RFR: 8352533: Report useful IOExceptions when jspawnhelper fails

[Aleksey Shipilev]

On Tue, 25 Mar 2025 19:35:36 GMT, Dan Lutker <dlutker at openjdk.org> wrote:

>> When jspawnhelper fails for whatever reason, but more prominently due to [JDK-8325621](https://bugs.openjdk.org/browse/JDK-8325621), it will report the errors into stdout, but not to the relevant `IOException`. So, if the application is configured to only capture the exception logs (e.g. through `java.util.logging`), we will miss any output from `jspawnhelper`, and user would be left without a clue what have happened. We have seen customers spending weeks trying to figure out what went wrong.
>> 
>> It would be good to provide useful `IOException` when `jspawnhelper` fails. We already have a precedent with vmError [printing helpful suggestions](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/utilities/vmError.cpp#L422) when VM fails, we can do a similar thing here. 
>> 
>> I am very open to bike-shedding about the actual message :)
>> 
>> Additional testing:
>>  - [x] Ad-hoc experiments with breaking jspawnhelper
>>  - [x] macos-aarch64-server-fastdebug, `java/lang/Process java/lang/ProcessBuilder`
>
> src/java.base/unix/native/libjava/ProcessImpl_md.c line 324:
> 
>> 322: #define SPAWN_HELPER_INTERNAL_ERROR_MSG "\n" \
>> 323:   "Possible reasons:\n" \
>> 324:   "  - Spawn helper ran into JDK version or configuration problems\n" \
> 
> Can we be clear and say "Spawn helper ran into a mismatch between the running JDK and the version on disk" or something similar?

We don't know the exact reason for jspawnhelper failure, so that would be a bad message that might push users to wrong resolution path. Instead, like `vmError`, we list most frequent possibilities and let users follow-up.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24149#discussion_r2012817709