Use a helper to do the NSRunAlertPanelReleativeToWindow() function

Author: gcasa

Source/NSAlert.m

@@ -1770,6 +1770,50 @@ void NSBeginInformationalAlertSheet(NSString *title,
   NSReleaseAlertPanel(panel);
 }
 
+// Helper to run a sheet on the main thread and capture the result.
+@interface _GSRunSheetHelper : NSObject
+{
+  GSAlertPanel *_panel;
+  NSWindow *_docWindow;
+  NSInteger _result;
+}
+- (id)initWithPanel:(GSAlertPanel *)panel docWindow:(NSWindow *)docWindow;
+- (void)runSheetOnMainThread;
+- (NSInteger)result;
+@end
+
+@implementation _GSRunSheetHelper
+- (id)initWithPanel:(GSAlertPanel *)panel docWindow:(NSWindow *)docWindow
+{
+  if ((self = [super init]) != nil)
+    {
+      _panel = RETAIN(panel);
+      _docWindow = docWindow; // not retaining window to avoid cycles
+      _result = NSAlertErrorReturn;
+    }
+  return self;
+}
+
+- (void)dealloc
+{
+  RELEASE(_panel);
+  [super dealloc];
+}
+
+- (void)runSheetOnMainThread
+{
+  [NSApp beginSheet: _panel
+       modalForWindow: _docWindow
+        modalDelegate: nil
+       didEndSelector: NULL
+          contextInfo: NULL];
+  _result = [_panel result];
+}
+
+- (NSInteger)result { return _result; }
+
+@end
+
 // Synchronous sheet-aware alert. If docWindow is nil, fall back to
 // NSRunAlertPanel which shows a modal alert. Otherwise display a sheet
 // attached to docWindow and run a modal loop until it completes.
@@ -1806,20 +1850,27 @@ void NSBeginInformationalAlertSheet(NSString *title,
 
   panel = getSomeSheet(&standardAlertPanel, defaultTitle, title, message,
                        defaultButton, alternateButton, otherButton);
+  /* Run the sheet on the main thread to ensure it is presented. */
+  if (GSCurrentThread() != GSAppKitThread)
+    {
+      _GSRunSheetHelper *h = [[_GSRunSheetHelper alloc] initWithPanel: panel
+                                                            docWindow: docWindow];
+      [h performSelectorOnMainThread: @selector(runSheetOnMainThread)
+                          withObject: nil
+                       waitUntilDone: YES];
+      result = [h result];
+      RELEASE(h);
+    }
+  else
+    {
+      [NSApp beginSheet: panel
+           modalForWindow: docWindow
+            modalDelegate: nil
+           didEndSelector: NULL
+              contextInfo: NULL];
+      result = [panel result];
+    }
 
-  /* Begin sheet synchronously; under GNUstep beginSheet calls runModalForWindow
-     which will invoke the modalDelegate didEndSelector; we call beginSheet
-     and then return the panel result. */
-  [NSApp beginSheet: panel
-       modalForWindow: docWindow
-        modalDelegate: nil
-       didEndSelector: NULL
-          contextInfo: NULL];
-
-  /* The sheet will run its modal session in -beginSheet; by the time
-     beginSheet returns, the sheet has already completed. Retrieve
-     the result and cleanup. */
-  result = [panel result];
   NSReleaseAlertPanel(panel);
   return result;
 }