From cfb25accce7ad5b0592a206addc872b0d9242bd9 Mon Sep 17 00:00:00 2001
From: Ivan Topolnjak <ivantopo@gmail.com>
Date: Fri, 17 Jul 2015 18:46:40 +0200
Subject: + core: introduce auto-start feature to make Kamon more
 test-friendly, related to #202.

---
 kamon-core/src/main/scala/kamon/Kamon.scala        | 22 ++++++++++++++++++++--
 .../test/scala/kamon/testkit/BaseKamonSpec.scala   |  2 +-
 2 files changed, 21 insertions(+), 3 deletions(-)

(limited to 'kamon-core/src')

diff --git a/kamon-core/src/main/scala/kamon/Kamon.scala b/kamon-core/src/main/scala/kamon/Kamon.scala
index d819588c..1c560d9f 100644
--- a/kamon-core/src/main/scala/kamon/Kamon.scala
+++ b/kamon-core/src/main/scala/kamon/Kamon.scala
@@ -16,6 +16,7 @@ package kamon
 
 import _root_.akka.actor
 import _root_.akka.actor._
+import _root_.akka.event.Logging
 import com.typesafe.config.{ ConfigFactory, Config }
 import kamon.metric._
 import kamon.trace.{ TracerModuleImpl, TracerModule }
@@ -25,10 +26,14 @@ object Kamon {
 
   private case class KamonCoreComponents(metrics: MetricsModule, tracer: TracerModule)
 
+  private val shouldAutoStart = isSystemPropertyEnabled("kamon.auto-start")
+  private val shouldWarnOnDuplicateStart = !isSystemPropertyEnabled("kamon.disable-duplicate-start-warning")
+
   @volatile private var _system: ActorSystem = _
   @volatile private var _coreComponents: Option[KamonCoreComponents] = None
 
   def start(config: Config): Unit = synchronized {
+
     def resolveInternalConfig: Config = {
       val internalConfig = config.getConfig("kamon.internal-config")
 
@@ -49,9 +54,15 @@ object Kamon {
       tracer.start(_system)
       _system.registerExtension(ModuleLoader)
 
-    } else sys.error("Kamon has already been started.")
+    } else if (shouldWarnOnDuplicateStart) {
+      val logger = Logging(_system, "Kamon")
+      logger.warning("An attempt to start Kamon has been made, but Kamon has already been started.")
+    }
   }
 
+  private def isSystemPropertyEnabled(propertyName: String): Boolean =
+    sys.props.get(propertyName).map(_.equals("true")).getOrElse(false)
+
   def start(): Unit =
     start(ConfigFactory.load)
 
@@ -79,7 +90,14 @@ object Kamon {
     apply(key)
 
   private def ifStarted[T](thunk: KamonCoreComponents ⇒ T): T =
-    _coreComponents.map(thunk(_)) getOrElse (sys.error("Kamon has not been started yet."))
+    _coreComponents.map(thunk(_)) getOrElse {
+      if (shouldAutoStart) {
+        start()
+        thunk(_coreComponents.get)
+
+      } else sys.error("Kamon has not been started yet. You must either explicitlt call Kamon.start(...) or enable " +
+        "automatic startup by adding -Dkamon.auto-start=true to your JVM options.")
+    }
 
 }
 
diff --git a/kamon-core/src/test/scala/kamon/testkit/BaseKamonSpec.scala b/kamon-core/src/test/scala/kamon/testkit/BaseKamonSpec.scala
index cb909ad9..61cc4e6b 100644
--- a/kamon-core/src/test/scala/kamon/testkit/BaseKamonSpec.scala
+++ b/kamon-core/src/test/scala/kamon/testkit/BaseKamonSpec.scala
@@ -28,7 +28,7 @@ import org.scalatest.{ BeforeAndAfterAll, Matchers, WordSpecLike }
 abstract class BaseKamonSpec(actorSystemName: String) extends TestKitBase with WordSpecLike with Matchers with ImplicitSender with BeforeAndAfterAll {
   lazy val collectionContext = Kamon.metrics.buildDefaultCollectionContext
   implicit lazy val system: ActorSystem = {
-    Kamon.start(config.withFallback(ConfigFactory.load()))
+    //Kamon.start(config.withFallback(ConfigFactory.load()))
     ActorSystem(actorSystemName, config)
   }
 
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