adutra commented on code in PR #4648:
URL: https://github.com/apache/polaris/pull/4648#discussion_r3395627890
##########
runtime/service/src/main/java/org/apache/polaris/service/events/PolarisEventListeners.java:
##########
@@ -136,4 +165,55 @@ private void deliverEvent(
public boolean hasListeners(PolarisEventType eventType) {
return eventTypesWithListeners.contains(eventType);
}
+
+ private static class ListenerExecutor implements Executor {
+
+ private final Executor delegate;
+ private final Queue<Runnable> queue;
+ private final AtomicBoolean draining = new AtomicBoolean(false);
+
+ ListenerExecutor(Executor delegate, int capacity) {
+ this.delegate = delegate;
+ this.queue =
+ capacity == -1 ? new ConcurrentLinkedQueue<>() : new
ArrayBlockingQueue<>(capacity);
+ }
+
+ @Override
+ public void execute(@NonNull Runnable task) {
+ if (!queue.offer(task)) {
+ throw new RejectedExecutionException("Event listener queue is full");
+ }
+ if (draining.compareAndSet(false, true)) {
+ try {
+ delegate.execute(this::drain);
+ } catch (Throwable t) {
+ draining.set(false);
+ throw t;
+ }
+ }
+ }
+
+ private void drain() {
+ try {
+ Runnable task;
+ while ((task = queue.poll()) != null) {
+ task.run();
+ }
+ } finally {
+ draining.set(false);
+ // A producer may have enqueued a task between the last poll() and the
set(false) above,
+ // and seen draining=true so it did not schedule a drain. Catch that
here.
+ if (!queue.isEmpty() && draining.compareAndSet(false, true)) {
+ try {
+ // re-schedule for fairness
+ delegate.execute(this::drain);
+ } catch (Exception e) {
Review Comment:
> This is why I was wondering about reusing Mutiny of some other framework
here 😅
Any async framework could be leveraged to coordinate failure handling in a
more composable way, for sure. The only caveat is that `Error`s are not
propagated, since the error handling is self-contained.
Here is a version with `CompletableFuture`:
```java
@Override
@SuppressWarnings("FutureReturnValueIgnored")
public void execute(@NonNull Runnable task) {
if (!queue.offer(task)) {
throw new RejectedExecutionException("Event listener queue is full");
}
if (draining.compareAndSet(false, true)) {
try {
scheduleDrain();
} catch (Throwable t) {
draining.set(false);
throw t;
}
}
}
private CompletableFuture<Void> scheduleDrain() {
return CompletableFuture.runAsync(this::drain, delegate)
.thenCompose(this::maybeReschedule)
.exceptionally(this::onError);
}
private void drain() {
try {
Runnable task;
while ((task = queue.poll()) != null) {
task.run();
}
} finally {
draining.set(false);
}
}
private CompletableFuture<Void> maybeReschedule(Void unused) {
if (!queue.isEmpty() && draining.compareAndSet(false, true)) {
// re-schedule for fairness
return scheduleDrain(); // this may throw; it would fail the stage it's
running in
}
return CompletableFuture.completedFuture(null);
}
private Void onError(Throwable error) {
draining.set(false);
LOGGER.warn("Failed to schedule listener executor drain; tasks may be
delayed", error);
return null;
}
```
And here is the version with Mutiny:
```java
Override
public void execute(@NonNull Runnable task) {
if (!queue.offer(task)) {
throw new RejectedExecutionException("Event listener queue is full");
}
if (draining.compareAndSet(false, true)) {
scheduleDrain().subscribe().with(unused -> {}); // doesn't throw
synchronously
}
}
private Uni<Void> scheduleDrain() {
return Uni.createFrom()
.item(this::drain)
.runSubscriptionOn(delegate)
.call(this::maybeReschedule)
.onFailure()
.recoverWithItem(this::onError);
}
private Void drain() {
try {
Runnable task;
while ((task = queue.poll()) != null) {
task.run();
}
} finally {
draining.set(false);
}
return null;
}
private Uni<Void> maybeReschedule(Object unused) {
if (!queue.isEmpty() && draining.compareAndSet(false, true)) {
// re-schedule for fairness
return scheduleDrain(); // doesn't throw synchronously
}
return Uni.createFrom().voidItem();
}
private Void onError(Throwable error) {
draining.set(false);
LOGGER.error(
"Failed to schedule listener executor drain; event delivery may be
delayed", error);
return null;
}
```
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