bug(#9): Fix interference between experiments

This change fixes the interference of multiple experiments running at
the same time due to some thread unsafe behaviour in the
JpaExperimentManager class.

The code has now been restructured to solve the issue and fix the thread
unsafe behaviour.

Closes #9.

1 files changed, 27 insertions, 14 deletions

diff --git a/opendc-integration-jpa/src/main/kotlin/nl/atlarge/opendc/platform/JpaExperimentManager.kt b/opendc-integration-jpa/src/main/kotlin/nl/atlarge/opendc/platform/JpaExperimentManager.kt
index ce69f84b..1d1e118d 100644
--- a/opendc-integration-jpa/src/main/kotlin/nl/atlarge/opendc/platform/JpaExperimentManager.kt
+++ b/opendc-integration-jpa/src/main/kotlin/nl/atlarge/opendc/platform/JpaExperimentManager.kt
@@ -24,6 +24,7 @@
 
 package nl.atlarge.opendc.platform
 
+import nl.atlarge.opendc.integration.jpa.transaction
 import nl.atlarge.opendc.integration.jpa.schema.Experiment as InternalExperiment
 import nl.atlarge.opendc.integration.jpa.schema.ExperimentState
 import javax.persistence.EntityManager
@@ -36,11 +37,11 @@ import javax.persistence.EntityManagerFactory
  * 					 from.
  * @author Fabian Mastenbroek (f.s.mastenbroek@student.tudelft.nl)
  */
-class JpaExperimentManager(private val factory: EntityManagerFactory) {
+class JpaExperimentManager(private val factory: EntityManagerFactory): AutoCloseable {
 	/**
 	 * The entity manager for this experiment.
 	 */
-	private val manager: EntityManager = factory.createEntityManager()
+	private var manager: EntityManager = factory.createEntityManager()
 
 	/**
 	 * The amount of experiments in the queue. This property makes a call to the database and does therefore not
@@ -60,21 +61,33 @@ class JpaExperimentManager(private val factory: EntityManagerFactory) {
 	 * @return The experiment that has been polled from the database or `null` if there are no experiments in the
 	 * 		   queue.
 	 */
-	fun poll(): Experiment<Unit>? {
-		manager.transaction.begin()
-		var experiment: InternalExperiment? = null
-		val results = manager.createQuery("SELECT e FROM experiments e WHERE e.state = :s",
+	fun poll(): JpaExperiment? {
+		var result: JpaExperiment? = null
+		manager.transaction {
+			var experiment: InternalExperiment? = null
+			val results = manager.createQuery("SELECT e FROM experiments e WHERE e.state = :s",
 				InternalExperiment::class.java)
-			.setParameter("s", ExperimentState.QUEUED)
-			.setMaxResults(1)
-			.resultList
+				.setParameter("s", ExperimentState.QUEUED)
+				.setMaxResults(1)
+				.resultList
 
 
-		if (!results.isEmpty()) {
-			experiment = results.first()
-			experiment!!.state = ExperimentState.CLAIMED
+			if (!results.isEmpty()) {
+				experiment = results.first()
+				experiment!!.state = ExperimentState.CLAIMED
+			}
+			result = experiment?.let { JpaExperiment(manager, it) }
 		}
-		manager.transaction.commit()
-		return experiment?.let { JpaExperiment(factory.createEntityManager(), it) }
+		manager = factory.createEntityManager()
+		return result
 	}
+
+	/**
+	 * Close this resource, relinquishing any underlying resources.
+	 * This method is invoked automatically on objects managed by the
+	 * `try`-with-resources statement.*
+	 *
+	 * @throws Exception if this resource cannot be closed
+	 */
+	override fun close() = manager.close()
 }