Nullpointer exception for pekko-instrumentation in version 1.1.0-M1 onward

[TjarkoG]

when testing pekko with the version 1.1.0-M1 which will be released soon we've ran into a nullpointer error when running with Kamon + kanela-instrumentation.

to Reproduce:
build.sbt

name := "pekko-quickstart-scala"

version := "1.0"

scalaVersion := "2.13.14"

lazy val pekkoVersion = "1.1.0-M1"

run/fork := true

libraryDependencies ++= Seq(
  "org.apache.pekko" %% "pekko-actor-typed" % pekkoVersion,
  "org.apache.pekko" %% "pekko-http" % pekkoVersion,
  "org.apache.pekko" %% "pekko-stream" % pekkoVersion,
  "ch.qos.logback" % "logback-classic" % "1.5.6",
  "io.kamon" %% "kamon-pekko" % "2.7.3",
  "io.kamon" %% "kamon-system-metrics" % "2.7.3",
  "io.kamon" %% "kamon-prometheus" % "2.7.3"
)

Main.scala:

//#full-example
package com.example

import com.typesafe.config.ConfigFactory
import org.apache.pekko.actor.ActorSystem
import org.apache.pekko.http.scaladsl.Http
import org.apache.pekko.http.scaladsl.client.RequestBuilding.Get
import org.apache.pekko.http.scaladsl.server.Directives

object Main extends Directives {
  def main(args: Array[String]): Unit = {
    val config = ConfigFactory.load()
    implicit val untyped: ActorSystem = ActorSystem.create("Test", config)
    Http()(untyped).singleRequest(Get("https://www.google.com")).onComplete(rsp => println(rsp.map(_.status)))(untyped.dispatcher)
  }
}

when starting with -javaagent:javaagent/kanela-agent.jar (version 1.0.18)

i'm receiving the exception:

org.apache.pekko.actor.ActorInitializationException: pekko://Test/system/IO-TCP/selectors/$a: exception during creation, root cause message: [Cannot invoke "org.apache.pekko.dispatch.DispatcherPrerequisites.settings()" because the return value of "kamon.instrumentation.pekko.instrumentations.DispatcherInfo$HasDispatcherPrerequisites.dispatcherPrerequisites()" is null]
	at org.apache.pekko.actor.ActorCell.create(ActorCell.scala:679)
	at org.apache.pekko.actor.ActorCell.invokeAll$1(ActorCell.scala:523)
	at org.apache.pekko.actor.ActorCell.systemInvoke(ActorCell.scala:545)
	at org.apache.pekko.dispatch.Mailbox.processAllSystemMessages(Mailbox.scala:297)
	at org.apache.pekko.dispatch.Mailbox.run(Mailbox.scala:232)
	at kamon.instrumentation.executor.ExecutorInstrumentation$InstrumentedForkJoinPool$TimingRunnable.run(ExecutorInstrumentation.scala:800)
	at org.apache.pekko.dispatch.ForkJoinExecutorConfigurator$PekkoForkJoinTask.exec(ForkJoinExecutorConfigurator.scala:61)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)
Caused by: java.lang.reflect.InvocationTargetException: null
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
	at org.apache.pekko.util.Reflect$.instantiate(Reflect.scala:82)
	at org.apache.pekko.actor.ArgsReflectConstructor.produce(IndirectActorProducer.scala:111)
	at org.apache.pekko.actor.Props.newActor(Props.scala:236)
	at org.apache.pekko.actor.ActorCell.newActor(ActorCell.scala:626)
	at org.apache.pekko.actor.ActorCell.create(ActorCell.scala:653)
	... 11 common frames omitted
Caused by: java.lang.NullPointerException: Cannot invoke "org.apache.pekko.dispatch.DispatcherPrerequisites.settings()" because the return value of "kamon.instrumentation.pekko.instrumentations.DispatcherInfo$HasDispatcherPrerequisites.dispatcherPrerequisites()" is null
	at kamon.instrumentation.pekko.instrumentations.InstrumentNewExecutorServiceOnPekko$.around(DispatcherInstrumentation.scala:130)
	at kamon.instrumentation.pekko.instrumentations.InstrumentNewExecutorServiceOnPekko.around(DispatcherInstrumentation.scala)
	at org.apache.pekko.dispatch.ThreadPoolConfig$ThreadPoolExecutorServiceFactory.createExecutorService(ThreadPoolBuilder.scala)
	at org.apache.pekko.dispatch.Dispatcher$LazyExecutorServiceDelegate.executor$lzycompute(Dispatcher.scala:54)
	at org.apache.pekko.dispatch.Dispatcher$LazyExecutorServiceDelegate.executor(Dispatcher.scala:54)
	at org.apache.pekko.dispatch.ExecutorServiceDelegate.execute(ThreadPoolBuilder.scala:232)
	at org.apache.pekko.dispatch.ExecutorServiceDelegate.execute$(ThreadPoolBuilder.scala:232)
	at org.apache.pekko.dispatch.Dispatcher$LazyExecutorServiceDelegate.execute(Dispatcher.scala:53)
	at org.apache.pekko.dispatch.Dispatcher.executeTask(Dispatcher.scala:91)
	at org.apache.pekko.dispatch.MessageDispatcher.unbatchedExecute(AbstractDispatcher.scala:177)
	at org.apache.pekko.dispatch.BatchingExecutor.execute(BatchingExecutor.scala:143)
	at org.apache.pekko.dispatch.BatchingExecutor.execute$(BatchingExecutor.scala:134)
	at org.apache.pekko.dispatch.MessageDispatcher.execute(AbstractDispatcher.scala:107)
	at org.apache.pekko.util.SerializedSuspendableExecutionContext.attach(SerializedSuspendableExecutionContext.scala:92)
	at org.apache.pekko.util.SerializedSuspendableExecutionContext.execute(SerializedSuspendableExecutionContext.scala:95)
	at org.apache.pekko.io.SelectionHandler$ChannelRegistryImpl.<init>(SelectionHandler.scala:200)
	at org.apache.pekko.io.SelectionHandler.<init>(SelectionHandler.scala:324)
	... 21 common frames omitted

i've tried to analyze the error and got to the point that
kamon/instrumentation/pekko/instrumentations/DispatcherInstrumentation.scala:164
does not seem to get triggered with pekko 1.1.0-M1 anymore resulting in dispatcherPrerequisites being null in
kamon/instrumentation/pekko/instrumentations/DispatcherInstrumentation.scala:125
but i cannot understand what change in pekko 1.0.3 <-> 1.1.0-M1 made that difference and how to fix it

[pjfanning]

Pekko 1.1.0-M1 is released. It is a milestone release but the jars are all up on Maven Central.

[pjfanning]

#1354 PR experiment does not seem to pick up this issue. Could be a gap in test coverage. @TjarkoG could you see if you could add a unit test that reproduces this?

[pjfanning]

There are some changes in the Pekko dispatch code in v1.1.0-M1. I wouldn't have thought them major.

https://github.com/apache/pekko/commits/0930982b9a5625e622c4c4c2a6f71dc9917cb336/actor/src/main/scala/org/apache/pekko/dispatch

apache/pekko#485 is the biggest change

[TjarkoG]

@pjfanning sry for the late response.
I've looked into it but the whole instrumentation logic is sadly out of my knowledge zone.
Took me way longer to gather the information i put above than im proud to admit :(

[pjfanning]

The strange thing is the #1354 CI tests pass for pekko. Any interest in just building your own kamon jars using the branch underlying #1354 ?

[TjarkoG]

i can try if this would help with our problem but im not to optimistic that it will help.
the problems with the "normal" jars are also only occurring when starting with the kanela-agent for instrumentation and when using the dispatcher "pekko.io.pinned-dispatcher" from the reference.conf "pekko.io.tcp"
edit:
i've build the jar locally based on #1354 and tried it with the same result

[TjarkoG]

@ivantopo do you have any idea how to create tests for that?

[pjfanning]

I created https://github.com/pjfanning/kamon-pekko-http-test based on the description here and this runs fine with no issues.

[TjarkoG]

Did you start it with the kanela java-agent?
Without it does work but we dont get the instrumentation

[pjfanning]

Did you start it with the kanela java-agent? Without it does work but we don't get the instrumentation

Thanks. I hadn't added kanela-agent. The issue happens with it enabled. I updated the sample project. I haven't used Kamon since its early days. I have my own fork that I use myself and it works with Pekko 1.1 (https://github.com/pjfanning/micrometer-pekko).

[pjfanning]

I may have messed up the test run but when I tried Scala 3.3.3 and 2.12.19, it seemed ok. Maybe this only happens with Scala 2.13.

[Philippus]

I'm getting this issue now with Pekko 1.1.0.

[Philippus]

I think it's related to inlining. This commit still works: apache/pekko@d829637. This one doesn't: apache/pekko@0f1db53. And if I disable inlining with the pekko.no.inline setting and compile pekko it works.
I'm using Scala 2.13.14.

[pjfanning]

I think it's related to inlining. This commit still works: apache/pekko@d829637. This one doesn't: apache/pekko@0f1db53. And if I disable inlining with the pekko.no.inline setting and compile pekko it works. I'm using Scala 2.13.14.

Seems plausible. Do you see the same behaviour as me - in that Scala 3 and Scala 2.12 work fine but that the NPE pops up with Scala 2.13? The Pekko inlining does not affect the Scala 3 release of Pekko.

[Philippus]

I think it's related to inlining. This commit still works: apache/pekko@d829637. This one doesn't: apache/pekko@0f1db53. And if I disable inlining with the pekko.no.inline setting and compile pekko it works. I'm using Scala 2.13.14.

Seems plausible. Do you see the same behaviour as me - in that Scala 3 and Scala 2.12 work fine but that the NPE pops up with Scala 2.13? The Pekko inlining does not affect the Scala 3 release of Pekko.

2.12.19 and 3.5.0 didn't give a NPE.

[Philippus]

Is this a bug in Kamon, or a bug in Pekko ?

[pjfanning]

Pekko 1.1 uses Scala 2 compiler inlining. Kamon doesn't seem to be able to find the inlined code in Pekko.

[leszekgruchala]

I do have the same issue with 2.13.14

[pjfanning]

To be clear, the Apache Pekko 1.1 releases won't be modified to suit Kamon. We reserve the right in minor releases to make some changes.
The issue here is that Kanela works a bit like AOP and expects to be able the manipulate Pekko byte code to gather metrics. It looks like the instrumentation logic in Kamon - specify for Pekko dispatchers - needs to be modified to work with Pekko 1.1.

@mdedetrich just adding to you to the issue just in case you have any thoughts on this.

If anyone has any thoughts on hooks that could be added to Pekko 1.2 or 2.0 that makes it easier for Kamon to instrument Pekko then feel free to raise issues or PRs in the Pekko repo(s).

[pjfanning]

I created #1361 as a workaround.

[pjfanning]

Users hitting this issue should also be able to disable dispatcher instrumentation. See https://github.com/kamon-io/Kamon/blob/124e223de4d7d806b47c76323f5d91edf626fa81/instrumentation/kamon-pekko/src/main/resources/reference.conf and check about excluding dispatchers.