ThreadTracker + Attempt on NPC Disappearing fix

Engineered the ThreadTracker: server-embedded deadlock auditing tool, which will print error messages in case of found deadlocks (also showing all in-use locks on the time of the issue).
Changed the player's id on DB now starting from 20mil, thus preventing players from overwriting NPC/mobs with same oid in-game. Requires proper testing to see if the issue has been cleared.

src/tools/locks/MonitoredReadLock.java

@@ -0,0 +1,147 @@
+/*
+ *     This file is part of the MapleSolaxiaV2 Maple Story Server
+ *
+ * Copyright (C) 2017 RonanLana
+ *
+ * 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 tools.locks;
+
+import constants.ServerConstants;
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.TimeZone;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+import java.util.concurrent.ScheduledFuture;
+import server.TimerManager;
+import net.server.Server;
+import net.server.audit.ThreadTracker;
+
+import tools.FilePrinter;
+
+/**
+ *
+ * @author RonanLana
+ */
+public class MonitoredReadLock extends ReentrantReadWriteLock.ReadLock {
+    private ScheduledFuture<?> timeoutSchedule = null;
+    private StackTraceElement[] deadlockedState = null;
+    private final MonitoredEnums id;
+    private final int hashcode;
+    private final Lock state = new ReentrantLock(true);
+    private final AtomicInteger reentrantCount = new AtomicInteger(0);
+    
+    public MonitoredReadLock(MonitoredReentrantReadWriteLock lock) {
+        super(lock);
+        this.id = lock.id;
+        hashcode = this.hashCode();
+    }
+    
+    @Override
+    public void lock() {
+        super.lock();
+        
+        if(ServerConstants.USE_THREAD_TRACKER) {
+            if(deadlockedState != null) {
+                DateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
+                dateFormat.setTimeZone(TimeZone.getTimeZone(ServerConstants.TIMEZONE));
+
+                //FilePrinter.printError(FilePrinter.DEADLOCK_ERROR, "[CRITICAL] " + dateFormat.format(new Date()) + " Deadlock occurred when trying to use the '" + id.name() + "' lock resources:\r\n" + printStackTrace(deadlockedState) + "\r\n\r\n");
+                ThreadTracker.getInstance().accessThreadTracker(true, true, id, hashcode);
+                deadlockedState = null;
+            }
+
+            registerLocking();
+        }
+    }
+    
+    @Override
+    public void unlock() {
+        if(ServerConstants.USE_THREAD_TRACKER) {
+            unregisterLocking();
+        }
+        super.unlock();
+    }
+    
+    @Override
+    public boolean tryLock() {
+        if(super.tryLock()) {
+            if(ServerConstants.USE_THREAD_TRACKER) {
+                if(deadlockedState != null) {
+                    //FilePrinter.printError(FilePrinter.DEADLOCK_ERROR, "Deadlock occurred when trying to use the '" + id.name() + "' lock resources:\r\n" + printStackTrace(deadlockedState) + "\r\n\r\n");
+                    ThreadTracker.getInstance().accessThreadTracker(true, true, id, hashcode);
+                    deadlockedState = null;
+                }
+
+                registerLocking();
+            }
+            return true;
+        } else {
+            return false;
+        }
+    }
+    
+    private void registerLocking() {
+        state.lock();
+        try {
+            ThreadTracker.getInstance().accessThreadTracker(false, true, id, hashcode);
+        
+            if(reentrantCount.incrementAndGet() == 1) {
+                final Thread t = Thread.currentThread();
+                timeoutSchedule = TimerManager.getInstance().schedule(new Runnable() {
+                    @Override
+                    public void run() {
+                        issueDeadlock(t);
+                    }
+                }, ServerConstants.LOCK_MONITOR_TIME);
+            }
+        } finally {
+            state.unlock();
+        }
+    }
+    
+    private void unregisterLocking() {
+        state.lock();
+        try {
+            if(reentrantCount.decrementAndGet() == 0) {
+                if(timeoutSchedule != null) {
+                    timeoutSchedule.cancel(false);
+                    timeoutSchedule = null;
+                }
+            }
+            
+            ThreadTracker.getInstance().accessThreadTracker(false, false, id, hashcode);
+        } finally {
+            state.unlock();
+        }
+    }
+    
+    private void issueDeadlock(Thread t) {
+        deadlockedState = t.getStackTrace();
+        //super.unlock();
+    }
+    
+    private static String printStackTrace(StackTraceElement[] list) {
+        String s = "";
+        for(int i = 0; i < list.length; i++) {
+            s += ("    " + list[i].toString() + "\r\n");
+        }
+        
+        return s;
+    }
+}