AbstractSwingUI: fix deadlock in chooseFiles method

Modeled after bac7815
(Thanks @ctrueden)

Author: imagejan

src/main/java/org/scijava/ui/swing/AbstractSwingUI.java

@@ -164,29 +164,41 @@ public File chooseFile(final File file, final String style) {
 
 	@Override
 	public File[] chooseFiles(final File[] files, final FileFilter filter) {
-		final JFileChooser chooser = new JFileChooser();
-		chooser.setMultiSelectionEnabled(true);
-		chooser.setSelectedFiles(files);
-		if (filter != null) {
-			javax.swing.filechooser.FileFilter fileFilter = new javax.swing.filechooser.FileFilter() {
-
-				@Override
-				public String getDescription() {
-					return filter.toString();
+		final File[][] result = new File[1][];
+		try {
+			// NB: We show the JFileChooser on the EDT because otherwise there could
+			// be a deadlock, particularly on macOS.
+			// See the {@link #chooseFile(File, String) chooseFile} method.
+			threadService.invoke(() -> {
+				final JFileChooser chooser = new JFileChooser();
+				chooser.setMultiSelectionEnabled(true);
+				chooser.setSelectedFiles(files);
+				if (filter != null) {
+					javax.swing.filechooser.FileFilter fileFilter = new javax.swing.filechooser.FileFilter() {
+
+						@Override
+						public String getDescription() {
+							return filter.toString();
+						}
+
+						@Override
+						public boolean accept(File f) {
+							if (filter.accept(f)) return true;
+							return false;
+						}
+					};
+					chooser.setFileFilter(fileFilter);
 				}
-
-				@Override
-				public boolean accept(File f) {
-					if (filter.accept(f)) return true;
-					return false;
+				int rval = chooser.showOpenDialog(appFrame);
+				if (rval == JFileChooser.APPROVE_OPTION) {
+					result[0] = chooser.getSelectedFiles();
 				}
-			};
-			chooser.setFileFilter(fileFilter);
+			});
 		}
-		int rval = chooser.showOpenDialog(appFrame);
-		if (rval != JFileChooser.APPROVE_OPTION)
-			return null;
-		return chooser.getSelectedFiles();
+		catch (final InvocationTargetException | InterruptedException exc) {
+			log.error(exc);
+		}
+		return result[0];
 	}
 
 	@Override