address `addr` still contains the value `val` (in the fashion of `futex(2)`).
If it doesn't then the call doesn't block. Else the calling thread is blocked
until a `PWQR_WAKE` command is received.
++
+`addr` must of course be a pointer to an aligned integer which stores the
+reference ticket in userland.
`PWQR_PARK`::
Puts the thread in park mode. Those are spare threads to avoid