CefSharp opens the Chromium browser when opening more than 1 instances of the program

[jkiller295]

Is there an existing issue for this?

• I have searched both open/closed issues, no issue already exists.

CefSharp Version

130.1.90

Operating System

Windows 11

Architecture

x86

.Net Version

.NET Framework 4.7

Implementation

WinForms

Reproduction Steps

1. Install CefSharp.Winforms 130.1.90 from Nuget
2. Add the following code to the Program.cs file, just above the line Application.EnableVisualStyles();

CefSettings settings = new CefSettings();
settings.LogSeverity = LogSeverity.Disable;
Cef.Initialize(settings);

3. Build the project. Open more than 1 instance of the program

Expected behavior

All the instances of the program should open normally.

Actual behavior

From the 2nd instance onwards, a Chromium browser opens with an error. FYI it is happening to the CefSharp.MinimalExample.WinForms sample solution downloaded from here too.

Regression?

It worked fine in 120.2.70 and up to 126.2.180.0.
127.3.50 onwards have this issue

Known Workarounds

No response

Does this problem also occur in the CEF Sample Application

Not Tested

Other information

No response

[amaitland]

Converted to discussion as this is not a bug, it's a change in upstream behavior.

All the instances of the program should open normally.

CEF now supports the Chromium process singleton, this brings with it changes to how CachePath/RootCachePath are accessed from multiple processes. See #4668 and chromiumembedded/cef#3609 for more details

What you are seeing is the expected behavior based on the example you've provided.

If Cef.Initialize returns false then you cannot continue.

[jkiller295]

It's just strange because all versions before 126.2.180.0 were working without any issues. I can't say it was luck because I've been using that version for years. Decided to upgrade to the latest version or anything after 126.2.180.0 and boom, problem.

How should I run multiple instances of my application? Or how do I change it to use in-memory cache like before?

[amaitland]

It's just strange because all versions before 126.2.180.0 were working without any issues. I can't say it was luck because I've been using that version for years. Decided to upgrade to the latest version or anything after 126.2.180.0 and boom, problem.

Not strange at all. CEF made major changes, 126 is the first version to switch to the Chrome Bootstrap.

#4835

How should I run multiple instances of my application?

You need unique CefSettings.RootCachePath per application instance.

[jkiller295]

Does it have to be unique for the RootCachePath or just CefCachePath will do?

[amaitland]

You need a unique RootCachePath per application instance.

You can load chrome://version to see what that is.

[MarkHaroldson]

I can work around the issue. Is there a way to override the error browser from even displaying? It seems to appear during the call the Cef.Initialize(). Even if the program detects that Initialized failed there does not appear to be any way to prevent the browser from displaying.

[amaitland]

Return true if the relaunch is handled or false for default relaunch behavior. Default behavior will create a new default styled Chrome window.

https://cefsharp.github.io/api/130.1.x/html/M_CefSharp_IBrowserProcessHandler_OnAlreadyRunningAppRelaunch.htm

The default upstream behaviour is to launch a new Chrome styled window. You can return true in IBrowserProcessHandler.OnAlreadyRunningAppRelaunch to override this behavior.

[MarkHaroldson]

Thanks!

What i figured out is that IBrowserProcessHandler.OnAlreadyRunningAppRelaunch is called in the context of the process that called Cef.Initialize() with the RootCachePath first and not the subsequent calls to Cef.Initialize().

[amaitland]

What i figured out is that IBrowserProcessHandler.OnAlreadyRunningAppRelaunch is called in the context of the process that called Cef.Initialize() with the RootCachePath first and not the subsequent calls to Cef.Initialize().

Correct. This allows you to implement the same behavior as Chromium.

Subsequent process launches communicates with first process saying open a new window, subsequent process closes. This New Window is what CEF launches by default matching the Chromium behavior.