On Fri, 28 Feb 2025 14:41:41 GMT, Alexander Zvegintsev <[email protected]> wrote:
> During the [JDK-8344891 Remove uses of sun.misc.ReflectUtil in > java.desktop](https://bugs.openjdk.org/browse/JDK-8344891) it was discovered > that `beans/finder/MethodFinder.findMethod' incorrectly returned null if a > signature was not in the cache and added it to the cache if it was already > there: > > > Method method = CACHE.get(signature); > return (method == null) ? method : CACHE.create(signature); > > This resulted in a [significant drop in > performance](https://bugs.openjdk.org/browse/JDK-8350573). > > ---- > > Before ReflectUtil was removed, it worked by coincidence: > > > Method method = CACHE.get(signature); > return (method == null) || isPackageAccessible(method.getDeclaringClass()) ? > method : CACHE.create(signature); > > > > > 1. `Cache#get` non-obviously creates a value in Cache, this in turn allowed > us to avoid the NPE in the `(method == null) || > isPackageAccessible(method.getDeclaringClass())` condition > > > https://github.com/openjdk/jdk/blob/d6c4be672f6348f8ed985416ed90d0447f5d5bb3/src/java.desktop/share/classes/com/sun/beans/util/Cache.java#L120-L126 > > 2. `isPackageAccessible(method.getDeclaringClass())` was evaluated as true > > This is how we previously returned the cached value. > > --- > > So the solution is obvious: > > > Method method = CACHE.get(signature); > return (method != null) ? method : CACHE.create(signature); > > > Testing is green. It's somewhat off-topic, yet I find it *worrying*. The `Cache.get` method starts with *unsynchronised access first*. https://github.com/openjdk/jdk/blob/e98df71d9c5120fbb73a4c2f49863775fe5db781/src/java.desktop/share/classes/com/sun/beans/util/Cache.java#L112-L114 It doesn't make sense… First of all, if the method can be accessed concurrently, which seems to be implied, the `table` field could be in an inconsistent state. This could result in hard-to-reproduce bugs. Secondly, the `Cache.get` invokes `removeStaleEntries` which has a `synchronized` block. That is the `get` method still requires explicit synchronisation. Having this in mind, *the unsynchronised access to the data structures doesn't gain anything*. Performance-wise, it would be better to wrap the call to `removeStaleEntries` and the required logic into `synchronized (this.queue)`. Thirdly, there's another call to `removeStaleEntries` in the `get` method, this time it's inside the `synchronized (this.queue)` block. ------------- PR Comment: https://git.openjdk.org/jdk/pull/23845#issuecomment-2691348842
