vy opened a new issue, #3430:
URL: https://github.com/apache/logging-log4j2/issues/3430
`InternalLoggerRegistry` is essentially a `Map<MessageFactory, Map<String,
WeakReference<Logger>>>`. [As
reported](/apache/logging-log4j2/issues/3399#issuecomment-2626946587) by
@tristantarrant, stale entries are not expunged in its current form. That is,
the inner map does not get compacted for entries whose associated
`WeakReference`s are reclaimed by the garbage collector. This might cause high
memory usage if an excessive amount of ephemeral loggers get registered.
Reclaimed references can be tracked by a `ReferenceQueue` passed to the
`WeakReference::new` and processed as follows:
```java
private final ReferenceQueue<Logger> staleLoggerRefs = new
ReferenceQueue<>();
private void expungeStaleEntries() {
Reference<? extends Logger> loggerRef;
while ((loggerRef = staleLoggerRefs.poll()) != null) {
Logger logger = loggerRef.get();
if (logger != null) {
removeLogger(logger);
}
}
}
```
When to run `expungeStaleEntries()` should be decided with care, since
`removeLogger()` mutates the registry map.
### On method invocation
All `ILR` methods (`getLogger()`, `computeIfAbsent()`, etc.) can first try
to expunge stale entries.
This approach is exercised by `WeakHashMap` itself and in #3427.
**Pros:**
- Implies no changes besides `ILR`
**Cons:**
- Read-only operations, which are accessed most, might try to acquire the
write-lock.
- If `ILR` is not accessed, stale entries will still be kept. Consider an
application where all `Logger`s are assigned, and a temporary operation creates
excessive amount of loggers and completes. All created temporary `Logger`
instances will be reclaimed by GC, yet will continue taking space for the
associated `Map.Entry<String, WeakReference<Logger>>`.
### By a janitor thread
`ILR` can start a janitor thread listening on the `ReferenceQueue<Logger>`.
**Cons:**
- `ILR` must have a life cycle (to start/stop the janitor thread) managed by
`LoggerContext`.
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