RFR: 8352489: Relax jspawnhelper version checks to informative

[David Holmes]

On Thu, 20 Mar 2025 09:52:02 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> See the bug for rationale. 
> 
> This goal for this improvement is to be easily backportable, so we can catch up with update releases. As such, it does a few borderline-trivial changes, and _does not_ change the jspawnhelper protocol. So the overwrite of `jspawnhelper` with this new version would be "compatible" in a very weak sense of the word.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `java/lang/ProcessBuilder`

The whole point of the improved version check was to catch this broken upgrade process:

> There is also the report from Ubuntu: https://bugs.launchpad.net/ubuntu/+source/openjdk-17/+bug/2055280 -- that unattended upgrade replaced the JDK under the running JVM, which effectively replaced the old jspawnhelper with an incompatible one. This is arguably the upgrade process problem, as JDK is not guaranteed to work when its contents are overwritten, but we want to catch that error consistently.

Otherwise we are just making it easier for the "end user" to shoot themselves in the foot. From that Ubuntu bug report the people involved don't seem to think it is an issue to replace an in-use JDK!

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PR Comment: https://git.openjdk.org/jdk/pull/24127#issuecomment-2740281510