RFR: JDK-8274320: os::fork_and_exec() should be using posix_spawn

[David Holmes]

On Sat, 25 Sep 2021 16:16:29 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> Hi, may I have reviews for this small patch please?
> 
> `os::fork_and_exec()`, used in the hotspot to spawn child programs (scripts etc) in error situations, should be using `posix_spawn()`. 
> 
> ATM it uses either `fork()` or `vfork()`. `vfork()` got deprecated on MacOS and we get build errors (JDK-8274293) - even though in this case it would be completely fine to use. This leaves us with `fork()` for MacOS, which has the known problems with large-footprint-parents. This matters here especially since we also use os::fork_and_exec to implement `-XX:OnError` for OOM situations.
> 
> We already use posix_spawn() as default for Runtime.exec() since JDK 15, and it is available on all our Unices. We also should use it here.
> 
> I kept the name of the function (fork_and_exec) since people know it, even though it's more incorrect now than before.
> 
> Tests:
> - manual tests using -XX:OnError with various scripts, including checking that env variables are passed correctly
> - manually ran runtime/ErrorHandling tests
> - GHAs

Hi Thomas,

There is a crucial difference between the requirements of os::fork_and_exec versus the Java Runtime.exec call - in the VM we need to use an async-signal-safe function where possible. fork() is async-signal-safe but posix_spawn is not.

Cheers,
David

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PR: https://git.openjdk.java.net/jdk/pull/5698