Concurrent Collections & Synchronization

private readonly object _lock = new();
private int _count = 0;

public void Increment() {
    lock (_lock) {
        _count++;
    }
}

lock is C#'s equivalent of Java's synchronized block. For collections shared across threads, System.Collections.Concurrent provides ready-made thread-safe types (ConcurrentDictionary<TKey, TValue>, ConcurrentQueue<T>) instead of manually locking around an ordinary Dictionary.

Common mistakes

• Reading and modifying a plain Dictionary from multiple threads with no lock at all — this is a race condition, and can even corrupt the dictionary's internal structure, not just produce a wrong value.