Hi,
I've been looking into this bug in HashMap where resize() is called multiple
times when putting whole map into another.
I come up with following patch:
http://cr.openjdk.java.net/~mvala/jdk/jdk/JDK-8210280/webrev.00/
I've tried to do it as little invasive as possible. New resize(int) method is
called just from putMapEntries for now. Notice that method is called with size
of the new map. I was experimenting with calling it with 'size()+s', but this
leads to unwanted space allocation when inserted map rewrites a lot of existing
keys.
I've benchmarked this with adding 10millions elements into existing map and it
gets ~50% improvement:
unpatched
Benchmark Mode Cnt Score Error Units
MyBenchmark.testMethod thrpt 10 1.248 ± 0.058 ops/s
patched
Benchmark Mode Cnt Score Error Units
MyBenchmark.testMethod thrpt 10 1.872 ± 0.109 ops/s
public class MyBenchmark {
static Map<Integer, Integer> mapTocopy = IntStream.range(1,
10_000_000).boxed().collect(Collectors.toMap(k -> k,
k -> k));
@Benchmark
public int testMethod() {
var map = new HashMap<Integer, Integer>();
map.put(-5, -5);
map.putAll(mapTocopy);
return map.size();
}
}
Any ideas for missed corner-cases or some good tests?
--
Michal Vala
OpenJDK QE
Red Hat Czech
