Q29: How does ConcurrentHashMap achieve high concurrency without lock overhead?
- Java 7: Used Segmented Locks (Array of 16 ReentrantLocks guarding bucket segments).
- Java 8+: Replaced segments with CAS (Compare-And-Swap) for empty bucket insertions and
synchronizedlocks on individual bucket head nodes for updates. Allows concurrent thread reads without locking and parallel bucket writes.
Key Takeaways
- Uses CAS for lock-free insertions on empty buckets.
- Locks individual bucket head nodes instead of locking the entire table.
Knowledge Check
How does ConcurrentHashMap manage read (get) operations across buckets?