VBox generates constant "psynch_cvwait" #316 errors on OSX

[tzaharia]

Tonight I noticed that when I have a VM running (Ubuntu, Windows, or TinyCoreLinux), errinfo on OSX (the host machine) returns constantly flowing errors like so:

$ sudo errinfo -n VBox
            EXEC          SYSCALL  ERR  DESC
    VBoxHeadless    psynch_cvwait  316 
    VBoxHeadless    psynch_cvwait  316 
    VBoxHeadless    psynch_cvwait  316 
    VBoxHeadless    psynch_cvwait  316 
    VBoxHeadless    psynch_cvwait  316 
    VBoxHeadless    psynch_cvwait  316 
    VBoxHeadless __semwait_signal   60  Operation timed out 
...

And when no VMs are running, having the VirtualBox GUI open returns constant stream of these errors (which go away when I exit it):

...
         VBoxSVC    psynch_cvwait  316 
         VBoxSVC    psynch_cvwait  316 
         VBoxSVC    psynch_cvwait  316 
...

I first noticed this when I was profiling an intensive ~8 second task in a VirtualBox VM. I used dtruss to trace system calls during the task, and found that about 25% of the time was spent in these psynch_cvwait calls, which was output like this (where 13035 is the VBoxHeadless PID):

sudo dtruss -f -a -p 13035
PID/THRD  RELATIVE  ELAPSD    CPU SYSCALL(args) 		 = return
...
13035/0x41f17:  10017630    1170     45 psynch_cvwait(0x100118610, 0x3D22A0103D22B00, 0x0)     = -1 Err#316
...

I can't find much info about Err # 316 on OSX. The XNU repo has a definition for it, but no info that I can find about this specific error:

​https://github.com/opensource-apple/xnu

OSX Version: 10.10.1 (4-core Macbook Pro -- all 4 cores enabled for the VMs) VBox Version: 4.3.20r96996 Guest OS's: Windows8, TinyCoreLinux, Ubuntu

Lmk if I can provide any more info! Thanks for your time.