On Wed, 3 Jan 2024 21:29:57 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%. > > Joshua Cao has updated the pull request incrementally with one additional > commit since the last revision: > > Cleanup benchmark I am good this this version. I would like a second Reviewer to ack this too. ------------- Marked as reviewed by shade (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/17116#pullrequestreview-1803734314
