gnodet commented on PR #704:
URL: https://github.com/apache/creadur-rat/pull/704#issuecomment-5106067152

   ### Latest commit: `MatcherBuilderTracker` + `StandardCollection` 
thread-safety fixes
   
   Based on the earlier audit discussion, this commit (18a41490) includes two 
additional fixes:
   
   #### 1. `MatcherBuilderTracker`: `HashMap` → `ConcurrentHashMap`
   
   The singleton `MatcherBuilderTracker` uses a `synchronized instance()` 
method, but once the instance is obtained, `addBuilderImpl()` and 
`getMatcherBuilder()` access the underlying `HashMap` without synchronization. 
In a parallel Maven build, concurrent `put()`/`get()` on a `HashMap` can cause 
infinite loops (hash bucket cycles) or lost entries.
   
   **Fix:** One-line change — `new HashMap<>()` → `new ConcurrentHashMap<>()`.
   
   #### 2. `StandardCollection`: `Supplier<AbstractFileProcessorBuilder>` 
instead of shared instances
   
   This is the `GitIgnoreBuilder`/`HgIgnoreBuilder` issue discussed 
[earlier](https://github.com/apache/creadur-rat/pull/704#issuecomment-5105540076).
 The `StandardCollection` enum constants stored shared singleton builder 
instances:
   
   ```java
   GIT(..., new GitIgnoreBuilder())
   MERCURIAL(..., new HgIgnoreBuilder())
   BAZAAR(..., new BazaarIgnoreBuilder())
   CVS(..., new CVSIgnoreBuilder())
   ```
   
   These builders contain mutable state:
   - `AbstractFileProcessorBuilder.levelBuilders` — a `TreeMap` populated 
during `build()`, then `clear()`'d
   - `HgIgnoreBuilder.state` — a `Syntax` enum toggled during parsing
   
   Since enum constants are singletons, concurrent threads calling `build()` on 
the same shared instance would corrupt each other's state.
   
   **Fix:** Store a `Supplier<AbstractFileProcessorBuilder>` instead, so each 
`fileProcessorBuilder()` call creates a fresh builder:
   
   ```java
   GIT(..., GitIgnoreBuilder::new)        // was: new GitIgnoreBuilder()
   MERCURIAL(..., HgIgnoreBuilder::new)   // was: new HgIgnoreBuilder()
   ```
   
   Both fixes pass the full build locally (`mvn clean install -B` — BUILD 
SUCCESS).


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