[8u60] RFR: 8078470: [Linux] Replace syscall use in os::fork_and_exec with glibc fork() and execve()

[David Holmes]

Hi Thomas,

On 23/04/2015 6:00 PM, Thomas Stüfe wrote:
> On Thu, Apr 23, 2015 at 9:50 AM, David Holmes <david.holmes at oracle.com
> <mailto:david.holmes at oracle.com>> wrote:
>     On 23/04/2015 5:24 PM, Thomas Stüfe wrote:
>         - would it be possible to use vfork() instead of fork()? Might
>         increase
>         the chance of fork() succeeding in out-of-memory scenarios. The way
>         fork/execve is used here is simple enough for vfork().
>
>     I'm reluctant to use vfork() as it is an unknown. The use of fork()
>     has been trialled by Google with no problem.
>
> I understand.
>
> We use vfork() by default on Linux and HP-UX since 3-4 years for
> Runtime.exec() without problems (but our implementation differs wildly
> from the standard one). But then, Runtime.exec does not get called in
> error situations, so the conditions may be different for
> os::fork_and_exec().

Right - os::fork_and_exec is potentially a lot more fragile given the 
potential execution context. Which prompted me to add a second test for 
the general OnError handling case. I also moved the tests to 
runtime/ErrorHandling to match the directory that exists in JDK 9.

Updated webrev:

http://cr.openjdk.java.net/~dholmes/8078470/webrev.v2/

Thanks,
David


>         - would it be possible to print out errno in case fork fails?
>
>
>     Sure.
>
>
> Thanks!
>
> ..Thomas
>
>     Thanks,
>     David
>
>         Regards, Thomas
>
>
>         On Thu, Apr 23, 2015 at 8:40 AM, David Holmes
>         <david.holmes at oracle.com <mailto:david.holmes at oracle.com>
>         <mailto:david.holmes at oracle.com
>         <mailto:david.holmes at oracle.com>>> wrote:
>
>              webrev: http://cr.openjdk.java.net/~dholmes/8078470/webrev/
>
>              bug: https://bugs.openjdk.java.net/browse/JDK-8078470
>
>              For historical reasons, dating back to LinuxThreads,
>              os::fork_and_exec uses direct syscalls to perform fork and
>         execve
>              functions. The fork syscall has been deprecated on linux
>         for quite
>              some time and some distributions are now shipping with
>         deprecated
>              syscalls removed - this results in a ENOSYS error and the
>         "OnError"
>              commands that utilize os::fork_and_exec no longer work.
>
>              The problem was discussed here:
>
>         http://mail.openjdk.java.net/pipermail/hotspot-dev/2015-April/017916.html
>
>              It seems the concerns surrounding direct use of glibc
>         fork() and
>              exec() are no longer legitimate and Martin Buchholz reports
>         that
>              Google replaced the syscalls with glibc calls some time ago
>         and have
>              not had any problems. So we propose to apply the same change
>              uniformly on Linux.
>
>              This is initially going into 8u60 via jdk8u-hs-dev due to time
>              constraints on the 8u60 schedule, and an internal limitation
>              preventing me from pushing this to 9 right now. But it will be
>              "backported" to 9 ASAP.
>
>              Thanks,
>              David
>
>
>