classes/sstate.bbclass: Enable thread lock when checkstatus

The checkstatus function fires an event to notify bitbake UI about
the progress of the task, this function is implemented using ThreadPool
and is causing event lose when multiple threads tries to fire an event
(writes over socket/fd).

[YOCTO #10330]

(From OE-Core rev: 6e0bb9d141438c0051c32b0d3a247915b71ccb82)

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/sstate.bbclass

@@ -851,15 +851,19 @@ def sstate_checkhashes(sq_fn, sq_task, sq_hash, sq_hashfn, d, siginfo=False):
 
         if tasklist:
             bb.event.fire(bb.event.ProcessStarted("Checking sstate mirror object availability", len(tasklist)), d)
+
             import multiprocessing
             nproc = min(multiprocessing.cpu_count(), len(tasklist))
 
+            bb.event.enable_threadlock()
             pool = oe.utils.ThreadedPool(nproc, len(tasklist),
                     worker_init=checkstatus_init, worker_end=checkstatus_end)
             for t in tasklist:
                 pool.add_task(checkstatus, t)
             pool.start()
             pool.wait_completion()
+            bb.event.disable_threadlock()
+
             bb.event.fire(bb.event.ProcessFinished("Checking sstate mirror object availability"), d)
             if whitelist and missing:
                 bb.fatal('Required artifacts were unavailable - exiting')