presto-main/src/main/java/io/prestosql/operator/ReferenceCount.java/ReferenceCount/ReferenceCount
class ReferenceCount:    public ReferenceCount(int initialCount)
    {
        checkArgument(initialCount >= 0, "initialCount must not be negative, got %s", initialCount);
        count = initialCount;
        if (initialCount == 0) {
            freeFuture.set(null);
        }
    }