Synchronization fixes

client/src/store/reducer.ts

@@ -213,7 +213,7 @@ function serverReceiveReducer(state: State, action: Action): State {
                                 enqueueMessage({type: MessageType.KERNEL, message: heartbeat}, artifactPath);
                                 deferred(flushMessageQueue)();
                             }
-                            return {...collaborativeSession, kernelContext, kernelCombinedEffect};  // TODO: do not change on heartbeats
+                            return {...collaborativeSession, kernelContext, kernelCombinedEffect};
                         }));
                 if (isEditingFeatureModel(state))
                     state = updateFeatureModel(state, action.payload.artifactPath!);

kernel/src/kernel/core/conflict_resolution.cljc

@@ -20,24 +20,24 @@
   site need not already have seen the same conflicts as the checked site)."
   [GC site-ID HB CC]
   (p ::conflict-aware?
-     (let [res (some #(let [CO-ID-a (first %)
-                            CO-ID-b (first (disj % CO-ID-a))]
-                        (and (VC/_< ((HB/lookup HB CO-ID-a) :VC) (GC/get-site-VC GC site-ID))
-                             (VC/_< ((HB/lookup HB CO-ID-b) :VC) (GC/get-site-VC GC site-ID))))
-                     (CC/get-all-conflicts CC))]
-       (log "conflict-aware?" site-ID res)
-       res)))
+     (boolean
+       (some #(let [CO-ID-a (first %)
+                    CO-ID-b (first (disj % CO-ID-a))]
+                (and (VC/_< ((HB/lookup HB CO-ID-a) :VC) (GC/get-site-VC GC site-ID))
+                     (VC/_< ((HB/lookup HB CO-ID-b) :VC) (GC/get-site-VC GC site-ID))))
+             (CC/get-all-conflicts CC)))))
 
 (defn synchronized?
   "Determines whether all sites are aware of a conflict, i.e., are in conflict resolution mode.
   Until synchronization, no resolution and voting is allowed.
   When all sites are conflict-aware (i.e., frozen), no more operations can be in flight - because
   if there were some, they would have been generated in a frozen state, which is not allowed."
-  [GC HB CC]
+  [GC HB CC own-site-ID]
   (p ::synchronized?
-     (let [res (every? #(conflict-aware? GC % HB CC) (GC/get-site-IDs GC))]
-       (log "synchronized?" res)
-       res)))
+     (let [other-client-site-IDS (GC/get-other-client-site-IDs GC own-site-ID)
+           synchronized? (every? #(conflict-aware? GC % HB CC) other-client-site-IDS)]
+       (log (count other-client-site-IDS) "sites are" (if synchronized? "synchronized" "not synchronized"))
+       synchronized?)))
 
 (defn conflict-descriptor
   "A conflict descriptor contains information about a conflict situation.
@@ -47,7 +47,7 @@
   in turn map from operations to another map, which maps from operations to conflicts.
   The :metadata key maps from operation IDs to metadata, e.g., human-readable descriptions.
   The :synchronized key maps to a boolean which indicates whether all sites are synchronized yet."
-  [MCGS CDAG HB CC GC]
+  [MCGS CDAG HB CC GC own-site-ID]
   (p ::conflict-descriptor
      (let [versions (reduce (fn [acc MCG]
                               (assoc acc (MOVIC/MCG-identifier MCG)
@@ -70,4 +70,4 @@
        {:versions     versions
         :conflicts    conflicts
         :metadata     metadata
-        :synchronized (synchronized? GC HB CC)})))
+        :synchronized (synchronized? GC HB CC own-site-ID)})))

kernel/src/kernel/core/garbage_collector.cljc

@@ -65,6 +65,17 @@
   [GC]
   (keys GC))
 
+(defn get-other-client-site-IDs
+  "Returns all sites known to the local site but the server and local site.
+  This is done for synchronization, where the server need not be considered as it does not
+  participate in conflict resolution. Also, the server is not per se obliged to send heartbeats
+  as clients when they become conflict-aware.
+  The local site is, when synchronizing, already conflict-aware by definition."
+  [GC own-site-ID]
+  (->> (get-site-IDs GC)
+       (remove #(= % :server))
+       (remove #(= % own-site-ID))))
+
 (defn get-site-VC
   "Returns the garbage collector's most recently received vector clock for a given site.
   This is useful to determine whether a site has succeeded some other vector clock."

kernel/src/kernel/shell/client.cljc

@@ -86,9 +86,7 @@
        (swap! (*context* :MCGS) #(MOVIC/MOVIC % CO @(*context* :CDAG) @(*context* :HB) @(*context* :base-FM) (*context* :CC)))
        ; not required, just to be clear that this information is only needed by the MOVIC call
        (swap! (*context* :CC) #(CC/with-most-recent % nil))
-       (let [next-FM (site/next-FM @(*context* :MCGS) @(*context* :CDAG) @(*context* :HB) @(*context* :CC) @(*context* :base-FM) @(*context* :GC))]
-         (reset! (*context* :FM) next-FM)
-         [next-FM CO]))))
+       [(site/next-FM!) CO])))
 
 (defn generate-inverse-operation!
   "**TODO**: Generates an inverse operation concurrent to all following operations.

kernel/src/kernel/shell/site.cljc

@@ -40,13 +40,23 @@
   "Based on the result the MOVIC algorithm returned, checks whether
   one CG was produced, in that case applying and returning the correct
   feature model. Otherwise, returns a conflict descriptor."
-  [MCGS CDAG HB CC base-FM GC]
-  (if (= (count MCGS) 1)
-    (log "no conflict occured, producing feature model")
+  [MCGS CDAG HB CC base-FM GC own-site-ID]
+  (case (count MCGS)
+    0 (log "no operations submitted yet, producing feature model")
+    1 (log "no conflict occured, producing feature model")
     (log "conflicts occured," (count MCGS) "maximum compatible groups created"))
-  (if (= (count MCGS) 1)
-    (topological-sort/apply-compatible* CDAG HB base-FM (first MCGS))
-    (conflict-resolution/conflict-descriptor MCGS CDAG HB CC GC)))
+  (case (count MCGS)
+    0 base-FM
+    1 (topological-sort/apply-compatible* CDAG HB base-FM (first MCGS))
+    (conflict-resolution/conflict-descriptor MCGS CDAG HB CC GC own-site-ID)))
+
+(defn next-FM!
+  "Calculates the next feature model or conflict descriptor, stores it
+  in the context and returns it."
+  []
+  (let [next-FM (next-FM @(*context* :MCGS) @(*context* :CDAG) @(*context* :HB) @(*context* :CC) @(*context* :base-FM) @(*context* :GC) (*context* :site-ID))]
+    (reset! (*context* :FM) next-FM)
+    next-FM))
 
 (defn receive-operation!
   "Receives an operation message at a site.
@@ -64,9 +74,7 @@
   (swap! (*context* :CC) #(CC/with-most-recent % (CO/get-ID CO)))
   (swap! (*context* :MCGS) #(MOVIC/MOVIC % CO @(*context* :CDAG) @(*context* :HB) @(*context* :base-FM) (*context* :CC)))
   (swap! (*context* :CC) #(CC/with-most-recent % nil))      ; not required, just to be clear
-  (let [next-FM (next-FM @(*context* :MCGS) @(*context* :CDAG) @(*context* :HB) @(*context* :CC) @(*context* :base-FM) @(*context* :GC))]
-    (reset! (*context* :FM) next-FM)
-    next-FM))
+  (next-FM!))
 
 (defn receive-heartbeat!
   "Receives a heartbeat message at a site.
@@ -75,7 +83,7 @@
   (log "receiving heartbeat message from" (message/get-site-ID message))
   (swap! (*context* :VC) #(VC/_merge (VC/increment % (*context* :site-ID)) (message/get-VC message)))
   (swap! (*context* :GC) #(GC/insert % (message/get-site-ID message) (message/get-VC message)))
-  @(*context* :FM))
+  (next-FM!))
 
 (defn receive-leave!
   "Receives a leave message at a site.