Improve shutdown of executor loader and mappings cache

Previously, the shutdown check would only happen once all futures were removed, as in a player joined that had to check the remaining protocols.
Now, the check will be done regularly once the plugin has fully been enabled and has the option to delay the shutdown until set on again (i.e. with ViaBackwards)

common/src/main/java/us/myles/ViaVersion/ViaManager.java

@@ -2,6 +2,7 @@ package us.myles.ViaVersion;
 
 import us.myles.ViaVersion.api.Via;
 import us.myles.ViaVersion.api.data.UserConnection;
+import us.myles.ViaVersion.api.platform.TaskId;
 import us.myles.ViaVersion.api.platform.ViaConnectionManager;
 import us.myles.ViaVersion.api.platform.ViaInjector;
 import us.myles.ViaVersion.api.platform.ViaPlatform;
@@ -27,6 +28,7 @@ public class ViaManager {
     private final ViaCommandHandler commandHandler;
     private final ViaPlatformLoader loader;
     private final Set<String> subPlatforms = new HashSet<>();
+    private TaskId mappingLoadingTask;
     private boolean debug;
 
     public ViaManager(ViaPlatform<?> platform, ViaInjector injector, ViaCommandHandler commandHandler, ViaPlatformLoader loader) {
@@ -86,6 +88,12 @@ public class ViaManager {
         // Load Platform
         loader.load();
         // Common tasks
+        mappingLoadingTask = Via.getPlatform().runRepeatingSync(() -> {
+            if (ProtocolRegistry.checkForMappingCompletion()) {
+                platform.cancelTask(mappingLoadingTask);
+                mappingLoadingTask = null;
+            }
+        }, 10L);
         if (ProtocolRegistry.SERVER_PROTOCOL < ProtocolVersion.v1_9.getId()) {
             if (Via.getConfig().isSimulatePlayerTick()) {
                 Via.getPlatform().runRepeatingSync(new ViaIdleThread(), 1L);

common/src/main/java/us/myles/ViaVersion/api/data/MappingDataLoader.java

@@ -6,6 +6,7 @@ import com.google.gson.JsonIOException;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonSyntaxException;
 import us.myles.ViaVersion.api.Via;
+import us.myles.ViaVersion.api.protocol.ProtocolRegistry;
 import us.myles.ViaVersion.util.GsonUtil;
 
 import java.io.File;
@@ -33,6 +34,7 @@ public class MappingDataLoader {
 
     public static void enableMappingsCache() {
         cacheJsonMappings = true;
+        ProtocolRegistry.setKeepExecutorLoaded(true);
     }
 
     /**

common/src/main/java/us/myles/ViaVersion/api/protocol/ProtocolRegistry.java

@@ -61,6 +61,7 @@ public class ProtocolRegistry {
     private static Map<Class<? extends Protocol>, CompletableFuture<Void>> mappingLoaderFutures = new HashMap<>();
     private static ThreadPoolExecutor mappingLoaderExecutor;
     private static boolean mappingsLoaded;
+    private static boolean keepExecutorLoaded;
 
     static {
         mappingLoaderExecutor = new ThreadPoolExecutor(5, 16, 45L, TimeUnit.SECONDS, new SynchronousQueue<>());
@@ -70,11 +71,10 @@ public class ProtocolRegistry {
         registerBaseProtocol(BASE_PROTOCOL, Range.lessThan(Integer.MIN_VALUE));
         registerBaseProtocol(new BaseProtocol1_7(), Range.all());
 
-        // Register built in protocols
         registerProtocol(new Protocol1_9To1_8(), ProtocolVersion.v1_9, ProtocolVersion.v1_8);
         registerProtocol(new Protocol1_9_1To1_9(), Arrays.asList(ProtocolVersion.v1_9_1.getId(), ProtocolVersion.v1_9_2.getId()), ProtocolVersion.v1_9.getId());
         registerProtocol(new Protocol1_9_3To1_9_1_2(), ProtocolVersion.v1_9_3, ProtocolVersion.v1_9_2);
-        // Only supported for 1.9.4 server to 1.9 (nothing else)
+
         registerProtocol(new Protocol1_9To1_9_1(), ProtocolVersion.v1_9, ProtocolVersion.v1_9_2);
         registerProtocol(new Protocol1_9_1_2To1_9_3_4(), Arrays.asList(ProtocolVersion.v1_9_1.getId(), ProtocolVersion.v1_9_2.getId()), ProtocolVersion.v1_9_3.getId());
         registerProtocol(new Protocol1_10To1_9_3_4(), ProtocolVersion.v1_10, ProtocolVersion.v1_9_3);
@@ -320,15 +320,26 @@ public class ProtocolRegistry {
         if (future == null) return;
 
         future.get();
-
-        synchronized (MAPPING_LOADER_LOCK) {
-            if (mappingsLoaded) return;
-
-            // Remove only after execution to block other potential threads
-            mappingLoaderFutures.remove(protocolClass);
-            if (mappingLoaderFutures.isEmpty()) {
-                shutdownLoaderExecutor();
     }
+
+    /**
+     * Shuts down the executor and uncaches mappings if all futures have been completed.
+     *
+     * @return true if the executor has now been shut down
+     */
+    public static boolean checkForMappingCompletion() {
+        synchronized (MAPPING_LOADER_LOCK) {
+            if (mappingsLoaded || keepExecutorLoaded) return false;
+
+            for (CompletableFuture<Void> future : mappingLoaderFutures.values()) {
+                // Return if any future hasn't completed yet
+                if (!future.isDone()) {
+                    return false;
+                }
+            }
+
+            shutdownLoaderExecutor();
+            return true;
         }
     }
 
@@ -336,6 +347,7 @@ public class ProtocolRegistry {
         mappingsLoaded = true;
         mappingLoaderExecutor.shutdown();
         mappingLoaderExecutor = null;
+        mappingLoaderFutures.clear();
         mappingLoaderFutures = null;
         if (MappingDataLoader.isCacheJsonMappings()) {
             MappingDataLoader.getMappingsCache().clear();
@@ -355,4 +367,13 @@ public class ProtocolRegistry {
             return mappingLoaderFutures.get(protocolClass);
         }
     }
+
+    /**
+     * If set to true, the executor and mappings will stay loaded, even if all current futures have been completed.
+     *
+     * @param keepExecutorLoaded whether to keep the executor and mappings loaded, even if all current futures have been completed
+     */
+    public static void setKeepExecutorLoaded(boolean keepExecutorLoaded) {
+        ProtocolRegistry.keepExecutorLoaded = keepExecutorLoaded;
+    }
 }