Issue1897 (#1980)

* refactorings: SimpleConnectionHolder -> SimpleConnectionState, SimpleClientConnection -> SimpleUndertowConnection, and SimpleClientConnectionMaker -> SimpleUndertowConnectionMaker

* 1. Breaking Changes: Renamed SimpleConnectionHolder -> SimpleConnectionState, SimpleClientConnection -> SimpleUndertowConnection, SimpleClientConnectionMaker -> SimpleUndertowConnectionMaker, and removed the reuseConnection() method from the SimpleConnectionMaker interface. 2. Performance optimizations. 3. Numerous refactorings 4. Major update to documentation 5. Minor re-organization of connection management logic

* fix accidental removal of fix from PR #1963

* ensure that debug logging helper code (such as loglabel() and ports() etc...) is not run unless debug logging is enabled

* ensure that SimpleUndertowConnectionMaker can only have a single instance in a multithreaded environment by making its instance reference volatile and making its default constructor private

* Make Correction to comments in ConsulRegistry.lookupServiceUpdate to explain how serviceUrls.size() == 0 will ensure that updateServiceCache() does not modify the service IP cache

* Small formatting update

---------

Co-authored-by: Michael Christoff <[email protected]>

Author: miklish

consul/src/main/java/com/networknt/consul/ConsulRegistry.java

@@ -326,9 +326,9 @@ private ConcurrentHashMap<String, List<URL>> lookupServiceUpdate(String protocol
             {
                 logger.info("Got updated urls from Consul: {} instances of service {} found", services.size(), serviceName);
 
-                // - Update has occurred: Ensure that the serviceUrls Map has at least one (possibly empty List)
-                //   entry for the serviceName key.
-                //   This will ensure that updateServiceCache() will do an update.
+                // Update has occurred - Ensure that the serviceUrls Map has at least one (possibly empty) List
+                // entry for the serviceName key. This will indicate to updateServiceCache() to do an update:
+                // - serviceUrls.size() > 0
                 if(services.size() == 0)
                     serviceUrls.put(serviceName, new ArrayList<>());
 
@@ -365,12 +365,12 @@ private ConcurrentHashMap<String, List<URL>> lookupServiceUpdate(String protocol
                 lookupServices.put(serviceName, 0L);
 
                 // Indicate to updateServiceCache() to leave cache unchanged for now:
-                // - serviceUrls.isEmpty() == true && serviceUrls.get(serviceName) != null && serviceUrls.get(serviceName).size() == 0
+                // - serviceUrls.size() == 0
             } else {
                 logger.info("Consul returned no service updates: No need to update local Consul discovery cache for service {}, lastIndex={}", serviceName, lastConsulIndexId);
 
                 // Indicate to updateServiceCache() to leave cache unchanged for now:
-                // - serviceUrls.isEmpty() == true && serviceUrls.get(serviceName) != null && serviceUrls.get(serviceName).size() == 0
+                // - serviceUrls.size() == 0
             }
         } else {
             logger.error("Local service cache may be out of date for {} - Consul connection failed", serviceName);