changes to CMK_GLOBAL_LOCATION_UPDATE so that it uses new loc-cache API

doc/charm++/manual.rst

@@ -3304,6 +3304,22 @@ charm/lib, named as *libcldb-foo.a*, where *foo* is the strategy name
 used above. Now one can use **-balance foo** as compile time option to
 **charmc** to link with the *foo* seed load balancer.
 
+Global Location Update
+~~~~~~~~~~~~~~~~~~~~~~
+
+When Charm++ is built with the ``CMK_GLOBAL_LOCATION_UPDATE`` option(``-DCMK_GLOBAL_LOCATION_UPDATE=1``), the
+runtime broadcasts updated object locations to all processors during each load
+balancing step. This eliminates the need for hop-count-based location discovery
+after migrations.
+
+.. important::
+
+   With ``CMK_GLOBAL_LOCATION_UPDATE`` enabled, **object migrations must
+   occur during global load balancing steps**. Anytime migration (e.g., via
+   ``migrateMe()``) is not supported in this mode. Applications must use the
+   ``AtSync()`` method to trigger load balancing.
+
+
 .. _lbexample:
 
 Simple Load Balancer Usage Example - Automatic with Sync LB

src/ck-core/cklocation.C

@@ -88,11 +88,18 @@ void UpdateLocation(MigrateInfo& migData)
   {
     return;
   }
-
   CkLocMgr* localLocMgr = (CkLocMgr*)CkLocalBranch(locMgrGid);
-  // CkLocMgr only uses element IDs, so extract just that part from the ObjID
-  localLocMgr->updateLocation(ck::ObjID(migData.obj.id).getElementID(), migData.to_pe);
-}
+  CkLocCache *cache = (CkLocCache *)CkLocalBranch(localLocMgr->getLocationCache());
+
+  CmiUInt8 elementID = ck::ObjID(migData.obj.id).getElementID();
+  CkArrayIndex idx = localLocMgr->lookupIdx(elementID);
+
+  CkLocEntry entry;
+  entry.id = elementID;
+  entry.pe = migData.to_pe;
+  entry.epoch = cache->getEpoch(elementID) + 1;
+
+  localLocMgr->updateLocation(idx, entry);}
 #  endif
 
 #endif
@@ -2794,6 +2801,9 @@ void CkLocMgr::multiHop(CkArrayMessage* msg)
   {  // Send a routing message letting original sender know new element location
     DEBS((AA "Sending update back to %d for element %" PRIu64 "\n" AB, srcPe,
           msg->array_element_id()));
+    #if CMK_GLOBAL_LOCATION_UPDATE
+    CkAssert(false && "Hop-count based location update should not occur with CMK_GLOBAL_LOCATION_UPDATE; all migrations must happen at load balancing steps via AtSync()");
+    #endif
     cache->requestLocation(msg->array_element_id(), srcPe);
   }
 }

src/ck-ldb/CentralLB.C

@@ -999,6 +999,9 @@ void CentralLB::ProcessReceiveMigration()
   future_migrates_expected = 0;
   for(i=0; i < m->n_moves; i++) {
     MigrateInfo& move = m->moves[i];
+    #if CMK_GLOBAL_LOCATION_UPDATE      
+      UpdateLocation(move); 
+    #endif
     const int me = CkMyPe();
     if (move.from_pe == me && move.to_pe != me) {
 #if CMK_DRONE_MODE
@@ -1020,11 +1023,6 @@ void CentralLB::ProcessReceiveMigration()
       if (!move.async_arrival) migrates_expected++;
       else future_migrates_expected++;
     }
-    else {
-#if CMK_GLOBAL_LOCATION_UPDATE      
-      UpdateLocation(move); 
-#endif
-    }
 
   }