Serialize context construction to avoid threading issues with shared contexts.

Source/OpenTK/Graphics/GraphicsContext.cs

@@ -32,7 +32,7 @@ namespace OpenTK.Graphics
 
         static bool share_contexts = true;
         static bool direct_rendering = true;
-        readonly static object context_lock = new object();        
+        readonly static object SyncRoot = new object();        
         // Maps OS-specific context handles to GraphicsContext weak references.
         readonly static Dictionary<ContextHandle, WeakReference> available_contexts = new Dictionary<ContextHandle, WeakReference>();
 
@@ -50,7 +50,7 @@ namespace OpenTK.Graphics
         {
             implementation = new OpenTK.Platform.Dummy.DummyGLContext(handle);
 
-            lock (context_lock)
+            lock (SyncRoot)
             {
                 available_contexts.Add((implementation as IGraphicsContextInternal).Context, new WeakReference(this));
             }
@@ -77,6 +77,8 @@ namespace OpenTK.Graphics
         /// Different hardware supports different flags, major and minor versions. Invalid parameters will be silently ignored.
         /// </remarks>
         public GraphicsContext(GraphicsMode mode, IWindowInfo window, int major, int minor, GraphicsContextFlags flags)
+        {
+            lock (SyncRoot)
             {
                 bool designMode = false;
                 if (mode == null && window == null)
@@ -101,8 +103,6 @@ namespace OpenTK.Graphics
 
                     IGraphicsContext shareContext = null;
                     if (GraphicsContext.ShareContexts)
-                {
-                    lock (context_lock)
                     {
                         // A small hack to create a shared context with the first available context.
                         foreach (WeakReference r in GraphicsContext.available_contexts.Values)
@@ -111,7 +111,6 @@ namespace OpenTK.Graphics
                             break;
                         }
                     }
-                }
 
                     // Todo: Add a DummyFactory implementing IPlatformFactory.
                     if (designMode)
@@ -123,16 +122,14 @@ namespace OpenTK.Graphics
                             case true: implementation = Factory.Embedded.CreateGLContext(mode, window, shareContext, direct_rendering, major, minor, flags); break;
                         }
 
-                lock (context_lock)
-                {
                     available_contexts.Add((this as IGraphicsContextInternal).Context, new WeakReference(this));
                 }
-            }
                 finally
                 {
                     Debug.Unindent();
                 }
             }
+        }
 
         #endregion
 
@@ -201,7 +198,7 @@ namespace OpenTK.Graphics
         {
             get
             {
-                lock (context_lock)
+                lock (SyncRoot)
                 {
                     if (available_contexts.Count > 0)
                     {
@@ -282,7 +279,7 @@ namespace OpenTK.Graphics
         /// </remarks>
         void CreateContext(bool direct, IGraphicsContext source)
         {
-            lock (context_lock)
+            lock (SyncRoot)
             {
                 available_contexts.Add((this as IGraphicsContextInternal).Context, new WeakReference(this));
             }
@@ -418,7 +415,7 @@ namespace OpenTK.Graphics
             if (!IsDisposed)
             {
                 Debug.Print("Disposing context {0}.", (this as IGraphicsContextInternal).Context.ToString());
-                lock (context_lock)
+                lock (SyncRoot)
                 {
                     available_contexts.Remove((this as IGraphicsContextInternal).Context);
                 }

Source/OpenTK/Platform/Windows/WinGLContext.cs

@@ -26,6 +26,8 @@ namespace OpenTK.Platform.Windows
     /// </summary>
     internal sealed class WinGLContext : DesktopGraphicsContext
     {
+        static object SyncRoot = new object();
+
         static IntPtr opengl32Handle;
         static bool wgl_loaded;
         const string opengl32Name = "OPENGL32.DLL";
@@ -35,6 +37,8 @@ namespace OpenTK.Platform.Windows
         #region --- Contructors ---
 
         static WinGLContext()
+        {
+            lock (SyncRoot)
             {
                 // Dynamically load the OpenGL32.dll in order to use the extension loading capabilities of Wgl.
                 if (opengl32Handle == IntPtr.Zero)
@@ -46,9 +50,15 @@ namespace OpenTK.Platform.Windows
                     Debug.WriteLine(String.Format("Loaded opengl32.dll: {0}", opengl32Handle));
                 }
             }
+        }
 
         public WinGLContext(GraphicsMode format, WinWindowInfo window, IGraphicsContext sharedContext,
             int major, int minor, GraphicsContextFlags flags)
+        {
+            // There are many ways this code can break when accessed by multiple threads. The biggest offender is
+            // the sharedContext stuff, which will only become valid *after* this constructor returns.
+            // The easiest solution is to serialize all context construction - hence the big lock, below.
+            lock (SyncRoot)
             {
                 if (window == null)
                     throw new ArgumentNullException("window", "Must point to a valid window.");
@@ -89,6 +99,7 @@ namespace OpenTK.Platform.Windows
                         if (flags != 0)
                         {
                             attributes.Add((int)ArbCreateContext.Flags);
+#warning "This is not entirely correct: Embedded is not a valid flag! We need to add a GetARBContextFlags(GraphicsContextFlags) method."
                             attributes.Add((int)flags);
                         }
                         attributes.Add(0);
@@ -128,6 +139,7 @@ namespace OpenTK.Platform.Windows
                     Wgl.Imports.ShareLists((sharedContext as IGraphicsContextInternal).Context.Handle, Handle.Handle);
                 }
             }
+        }
 
         #endregion