RFR: 8309390: [JVMCI] improve copying system properties into libgraal [v3]

[Doug Simon]

On Mon, 12 Jun 2023 03:00:23 GMT, Tom Rodriguez <never at openjdk.org> wrote:

>> Doug Simon has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains one commit:
>> 
>>   copy system properties into libgraal more efficiently
>
> src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/services/Services.java line 314:
> 
>> 312:             String key = toJavaString(unsafe, unsafe.getLong(prop + keyOffset));
>> 313:             long valueAddress = unsafe.getLong(prop + valueOffset);
>> 314:             if (valueAddress != 0) {
> 
> Is the lazy value construction really necessary?  It seems like it requires quite a bit of extra machinery.

In big apps, I image there can be quite some large system property values (e.g. `java.class.path`) so we don't want to pay memory overhead per libgraal isolate for such properties as they're ignored by libgraal.

I realized I can reduce the extra machinery based on the fact that `SystemProperties` is unmodifiable: https://github.com/openjdk/jdk/pull/14291/commits/6c346d35923402fb5d6ae0ef83214f8f0ca07b69
The only method that still eager converts the string is `SystemProperties.values()` but that's fine as it's not used by JVMCI or Graal.
I think the trade off is now acceptable?

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PR Review Comment: https://git.openjdk.org/jdk/pull/14291#discussion_r1226352693