On Sun, 20 Feb 2022 19:08:39 GMT, liach <d...@openjdk.java.net> wrote:
>>> @liach implementations `size()` seems O1, and returns a single int number >>> field, but it actually defers in some Map implementations. >> >> @liach for example, in ConcurrentSkipListMap and ConcurrentHashMap, `size()` >> function is far complicated than reading a field, thus calling it twice >> meaninglessly is not a wise choice. > > Imo you should just remove the `if (expectedSize == 0)` check than using this > somewhat ugly trick to avoid calling `size()` twice (the second call is only > used for this relatively useless fast-path, especially for the concurrent > collections you refer to) In fact, if we do worry about the performance of adding from maps, calling `map.forEach(this::put);` would be a better alternative both in concurrency (as the concurrent map itself takes charage) and object allocation-wise (no allocation of immutable entry objects), but that belongs to another issue. ------------- PR: https://git.openjdk.java.net/jdk/pull/7431
