How to lock on single ConcurrentHashMap object for modification without blocking whole map?

Question

Is there an easy way to lock on ConcurrentHashMap object during its modification without blocking whole map? As far as I know here is simple way in Java 8 - method competeIfPresent , but unfortunately I've got 1.7 java on project.

private Map<Long, AtomicInteger> idForCountMap;

public void decrement(Long id) {
    AtomicInteger count = idForCountMap.get(id);
    if (count != null){
    count.decrementAndGet();
    // do some additional operations
    }
}

Here is an example. How can I perform decrement opeperation as atomic one WITHOUT blocking whole map?

ps suppose it's quite common situation, but I could not find fine explained answer.

Answer 1

I think it will workout if you can bring a shared key for the mapped value, and acquire a lock on the key for the complete operation.

public void decrement(SharedKey id) {
synchronized(id){
     AtomicInteger count = idForCountMap.get(id);
     if (count != null){
        count.decrementAndGet();
        // do some additional operations
     }
}
}