bitbake: server/process: Avoid risk of exception deadlocks

The open coded lock acquire/release in the UI event handler doesn't
cover the case an exception occurs and if one did, it could deadlock
the code. Switch to use 'with' statements which would handle this
possibility.

We have seen deadlocks in the UI at exit this so this removes a
possible cause.

(Bitbake rev: bd12792f28efd2f03510653ec947ebf961315272)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/server/process.py

@@ -667,18 +667,14 @@ class BBUIEventQueue:
         self.t.start()
 
     def getEvent(self):
-        self.eventQueueLock.acquire()
+        with self.eventQueueLock:
+            if len(self.eventQueue) == 0:
+                return None
 
-        if len(self.eventQueue) == 0:
-            self.eventQueueLock.release()
-            return None
+            item = self.eventQueue.pop(0)
+            if len(self.eventQueue) == 0:
+                self.eventQueueNotify.clear()
 
-        item = self.eventQueue.pop(0)
-
-        if len(self.eventQueue) == 0:
-            self.eventQueueNotify.clear()
-
-        self.eventQueueLock.release()
         return item
 
     def waitEvent(self, delay):
@@ -686,10 +682,9 @@ class BBUIEventQueue:
         return self.getEvent()
 
     def queue_event(self, event):
-        self.eventQueueLock.acquire()
-        self.eventQueue.append(event)
-        self.eventQueueNotify.set()
-        self.eventQueueLock.release()
+        with self.eventQueueLock:
+            self.eventQueue.append(event)
+            self.eventQueueNotify.set()
 
     def send_event(self, event):
         self.queue_event(pickle.loads(event))