Experimental IOLocalContextStorage

build.sbt

@@ -26,7 +26,7 @@ ThisBuild / crossScalaVersions := Seq(Scala213, "3.2.2")
 ThisBuild / scalaVersion := Scala213 // the default Scala
 
 val CatsVersion = "2.9.0"
-val CatsEffectVersion = "3.5.0"
+val CatsEffectVersion = "3.5.0-30-0a69caf"
 val CatsMtlVersion = "1.3.1"
 val FS2Version = "3.6.1"
 val MUnitVersion = "1.0.0-M7"
@@ -154,7 +154,7 @@ lazy val `java-common` = project
   .settings(
     name := "otel4s-java-common",
     libraryDependencies ++= Seq(
-      "org.typelevel" %%% "cats-effect-kernel" % CatsEffectVersion,
+      "org.typelevel" %%% "cats-effect" % CatsEffectVersion,
       "org.typelevel" %%% "cats-mtl" % CatsMtlVersion,
       "io.opentelemetry" % "opentelemetry-sdk" % OpenTelemetryVersion,
       "org.scalameta" %%% "munit" % MUnitVersion % Test
@@ -241,6 +241,7 @@ lazy val examples = project
     ),
     run / fork := true,
     javaOptions += "-Dotel.java.global-autoconfigure.enabled=true",
+    javaOptions += "-Dcats.effect.tracing.dumpLocals",
     envVars ++= Map(
       "OTEL_PROPAGATORS" -> "b3multi",
       "OTEL_SERVICE_NAME" -> "Trace Example"

examples/src/main/scala/ContextStorageExample.scala

@@ -0,0 +1,38 @@
+import cats.effect.IO
+import cats.effect.IOApp
+import cats.effect.IOLocal
+import cats.effect.Resource
+import cats.effect.unsafe.IOLocals
+import io.opentelemetry.context.Context
+import io.opentelemetry.context.ContextKey
+import io.opentelemetry.context.ContextStorage
+import org.typelevel.otel4s.java.IOLocalContextStorage
+import java.util.logging._
+
+object ContextStorageExample extends IOApp.Simple {
+
+  val key = ContextKey.named[String]("test")
+
+  val printKey =
+    IO(Option(Context.current().get(key))).flatMap(v => IO.println(v))
+
+  def run =
+    for {
+      _ <- IO {
+        val rootLog = Logger.getLogger("")
+        rootLog.setLevel(Level.FINE)
+        rootLog.getHandlers().head.setLevel(Level.FINE)
+      }
+      ioLocal <- IOLocal(null: Context)
+      storage = new IOLocalContextStorage(ioLocal)
+      _ <- IO(ContextStorage.addWrapper(_ => storage))
+      ctx = Context.root()
+      _ = IOLocals.set(ioLocal, Context.root())
+      _ <- Resource
+        .make(IO(ctx.`with`(key, "hello").makeCurrent()))(scope =>
+          IO(scope.close())
+        )
+        .surround(printKey)
+      _ <- printKey
+    } yield ()
+}

java/common/src/main/scala/org/typelevel/otel4s/java/IOLocalContextStorage.scala

@@ -0,0 +1,24 @@
+package org.typelevel.otel4s.java
+
+import cats.effect.IOLocal
+import cats.effect.unsafe.IOLocals
+import io.opentelemetry.context.Context
+import io.opentelemetry.context.ContextStorage
+import io.opentelemetry.context.Scope
+
+class IOLocalContextStorage(
+    ioLocal: IOLocal[Context]
+) extends ContextStorage {
+
+  override def attach(toAttach: Context): Scope = {
+    val previous = current()
+    IOLocals.set(ioLocal, toAttach)
+    new Scope {
+      def close() = IOLocals.set(ioLocal, previous)
+    }
+  }
+
+  override def current(): Context =
+    IOLocals.get(ioLocal)
+
+}