 
 	/**
@@ -32,14 +44,11 @@ public class RepeatingSchedule implements Schedule {
 	 */
 	@Override
 	public Optional<Instant> getNextExecutionTime(Instant referenceInstant) {
-		if (this.lastExecution == null) {
+		return Optional.of(this.start.plus(elapsedIntervals * multiple, unit));
-			this.lastExecution = referenceInstant;
-		}
-		return Optional.of(this.lastExecution.plus(multiple, unit));
 	}
 
 	@Override
 	public void markExecuted(Instant instant) {
-		this.lastExecution = instant;
+		this.elapsedIntervals++;
 	}
 }

src/main/java/nl/andrewlalis/simply_scheduled/schedule/Task.java

@@ -14,20 +14,40 @@ public class Task implements Comparable<Task>{
 	private final Runnable runnable;
 	private final Schedule schedule;
 
+	/**
+	 * Constructs a new task that will run the given runnable according to the
+	 * given schedule. Allows for specifying a {@link Clock}, this is mostly
+	 * useful for testing purposes.
+	 * @param clock The clock to use for time-sensitive operations.
+	 * @param runnable The code to run when the task is executed.
+	 * @param schedule The schedule which determines when the task is executed.
+	 */
 	public Task(Clock clock, Runnable runnable, Schedule schedule) {
 		this.clock = clock;
 		this.runnable = runnable;
 		this.schedule = schedule;
 	}
 
-	public static Task of(Runnable runnable, Schedule schedule) {
+	/**
-		return new Task(Clock.systemDefaultZone(), runnable, schedule);
+	 * Constructs a new task that will run the given runnable according to the
+	 * given schedule.
+	 * @param runnable The code to run when the task is executed.
+	 * @param schedule The schedule which determines when the task is executed.
+	 */
+	public Task(Runnable runnable, Schedule schedule) {
+		this(Clock.systemDefaultZone(), runnable, schedule);
 	}
 
+	/**
+	 * @return The runnable which will be executed when this task is scheduled.
+	 */
 	public Runnable getRunnable() {
 		return runnable;
 	}
 
+	/**
+	 * @return The schedule for this task.
+	 */
 	public Schedule getSchedule() {
 		return schedule;
 	}

src/test/java/nl/andrewlalis/simply_scheduled/BasicSchedulerTest.java

@@ -1,6 +1,5 @@
 package nl.andrewlalis.simply_scheduled;
 
-import nl.andrewlalis.simply_scheduled.schedule.MinutelySchedule;
 import nl.andrewlalis.simply_scheduled.schedule.RepeatingSchedule;
 import nl.andrewlalis.simply_scheduled.schedule.Schedule;
 import nl.andrewlalis.simply_scheduled.schedule.Task;
@@ -8,6 +7,7 @@ import org.junit.jupiter.api.Test;
 
 import java.time.Clock;
 import java.time.Instant;
+import java.time.LocalDateTime;
 import java.time.ZoneOffset;
 import java.time.temporal.ChronoUnit;
 import java.util.concurrent.Executors;
@@ -16,7 +16,11 @@ import java.util.concurrent.atomic.AtomicInteger;
 
 import static org.junit.jupiter.api.Assertions.*;
 
-public class SchedulerTest {
+/**
+ * Tests the functionality of the {@link BasicScheduler} to reliably execute
+ * scheduled tasks.
+ */
+public class BasicSchedulerTest {
 
 	@Test
 	void testSchedule() {
@@ -28,7 +32,7 @@ public class SchedulerTest {
 			flag.set(true);
 			System.out.println("\tExecuted task.");
 		};
-		Task task = new Task(clock, taskRunnable, new MinutelySchedule(3));
+		Task task = new Task(clock, taskRunnable, new RepeatingSchedule(ChronoUnit.SECONDS, 2, clock.instant().plusSeconds(1)));
 		scheduler.addTask(task);
 		scheduler.start();
 		System.out.println("Now: " + clock.instant().toString());
@@ -45,24 +49,24 @@ public class SchedulerTest {
 	}
 
 	@Test
-	void testRepeatingSchedule() {
+	void testRepeatingSchedule() throws InterruptedException {
-		Scheduler scheduler = new BasicScheduler(Clock.systemUTC(), Executors.newWorkStealingPool());
+		Scheduler scheduler = new BasicScheduler(Clock.systemUTC(), Executors.newFixedThreadPool(3));
-		Schedule schedule = new RepeatingSchedule(ChronoUnit.SECONDS, 1);
+		Instant startInstant = Instant.now(Clock.systemUTC());
+		Schedule schedule = new RepeatingSchedule(ChronoUnit.SECONDS, 1, startInstant);
 		AtomicInteger value = new AtomicInteger(0);
 		Runnable taskRunnable = () -> {
 			value.set(value.get() + 1);
-			System.out.println("\tExecuted task.");
+			System.out.println("\tExecuted task at " + LocalDateTime.now());
 		};
-		scheduler.addTask(Task.of(taskRunnable, schedule));
+		scheduler.addTask(new Task(taskRunnable, schedule));
 		assertEquals(0, value.get());
 		scheduler.start();
-		System.out.println("Waiting 3.5 seconds for 3 iterations.");
+
-		try {
 		Thread.sleep(3500);
-		} catch (InterruptedException e) {
+		// We expect the task to have run 4 times:
-			e.printStackTrace();
+		// at t=0, t=1, t=2, and t=3.
-		}
+		assertEquals(4, value.get());
-		assertEquals(3, value.get());
+
 		scheduler.stop(true);
 	}
 }