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 >
