Fix WebView processes hanging around on unclean shutdown.

The processes now voluntarily exit themselves if the parent process exits.

RELEASE-NOTES.md

@@ -43,7 +43,7 @@ END TEMPLATE-->
 
 ### Bugfixes
 
-*None yet*
+* Ensure `Robust.Client.WebView` processes get shut down if game process exits uncleanly.
 
 ### Other
 
@@ -74,7 +74,7 @@ END TEMPLATE-->
 
 * Fixes a physics bug that could cause deleted entities to remain on the physics map.
 * Fixes a bug in entity lookup code that could cause clients to get stuck in an infinite loop.
- 
+
 ### Other
 
 * `Robust.Client.WebView` has been brought alive again.

Robust.Client.WebView/Cef/Program.cs

@@ -1,4 +1,7 @@
 using System;
+using System.Diagnostics;
+using System.Globalization;
+using System.Threading;
 using Xilium.CefGlue;
 
 namespace Robust.Client.WebView.Cef
@@ -19,6 +22,8 @@ namespace Robust.Client.WebView.Cef
 
             var mainArgs = new CefMainArgs(argv);
 
+            StartWatchThread();
+
             // This will block executing until the subprocess is shut down.
             var code = CefRuntime.ExecuteProcess(mainArgs, new RobustCefApp(null), IntPtr.Zero);
 
@@ -29,5 +34,44 @@ namespace Robust.Client.WebView.Cef
 
             return code;
         }
+
+        private static void StartWatchThread()
+        {
+            //
+            // CEF has this nasty habit of not shutting down all its processes if the parent crashes.
+            // Great!
+            //
+            // We use a separate thread in each CEF child process to watch the main PID.
+            // If it exits, we kill ourselves after a couple seconds.
+            //
+
+            if (Environment.GetEnvironmentVariable("ROBUST_CEF_BROWSER_PROCESS_ID") is not { } parentIdString)
+                return;
+
+            if (Environment.GetEnvironmentVariable("ROBUST_CEF_BROWSER_PROCESS_MODULE") is not { } parentModuleString)
+                return;
+
+            if (!int.TryParse(parentIdString, CultureInfo.InvariantCulture, out var parentId))
+                return;
+
+            var process = Process.GetProcessById(parentId);
+            if ((process.MainModule?.FileName ?? "") != parentModuleString)
+            {
+                process.Dispose();
+                return;
+            }
+
+            new Thread(() => WatchThread(process)) { Name = "CEF Watch Thread", IsBackground = true }
+                .Start();
+        }
+
+        private static void WatchThread(Process p)
+        {
+            p.WaitForExit();
+
+            Thread.Sleep(3000);
+
+            Environment.Exit(1);
+        }
     }
 }

Robust.Client.WebView/Cef/WebViewManagerCef.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics;
 using System.IO;
 using System.Net;
 using System.Reflection;
@@ -85,6 +86,10 @@ namespace Robust.Client.WebView.Cef
 
             _app = new RobustCefApp(_sawmill);
 
+            var process = Process.GetCurrentProcess();
+            Environment.SetEnvironmentVariable("ROBUST_CEF_BROWSER_PROCESS_ID", process.Id.ToString());
+            Environment.SetEnvironmentVariable("ROBUST_CEF_BROWSER_PROCESS_MODULE", process.MainModule?.FileName ?? "");
+
             // So these arguments look like nonsense, but it turns out CEF is just *like that*.
             // The first argument is literally nonsense, but it needs to be there as otherwise the second argument doesn't apply
             // The second argument turns off CEF's bullshit error handling, which breaks dotnet's error handling.