merlimat commented on a change in pull request #14283:
URL: https://github.com/apache/pulsar/pull/14283#discussion_r806485471
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File path:
pulsar-metadata/src/main/java/org/apache/pulsar/metadata/cache/impl/MetadataCacheImpl.java
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@@ -261,12 +261,17 @@ public void invalidate(String path) {
}
@Override
- public void refresh(String path) {
+ public CompletableFuture<Void> refresh(String path) {
// Refresh object of path if only it is cached before.
- if (objCache.getIfPresent(path) != null) {
- objCache.synchronous().invalidate(path);
- objCache.synchronous().refresh(path);
- }
+ CompletableFuture<Void> promise = new CompletableFuture<>();
+ this.store.getMetadataCacheScheduler().executeOrdered(path, () -> {
+ if (objCache.getIfPresent(path) != null) {
+ objCache.synchronous().invalidate(path);
+ objCache.synchronous().refresh(path);
+ }
+ promise.complete(null);
+ });
+ return promise;
Review comment:
> I'm not sure if it helps, but in [Caffeine
3.x](https://github.com/ben-manes/caffeine/releases/tag/v3.0.0) the refresh
behavior was improved to be linearizable. It also now returns te in-flight
CompletableFuture. You might consider upgrading.
We're still compiling with compatibility to Java 8, so we're not yet able to
do so, though we plan to raise min Java compile version soon and we'll
certainly upgrade to Caffeine 3.x then.
> I am also not sure why this is invalidating and refreshing. Since the
value is no longer present then the refresh is simply a cache load, and itself
delegates to AsyncCache.get(key), which of course also returns that future. You
might also consider using if (objCache.asMap().remove(key) != null) { ... }
instead of the get/invalidate.
The reason was that in 2.x `refresh()` doesn't return a future so we don't
know when it's completed. Because of that, in order to not return a stale
object from the cache, we trigger the invalidation just before.
> Trying to grok the code, I'd probably use
objCache.asMap().computeIfPresent(key, (k, future) -> ...) to explicitly store
a new future and return that upstream. Then it is all an atomic swap with very
clear code that localizes and shows your intent.
That's a very good point. I think that is probably the best approach (at
least until we get to Caffeine 3.x).
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