Hello again; I have updated the patch with the received review feedback. The revised webrev is here:
http://cr.openjdk.java.net/~mduigou/JDK-8011200/1/webrev/ The important changes in this revision: - The behaviour of the readObject/writeObject serialization for both classes now more closely mirrors the behaviour of clone(). For ArrayList this means that the deserialized list has a capacity the same as the size. ie. as if trimToSize() was called. For HashMap, the opposite is true, the capacity is the same as was in effect when the object was serialized. (HashMap also tries to protect itself from nonsensical/harmful input). The implementation changes to serialization preserve forward and backward compatibility--all serialized objects are compatible with all implementations. I will file a spec change request for the addition of ", a power of 2" to the @serialData tag for this existing but previously unstated requirement. - Use of Arrays.fill has been reverted. I did change one fill case so that the loop can be optimized. (size field was being updated with each iteration). I very slightly expanded the docs. This is starting to look like a nice set of changes. Mike On Apr 1 2013, at 21:44 , Mike Duigou wrote: > Hello all; > > Last night while pushing another changeset I accidentally pushed a changeset > for JKD-7143928. Since the review and testing was not complete on this issue > I have backed out that changeset and created a new bug number to continue > development. The new webrev to complete the review is: > > http://cr.openjdk.java.net/~mduigou/JDK-8011200/0/webrev/ > > It is currently unchanged from the last posted changeset for 7143928. > > Mike > > On Apr 1 2013, at 19:00 , Mike Duigou wrote: > >> Hello all; >> >> I have posted an updated version of the empty ArrayList and HashMap patch. >> >> http://cr.openjdk.java.net/~mduigou/JDK-7143928/1/webrev/ >> >> This revised implementation introduces *no new fields* to either class. For >> ArrayList the lazy allocation of the backing array occurs only if the list >> is created at default size. According to our performance analysis team, >> approximately 85% of ArrayList instances are created at default size so this >> optimization will be valid for an overwhelming majority of cases. >> >> For HashMap, creative use is made of the threshold field to track the >> requested initial size until the bucket array is needed. On the read side >> the empty map case is tested with isEmpty(). On the write size a comparison >> of (table == EMPTY_TABLE) is used to detect the need to inflate the bucket >> array. In readObject there's a little more work to try to choose an >> efficient initial capacity. >> >> Mike >> >> On Mar 26 2013, at 17:25 , Mike Duigou wrote: >> >>> Hello all; >>> >>> This is a review for optimization work that came out of internal analysis >>> of Oracle's Java applications. It's based upon analysis that shows that in >>> large applications as much as 10% of maps and lists are initialized but >>> never receive any entries. A smaller number spend a large proportion of >>> their lifetime empty. We've found similar results across other workloads as >>> well. This patch is not a substitute for pre-sizing your collections and >>> maps--doing so will *always* have better results. >>> >>> This patch extends HashMap and ArrayList to provide special handling for >>> newly created instances that avoids creating the backing array until >>> needed. There is a very small additional cost for detecting when to inflate >>> the map or list that is measurable in interpreted tests but disappears in >>> JITed code. >>> >>> http://cr.openjdk.java.net/~mduigou/JDK-7143928/0/webrev/ >>> >>> We expect that should this code prove successful in Java 8 it will be >>> backported to Java 7 updates. >>> >>> The unit test may appear to be somewhat unrelated. It was created after >>> resolving a bug in an early version of this patch to detect the issue >>> encountered (LinkedHashMap.init() was not being called in readObject() when >>> the map was empty). >>> >>> Mike >> >
