Bug 567826 - [GTK] JVM crash on Display.dispose() due to Clipboard

If 'SWT.Dispose' handler is a bit slow, user might be able to switch to
other application and Ctrl+C there. When this happens, Linux calls
'ClipboardProxy.clearFunc()' with the following stack:

  Native: clipboard_unset() at gtk/gtkclipboard.c:782
  Native: selection_clear_event_cb() at gtk/gtkclipboard.c:424
  Native: <emit signal for 'GDK_SELECTION_CLEAR'>
  Native: gtk_widget_event_internal() at gtk/gtkwidget.c:7808
  Native: gtk_main_do_event() at gtk/gtkmain.c:1860
  Java:   org.eclipse.swt.internal.gtk.GTK._gtk_main_do_event()
  Java:   org.eclipse.swt.widgets.Display.eventProc()
  Java:   org.eclipse.swt.internal.gtk.OS._g_main_context_iteration()
  Java:   org.eclipse.swt.widgets.Display.readAndDispatch()
  Java:   org.eclipse.swt.widgets.Display.release()

If 'Callback' for 'clearFunc' is already disposed, JVM crashes.

The solution is to dispose callback after 'Display.readAndDispatch()' in
'Display.release()'.

This patch has a curious side effect: if 'SWT.Dispose' handler is slow,
Shell is now visible (and eventually shows "not responding") for its
duration. I understand that this is because 'gtk_clipboard_store()'
also does some unexpected event processing. I consider this side effect
as not a regression because the same behavior is seen when clipboard is
not owned by SWT by the time of 'Display.dispose()'.

Change-Id: I2cc11600f06030243e55d70f24b881dcb9b67503
Signed-off-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>

3 files changed, 86 insertions, 3 deletions

diff --git a/bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/ClipboardProxy.java b/bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/ClipboardProxy.java
index 5eee958934..54cde28b5e 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/ClipboardProxy.java
+++ b/bundles/org.eclipse.swt/Eclipse SWT Drag and Drop/gtk/org/eclipse/swt/dnd/ClipboardProxy.java
@@ -14,7 +14,6 @@
 package org.eclipse.swt.dnd;
 
 
-import org.eclipse.swt.*;
 import org.eclipse.swt.internal.*;
 import org.eclipse.swt.internal.gtk.*;
 import org.eclipse.swt.widgets.*;
@@ -43,7 +42,7 @@ static ClipboardProxy _getInstance(final Display display) {
 	if (proxy != null) return proxy;
 	proxy = new ClipboardProxy(display);
 	display.setData(ID, proxy);
-	display.addListener(SWT.Dispose, event -> {
+	display.disposeExec(() -> {
 		ClipboardProxy clipbordProxy = (ClipboardProxy)display.getData(ID);
 		if (clipbordProxy == null) return;
 		display.setData(ID, null);
diff --git a/bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/SWT.java b/bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/SWT.java
index d13183afd2..5b87b09228 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/SWT.java
+++ b/bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/SWT.java
@@ -258,11 +258,17 @@ public class SWT {
 	public static final int Resize = 11;
 
 	/**
-	 * The dispose event type (value is 12).
+	 * The dispose event type (value is 12).<br>
+	 * <br>
+	 * Note: {@link Display} still runs {@link Display#readAndDispatch}
+	 * after sending this event. If you want to dispose any resources,
+	 * this might cause problems. Use {@link Display#disposeExec}
+	 * instead.
 	 *
 	 * @see org.eclipse.swt.widgets.Widget#addListener
 	 * @see org.eclipse.swt.widgets.Display#addListener
 	 * @see org.eclipse.swt.widgets.Display#addFilter
+	 * @see org.eclipse.swt.widgets.Display#disposeExec
 	 * @see org.eclipse.swt.widgets.Event
 	 *
 	 * @see org.eclipse.swt.widgets.Widget#addDisposeListener
diff --git a/tests/org.eclipse.swt.tests.gtk/ManualTests/org/eclipse/swt/tests/gtk/snippets/Bug567826_CrashClipboardExit.java b/tests/org.eclipse.swt.tests.gtk/ManualTests/org/eclipse/swt/tests/gtk/snippets/Bug567826_CrashClipboardExit.java
new file mode 100644
index 0000000000..6e70335243
--- /dev/null
+++ b/tests/org.eclipse.swt.tests.gtk/ManualTests/org/eclipse/swt/tests/gtk/snippets/Bug567826_CrashClipboardExit.java
@@ -0,0 +1,78 @@
+/*******************************************************************************
+ * Copyright (c) 2020 Syntevo and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Syntevo - initial API and implementation
+ *******************************************************************************/
+
+package org.eclipse.swt.tests.gtk.snippets;
+
+import org.eclipse.swt.SWT;
+import org.eclipse.swt.dnd.Clipboard;
+import org.eclipse.swt.dnd.DND;
+import org.eclipse.swt.dnd.TextTransfer;
+import org.eclipse.swt.dnd.Transfer;
+import org.eclipse.swt.layout.FillLayout;
+import org.eclipse.swt.widgets.*;
+
+public class Bug567826_CrashClipboardExit {
+	public static void main (String [] args) {
+		Display display = new Display ();
+
+		FillLayout layout = new FillLayout();
+		layout.marginHeight = 10;
+		layout.marginWidth = 10;
+
+		Shell shell = new Shell(display);
+		shell.setLayout(layout);
+
+		Label hint = new Label(shell, SWT.NONE);
+		hint.setText(
+			"1) Close this Shell\n" +
+			"2) There will be a 10 sec Thread.sleep()\n" +
+			"3) During the sleep, switch to other app and copy some text to clipboard\n" +
+			"4) JVM will crash.\n"
+		);
+
+		Clipboard clipboard = new Clipboard(display);
+		Object[] data = new Object[]{"Test clipboard contents"};
+		Transfer[] types = new Transfer[]{TextTransfer.getInstance()};
+		clipboard.setContents(data, types, DND.CLIPBOARD);
+
+		final String clipboardProxyID = "CLIPBOARD PROXY OBJECT";
+		if (null == display.getData(clipboardProxyID))
+			System.out.println("Unexpected: ClipboardProxy is not present");
+
+		display.addListener(SWT.Dispose, event -> {
+			System.out.println("SWT.Dispose for Display: waiting");
+			if (null != display.getData(clipboardProxyID))
+				System.out.println("ClipboardProxy is not disposed in SWT.Dispose. Shouldn't happen without the patch.");
+
+			// Give time to switch to other window
+			try {
+				Thread.sleep(10000);
+			} catch (InterruptedException ex) {
+				ex.printStackTrace();
+			}
+
+			System.out.println("SWT.Dispose for Display: continuing");
+		});
+
+		shell.pack();
+		shell.open();
+
+		while (!shell.isDisposed()) {
+			if (!display.readAndDispatch ())
+				display.sleep ();
+		}
+
+		display.dispose ();
+	}
+}