fix JsonMemoryFootprintSpec with JDK 21

[xuwei-k]

Pull Request Checklist

• Have you read through the contributor guidelines?
• Have you squashed your commits?
• Have you added copyright headers to new files?
• Have you updated the documentation?
• Have you added tests for any changed functionality?

Fixes

Purpose

pending some test if JDK 21 because fail.

Background Context

openjdk/jdk@17ce097#diff-cdf6d0587f1021c14e1af0d9cab581de2809cd1dbcf8bd87f5a5a304dc087263R333

add int putMode since JDK 21.

inspect java.util.LinkedHashMap by jol

JDK 17

java.util.LinkedHashMap object internals:
 OFFSET  SIZE       TYPE DESCRIPTION                    VALUE
      0     4            (object header)                01 00 00 00 (00000001 00000000 00000000 00000000) (1)
      4     4            (object header)                00 00 00 00 (00000000 00000000 00000000 00000000) (0)
      8     4            (object header)                d8 65 11 00 (11011000 01100101 00010001 00000000) (1140184)
     12     4        Set AbstractMap.keySet             (access denied)
     16     4 Collection AbstractMap.values             (access denied)
     20     4        int HashMap.size                   (access denied)
     24     4        int HashMap.modCount               (access denied)
     28     4        int HashMap.threshold              (access denied)
     32     4      float HashMap.loadFactor             (access denied)
     36     4     Node[] HashMap.table                  (access denied)
     40     4        Set HashMap.entrySet               (access denied)
     44     1    boolean LinkedHashMap.accessOrder      (access denied)
     45     3            (alignment/padding gap)        N/A
     48     4      Entry LinkedHashMap.head             (access denied)
     52     4      Entry LinkedHashMap.tail             (access denied)
Instance size: 56 bytes
Space losses: 3 bytes internal + 0 bytes external = 3 bytes total

JDK 21

java.util.LinkedHashMap object internals:
 OFFSET  SIZE       TYPE DESCRIPTION                    VALUE
      0     4            (object header)                01 00 00 00 (00000001 00000000 00000000 00000000) (1)
      4     4            (object header)                00 00 00 00 (00000000 00000000 00000000 00000000) (0)
      8     4            (object header)                b8 d7 0f 00 (10111000 11010111 00001111 00000000) (1038264)
     12     4        Set AbstractMap.keySet             (access denied)
     16     4 Collection AbstractMap.values             (access denied)
     20     4        int HashMap.size                   (access denied)
     24     4        int HashMap.modCount               (access denied)
     28     4        int HashMap.threshold              (access denied)
     32     4      float HashMap.loadFactor             (access denied)
     36     4     Node[] HashMap.table                  (access denied)
     40     4        Set HashMap.entrySet               (access denied)
     44     4        int LinkedHashMap.putMode          (access denied)
     48     1    boolean LinkedHashMap.accessOrder      (access denied)
     49     3            (alignment/padding gap)        N/A
     52     4      Entry LinkedHashMap.head             (access denied)
     56     4      Entry LinkedHashMap.tail             (access denied)
     60     4            (loss due to the next object alignment)
Instance size: 64 bytes
Space losses: 3 bytes internal + 4 bytes external = 7 bytes total

References

[mkurz]

Instead of making the tests pending on JDK21, how about testing against the actual values? See

• Run tests on Java 21 #968

[mkurz]

Thanks again, however I merged

• Run tests on Java 21 #968

instead which makes a bit more sense in this case IMHO.