RFR: 8352533: Report useful IOExceptions when jspawnhelper fails [v4]

[David Holmes]

On Tue, 13 May 2025 12:51:56 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> You are right and I am confused. I always assumed that the primary function of jspawnhelper was to make vfork safe. Historically, that was the typical reason for an intermediate exec() to a helper - basically, you first exec() the helper as quickly as possible to get your own process memory. Then you do all the things you need to do in preparation for the final exec(), then exec again.
>> 
>> I am surprised that this has worked with vfork() so flawlessly all this time. Maybe it didn't; maybe the libc's have all internally replaced vfork() with fork(), since fork() is fast enough nowadays.
>> 
>> I actually don't understand why the jspawnhelper is even needed for posix_spawn, since all the things one does in jspawnhelper can be done also via posix_spawn process attributes.
>
> Hmm, glibc keeps it very vague in the vfork() manpage, stating that "On some implementations, vfork() is equivalent to fork()." AIX manpage says just "The vfork subroutine is supported as a compatibility interface for older Berkeley Software Distribution (BSD) system programs" which sounds to me its just an alias for fork(). MacOS has no vfork anymore.
> 
> So maybe Solaris was the last platform with a true vfork.

@tstuefe the helper was needed in part to enable a chdir between fork and exec - see this comment: https://bugs.openjdk.org/browse/JDK-5049299?focusedId=12148272&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-12148272

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PR Review Comment: https://git.openjdk.org/jdk/pull/24149#discussion_r2087830040