Improvements in ThreadLocalStorage

5 files changed, 120 insertions, 9 deletions

diff --git a/build.sbt b/build.sbt
index 3d77510f..d553d3ed 100644
--- a/build.sbt
+++ b/build.sbt
@@ -17,7 +17,7 @@
 lazy val kamon = (project in file("."))
   .settings(moduleName := "kamon")
   .settings(noPublishing: _*)
-  .aggregate(core, testkit, coreTests)
+  .aggregate(core, testkit, coreTests, coreBench)
 
 val commonSettings = Seq(
   scalaVersion := "2.12.4",
@@ -74,3 +74,14 @@ lazy val coreTests = (project in file("kamon-core-tests"))
       "ch.qos.logback" % "logback-classic" % "1.2.2" % "test"
     )
   ).dependsOn(testkit)
+
+
+lazy val coreBench = (project in file("kamon-core-bench"))
+  .enablePlugins(JmhPlugin)
+  .settings(
+    moduleName := "kamon-core-bench",
+    resolvers += Resolver.mavenLocal,
+    fork in Test := true)
+  .settings(noPublishing: _*)
+  .settings(commonSettings: _*)
+  .dependsOn(core)
\ No newline at end of file
diff --git a/kamon-core-bench/src/main/scala/kamon/bench/ThreadLocalStorageBenchmark.scala b/kamon-core-bench/src/main/scala/kamon/bench/ThreadLocalStorageBenchmark.scala
new file mode 100644
index 00000000..96588798
--- /dev/null
+++ b/kamon-core-bench/src/main/scala/kamon/bench/ThreadLocalStorageBenchmark.scala
@@ -0,0 +1,81 @@
+/* =========================================================================================
+ * Copyright © 2013-2018 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.bench
+
+import java.util.concurrent.TimeUnit
+
+import kamon.context.Storage.Scope
+import kamon.context.{Context, Key, Storage}
+import org.openjdk.jmh.annotations._
+
+@State(Scope.Benchmark	)
+class ThreadLocalStorageBenchmark {
+
+  val TestKey: Key[Int] = Key.local("test-key", 0)
+  val ScopeWithKey: Context = Context.create().withKey(TestKey, 43)
+
+  val TLS: Storage =  new OldThreadLocal
+  val FTLS: Storage =  new Storage.ThreadLocal
+
+
+  @Benchmark
+  @BenchmarkMode(Array(Mode.AverageTime))
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  @Fork
+  def currentThreadLocal: Context = {
+    val scope = TLS.store(ScopeWithKey)
+    TLS.current()
+    scope.close()
+    TLS.current()
+  }
+
+  @Benchmark
+  @BenchmarkMode(Array(Mode.AverageTime))
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  @Fork
+  def fastThreadLocal: Context = {
+    val scope = FTLS.store(ScopeWithKey)
+    FTLS.current()
+    scope.close()
+    FTLS.current()
+  }
+}
+
+
+class OldThreadLocal extends Storage {
+  private val tls = new java.lang.ThreadLocal[Context]() {
+    override def initialValue(): Context = Context.Empty
+  }
+
+  override def current(): Context =
+    tls.get()
+
+  override def store(context: Context): Scope = {
+    val newContext = context
+    val previousContext = tls.get()
+    tls.set(newContext)
+
+    new Scope {
+      override def context: Context = newContext
+      override def close(): Unit = tls.set(previousContext)
+    }
+  }
+}
+
+object OldThreadLocal {
+  def apply(): OldThreadLocal = new OldThreadLocal()
+}
\ No newline at end of file
diff --git a/kamon-core-tests/src/test/scala/kamon/context/ThreadLocalStorageSpec.scala b/kamon-core-tests/src/test/scala/kamon/context/ThreadLocalStorageSpec.scala
index 12e0ca58..d2c4e57e 100644
--- a/kamon-core-tests/src/test/scala/kamon/context/ThreadLocalStorageSpec.scala
+++ b/kamon-core-tests/src/test/scala/kamon/context/ThreadLocalStorageSpec.scala
@@ -45,7 +45,6 @@ class ThreadLocalStorageSpec extends WordSpec with Matchers {
       TLS.current() shouldBe Context.Empty
     }
 
-
   }
 
   val TLS: Storage = new Storage.ThreadLocal
diff --git a/kamon-core/src/main/scala/kamon/context/Storage.scala b/kamon-core/src/main/scala/kamon/context/Storage.scala
index 4f4e6cbb..f116142d 100644
--- a/kamon-core/src/main/scala/kamon/context/Storage.scala
+++ b/kamon-core/src/main/scala/kamon/context/Storage.scala
@@ -15,6 +15,8 @@
 
 package kamon.context
 
+import kamon.context.Storage.ThreadLocal.ContextHolder
+
 trait Storage {
   def current(): Context
   def store(context: Context): Storage.Scope
@@ -27,28 +29,45 @@ object Storage {
     def close(): Unit
   }
 
-
+  /**
+    * Wrapper that implements optimized {@link ThreadLocal} access pattern ideal for heavily used
+    * ThreadLocals.
+    *
+    * It is faster to use a mutable holder object and always perform ThreadLocal.get() and never use
+    * ThreadLocal.set(), because the value is more likely to be found in the ThreadLocalMap direct hash
+    * slot and avoid the slow path ThreadLocalMap.getEntryAfterMiss().
+    *
+    * Important: this thread local will live in ThreadLocalMap forever, so use with care.
+    */
   class ThreadLocal extends Storage {
-    private val tls = new java.lang.ThreadLocal[Context]() {
-      override def initialValue(): Context = Context.Empty
+    private val tls = new java.lang.ThreadLocal[ContextHolder]() {
+      override def initialValue() = new ContextHolder(Context.Empty)
     }
 
     override def current(): Context =
-      tls.get()
+      get()
 
     override def store(context: Context): Scope = {
       val newContext = context
-      val previousContext = tls.get()
-      tls.set(newContext)
+      val previousContext = get()
+      set(newContext)
 
       new Scope {
         override def context: Context = newContext
-        override def close(): Unit = tls.set(previousContext)
+        override def close(): Unit = set(previousContext)
       }
     }
+
+    private def get():Context =
+      tls.get().value
+
+    private def set(value:Context) : Unit =
+      tls.get().value = value
   }
 
   object ThreadLocal {
     def apply(): ThreadLocal = new ThreadLocal()
+
+    final class ContextHolder(var value:Context)
   }
 }
\ No newline at end of file
diff --git a/project/plugins.sbt b/project/plugins.sbt
index 323e4f2f..3192be2f 100644
--- a/project/plugins.sbt
+++ b/project/plugins.sbt
@@ -1,4 +1,5 @@
 resolvers += Resolver.bintrayIvyRepo("kamon-io", "sbt-plugins")
 addSbtPlugin("io.kamon" % "kamon-sbt-umbrella" % "0.0.15")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "1.5.0")
+addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.3.3")