compatibility impact of JDK-8325621 (Improve jspawnhelper version checks)

[Liam Miller-Cushon]

Hi,

I have a data point to share on the compatibility impact of
JDK-8325621 (Improve jspawnhelper version checks), which was
backported to earlier release trains.

As a result of that change, doing an in-place upgrade from 22.0.1 to
22.0.2 breaks long-running Java applications that create subprocesses.
This is an expected consequence of the change, which adds version
checks to jspawnhelper to detect if a JVM is updated in-place to a
version with an incompatible jspawnhelper.

I'm curious if the list has suggestions on the best way to mitigate
the compatibility impact. One possibility is that replacing a JVM
in-place for a running process should never happen, and installers
should use new directories, or ensure any long-running Java processes
are shut down during the upgrade. Is that considered a best practice?

Here's a demo of the issue I saw:

$ cat T.java
public class T {
  public static void main(String[] args) throws Exception {
    while (true) {
      Thread.sleep(1000);
      System.err.println(Runtime.version());
      ProcessBuilder pb = new ProcessBuilder("/usr/bin/date");
      pb.redirectError(ProcessBuilder.Redirect.INHERIT);
      pb.redirectOutput(ProcessBuilder.Redirect.INHERIT);
      pb.start();
    }
  }
}

$ ./jdk-22.0.1/bin/java -fullversion
openjdk full version "22.0.1+8-16"
$ ./jdk-22.0.2/bin/java -fullversion
openjdk full version "22.0.2+9-70"

$ javac T.java
$ rsync -a jdk-22.0.1/ jdk/
$ ./jdk/bin/java T &
$ rsync -a jdk-22.0.2/ jdk/
...
jspawnhelper version 22.0.2+9-70
This command is not for general use and should only be run as the
result of a call to
ProcessBuilder.start() or Runtime.exec() in a java application
Exception in thread "main" java.io.IOException: Cannot run program
"/usr/bin/date": error=0, Failed to exec spawn helper: pid: 3740946,
exit value: 1
        at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1170)
        at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1089)
        at T.main(T.java:12)
Caused by: java.io.IOException: error=0, Failed to exec spawn helper:
pid: 3740946, exit value: 1
        at java.base/java.lang.ProcessImpl.forkAndExec(Native Method)
        at java.base/java.lang.ProcessImpl.<init>(ProcessImpl.java:295)
        at java.base/java.lang.ProcessImpl.start(ProcessImpl.java:225)
        at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1126)
        ... 2 more