Revised cache transaction handling.

Use a RAII object to manage cache transactions, and reset queries immediately after they are done, to avoid auto-commit transactions lasting long periods of time. Re-write the commit and step logic to handle SQLITE_BUSY, with progressively increasing waits when there is DB contention (multiple processes accessing the DB).

src/Airports/gnnode.cxx

@@ -43,7 +43,10 @@ double FGTaxiNode::getElevationFt()
       SGGeod newPos = mPosition;
       newPos.setElevationM(elevationEnd);
     // this will call modifyPosition to update mPosition
-      NavDataCache::instance()->updatePosition(guid(), newPos);
+      NavDataCache* cache = NavDataCache::instance();
+      NavDataCache::Transaction txn(cache);
+      cache->updatePosition(guid(), newPos);
+      txn.commit();
     }
   }
   

src/Airports/simple.cxx

@@ -396,17 +396,12 @@ void FGAirport::loadSceneryDefinitions() const
     return;
   }
   
-  try {
-    cache->beginTransaction();
+    flightgear::NavDataCache::Transaction txn(cache);
     SGPropertyNode_ptr rootNode = new SGPropertyNode;
     readProperties(path.str(), rootNode);
     const_cast<FGAirport*>(this)->readThresholdData(rootNode);
     cache->stampCacheFile(path);
-    cache->commitTransaction();
-  } catch (sg_exception& e) {
-    cache->abortTransaction();
-    throw e;
-  }
+    txn.commit();
 }
 
 void FGAirport::readThresholdData(SGPropertyNode* aRoot)
@@ -480,11 +475,13 @@ void FGAirport::validateTowerData() const
   // cached values are correct, we're all done
     return;
   }
-    
+   
+  flightgear::NavDataCache::Transaction txn(cache);
   SGPropertyNode_ptr rootNode = new SGPropertyNode;
   readProperties(path.str(), rootNode);
   const_cast<FGAirport*>(this)->readTowerData(rootNode);
   cache->stampCacheFile(path);
+  txn.commit();
 }
 
 void FGAirport::readTowerData(SGPropertyNode* aRoot)
@@ -529,9 +526,12 @@ bool FGAirport::validateILSData()
   
   SGPropertyNode_ptr rootNode = new SGPropertyNode;
   readProperties(path.str(), rootNode);
+
+  flightgear::NavDataCache::Transaction txn(cache);
   readILSData(rootNode);
   cache->stampCacheFile(path);
-  
+  txn.commit();
+    
 // we loaded data, tell the caller it might need to reload things
   return true;
 }

src/Airports/xmlloader.cxx

@@ -55,7 +55,7 @@ void XMLLoader::load(FGAirportDynamics* d)
   SG_LOG(SG_NAVAID, SG_INFO, "reading groundnet data from " << path);
   SGTimeStamp t;
   try {
-    cache->beginTransaction();
+    flightgear::NavDataCache::Transaction txn(cache);
     t.stamp();
     {
       // drop all current data
@@ -65,9 +65,9 @@ void XMLLoader::load(FGAirportDynamics* d)
       readXML(path.str(), visitor);
     } // ensure visitor is destroyed so its destructor runs
     cache->stampCacheFile(path);
-    cache->commitTransaction();
+    txn.commit();
   } catch (sg_exception& e) {
-    cache->abortTransaction();
+    SG_LOG(SG_NAVAID, SG_INFO, "parsing groundnet XML failed:" << e.getFormattedMessage());
   }
 
   SG_LOG(SG_NAVAID, SG_INFO, "parsing groundnet XML took " << t.elapsedMSec());

src/Navaids/NavDataCache.hxx

@@ -85,11 +85,6 @@ public:
   string_list readStringListProperty(const std::string& key);
   void writeStringListProperty(const std::string& key, const string_list& values);
   
-// transaction API wrappers
-  void beginTransaction();
-  void commitTransaction();
-  void abortTransaction();
-  
   /**
    * retrieve an FGPositioned from the cache.
    * This may be trivial if the object is previously loaded, or require actual
@@ -250,12 +245,31 @@ public:
   
   PositionedIDVec findAirportParking(PositionedID airport, const std::string& flightType,
                                      int radius);
+
+
+    class Transaction
+    {
+    public:
+        Transaction(NavDataCache* cache);
+        ~Transaction();
+        
+        void commit();
+    private:
+        NavDataCache* _instance;
+        bool _committed;
+    };
 private:
   NavDataCache();
   
   friend class RebuildThread;
   void doRebuild();
   
+  friend class Transaction;
+  
+    void beginTransaction();
+    void commitTransaction();
+    void abortTransaction();
+    
   class NavDataCachePrivate;
   std::auto_ptr<NavDataCachePrivate> d;      
 };