Make debug message callback Send + Sync.

The debug callback function was not required to be Send+Sync.
This caused the native `Context` struct to become !Send + !Sync, which
is problematic because an OpenGL context can be passed to another
thread.

src/lib.rs

@@ -37,7 +37,7 @@ pub type Renderbuffer = <Context as HasContext>::Renderbuffer;
 pub type Query = <Context as HasContext>::Query;
 pub type UniformLocation = <Context as HasContext>::UniformLocation;
 pub type TransformFeedback = <Context as HasContext>::TransformFeedback;
-pub type DebugCallback = Box<dyn FnMut(u32, u32, u32, u32, &str)>;
+pub type DebugCallback = Box<dyn FnMut(u32, u32, u32, u32, &str) + Send + Sync>;
 
 pub struct ActiveUniform {
  pub size: i32,
@@ -1191,7 +1191,7 @@ pub trait HasContext {
 
  unsafe fn debug_message_callback<F>(&mut self, callback: F)
  where
- F: FnMut(u32, u32, u32, u32, &str) + 'static;
+ F: FnMut(u32, u32, u32, u32, &str) + Send + Sync + 'static;
 
  unsafe fn get_debug_message_log(&self, count: u32) -> Vec<DebugMessageLogEntry>;
 

src/native.rs

@@ -19,6 +19,9 @@ struct DebugCallbackRawPtr {
  callback: *mut std::os::raw::c_void,
 }
 
+unsafe impl Send for DebugCallbackRawPtr {}
+unsafe impl Sync for DebugCallbackRawPtr {}
+
 impl Drop for DebugCallbackRawPtr {
  fn drop(&mut self) {
  unsafe {
@@ -2707,7 +2710,7 @@ impl HasContext for Context {
 
  unsafe fn debug_message_callback<F>(&mut self, callback: F)
  where
- F: FnMut(u32, u32, u32, u32, &str) + 'static,
+ F: FnMut(u32, u32, u32, u32, &str) + Send + Sync + 'static,
  {
  match self.debug_callback {
  Some(_) => {