some improvements related to concurrency

Author: peacekeeper

core/src/main/java/xdi2/core/impl/json/JSONContextNode.java

@@ -295,7 +295,6 @@ public Relation map(JsonElement jsonElement) {
 						if (contextNode == null) {
 
 							log.warn("In context node " + JSONContextNode.this.getXDIAddress() + " found incoming relation " + XDIaddress + " from non-existent context node " + contextNodeXDIAddress);
-
 							return null;
 						}
 

core/src/main/java/xdi2/core/impl/json/JSONGraph.java

@@ -2,12 +2,12 @@
 
 import java.io.IOException;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -51,7 +51,7 @@ public class JSONGraph extends AbstractGraph implements Graph {
 
 		this.jsonRootContextNode = new JSONContextNode(this, null, null, XDIConstants.XDI_ADD_ROOT);
 
-		this.jsonObjectsCached = new HashMap<String, JsonObject> ();
+		this.jsonObjectsCached = new ConcurrentHashMap<String, JsonObject> ();
 		this.jsonObjectsCachedWithPrefix = new HashSet<String> ();
 
 		this.useCache = false;

core/src/main/java/xdi2/core/impl/json/JSONLiteralNode.java

@@ -1,5 +1,9 @@
 package xdi2.core.impl.json;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 
 import xdi2.core.ContextNode;
@@ -11,6 +15,8 @@ public class JSONLiteralNode extends AbstractLiteralNode implements LiteralNode
 
 	private static final long serialVersionUID = 5656043671598618588L;
 
+	private static final Logger log = LoggerFactory.getLogger(JSONLiteralNode.class);
+
 	public JSONLiteralNode(ContextNode contextNode) {
 
 		super(contextNode);
@@ -23,7 +29,15 @@ public Object getLiteralData() {
 
 		JsonObject jsonObject = ((JSONGraph) this.getGraph()).jsonLoad(jsonContextNode.getXDIAddress().toString());
 
-		return AbstractLiteralNode.jsonElementToLiteralData(jsonObject.get(XDIConstants.XDI_ARC_LITERAL.toString()));
+		JsonElement jsonElement = jsonObject.get(XDIConstants.XDI_ARC_LITERAL.toString());
+
+		if (jsonElement == null) {
+
+			log.warn("In literal node " + this.getContextNode() + " found non-existent value.");
+			return null;
+		}
+
+		return AbstractLiteralNode.jsonElementToLiteralData(jsonElement);
 	}
 
 	@Override

core/src/main/java/xdi2/core/impl/json/memory/MemoryJSONStore.java

@@ -1,11 +1,13 @@
 package xdi2.core.impl.json.memory;
 
 import java.io.IOException;
-import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.concurrent.ConcurrentHashMap;
 
+import com.google.gson.JsonArray;
+import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 
 import xdi2.core.impl.json.AbstractJSONStore;
@@ -17,7 +19,7 @@ public class MemoryJSONStore extends AbstractJSONStore implements JSONStore {
 
 	public MemoryJSONStore() {
 
-		this.jsonObjects = new HashMap<String, JsonObject> ();
+		this.jsonObjects = new ConcurrentHashMap<String, JsonObject> ();
 	}
 
 	@Override
@@ -32,10 +34,44 @@ public void close() {
 		this.jsonObjects = null;
 	}
 
+	private static JsonElement deepCopy(JsonElement jsonElement) {
+
+		if (jsonElement instanceof JsonObject) return deepCopy((JsonObject) jsonElement);
+		if (jsonElement instanceof JsonArray) return deepCopy((JsonArray) jsonElement);
+
+		return jsonElement;
+	}
+
+	private static JsonObject deepCopy(JsonObject jsonObject) {
+
+		JsonObject result = new JsonObject();
+		for (Map.Entry<String, JsonElement> entry : jsonObject.entrySet()) {
+
+			result.add(entry.getKey(), deepCopy(entry.getValue()));
+		}
+
+		return result;
+	}
+
+	private static JsonArray deepCopy(JsonArray jsonArray) {
+
+		JsonArray result = new JsonArray();
+
+		for (JsonElement element : jsonArray) {
+
+			result.add(deepCopy(element));
+
+		}
+		return result;
+	}
+
 	@Override
 	public JsonObject load(String id) throws IOException {
 
-		return this.jsonObjects.get(id);
+		JsonObject jsonObject = this.jsonObjects.get(id);
+		if (jsonObject == null) return null;
+
+		return deepCopy(jsonObject);
 	}
 
 	@Override