RFR: 8285947: Avoid redundant HashMap.containsKey calls in ZoneName

[Andrey Turbanov]

On Fri, 29 Apr 2022 06:31:22 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

> `Map.containsKey` call is sometimes unnecessary, when it's known that Map doesn't contain `null` values.
> Instead we can just use Map.get and compare result with `null`.
> I found one of such place, where Map.containsKey calls could be eliminated - `java.time.format.ZoneName`.
> it gives a bit of performance for `toZid`.
> 
> 
> Benchmark                             Mode  Cnt   Score   Error  Units
> ZoneNamesBench.useExistingCountry     avgt    5  10,738 ± 0,065  ns/op
> ZoneNamesBench.useExistingCountryOld  avgt    5  13,679 ± 0,089  ns/op
> 
> 
> <details>
> <summary>Benchmark</summary>
> 
> 
> @BenchmarkMode(value = Mode.AverageTime)
> @OutputTimeUnit(TimeUnit.NANOSECONDS)
> @Warmup(iterations = 10, time = 1, timeUnit = TimeUnit.SECONDS)
> @Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
> @Fork(1)
> @State(Scope.Benchmark)
> public class ZoneNamesBench {
> 
>     @Benchmark
>     public String useExistingCountry() {
>         return ZoneName.toZid("Africa/Tunis", Locale.ITALY);
>     }
> 
>     @Benchmark
>     public String useExistingCountryOld() {
>         return ZoneName.toZidOld("Africa/Tunis", Locale.ITALY);
>     }
> }
> 
> 
> 
>     public static String toZid(String zid, Locale locale) {
>         String mzone = zidToMzone.get(zid);
>         if (mzone == null) {
>             String alias = aliases.get(zid);
>             if (alias != null) {
>                 zid = alias;
>                 mzone = zidToMzone.get(zid);
>             }
>         }
>         if (mzone != null) {
>             Map<String, String> map = mzoneToZidL.get(mzone);
>             if (map == null || ((zid = map.get(locale.getCountry())) == null)) {
>                 zid = mzoneToZid.get(mzone);
>             }
>         }
>         return toZid(zid);
>     }
> 
>     public static String toZid(String zid) {
>         return aliases.getOrDefault(zid, zid);
>     }
> 
>     public static String toZidOld(String zid, Locale locale) {
>         String mzone = zidToMzone.get(zid);
>         if (mzone == null && aliases.containsKey(zid)) {
>             zid = aliases.get(zid);
>             mzone = zidToMzone.get(zid);
>         }
>         if (mzone != null) {
>             Map<String, String> map = mzoneToZidL.get(mzone);
>             if (map != null && map.containsKey(locale.getCountry())) {
>                 zid = map.get(locale.getCountry());
>             } else {
>                 zid = mzoneToZid.get(mzone);
>             }
>         }
>         return toZidOld(zid);
>     }
> 
>     public static String toZidOld(String zid) {
>         if (aliases.containsKey(zid)) {
>             return aliases.get(zid);
>         }
>         return zid;
>     }
> 
> </details>

Hm, build of this branch fails with Crash on `Optimizing the exploded image` on one of my machines. �� 

EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x0000000000000000, pid=57300, tid=10552


[hs_err_pid49380.log](https://github.com/openjdk/jdk/files/8594756/hs_err_pid49380.log)
[hs_err_pid57300.log](https://github.com/openjdk/jdk/files/8594758/hs_err_pid57300.log)

-------------

PR: https://git.openjdk.java.net/jdk/pull/8463