In very rare circunstancies, I see 2 cores working on my X6, building java/openjdk. Normally only work one. It can be late 10-15 minutes and, solving this, can be transform probably for me to only 2-3, or 6-8 in dual core. Showing this documentation: http://hg.openjdk.java.net/build-infra/jdk8/raw-file/tip/README-builds.html openjdk can be build on multi-thread. Now, I haven't time for check. Really, I don't know if this is considered a bug. Regards.
We turned off parallel build recently because there were several reports that it does not work for them. http://svnweb.freebsd.org/changeset/ports/356867
Ok sorry, I don't show/remember the UNSAFE variable on Makefile.