RFR: 8011882: Replace spin loops as back off when suspending

[Rickard Bäckman]

Hi all,

can I please have reviews for this change. 

In the current implementation do_suspend uses spin loops to wait until a thread has been suspended. I would like to change that to use semaphores to reduce CPU usage and also make it easier to have a deterministic timeout. Since we are posting to the semaphore in the signal handler we can't use pthread_semaphore since it isn't async safe, which is why all implementations uses low-level os-specific semaphore constructs.

Bug: http://bugs.sun.com/view_bug.do?bug_id=8011882
Webrev: http://cr.openjdk.java.net/~rbackman/8011882/

Thanks
/R