On Mon, 22 Jan 2024 22:13:50 GMT, Joshua Cao <d...@openjdk.org> wrote:
>> ConcurrentHashMap's copy constructor calls `putAll()` -> `tryPresize()` -> >> `transfer()`. When coming from the copy constructor, the Map is empty, so >> there is nothing to transfer. But `transfer()` will still copy all the empty >> nodes from the old table to the new table. >> >> This patch avoids this work by only calling `tryPresize()` if the table is >> already initialized. If `table` is null, the initialization is deferred to >> `putVal()`, which calls `initTable()`. >> >> --- >> >> ### JMH results for testCopyConstructor >> >> before patch: >> >> >> Result "org.openjdk.bench.java.util.concurrent.Maps.testCopyConstructor": >> 937395.686 ±(99.9%) 99074.324 ns/op [Average] >> (min, avg, max) = (825732.550, 937395.686, 1072024.041), stdev = 92674.184 >> CI (99.9%): [838321.362, 1036470.010] (assumes normal distribution) >> >> >> after patch: >> >> >> Result "org.openjdk.bench.java.util.concurrent.Maps.testCopyConstructor": >> 620871.469 ±(99.9%) 59195.406 ns/op [Average] >> (min, avg, max) = (545304.633, 620871.469, 689013.573), stdev = 55371.419 >> CI (99.9%): [561676.063, 680066.875] (assumes normal distribution) >> >> >> Average time is decreased by about 33%. >> >> ### JMH results for testPutAll (size = 10000) >> >> before patch: >> >> >> Result >> "org.openjdk.bench.java.util.concurrent.Maps.testConcurrentHashMapPutAll": >> 4315291.542 ±(99.9%) 336034.190 ns/op [Average] >> (min, avg, max) = (3974688.194, 4315291.542, 4871772.209), stdev = >> 314326.589 >> CI (99.9%): [3979257.352, 4651325.731] (assumes normal distribution) >> >> >> after patch: >> >> >> Result >> "org.openjdk.bench.java.util.concurrent.Maps.testConcurrentHashMapPutAll": >> 3006955.723 ±(99.9%) 271757.969 ns/op [Average] >> (min, avg, max) = (2801264.198, 3006955.723, 3553084.135), stdev = >> 254202.573 >> CI (99.9%): [2735197.754, 3278713.692] (assumes normal distribution) >> >> >> Average time is decreased about 30%. > > Joshua Cao has updated the pull request incrementally with one additional > commit since the last revision: > > pass initial size to putAll benchmark map construction Looks good now. ------------- Marked as reviewed by simonis (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/17116#pullrequestreview-1839420378
