From 1f053cd0fa7a28a40e2733eb0bc2f099f943d60c Mon Sep 17 00:00:00 2001
From: 41zu <dominikator.mueka@googlemail.com>
Date: Tue, 28 Oct 2025 12:25:53 +0100
Subject: [PATCH] Remove synchronisation on "Device.class", because it is
 deadlock prone.

Information about the deadlock was posted on the RAP mailing list: https://www.eclipse.org/lists/rap-dev/msg01480.html
---
 .../swt/internal/widgets/DisplaysHolder.java  | 30 +++++----
 .../src/org/eclipse/swt/widgets/Display.java  | 62 +++----------------
 2 files changed, 28 insertions(+), 64 deletions(-)

diff --git a/bundles/org.eclipse.rap.rwt/src/org/eclipse/swt/internal/widgets/DisplaysHolder.java b/bundles/org.eclipse.rap.rwt/src/org/eclipse/swt/internal/widgets/DisplaysHolder.java
index ac74ec87e7..f4dd45ebe6 100644
--- a/bundles/org.eclipse.rap.rwt/src/org/eclipse/swt/internal/widgets/DisplaysHolder.java
+++ b/bundles/org.eclipse.rap.rwt/src/org/eclipse/swt/internal/widgets/DisplaysHolder.java
@@ -12,23 +12,31 @@
 package org.eclipse.swt.internal.widgets;
 
 import java.lang.ref.WeakReference;
+import java.util.Collections;
+import java.util.Map;
+import java.util.WeakHashMap;
 
 import org.eclipse.swt.widgets.Display;
 
 
-public class DisplaysHolder {
-  private WeakReference<Display>[] displays;
-  
-  @SuppressWarnings("unchecked")
+public final class DisplaysHolder {
+
+  private final Map<Thread, WeakReference<Display>> displays;
+
   public DisplaysHolder() {
-    displays = new WeakReference[ 4 ];
+    displays = Collections.synchronizedMap( new WeakHashMap<>() );
   }
-  
-  public WeakReference<Display>[] getDisplays() {
-    return displays;
+
+  public void addDisplay( Thread tread, Display display ) {
+    displays.put( tread, new WeakReference<>( display ) );
   }
-  
-  public void setDisplays( WeakReference<Display>[] displays ) {
-    this.displays = displays;
+
+  public Display getDisplay( Thread thread ) {
+    WeakReference<Display> wr = displays.get( thread );
+    if ( wr != null ) {
+      return wr.get();
+    }
+    return null;
   }
+
 }
diff --git a/bundles/org.eclipse.rap.rwt/src/org/eclipse/swt/widgets/Display.java b/bundles/org.eclipse.rap.rwt/src/org/eclipse/swt/widgets/Display.java
index aaf9df5878..10a9480663 100644
--- a/bundles/org.eclipse.rap.rwt/src/org/eclipse/swt/widgets/Display.java
+++ b/bundles/org.eclipse.rap.rwt/src/org/eclipse/swt/widgets/Display.java
@@ -19,7 +19,6 @@
 import static org.eclipse.rap.rwt.remote.JsonMapping.readRectangle;
 
 import java.io.IOException;
-import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
@@ -939,17 +938,11 @@ private void detachThread() {
    * @return the display for the given thread
    */
   public static Display findDisplay( Thread thread ) {
-    synchronized( Device.class ) {
-      for( WeakReference<Display> displayRef : getDisplays() ) {
-        if( displayRef != null ) {
-          Display display = displayRef.get();
-          if( display != null && !display.isDisposed() && display.thread == thread ) {
-            return display;
-          }
-        }
-      }
+    Display display = getDisplay( thread );
+    if (display == null || display.thread != thread || display.isDisposed()) {
       return null;
     }
+    return display;
   }
 
   /**
@@ -2217,57 +2210,20 @@ public boolean getTouchEnabled() {
     return false;
   }
 
-  @SuppressWarnings("unchecked")
   private void register() {
-    synchronized( Device.class ) {
-      boolean registered = false;
-      WeakReference<Display>[] displays = getDisplays();
-      for( int i = 0; !registered && i < displays.length; i++ ) {
-        if( canDisplayRefBeReplaced( displays[ i ] ) ) {
-          displays[ i ] = new WeakReference<>( this );
-          registered = true;
-        }
-      }
-      if( !registered ) {
-        WeakReference<Display>[] newDisplays = new WeakReference[ displays.length + 4 ];
-        System.arraycopy( displays, 0, newDisplays, 0, displays.length );
-        newDisplays[ displays.length ] = new WeakReference<>( this );
-        setDisplays( newDisplays );
-      }
-    }
-  }
-
-  private boolean canDisplayRefBeReplaced( WeakReference<Display> displayRef ) {
-    boolean result = false;
-    if( displayRef == null ) {
-      result = true;
-    } else {
-      Display display = displayRef.get();
-      if( display == null || display.thread == thread ) {
-        result = true;
-      }
-    }
-    return result;
+    addDisplay( this );
   }
 
   private void deregister() {
-    synchronized( Device.class ) {
-      WeakReference<Display>[] displays = getDisplays();
-      for( int i = 0; i < displays.length; i++ ) {
-        WeakReference<Display> current = displays[ i ];
-        if( current != null && this == current.get() ) {
-          displays[ i ] = null;
-        }
-      }
-    }
+
   }
 
-  private static WeakReference<Display>[] getDisplays() {
-    return ContextProvider.getApplicationContext().getDisplaysHolder().getDisplays();
+  private static Display getDisplay( Thread thread ) {
+    return ContextProvider.getApplicationContext().getDisplaysHolder().getDisplay( thread );
   }
 
-  private void setDisplays( WeakReference<Display>[] displays ) {
-    getApplicationContext().getDisplaysHolder().setDisplays( displays );
+  private void addDisplay( Display display ) {
+    getApplicationContext().getDisplaysHolder().addDisplay( thread, display );
   }
 
   /////////////////////