RFR: 8324573: HashMap::putAll should resize to sum of both map sizes

[Joshua Cao]

This change mirrors what we did for ConcurrentHashMap in https://github.com/openjdk/jdk/pull/17116. When we add all entries from one map to anther, we should resize that map to the size of the sum of both maps.

I used the command below to run the benchmarks. I set a high heap to reduce garbage collection noise.

java -Xms25G -jar benchmarks.jar -p size=100000 -p addSize=100000 -gc true org.openjdk.bench.java.util.HashMapBench


Before change


Benchmark            (addSize)        (mapType)  (size)  Mode  Cnt   Score   Error  Units
HashMapBench.putAll     100000         HASH_MAP  100000  avgt    4  22.927 ± 3.170  ms/op
HashMapBench.putAll     100000  LINKED_HASH_MAP  100000  avgt    4  25.198 ± 2.189  ms/op


After change


Benchmark            (addSize)        (mapType)  (size)  Mode  Cnt   Score   Error  Units
HashMapBench.putAll     100000         HASH_MAP  100000  avgt    4  16.780 ± 0.526  ms/op
HashMapBench.putAll     100000  LINKED_HASH_MAP  100000  avgt    4  19.721 ± 0.349  ms/op


We see about average time improvements of 26% in HashMap and 20% in LinkedHashMap.

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Commit messages:
 - 8324573: HashMap::putAll should resize to sum of both map sizes

Changes: https://git.openjdk.org/jdk/pull/17544/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17544&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324573
  Stats: 39 lines in 2 files changed: 13 ins; 7 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/17544.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17544/head:pull/17544

PR: https://git.openjdk.org/jdk/pull/17544