Add UID to Slf4j MDC (#31039)

This UID can be used to distinguish logging from different
ActorSystem incarnations even when they have the same host
and port.

This UID already existed in akka-remote, but to avoid
introducing a dependency between akka-slf4j and akka-remote
this change pulls it up to the ActorSystem.

akka-actor/src/main/mima-filters/2.6.18.backward.excludes/system-uid.excludes

@@ -0,0 +1,2 @@
+# marked DoNotInherit, so fine to add methods
+ProblemFilters.exclude[ReversedMissingMethodProblem]("akka.actor.ExtendedActorSystem.uid")

akka-actor/src/main/scala/akka/actor/ActorSystem.scala

@@ -775,6 +775,11 @@ abstract class ExtendedActorSystem extends ActorSystem {
    */
   private[akka] def printTree: String
 
+  /**
+   * INTERNAL API: random uid assigned at ActorSystem startup
+   */
+  @InternalApi private[akka] def uid: Long
+
   /**
    * INTERNAL API: final step of `terminate()`
    */
@@ -800,6 +805,8 @@ private[akka] class ActorSystemImpl(
     setup: ActorSystemSetup)
     extends ExtendedActorSystem {
 
+  val uid: Long = ThreadLocalRandom.current.nextLong()
+
   if (!name.matches("""^[a-zA-Z0-9][a-zA-Z0-9-_]*$"""))
     throw new IllegalArgumentException(
       "invalid ActorSystem name [" + name +

akka-remote/src/main/scala/akka/remote/AddressUidExtension.scala

@@ -4,8 +4,6 @@
 
 package akka.remote
 
-import java.util.concurrent.ThreadLocalRandom
-
 import akka.actor.ActorSystem
 import akka.actor.ClassicActorSystemProvider
 import akka.actor.ExtendedActorSystem
@@ -35,13 +33,11 @@ class AddressUidExtension(val system: ExtendedActorSystem) extends Extension {
 
   private def arteryEnabled = system.provider.asInstanceOf[RemoteActorRefProvider].remoteSettings.Artery.Enabled
 
-  val longAddressUid: Long = {
+  val longAddressUid: Long =
-    val tlr = ThreadLocalRandom.current
+    if (arteryEnabled) system.uid
-    if (arteryEnabled) tlr.nextLong()
     // with the old remoting we need to make toInt.toLong return the same number
     // to keep wire compatibility
-    else tlr.nextInt().toLong
+    else system.uid.toInt.toLong
-  }
 
   // private because GenJavaDoc fails on deprecated annotated lazy val
   private lazy val _addressUid: Int = {

akka-slf4j/src/main/scala/akka/event/slf4j/Slf4jLogger.scala

@@ -60,8 +60,10 @@ class Slf4jLogger extends Actor with SLF4JLogging with RequiresMessageQueue[Logg
   val mdcAkkaSourceAttributeName = "akkaSource"
   val mdcAkkaTimestamp = "akkaTimestamp"
   val mdcAkkaAddressAttributeName = "akkaAddress"
+  val mdcAkkaUidAttributeName = "akkaUid"
 
   private def akkaAddress = context.system.asInstanceOf[ExtendedActorSystem].provider.addressString
+  private val akkaUid: String = context.system.asInstanceOf[ExtendedActorSystem].uid.toString
 
   def receive = {
 
@@ -122,6 +124,7 @@ class Slf4jLogger extends Actor with SLF4JLogging with RequiresMessageQueue[Logg
     MDC.put(mdcAkkaTimestamp, formatTimestamp(logEvent.timestamp))
     MDC.put(mdcActorSystemAttributeName, context.system.name)
     MDC.put(mdcAkkaAddressAttributeName, akkaAddress)
+    MDC.put(mdcAkkaUidAttributeName, akkaUid)
     logEvent.mdc.foreach { case (k, v) => MDC.put(k, String.valueOf(v)) }
 
     try logStatement

akka-slf4j/src/test/scala/akka/event/slf4j/Slf4jLoggerSpec.scala

@@ -93,6 +93,7 @@ class Slf4jLoggerSpec extends AkkaSpec(Slf4jLoggerSpec.config) with BeforeAndAft
       val s = outputString
       s should include("akkaSource=akka://Slf4jLoggerSpec/user/logProducer")
       s should include("akkaAddress=akka://Slf4jLoggerSpec")
+      s should include("akkaUid=")
       s should include("level=[ERROR]")
       s should include("logger=[akka.event.slf4j.Slf4jLoggerSpec$LogProducer]")
       (s should include).regex(sourceThreadRegex)