On Thu, 1 Oct 2020 08:22:35 GMT, Aleksey Shipilev <sh...@openjdk.org> wrote:
>> This patch replaces a LinkedList data structure used in the >> net.http.Http2Connection class with an ArrayList. This >> issue relates to [JDK-8246048: Replace LinkedList with ArrayLists in >> java.net](https://bugs.openjdk.java.net/browse/JDK-8246048). Some >> justifications for this change are as follows: >> >> - Sequential Access Times for ArrayLists are improved due to locality of >> reference (i.e ArrayList elements stored in same >> memory neighborhood) >> - Get(index) operations are O(1) time complexity for ArrayLists as opposed >> to worst-case O(N-1) for LinkedLists >> - While insertion operations can be expensive (O(N) in the worst case), >> these operations appear to be >> infrequent/non-existent in this case. >> >> Additional justifications or challenges to those listed are welcome! The >> general idea is that ArrayLists out-perform >> LinkedLists in this scenario. > > src/java.net.http/share/classes/jdk/internal/net/http/Http2Connection.java > line 703: > >> 701: if (initialCause == null) this.cause = t; >> 702: client2.deleteConnection(this); >> 703: List<Stream<?>> c = new ArrayList<>(streams.values()); > > Why can't we dispense with this copy completely, and instead just iterate > `streams.values()`? Good point Aleksey. I guess that the original intent was to avoid `ConcurrentModificationException`. However I see that `streams` is a `ConcurrentHashMap` now. So maybe we could dispense of the copy: ` private final Map<Integer,Stream<?>> streams = new ConcurrentHashMap<>();` Could be worth changing the type from `Map<Integer,Stream<?>>` to `ConcurrentMap<Integer,Stream<?>>` in the declaration above if we decide to get rid of the copy though. ------------- PR: https://git.openjdk.java.net/jdk/pull/431
