Instrumenting Executors - issues in Spring Cloud Sleuth and JDK16

[Remi Forax]

----- Mail original -----
> De: "Marcin Grzejszczak" <mgrzejszczak at vmware.com>
> À: "core-libs-dev" <core-libs-dev at openjdk.java.net>
> Envoyé: Vendredi 9 Avril 2021 16:29:32
> Objet: Instrumenting Executors - issues in Spring Cloud Sleuth and JDK16

> Hi!
> 
> I'm the lead of Spring Cloud Sleuth [1], a project dedicated to working with
> distributed tracing. We're propagating the tracing context e.g. through
> threads. That means that when a user spawns a new thread we need to pass the
> context from the old thread to the new one. Example - if the user uses an
> Executor or an ExecutorService (e.g. via calling the execute(Runnable r)
> method) then we need to wrap the Runnable in its trace representation. That
> means that we retrieve the context from Thread A , pass it in the constructor
> of the TraceRunnable and then restore it once the run method is called in
> Thread B.
> 
> The problem in Sleuth that we have with JDK16 is that we can't use reflection to
> ensure that we're wrapping all methods of any Executors [2]. In other words we
> want to create a proxy around an existing Executor and wrap all methods.
> Currently, we're using reflection cause Executor implementations such as
> `ScheduledThreadPoolExecutor` have quite a few protected methods that we can't
> access. What we would like to achieve is a delegation mechanism that we can
> wrap all objects that the given Executor is using within their API (such as
> Runnables, Callables, other Executors) in their trace representation and then
> delegate calls for all methods to the wrapped object. That would also mean the
> delegation to currently protected methods.
> 
> If there's another way to achieve this other than opening the
> java.util.concurrent API then I would very much like to use it. Currently with
> JDK16 it's not possible to instrument that code so context propagation might be
> buggy when dealing with executors.

I'm not sure if you are using an agent or not, if you are using an agent, you can redefine a module
https://docs.oracle.com/en/java/javase/16/docs/api/java.instrument/java/lang/instrument/Instrumentation.html#redefineModule(java.lang.Module,java.util.Set,java.util.Map,java.util.Map,java.util.Set,java.util.Map)

regards,
Rémi

> 
> Marcin Grzejszczak
> Staff Engineer, Spring Cloud