Cef.Shutdown() hangs if ChromiumWebBrowser is already disposed

[peters]

If you call the ChromiumWebBrowser.Dispose() method before calling Cef.Shutdown() the application will hang and is unable to shutdown. Removing the call to dispose fixes the issue.

This is observed on the latest 39.0.0-pre02 -pre release.

var browser = new ChromiumWebBrowser();
browser.Dispose();
Cef.Shutdown();

Ref: ChromiumWebBrowser.cs
Ref: Cef.h

There has to be some weirdness involved in relation to AddDisposable/RemoveDisposable.

/cc @amaitland

[amaitland]

@peters Can you try again with master? or the latest CI build? Some work was done recently to improve dispose, see #786

[peters]

@amaitland i'll try the latest CI build tomorrow :)

[amaitland]

'-pre03' is out, hopefully solves your issue.

[amaitland]

From what I can tell this has been resolved. Feel free to re-open if there's a problem 👍

[peters]

@amaitland Upgraded to latest pre, the issue is still present. I don't have time for researching this right now, but i'll report back when i've identified the cause :)

[rassilon]

Well, could you help enlighten us about where the application is hanging on various threads?
See #872 comment for an instance where accidentally creating COM objects on a CEF thread caused shutdown to hang for me.

Thanks,
Bill

[rassilon]

For posterity, note that this isn't an answer, but I ran into (but didn't have time to debug a similar issue).

I was adding an Unhandled Exception handler to my CefSharp WinForms application and it needs to have the app exit afterwards.

Here's what I ended up with in Program.cs:Main:

        AppDomain.CurrentDomain.UnhandledException += CurrentDomain_UnhandledException;
        Application.ThreadException += Application_ThreadException;

(I was testing this logic by throwing an InvalidOperationException from a click handler of a menu bar item.)

Without the ThreadException handler I was still getting WinForm's Unhandled Exception dialog (Continue, Quit) kind of thing.

Here are my two handler functions:

    static void Application_ThreadException(object sender, ThreadExceptionEventArgs e)
    {
        CurrentDomain_UnhandledException(sender, new UnhandledExceptionEventArgs(e.Exception, false));
    }

    private static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
    {
        Exception ex = null;
        if (e.ExceptionObject != null)
        {
            ex = e.ExceptionObject as Exception;
        }
        try
        {
            if (ex != null)
            {
                Logger.Log.Exception("AppDomain_UnhandledException", ex);
            }
            // Ensure Application.Run exits cleanly to Main, so that the app won't
            // hang on shutdown.
            Application.Exit();
        }
        catch (Exception ex2)
        {
            Debug.Assert(false, "Exception in unhandled exception handler: " + ex2.ToString());
        }
    }

The trick here is to not get over anxious. I had initially just wanted to call Environment.Exit(1) directly here after calling Application.Exit(), but that caused the app shutdown to hang.

Bill

[Galen02]

I've been having this same hanging problem for a long time. I believe I've found what is at least a work-around to it. I was delaying calling Cef.Initialize() until I needed the functionality. As a result I was not calling Initialize in the main thread. Now, when I call initialize in the main thread at the start of the application it no longer hangs. I also call Cef.Shutdown() from the main thread when the application exits. I hope this helps out.

[amaitland]

Closing this one for now, if someone can reproduce the problem with master then happy to reopen.

For reference I've updated the Initailize/Shutdown documentation as per the API see 4222856

http://magpcss.org/ceforum/apidocs3/projects/%28default%29/%28_globals%29.html#CefInitialize%28constCefMainArgs&,constCefSettings&,CefRefPtr%3CCefApp%3E,void*%29
http://magpcss.org/ceforum/apidocs3/projects/%28default%29/%28_globals%29.html#CefShutdown%28%29