Made a bunch of API holders use AtomicReference

Plan/api/src/main/java/com/djrapitops/plan/capability/CapabilityService.java

@@ -18,6 +18,7 @@ package com.djrapitops.plan.capability;
 
 import java.util.List;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 
 /**
@@ -49,7 +50,7 @@ public interface CapabilityService {
      * @param isEnabledListener The boolean given to the method tells if Plan has enabled successfully.
      */
     default void registerEnableListener(Consumer<Boolean> isEnabledListener) {
-        ListHolder.ENABLE_LISTENERS.add(isEnabledListener);
+        ListHolder.ENABLE_LISTENERS.get().add(isEnabledListener);
     }
 
     /**
@@ -64,6 +65,8 @@ public interface CapabilityService {
     }
 
     class ListHolder {
-        volatile static List<Consumer<Boolean>> ENABLE_LISTENERS = new CopyOnWriteArrayList<>();
+        volatile static AtomicReference<List<Consumer<Boolean>>> ENABLE_LISTENERS = new AtomicReference<>(
+                new CopyOnWriteArrayList<>()
+        );
     }
 }

Plan/api/src/main/java/com/djrapitops/plan/delivery/web/ResolverService.java

@@ -20,6 +20,7 @@ import com.djrapitops.plan.delivery.web.resolver.Resolver;
 
 import java.util.List;
 import java.util.Optional;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.regex.Pattern;
 
 /**
@@ -34,7 +35,7 @@ import java.util.regex.Pattern;
 public interface ResolverService {
 
     static ResolverService getInstance() {
-        return Optional.ofNullable(ResolverService.Holder.service)
+        return Optional.ofNullable(ResolverService.Holder.service.get())
                 .orElseThrow(() -> new IllegalStateException("ResolverService has not been initialised yet."));
     }
 
@@ -88,14 +89,14 @@ public interface ResolverService {
     List<Resolver> getResolvers(String target);
 
     class Holder {
-        volatile static ResolverService service;
+        volatile static AtomicReference<ResolverService> service = new AtomicReference<>();
 
         private Holder() {
             /* Static variable holder */
         }
 
         static void set(ResolverService service) {
-            ResolverService.Holder.service = service;
+            ResolverService.Holder.service.set(service);
         }
     }
 }

Plan/api/src/main/java/com/djrapitops/plan/delivery/web/ResourceService.java

@@ -19,6 +19,7 @@ package com.djrapitops.plan.delivery.web;
 import com.djrapitops.plan.delivery.web.resource.WebResource;
 
 import java.util.Optional;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 
 /**
@@ -29,7 +30,7 @@ import java.util.function.Supplier;
 public interface ResourceService {
 
     static ResourceService getInstance() {
-        return Optional.ofNullable(ResourceService.Holder.service)
+        return Optional.ofNullable(ResourceService.Holder.service.get())
                 .orElseThrow(() -> new IllegalStateException("ResourceService has not been initialised yet."));
     }
 
@@ -102,14 +103,14 @@ public interface ResourceService {
     }
 
     class Holder {
-        volatile static ResourceService service;
+        volatile static AtomicReference<ResourceService> service = new AtomicReference<>();
 
         private Holder() {
             /* Static variable holder */
         }
 
         static void set(ResourceService service) {
-            ResourceService.Holder.service = service;
+            ResourceService.Holder.service.set(service);
         }
     }
 }

Plan/api/src/main/java/com/djrapitops/plan/extension/ExtensionService.java

@@ -19,6 +19,7 @@ package com.djrapitops.plan.extension;
 import com.djrapitops.plan.extension.extractor.ExtensionExtractor;
 
 import java.util.Optional;
+import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * Interface for registering {@link DataExtension}s.
@@ -44,7 +45,7 @@ public interface ExtensionService {
      * @throws IllegalStateException If Plan is installed, but not enabled.
      */
     static ExtensionService getInstance() {
-        return Optional.ofNullable(Holder.service)
+        return Optional.ofNullable(Holder.service.get())
                 .orElseThrow(() -> new IllegalStateException("ExtensionService has not been initialised yet."));
     }
 
@@ -70,14 +71,14 @@ public interface ExtensionService {
     void unregister(DataExtension extension);
 
     class Holder {
-        volatile static ExtensionService service;
+        volatile static AtomicReference<ExtensionService> service = new AtomicReference<>();
 
         private Holder() {
             /* Static variable holder */
         }
 
         static void set(ExtensionService service) {
-            Holder.service = service;
+            Holder.service.set(service);
         }
     }
 

Plan/api/src/main/java/com/djrapitops/plan/query/QueryService.java

@@ -21,6 +21,7 @@ import java.sql.SQLException;
 import java.util.Optional;
 import java.util.UUID;
 import java.util.concurrent.Future;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 
 /**
@@ -40,7 +41,7 @@ public interface QueryService {
      * @throws IllegalStateException If Plan is installed, but not enabled.
      */
     static QueryService getInstance() {
-        return Optional.ofNullable(Holder.service)
+        return Optional.ofNullable(Holder.service.get())
                 .orElseThrow(() -> new IllegalStateException("QueryService has not been initialised yet."));
     }
 
@@ -149,14 +150,14 @@ public interface QueryService {
     }
 
     class Holder {
-        volatile static QueryService service;
+        volatile static AtomicReference<QueryService> service = new AtomicReference<>();
 
         private Holder() {
             /* Static variable holder */
         }
 
         static void set(QueryService service) {
-            Holder.service = service;
+            Holder.service.set(service);
         }
     }
 

Plan/api/src/main/java/com/djrapitops/plan/settings/SettingsService.java

@@ -18,6 +18,7 @@ package com.djrapitops.plan.settings;
 
 import java.util.List;
 import java.util.Optional;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Supplier;
 
 /**
@@ -33,7 +34,7 @@ import java.util.function.Supplier;
 public interface SettingsService {
 
     static SettingsService getInstance() {
-        return Optional.ofNullable(Holder.service)
+        return Optional.ofNullable(Holder.service.get())
                 .orElseThrow(() -> new IllegalStateException("SettingsService has not been initialised yet."));
     }
 
@@ -65,14 +66,14 @@ public interface SettingsService {
     List<String> getStringList(String path, Supplier<List<String>> defaultValue);
 
     class Holder {
-        volatile static SettingsService service;
+        volatile static AtomicReference<SettingsService> service = new AtomicReference<>();
 
         private Holder() {
             /* Static variable holder */
         }
 
         static void set(SettingsService service) {
-            Holder.service = service;
+            Holder.service.set(service);
         }
     }
 

Plan/common/src/main/java/com/djrapitops/plan/capability/CapabilitySvc.java

@@ -28,7 +28,7 @@ import java.util.function.Consumer;
 public class CapabilitySvc implements CapabilityService {
 
     public static void notifyAboutEnable(boolean isEnabled) {
-        for (Consumer<Boolean> enableListener : CapabilityService.ListHolder.ENABLE_LISTENERS) {
+        for (Consumer<Boolean> enableListener : CapabilityService.ListHolder.ENABLE_LISTENERS.get()) {
             enableListener.accept(isEnabled);
         }
     }