Java Concurrency Bug: HashMap Corruption Leads to Hard-to-Diagnose Issues

My Java application occasionally hangs or throws OutOfMemoryError when multiple threads update a shared HashMap. I can’t reliably reproduce it and debugging is difficult. What might be happening?

HashMap is not thread-safe. Concurrent writes can corrupt its internal structure—leading to infinite loops during iteration or excessive memory usage (especially in older Java versions)—potentially causing crashes or OOM errors Reddit+2InfoQ+2Bomberbot+2. Fix: • Replace HashMap with ConcurrentHashMap for thread-safe concurrent updates. • If necessary, use synchronized blocks or Collections.synchronizedMap(...) to guard access. • Ensure atomic operations such as using computeIfAbsent() for safe updates.