! all: Kamon now works as a single instance in a companion object.

1 files changed, 53 insertions, 0 deletions

diff --git a/kamon-core/src/main/scala/kamon/util/LazyActorRef.scala b/kamon-core/src/main/scala/kamon/util/LazyActorRef.scala
new file mode 100644
index 00000000..855bf1fc
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/util/LazyActorRef.scala
@@ -0,0 +1,53 @@
+package kamon.util
+
+import java.util
+import java.util.concurrent.ConcurrentLinkedQueue
+
+import akka.actor.{ Actor, ActorRef }
+import org.HdrHistogram.WriterReaderPhaser
+
+import scala.annotation.tailrec
+
+/**
+ *  A LazyActorRef accumulates messages sent to an actor that doesn't exist yet. Once the actor is created and
+ *  the LazyActorRef is pointed to it, all the accumulated messages are flushed and any new message sent to the
+ *  LazyActorRef will immediately be sent to the pointed ActorRef.
+ *
+ *  This is intended to be used during Kamon's initialization where some components need to use ActorRefs to work
+ *  (like subscriptions and the trace incubator) but our internal ActorSystem is not yet ready to create the
+ *  required actors.
+ */
+class LazyActorRef {
+  private val _refPhaser = new WriterReaderPhaser
+  private val _backlog = new ConcurrentLinkedQueue[(Any, ActorRef)]()
+  @volatile private var _target: Option[ActorRef] = None
+
+  def tell(message: Any)(implicit sender: ActorRef = Actor.noSender): Unit = {
+    val criticalEnter = _refPhaser.writerCriticalSectionEnter()
+    try {
+      _target.map(_.tell(message, sender)) getOrElse {
+        _backlog.add((message, sender))
+      }
+
+    } finally { _refPhaser.writerCriticalSectionExit(criticalEnter) }
+  }
+
+  def point(target: ActorRef): Unit = {
+    @tailrec def drain(q: util.Queue[(Any, ActorRef)]): Unit = if (!q.isEmpty) {
+      val (msg, sender) = q.poll()
+      target.tell(msg, sender)
+      drain(q)
+    }
+
+    try {
+      _refPhaser.readerLock()
+
+      if (_target.isEmpty) {
+        _target = Some(target)
+        _refPhaser.flipPhase(1000L)
+        drain(_backlog)
+
+      } else sys.error("A LazyActorRef cannot be pointed more than once.")
+    } finally { _refPhaser.readerUnlock() }
+  }
+}