release resources when pluginunload

engine/src/shell/platform/unity/darwin/ios/uiwidgets_system.mm

   unity_uiwidgets_->SetWakeUpCallback(nullptr);
   unity_uiwidgets_ = nullptr;
 
+  UnitySurfaceManager::ReleaseResource();
+
   unity_interfaces_ = nullptr;
 }
 

engine/src/shell/platform/unity/darwin/ios/unity_surface_manager.h

 
   //openGL contexts pool
   static std::vector<GLContextPair> gl_context_pool_;
-
+  static void ReleaseResource();
 
   void* CreateRenderTexture(size_t width, size_t height);
 
   uint32_t GetFbo();
 
  private:
-  GLContextPair GetFreeOpenGLContext();
+  static GLContextPair GetFreeOpenGLContext();
   void RecycleOpenGLContext(EAGLContext* gl, EAGLContext* gl_resource);
   //pixel buffer handles
   CVPixelBufferRef pixelbuffer_ref = nullptr;

engine/src/shell/platform/unity/darwin/ios/unity_surface_manager.mm

   {
     EAGLContext* gl = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
     EAGLContext* gl_resource = [[EAGLContext alloc] initWithAPI:[gl API] sharegroup: [gl sharegroup]];
-    gl_context_pool_.push_back(GLContextPair(gl, gl_resource));
+    return GLContextPair(gl, gl_resource);
   }
   auto context_pair = gl_context_pool_.back();
   gl_context_pool_.pop_back();
   ClearCurrentContext();
 
   gl_context_pool_.push_back(GLContextPair(gl, gl_resource));
+}
+
+void UnitySurfaceManager::ReleaseResource()
+{
+  while(gl_context_pool_.size() > 0)
+  {
+    gl_context_pool_.pop_back();
+  }
 }
 
 UnitySurfaceManager::UnitySurfaceManager(IUnityInterfaces* unity_interfaces)

engine/src/shell/platform/unity/darwin/macos/uiwidgets_system.mm

   unity_uiwidgets_->SetWakeUpCallback(nullptr);
   unity_uiwidgets_ = nullptr;
 
+  UnitySurfaceManager::ReleaseResource();
+
   unity_interfaces_ = nullptr;
 }
 

engine/src/shell/platform/unity/darwin/macos/unity_surface_manager.h

 
   //openGL contexts pool
   static std::vector<GLContextPair> gl_context_pool_;
+  static void ReleaseResource();
 
   void* CreateRenderTexture(size_t width, size_t height);
 
   uint32_t GetFbo();
 
  private:
-  GLContextPair GetFreeOpenGLContext();
+  static GLContextPair GetFreeOpenGLContext();
   void RecycleOpenGLContext(NSOpenGLContext* gl, NSOpenGLContext* gl_resource);
   //pixel buffer handles
   CVPixelBufferRef pixelbuffer_ref = nullptr;

engine/src/shell/platform/unity/darwin/macos/unity_surface_manager.mm

       gl_resource = [[NSOpenGLContext alloc] initWithFormat:pixelFormat shareContext:gl];  
     
       if (gl_resource == nil) {
-        CGLReleaseContext(gl.CGLContextObj);
+        CGLReleaseContext([gl CGLContextObj]);
-
-
-
-    gl_context_pool_.push_back(GLContextPair(gl, gl_resource));
+    return GLContextPair(gl, gl_resource);
   }
 
   auto context_pair = gl_context_pool_.back();
   ClearCurrentContext();
 
   gl_context_pool_.push_back(GLContextPair(gl, gl_resource));
+}
+
+void UnitySurfaceManager::ReleaseResource()
+{
+  while(gl_context_pool_.size() > 0)
+  {
+    auto context_pair = gl_context_pool_.back();
+    CGLReleaseContext([context_pair.gl_context_ CGLContextObj]);
+    CGLReleaseContext([context_pair.gl_resource_context_ CGLContextObj]);
+    gl_context_pool_.pop_back();
+  }
 }
 
 UnitySurfaceManager::UnitySurfaceManager(IUnityInterfaces* unity_interfaces)