In version 30 of jboss-parent-pom, David Lloyd added the ability to
easily produce multi-release jars [1]. While several components
consumed by WildFly currently produce multi-release jars (e.g.
wildfly-common, Undertow, Infinispan, etc.), as far as I am aware,
none of the modules in WildFly (or wf-core) do this.
I recently created a pull request to WildFly [2] that ports a
collection class from Undertow [3], which, when built using Java 9+,
results in faster expiration scheduling for persistent HttpSessions
and local @Stateful EJBs. While the changes introduced in this PR are
still compatible with JDK 8 [4], this optimization will not be
available to users unless they build wildfly using JDK 9+ in order to
produce the requisite multi-release jar for the
wildfly-clustering-ee-cache module.
What do people think about this?
Is there any reason why we should *not* compile using JDK 11 when
building releases (while still maintaining Java 8 source
compatibility, of course)?
One issue I can think of is CI. We'd probably need to alter jobs to build with JDK 11 and then test with JDK 8. I think our integration testsuite runs for JDK 8 should be running a server built the way a released server is built.
The tests in the subsystems wouldn't run with JDK 8 unless we had separate jobs just for that purpose (which is no big deal.)
To be fair, our JDK 11 CI jobs are building with JDK 11 and then testing that, and our releases are built with JDK 8. So the existence of a mismatch is not new. My impression though is JDK 8 remains dominant, so shifting the mismatch to the JDK 8 side is a concern.
This isn't a showstopper kind of thing for me, it's just something to think about and make a conscious plan.
Even if we continue to create releases using JDK 8 builds, does anyone
object to giving users the option to build WildFly with multi-release
module jars when compiling with a more recent JDK version?
I don't.
[1] https://issues.redhat.com/browse/WFLY-10178
[2] https://github.com/wildfly/wildfly/pull/13334
[3] https://github.com/undertow-io/undertow/blob/master/core/src/main/java9/io/undertow/util/FastConcurrentDirectDeque.java
[4] https://ci.wildfly.org/buildConfiguration/WFPR/207451
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