Add sync catcher to the blocking pipeline methods

Core/src/main/java/com/plotsquared/core/util/ThreadUtils.java

@@ -0,0 +1,57 @@
+/*
+ *       _____  _       _    _____                                _
+ *      |  __ \| |     | |  / ____|                              | |
+ *      | |__) | | ___ | |_| (___   __ _ _   _  __ _ _ __ ___  __| |
+ *      |  ___/| |/ _ \| __|\___ \ / _` | | | |/ _` | '__/ _ \/ _` |
+ *      | |    | | (_) | |_ ____) | (_| | |_| | (_| | | |  __/ (_| |
+ *      |_|    |_|\___/ \__|_____/ \__, |\__,_|\__,_|_|  \___|\__,_|
+ *                                    | |
+ *                                    |_|
+ *            PlotSquared plot management system for Minecraft
+ *                  Copyright (C) 2020 IntellectualSites
+ *
+ *     This program is free software: you can redistribute it and/or modify
+ *     it under the terms of the GNU General Public License as published by
+ *     the Free Software Foundation, either version 3 of the License, or
+ *     (at your option) any later version.
+ *
+ *     This program is distributed in the hope that it will be useful,
+ *     but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *     GNU General Public License for more details.
+ *
+ *     You should have received a copy of the GNU General Public License
+ *     along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package com.plotsquared.core.util;
+
+import com.plotsquared.core.PlotSquared;
+import lombok.experimental.UtilityClass;
+
+@UtilityClass public class ThreadUtils {
+
+    /**
+     * Throws {@link IllegalStateException} if the method
+     * is called from the server main thread
+     *
+     * @param message Message describing the issue
+     */
+    public void catchSync(final String message) {
+        if (PlotSquared.get().isMainThread(Thread.currentThread())) {
+            throw new IllegalStateException(message);
+        }
+    }
+
+    /**
+     * Throws {@link IllegalStateException} if the method
+     * is not called from the server main thread
+     *
+     * @param message Message describing the issue
+     */
+    public void catchAsync(final String message) {
+        if (!PlotSquared.get().isMainThread(Thread.currentThread())) {
+            throw new IllegalStateException(message);
+        }
+    }
+
+}

Core/src/main/java/com/plotsquared/core/uuid/UUIDPipeline.java

@@ -27,6 +27,7 @@ package com.plotsquared.core.uuid;
 
 import com.google.common.collect.Lists;
 import com.plotsquared.core.PlotSquared;
+import com.plotsquared.core.util.ThreadUtils;
 import com.plotsquared.core.util.task.TaskManager;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -144,6 +145,7 @@ public class UUIDPipeline {
      * @return The mapped uuid. Will return null if the request timed out.
      */
     @Nullable public UUID getSingle(@NotNull final String username, final long timeout) {
+        ThreadUtils.catchSync("Blocking UUID retrieval from the main thread");
         try {
             this.getUUIDs(Collections.singletonList(username)).get(timeout, TimeUnit.MILLISECONDS);
         } catch (InterruptedException | ExecutionException e) {
@@ -162,6 +164,7 @@ public class UUIDPipeline {
      * @return The mapped username. Will return null if the request timeout.
      */
     @Nullable public String getSingle(@NotNull final UUID uuid, final long timeout) {
+        ThreadUtils.catchSync("Blocking username retrieval from the main thread");
         try {
             this.getNames(Collections.singletonList(uuid)).get(timeout, TimeUnit.MILLISECONDS);
         } catch (InterruptedException | ExecutionException e) {