Ensuring DStack thread safety

Author: PicoCreator

src/main/java/picoded/dstack/DStack.java

@@ -12,10 +12,10 @@
 public class DStack extends CoreStack {
 
 	// List of provider backends - to fetch / initialize from
-	protected ProviderConfig providerConfig = null;
+	protected final ProviderConfig providerConfig;
 
 	// Namespace listing
-	protected GenericConvertList<Object> namespace = null;
+	protected final GenericConvertList<Object> namespace;
 
 	/**
 	 * Constructor with configuration map

src/main/java/picoded/dstack/mongodb/MongoDBStack.java

@@ -180,7 +180,8 @@ public static String getFullConnectionURL_secondary(GenericConvertMap<String, Ob
 		// Hanlding of option string, default sec_opt uses `secondaryPreferred`
 		GenericConvertMap<String, Object> optMap = new GenericConvertHashMap<>();
 		optMap.putAll(config.getGenericConvertStringMap("opt", defaultOptJson));
-		optMap.putAll(config.getGenericConvertStringMap("sec_opt", "{ \"readPreference\":\"secondaryPreferred\" }"));
+		optMap.putAll(config.getGenericConvertStringMap("sec_opt",
+			"{ \"readPreference\":\"secondaryPreferred\" }"));
 
 		// The opt string overwrite
 		String optStr = config.getString("sec_opt_str", mapToOptStr(optMap));

src/main/java/picoded/dstack/stack/ProviderConfig.java

@@ -63,7 +63,7 @@ public ProviderConfig(List<Object> inConfigList) {
 	/**
 	 * Stores the internal config mapping by its name
 	 **/
-	protected Map<String, GenericConvertMap<String, Object>> providerConfigMap = new HashMap<>();;
+	protected final Map<String, GenericConvertMap<String, Object>> providerConfigMap = new HashMap<>();;
 
 	/**
 	 * Loads a configuration array of backend providers for dstack, into the provider map
@@ -133,13 +133,13 @@ public CoreStack getProviderStack(String name) {
 			return cache;
 		}
 
-		synchronized(providerStackMap) {
+		synchronized (providerStackMap) {
 			// Check the cache again (avoid race condition)
 			cache = providerStackMap.get(name);
 			if (cache != null) {
 				return cache;
 			}
-
+			
 			// Cache not found, get config to initialize a new stack
 			GenericConvertMap<String, Object> providerConfig = getStackConfig(name);
 			if (providerConfig == null) {
@@ -153,7 +153,7 @@ public CoreStack getProviderStack(String name) {
 			// Return result
 			return cache;
 		}
-
+		
 	}
 
 	/**