From c712826c0750ce17e33f24dd37324e4e1590bb8a Mon Sep 17 00:00:00 2001
From: "J. Neugebauer" <ngb@helmholtz-bi.de>
Date: Fri, 31 Dec 2021 15:28:21 +0100
Subject: [PATCH] Made access to layers synchronized

---
 src/schule/ngb/zm/Zeichenleinwand.java | 38 +++++++++++++++++---------
 1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/src/schule/ngb/zm/Zeichenleinwand.java b/src/schule/ngb/zm/Zeichenleinwand.java
index b77809f..890778b 100644
--- a/src/schule/ngb/zm/Zeichenleinwand.java
+++ b/src/schule/ngb/zm/Zeichenleinwand.java
@@ -29,9 +29,11 @@ public class Zeichenleinwand extends Canvas {
 
 		// Liste der Ebenen initialisieren und die Standardebenen einfügen
 		layers = new LinkedList<>();
-		layers.add(new ColorLayer(Constants.STD_BACKGROUND));
-		layers.add(new DrawingLayer());
-		layers.add(new ShapesLayer());
+		synchronized( layers ) {
+			layers.add(new ColorLayer(Constants.STD_BACKGROUND));
+			layers.add(new DrawingLayer());
+			layers.add(new ShapesLayer());
+		}
 	}
 
 	/**
@@ -47,8 +49,10 @@ public class Zeichenleinwand extends Canvas {
 		this.setPreferredSize(this.getSize());
 		this.setMinimumSize(this.getSize());
 
-		for( Layer layer : layers ) {
-			layer.setSize(width, height);
+		synchronized( layers ) {
+			for( Layer layer : layers ) {
+				layer.setSize(width, height);
+			}
 		}
 	}
 
@@ -59,8 +63,10 @@ public class Zeichenleinwand extends Canvas {
 	 */
 	public void addLayer( Layer layer ) {
 		if( layer != null ) {
-			layer.setSize(getWidth(), getHeight());
-			layers.add(layer);
+			synchronized( layers ) {
+				layer.setSize(getWidth(), getHeight());
+				layers.add(layer);
+			}
 		}
 	}
 
@@ -71,8 +77,10 @@ public class Zeichenleinwand extends Canvas {
 	 */
 	public void addLayer( int i, Layer layer ) {
 		if( layer != null ) {
-			layer.setSize(getWidth(), getHeight());
-			layers.add(i, layer);
+			synchronized( layers ) {
+				layer.setSize(getWidth(), getHeight());
+				layers.add(i, layer);
+			}
 		}
 	}
 
@@ -140,8 +148,10 @@ public class Zeichenleinwand extends Canvas {
 	}
 
 	public void dispose() {
-		for( Layer layer : layers ) {
-			layer.dispose();
+		synchronized( layers ) {
+			for( Layer layer : layers ) {
+				layer.dispose();
+			}
 		}
 	}
 
@@ -163,8 +173,10 @@ public class Zeichenleinwand extends Canvas {
 						Graphics2D g2d = (Graphics2D) strategy.getDrawGraphics();
 						g2d.clearRect(0, 0, getWidth(), getHeight());
 
-						for( Layer layer : layers ) {
-							layer.draw(g2d);
+						synchronized( layers ) {
+							for( Layer layer : layers ) {
+								layer.draw(g2d);
+							}
 						}
 
 						g2d.dispose();