Add initial directories and files

git-svn-id: https://svn.code.sf.net/p/xlogo4schools/svn/trunk@1 3b0d7934-f7ef-4143-9606-b51f2e2281fd

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diff --git a/logo/src/xlogo/MemoryChecker.java b/logo/src/xlogo/MemoryChecker.java
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+/* XLogo4Schools - A Logo Interpreter specialized for use in schools, based on XLogo by Lo�c Le Coq
+ * Copyright (C) 2013 Marko Zivkovic
+ * 
+ * Contact Information: marko88zivkovic at gmail dot com
+ * 
+ * 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 2 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, write to the Free 
+ * Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, 
+ * MA 02110-1301, USA.
+ * 
+ * 
+ * This Java source code belongs to XLogo4Schools, written by Marko Zivkovic
+ * during his Bachelor thesis at the computer science department of ETH Z�rich,
+ * in the year 2013 and/or during future work.
+ * 
+ * It is a reengineered version of XLogo written by Lo�c Le Coq, published
+ * under the GPL License at http://xlogo.tuxfamily.org/
+ * 
+ * Contents of this file were initially written by Lo�c Le Coq,
+ * a lot of modifications, extensions, refactorings have been applied by Marko Zivkovic 
+ */
+
+/**
+ * Title : XLogo
+ * Description : XLogo is an interpreter for the Logo
+ * programming language
+ * 
+ * @author Loïc Le Coq
+ **/
+package xlogo;
+
+import xlogo.messages.async.dialog.DialogMessenger;
+import xlogo.storage.global.GlobalConfig;
+
+/**
+ * This class is a thread that prevents from memory Overflow <br>
+ * Those problems could happen when a program loops indefinitely<br>
+ * Eg:<br>
+ * <br>
+ * <tt>
+ * To bad<br>
+ * fd 1 rt 1 <br>
+ * bad<br>
+ * this lines will explode memory<br>
+ * end <br>
+ * </tt>
+ * 
+ * @author loic
+ * 
+ * @author Marko Zivkovic - Extensive tests and provocation of the memory usage error message have shown
+ * that in XLogo4Schools, using a maximum 128MB heap, the memory threshold is never reached
+ * (Or very, very late in a gigantic recursion).
+ * 
+ */
+public class MemoryChecker extends Thread
+{
+	/**
+	 * The main frame
+	 */
+	private Application	cadre;
+	/**
+	 * This boolean indicates if the thread has to continue.<br>
+	 * If false, the thread will stop.
+	 */
+	private boolean		alive;
+	
+	/**
+	 * Constructs the Memory Checker for the main Frame
+	 * 
+	 * @param cadre
+	 *            the main Frame
+	 */
+	public MemoryChecker(Application cadre)
+	{
+		this.cadre = cadre;
+	}
+	
+	private static int maxSleepTime = 10000;
+	private static int minSleepTime = 500;
+	private static int sleepRange = maxSleepTime - minSleepTime;
+	
+	/**
+	 * The Run Method for the Thread
+	 */
+	public void run()
+	{		
+		/*
+		 * Marko : I reduced the amount of calculations done in every iteration.
+		 * Before it included 1 subtraction and 2 divisions and a fetch from GlobalConfig,
+		 * now only 1 subtraction is used to determine consumed > consumptionThreshold
+		 * and another long comparison was added to regulate frequency of memory checks.
+		 */
+		long consumptionThreshold =  GlobalConfig.getMemoryThreshold();
+		long listenThreshold = (long) (0.8 * consumptionThreshold);
+
+		
+		/*
+		 * I increased default sleeping time to about 10 seconds, because a check every 1 second is too much overhead for doing nothing useful.
+		 * However, as soon as the listenThreshold is reached, the sleepTime will start to decrease.
+		 * Only once the listenThreshold is reached,
+		 * the MemoryChecker becomes important to prevent an OutOfMemoryError and start suggesting the garbage collector to work.)
+		 */
+		int sleepTime = maxSleepTime;
+		
+		alive = true;
+		
+		while (alive)
+		{
+			try
+			{
+				Thread.sleep(sleepTime);
+			}
+			catch (InterruptedException ignore)
+			{}
+			long free = Runtime.getRuntime().freeMemory();
+			long total = Runtime.getRuntime().totalMemory();
+			long consumed = (total - free);
+			
+			if (consumed >= listenThreshold)
+			{
+				sleepTime = (int) (maxSleepTime - consumed / total * sleepRange);
+				
+				/*
+				 * Marko : 
+				 * In XLogo, when the error dialog was displayed, it usually kept displaying several times, disrupting any further use of the interpreter.
+				 * The only out was to restart the application. This indicates that, although heavy memory usage was detected by this thread,
+				 * the garbage collector did not yet start to free memory from dead objects.
+				 * (Discussions about GC in the Internet indicate that the Java GC starts working as soon as a heap generation gets full.
+				 * It is possible that the young generation is not full enough when 0.9*MaxMemory is reached, thus the message keeps appearing all the time,
+				 * because memory is not sufficiently cleaned up.)
+				 * Therefore, at least suggest the GC that it would be a good moment for garbage collection, and help recover. That's the best we can do.
+				 */
+				System.gc();
+			}
+			else
+				sleepTime = maxSleepTime; 
+			
+			if (consumed > consumptionThreshold)
+			{
+				cadre.error = true;
+				alive = false;
+				DialogMessenger.getInstance().dispatchError(Logo.messages.getString("erreur"),
+						Logo.messages.getString("depassement_memoire"));
+			}
+		}
+	}
+	
+	/**
+	 * Causes the memory checker loop to break.
+	 * @author Marko
+	 */
+	public void kill()
+	{
+		alive = false;
+	}
+	
+}