commit 1c19b87d7380ffba4734808b301340c1018c6c36
author Mike Burrows <m3b@google.com> Mon May 23 15:19:46 2016 -0700
committer Mike Burrows <m3b@google.com> Mon May 23 15:19:46 2016 -0700
tree 7a32c009e4b99f61fe51791946e350eb6324608c
parent d0654bb54ce310d9f4a21d4cdebca66732daab72

v.io/x/lib/nsync: bug fix when not transfering waiters from CV to Mu

In CV's wakeWaiters() call, I set the mutex's muDesigWaker bit
if all the threads signalled are woken, and none are transferred.
Unfortunately, I did this irrespective of the state of the mutex.
It's legal to set the muDesigWaker only if neither the spinlock or
mutex or held by a thread other than the current thread.

This change tests for that condition.  It also does sets muDesigWaker if it can
on the first try.  It does not wait, since setting this bit is an optimization.

This change also adds a new test (cv_timeout_stress_test.go) which
unconvered the bug, and an AssertHeld() call on mutex.

Change-Id: I4cf01178361e2c39c9d1451bdda268ad05829805