WGL: Lock shared context before creating a new one

src/Windows/Avalonia.Win32/OpenGl/WglContext.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Reactive.Disposables;
+using System.Threading;
 using Avalonia.OpenGL;
 using Avalonia.Platform;
 using Avalonia.Win32.Interop;
@@ -69,6 +70,12 @@ namespace Avalonia.Win32.OpenGl
         public bool IsLost { get; private set; }
         public IDisposable EnsureCurrent() => MakeCurrent();
 
+        internal IDisposable Lock()
+        {
+            Monitor.Enter(_lock);
+            return Disposable.Create(_lock, Monitor.Exit);
+        }
+
 
         public IntPtr CreateConfiguredDeviceContext(IntPtr hWnd)
         {

src/Windows/Avalonia.Win32/OpenGl/WglDisplay.cs

@@ -138,20 +138,25 @@ namespace Avalonia.Win32.OpenGl
                 {
                     if(version.Type != GlProfileType.OpenGL)
                         continue;
-                    var context = WglCreateContextAttribsArb(dc, shareContext?.Handle ?? IntPtr.Zero,
-                        new[]
-                        {
-                            // major
-                            WGL_CONTEXT_MAJOR_VERSION_ARB, version.Major,
-                            // minor
-                            WGL_CONTEXT_MINOR_VERSION_ARB,  version.Minor,
-                            // core profile
-                            WGL_CONTEXT_PROFILE_MASK_ARB, 1, 
-                            // debug 
-                            // WGL_CONTEXT_FLAGS_ARB, 1,
-                            // end
-                            0, 0
-                        });
+                    IntPtr context;
+                    using (shareContext?.Lock())
+                    {
+                        context = WglCreateContextAttribsArb(dc, shareContext?.Handle ?? IntPtr.Zero,
+                            new[]
+                            {
+                                // major
+                                WGL_CONTEXT_MAJOR_VERSION_ARB, version.Major,
+                                // minor
+                                WGL_CONTEXT_MINOR_VERSION_ARB, version.Minor,
+                                // core profile
+                                WGL_CONTEXT_PROFILE_MASK_ARB, 1,
+                                // debug 
+                                // WGL_CONTEXT_FLAGS_ARB, 1,
+                                // end
+                                0, 0
+                            });
+                    }
+
                     using(new WglRestoreContext(dc, context, null))
                         GlDebugMessageCallback(Marshal.GetFunctionPointerForDelegate(_debugCallback), IntPtr.Zero);
                     if (context != IntPtr.Zero)