1 files changed, 69 insertions, 0 deletions
diff --git a/kamon-core/src/legacy-main/scala/kamon/util/LazyActorRef.scala b/kamon-core/src/legacy-main/scala/kamon/util/LazyActorRef.scala
new file mode 100644
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+++ b/kamon-core/src/legacy-main/scala/kamon/util/LazyActorRef.scala
@@ -0,0 +1,69 @@
+/*
+ * =========================================================================================
+ * Copyright © 2013-2015 the kamon project <http://kamon.io/>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+ * either express or implied. See the License for the specific language governing permissions
+ * and limitations under the License.
+ * =========================================================================================
+ */
+
+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() }
+  }
+}