- Make the layer going over the estimated size raise an exception

- Add a heuristic for estimating the layer size if it is 0
- Add a method where we can add a custom defined map of image -> size

util/queueprocess.py

@@ -40,7 +40,11 @@ class QueueProcess(object):
 def _run(get_producer, queues, chunk_size, args):
   producer = get_producer(*args)
   while True:
-    data = producer(chunk_size) or None
+    try:
+      data = producer(chunk_size) or None
+    except Exception as ex:
+      data = ex
+
     for queue in queues:
       try:
         queue.put(data, block=True, timeout=10)
@@ -48,7 +52,7 @@ def _run(get_producer, queues, chunk_size, args):
         # One of the listeners stopped listening.
         return
             
-    if data is None:
+    if data is None or isinstance(data, Exception):
       break
 
     # Important! This allows the thread that writes the queue data to the pipe