Fix wrong isEmpty method of ConcurrentOpenLongPairRangeSet

[BewareMyPower]

Motivation

The ConcurrentOpenLongPairRangeSet#isEmpty implementation is wrong. See

        AtomicBoolean isEmpty = new AtomicBoolean(false);
        rangeBitSetMap.forEach((key, val) -> {
            if (!isEmpty.get()) { // [1] isEmpty is always false, so this condition always meets
                return;
            isEmpty.set(val.isEmpty()); // it never reaches here
        });
        return isEmpty.get(); // [2] So if rangeBitSetMap is not empty, isEmpty() always return true

The comment of [1] should be isEmpty.get(), not !isEmpty.get(). However, the implementation is still bad because forEach method will iterate over the whole map. If the map has many entries, the performance cost will not be ignorable.

Modifications

• Fix ConcurrentOpenLongPairRangeSet#isEmpty. Instead of calling forEach, here we use a trivial for loop and break the loop if there is an entry whose value is a non-empty set.
• Add a test (testIsEmpty), which adds an empty set to ConcurrentOpenLongPairRangeSet. Before this patch, the isEmpty() returns false, which is incorrect.

Verifying this change

• Make sure that the change passes the CI checks.

This change added test ConcurrentOpenLongPairRangeSetTest#testIsEmpty.

[michaeljmarshall]

LGTM

[Jason918]

LGTM