RFR(s): 8212828: (process) Change the Process launch mechanism default on Linux to be posix_spawn

[Thomas Stüfe]

Hi all

Bug: https://bugs.openjdk.java.net/browse/JDK-8213192
webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8213192--(process)-change-the-process-launch-mechanism-default-on-linux-to-be-posix_spawn/webrev.00/webrev/index.html

(@Roger: I hope you do not mind? The bug is assigned to you but since I
happened to play around with posix_spawn I prepared this webrev. If you
rather do this change, that is fine and I will leave it to you.)

When we added the possibility to use posix_spawn as underlying
implementation for Runtime.exec() on Linux with
https://bugs.openjdk.java.net/browse/JDK-8212828, we agreed to keep VFORK
as default until work on 13 starts. So now would be a good time to switch
the default to posix_spawn to get a good testing window. Note that at SAP
we run our VMs internally with posix_spawn as default since some months and
have not seen problems.

As for the fix, I added a test which tests that the default is indeed
posix_spawn - not sure whether this is overdoing it though. Also, I use
strace for the test, and /bin/true, and while strace is usually available
and reachable by path resolution, I am afraid on some test machines it may
not. What do you think, should I leave the test out?

The fix ran through all java/lang/ProcessBuilder jtreg tests ok.

Thanks, Thomas