Wait for unfinished tasks of the Bukkit scheduler before closing

the executor service

src/main/java/fr/xephi/authme/AuthMe.java

@@ -74,9 +74,11 @@ import java.net.URL;
 import java.util.Calendar;
 import java.util.Collection;
 import java.util.Date;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.logging.Level;
 import java.util.logging.Logger;
 
 /**
@@ -535,6 +537,40 @@ public class AuthMe extends JavaPlugin {
             moduleManager.unloadModules();
         }
 
+        List<BukkitTask> pendingTasks = getServer().getScheduler().getPendingTasks();
+        for (Iterator<BukkitTask> iterator = pendingTasks.iterator(); iterator.hasNext();) {
+            BukkitTask pendingTask = iterator.next();
+            if (pendingTask.getOwner().equals(this) || pendingTask.isSync()) {
+                //remove all unrelevant tasks
+                iterator.remove();
+            }
+        }
+
+        getLogger().log(Level.INFO, "Waiting for {0} tasks to finish", pendingTasks.size());
+        int progress = 0;
+        try {
+            for (BukkitTask pendingTask : pendingTasks) {
+                int maxTries = 5;
+                int taskId = pendingTask.getTaskId();
+                while (getServer().getScheduler().isCurrentlyRunning(taskId)) {
+                    if (maxTries <= 0) {
+                        getLogger().log(Level.INFO, "Async task {0} times out after to many tries", taskId);
+                        break;
+                    }
+
+                    //one second
+                    Thread.sleep(1000);
+                    maxTries--;
+                }
+
+                progress++;
+                getLogger().log(Level.INFO, "Progress: {0} / {1}", new Object[]{progress, pendingTasks.size()});
+            }
+        } catch (InterruptedException interruptedException) {
+
+        }
+
+
         // Close the database
         if (database != null) {
             database.close();