developer-rpai commented on code in PR #18378:
URL: https://github.com/apache/iceberg/pull/18378#discussion_r4200674952
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core/src/main/java/org/apache/iceberg/rest/auth/AuthSessionCache.java:
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@@ -37,6 +38,17 @@ public class AuthSessionCache implements AutoCloseable {
private static final Logger LOG =
LoggerFactory.getLogger(AuthSessionCache.class);
+ /**
+ * A single daemon thread, shared by all cache instances for eviction tasks.
A shared executor
+ * avoids registering one JVM shutdown hook per cache instance: each hook
thread is constructed
+ * on the creating thread and would otherwise copy that thread's inheritable
thread-locals,
+ * pinning state such as closed Spark sessions for the life of the JVM. The
worker thread is
+ * created with inheritable thread-local variables disabled so it cannot pin
the creating
+ * thread's state either. The executor is deliberately exposed only as a
plain {@link Executor}
+ * (never an {@link ExecutorService}) so that {@link #close()} does not shut
it down.
+ */
+ private static final Executor SHARED_EVICTION_EXECUTOR =
newSharedEvictionExecutor();
Review Comment:
Good question. I checked whether the existing helper could work here, but it
cannot express what this executor needs, for two reasons:
1. `newExitingWorkerPool` wraps the pool with
`MoreExecutors.getExitingExecutorService`, which registers a JVM shutdown hook.
That hook is exactly what this PR removes: the hook thread is constructed on
the creating thread and copies its inheritable thread-locals, pinning state
such as Spark sessions for the life of the JVM (the problem reported in #18377).
2. Its thread factory (Guava `ThreadFactoryBuilder`) creates threads that
inherit thread-locals. This worker is deliberately created with
`inheritThreadLocals=false` so it cannot pin the creating thread's state either.
So reusing the helper would reintroduce both issues this PR fixes. The
custom factory is only there for the `inheritThreadLocals=false` semantic,
which `ThreadPools` cannot express today. Happy to add a `ThreadPools` overload
accepting a custom `ThreadFactory` if you would prefer the reuse, but the plain
helper is not a drop-in here.
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