1. I am experimenting with adding Thread support to ScopedContext as we speak.
It should be straightforward.
I am not sure we ever want to deal with ScopedValue. ScopedContext provides the
same functionality plus integration with logging.
Ralph
> On Mar 20, 2024, at 4:22 AM, Piotr P. Karwasz <piotr.karw...@gmail.com> wrote:
>
> Hi Ralph,
>
> On Tue, 19 Mar 2024 at 07:45, Ralph Goers <ralph.go...@dslextreme.com> wrote:
>> 2. The links you provide describe the problem of passing contexts to threads
>> magnificently. Unfortunately, they solve it by requiring you NOT to use
>> standard JDK tooling for managing threads. I am not prepared to be dependent
>> on any specific framework other than the JDK.
>> ...
>> 3. As I stated, I am not prepared to provide a solution that is dependent on
>> another framework. However that framework is welcome to integrate with us.
>
> I would propose to meet those libraries half-way:
>
> * we extend our SPI to provide a fast method to copy the contents of
> the ThreadLocal used by ThreadContextMap, restore it on another thread
> or clear it,
> * the `context-propagation` library integrates our newly added SPI.
>
>> 2. As I noted, adding a wrapper around a Logger doesn’t accomplish anything,
>> at least in terms of getting data into LogEvents.
>
> The wrapper could do something like:
>
> public void info(String message) {
> if (logger.isEnabled(null, Level.INFO, message)) {
> try (CloseableThreadContext.Instance ignored =
> CloseableThreadContext.putAll(context)) {
> logger.info(message);
> }
> }
> }
>
> using only Log4j API. Log4j Core could do better of course.
>
>> SLF4J has recently introduced
>> https://www.slf4j.org/apidocs-2.1.0-alpha0/org.slf4j/org/slf4j/MDCAmbit.html
>> which to me looks like a horrible way to add a “scope-based” context as it
>> relies on the user to perform cleanup.
>
> This is a horrible workaround of the way "try-with-resources" work,
> when "catch" clauses are also present. Since the resource is closed
> **before** the "catch" code is executed, the new context keys are no
> longer available in the "catch" clauses.
>
>> Java 21 introduces ScopedValues -
>> https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/ScopedValue.html.
>> It does allow ScopedValues to be passed to child threads but I haven’t
>> experimented with it enough yet to know how it really works.
>
> In the future we will certainly switch to this, but for now I would
> keep all usages of `ScopedValue` in an `o.a.l.l.experimental` package,
> so that users know that we can remove it any time we want.
>
> Piotr
