Vasili Gulevich

[The alternative](https://github.com/eclipse-platform/eclipse.platform.swt/pull/1743) is quite complex in comparison and does not avoid the asyncExec().

> Should this one be looked at or #1743 is considered superior to it? @akurtakov this PR contains a bug (throws exceptions when columns are deleted), and is marked Draft...

TODO: add download link to error message

While this is next to impossible to reproduce, the problem is very clear: https://github.com/eclipse-platform/eclipse.platform.swt/blob/9b2ef91d97554e288824bf4468b1752e9ab04b10/bundles/org.eclipse.swt/Eclipse%20SWT/cocoa/org/eclipse/swt/widgets/DirectoryDialog.java#L198 For some reason `OS.objc_msgSend(OS.class_NSOpenPanel, OS.sel_openPanel);` has hanged up, then returned null.

> [@basilevs](https://github.com/basilevs) : could you provide a fix? I don't know how to fix the deadlock. Better error reporting: #1956

# Hypothesis This might be a leak. The [NSOpenPanel should not be retained in macOS 10.7 and newer](https://stackoverflow.com/a/18478175/125562), but we do. [Using the Open and Save Panels](https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/UsingtheOpenandSavePanels/UsingtheOpenandSavePanels.html#//apple_ref/doc/uid/TP40010672-CH4-DontLinkElementID_26)

> `SWT.SetData` callbacks inside `Tree.cellDataProc()` into `Display.asyncExec()` Is there any hope to remove other asyncExecs from this PR? They were done for tangentially same reason, are not they? Please do...

@jukzi is this reproducible locally? Does it happen on Windows only?

Black screen is a symptom that someone has logged in to the host via RDP and then disconnected normally. Ask to reboot the host and not to touch RDP. Also,...

> for example by executing the failing test only. I suggest to create a dedicated test that would fail only if no PAINT events are happening and run that in...