Unexpected Behavior from HashMap in Concurrency: Data Corruption or OOM

When multiple threads concurrently write to a shared HashMap, my Java application occasionally freezes or throws OutOfMemoryError. The issue is intermittent and hard to replicate.

HashMap is not thread-safe. Concurrent modifications can corrupt its internal structure—potentially leading to infinite loops during iteration or excessive memory growth ([turn0search0]turn0search3). Fix: • Replace HashMap with ConcurrentHashMap for safe concurrent access. • Or use Collections.synchronizedMap(...) with proper synchronization. • Use atomic update patterns (like computeIfAbsent()), avoiding shared mutable access without coordination.