Move common caching class loading functionality to the separate class#10979
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…er class Use it for UberClassLoder, as a result - UberClassLoder caches all results of loadClass function (not only findClass)
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jeromepochat
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Aug 28, 2025
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Hi! This refactor makes total sense, encouraging single-responsibility principle. Thanks!
I just left minor suggestion about Optional usage, feel free to ignore!
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| private final ConcurrentHashMap<String, Object> cache = new ConcurrentHashMap<>(); | ||
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| public CachingClassLoader(String name, ClassLoader parent) { | ||
| super(name, parent); | ||
| } | ||
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| @Override | ||
| protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException { | ||
| Object classOrEmpty = cache.computeIfAbsent(name, key -> { | ||
| try { | ||
| return super.loadClass(name, false); | ||
| } catch (ClassNotFoundException e) { | ||
| // Not found. | ||
| return Optional.empty(); | ||
| } | ||
| }); | ||
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| if (classOrEmpty == Optional.empty()) { | ||
| throw new ClassNotFoundException(name); | ||
| } | ||
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| Class<?> clazz = (Class<?>) classOrEmpty; | ||
| if (resolve) { | ||
| resolveClass(clazz); | ||
| } | ||
| return clazz; | ||
| } | ||
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| public void clearCacheMisses() { | ||
| cache.values().removeIf(v -> v == Optional.empty()); | ||
| } |
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suggestion: Maybe the using Optional as map value type could make its usage more natural. WDYT?
Suggested change
| private final ConcurrentHashMap<String, Object> cache = new ConcurrentHashMap<>(); | |
| public CachingClassLoader(String name, ClassLoader parent) { | |
| super(name, parent); | |
| } | |
| @Override | |
| protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException { | |
| Object classOrEmpty = cache.computeIfAbsent(name, key -> { | |
| try { | |
| return super.loadClass(name, false); | |
| } catch (ClassNotFoundException e) { | |
| // Not found. | |
| return Optional.empty(); | |
| } | |
| }); | |
| if (classOrEmpty == Optional.empty()) { | |
| throw new ClassNotFoundException(name); | |
| } | |
| Class<?> clazz = (Class<?>) classOrEmpty; | |
| if (resolve) { | |
| resolveClass(clazz); | |
| } | |
| return clazz; | |
| } | |
| public void clearCacheMisses() { | |
| cache.values().removeIf(v -> v == Optional.empty()); | |
| } | |
| private final ConcurrentHashMap<String, Optional<Class<?>>> cache = new ConcurrentHashMap<>(); | |
| public CachingClassLoader(String name, ClassLoader parent) { | |
| super(name, parent); | |
| } | |
| @Override | |
| protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException { | |
| Optional<Class<?>> classOrEmpty = cache.computeIfAbsent(name, key -> { | |
| try { | |
| return Optional.of(super.loadClass(name, false)); | |
| } catch (ClassNotFoundException e) { | |
| // Not found. | |
| return Optional.empty(); | |
| } | |
| }); | |
| if (classOrEmpty.isEmpty()) { | |
| throw new ClassNotFoundException(name); | |
| } | |
| Class<?> clazz = classOrEmpty.get(); | |
| if (resolve) { | |
| resolveClass(clazz); | |
| } | |
| return clazz; | |
| } | |
| public void clearCacheMisses() { | |
| cache.values().removeIf(Optional::isEmpty); | |
| } |
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Wrapping with Optional consumes a bit more memory, so I decided not to use it. However, I agree it makes the code more natural. Let's wait for further reviews before making a final decision.
timja
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Sep 1, 2025
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/label ready-for-merge
This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.
Thanks!
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Move common class-loading caching functionality into CachingClassLoader.
Update UberClassLoader to use CachingClassLoader, so now all results of loadClass() (not just findClass()) are cached.
This improves performance, especially because UberClassLoader uses a ExistenceCheckingClassLoader wrapper for the parent class loader, which introduces overhead.
By caching class-loading results for the parent as well, we avoid redundant lookups and reduce that overhead.
Testing done
Manual testing on local setup, jenkins ci gates.
Proposed changelog entries
Proposed changelog category
/label internal
Proposed upgrade guidelines
N/A
Submitter checklist
@Restrictedor have@since TODOJavadocs, as appropriate.@Deprecated(since = "TODO")or@Deprecated(forRemoval = true, since = "TODO"), if applicable.evalto ease future introduction of Content Security Policy (CSP) directives (see documentation).Desired reviewers
@basil, @timja
Before the changes are marked as ready-for-merge:
Maintainer checklist
upgrade-guide-neededlabel is set and there is a Proposed upgrade guidelines section in the pull request title (see example).lts-candidateto be considered (see query).