RFR: 8292741: Convert JvmtiTagMapTable to ResourceHashtable [v7]

[Coleen Phillimore]

On Thu, 15 Dec 2022 01:57:27 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> I agree that this is ambigious. The `jvmtiTagMap` calls `add/update` methods of `jvmtiTagMapTable` which in turn calls `resourceHashTable` methods `put` and `put_if_absent`.
>> `put` and `put_if_absent` can be used for both adding and updating and reporting it in returned values.
>> `jvmtiTagMap` calls to `jvmtiTagMapTable` add/update  DO NOT CARE about the returned values. For these calls, it doesn't mater if an add (update) method resulted in an update (add). 
>> So which one of the following cases would be correct?
>>  - Based on the `jvmtiTagMap` calls, let the add/update be void and ignore the differences of what really happens in the table. Or
>>  - Based on the `resourceHashTable` bool-valued `put` and `put_if_absent` methods, let the add/update be bool-values and leave the decision on "what really happened in the table" to the callers in `jvmtiTagMap`. (current implementation)
>
> The issue is not the underlying RHT methods but the semantics of the `jvmtiTagMap` methods. If a call to add always expects to add then it should be a fatal error if it actually did an update as that indicates something is broken. Similarly if an update actually does an add.

The JvmtiTagMap code adds/updates and removes the entries like below in two places which could probably be simplified, but I think that's outside the scope of this RFE.   I suggest removing the bool return from add, remove and update, and add the assert(true) in the remove case.  There's already an assert that add/update happened in the other cases.

 ``` // if the object is not already tagged then we tag it
  if (found_tag == 0) {
    if (tag != 0) {
      hashmap->add(o, tag);
    } else {
      // no-op
    }
  } else {
    // if the object is already tagged then we either update
    // the tag (if a new tag value has been provided)
    // or remove the object if the new tag value is 0.
    if (tag == 0) {
      hashmap->remove(o);
    } else {
      hashmap->update(o, tag);
    }
  }

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PR: https://git.openjdk.org/jdk/pull/11288