the hook lists
+
+Background Requests Servicing Algorithm (v1)
+
+
+list_in : currently serviced requests
+list_out : queue of requests waiting for processing
+
+
+1. Before processing
+ if list_in is empty
+ - Add all requests in list_out to list_in, empty list_out
+ - for each request in list_in
+ - add hooks to context
+ - set hooks'in_progress flag to TRUE
+ - seek trace to start
+
+2. call process traceset middle for a chunk
+ (assert list_in is not empty! : should not even be called in that case)
+
+3. After the chunk
+ 3.1 call after_chunk hooks from list_in
+ 3.2 if end of trace reached
+ - for each request in list_in
+ - set hooks'in_progress flag to FALSE
+ - set hooks'ready flag to TRUE
+ - call end request
+ - remove hooks from context
+ - remove request
+ - return FALSE (scheduler stopped)
+ 3.3 else
+ - return TRUE (scheduler still registered)
+