RFR: 8352533: Report useful IOExceptions when jspawnhelper fails

[Dan Lutker]

On Fri, 21 Mar 2025 10:00:26 GMT, Aleksey Shipilev <shade 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?

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PR Review Comment: https://git.openjdk.org/jdk/pull/24149#discussion_r2012814473