From 229029f2da1156f5ef6c2a556575e7685cb6bfa1 Mon Sep 17 00:00:00 2001
From: Victor Berger <vberger@users.noreply.github.com>
Date: Wed, 18 Oct 2017 20:40:21 +0200
Subject: [PATCH] Formalize thread-safety guarantees (#322)

---
 CHANGELOG.md                    |  2 ++
 src/lib.rs                      |  7 +++++++
 src/os/unix.rs                  | 10 ++++++++--
 tests/events_loop_proxy_send.rs |  8 --------
 tests/send_objects.rs           | 23 +++++++++++++++++++++++
 5 files changed, 40 insertions(+), 10 deletions(-)
 delete mode 100644 tests/events_loop_proxy_send.rs
 create mode 100644 tests/send_objects.rs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1cfa5bdc..62d62ca2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,8 @@
 - Added method `MonitorId::get_hidpi_factor`.
 - Deprecated `get_inner_size_pixels` and `get_inner_size_points` methods of `Window` in favor of
 `get_inner_size`.
+- **Breaking:** `EventsLoop` is `!Send` and `!Sync` because of platform-dependant constraints,
+  but `Window`, `WindowId`, `DeviceId` and `MonitorId` guaranteed to be `Send`.
 
 # Version 0.8.3 (2017-10-11)
 
diff --git a/src/lib.rs b/src/lib.rs
index 165713ff..90653659 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -167,8 +167,14 @@ pub struct DeviceId(platform::DeviceId);
 /// an events loop opens a connection to the X or Wayland server.
 ///
 /// To wake up an `EventsLoop` from a another thread, see the `EventsLoopProxy` docs.
+///
+/// Note that the `EventsLoop` cannot be shared accross threads (due to platform-dependant logic
+/// forbiding it), as such it is neither `Send` nor `Sync`. If you need cross-thread access, the
+/// `Window` created from this `EventsLoop` _can_ be sent to an other thread, and the
+/// `EventsLoopProxy` allows you to wakeup an `EventsLoop` from an other thread.
 pub struct EventsLoop {
     events_loop: platform::EventsLoop,
+    _marker: ::std::marker::PhantomData<*mut ()> // Not Send nor Sync
 }
 
 /// Returned by the user callback given to the `EventsLoop::run_forever` method.
@@ -192,6 +198,7 @@ impl EventsLoop {
     pub fn new() -> EventsLoop {
         EventsLoop {
             events_loop: platform::EventsLoop::new(),
+            _marker: ::std::marker::PhantomData,
         }
     }
 
diff --git a/src/os/unix.rs b/src/os/unix.rs
index e743e426..e6d43628 100644
--- a/src/os/unix.rs
+++ b/src/os/unix.rs
@@ -41,7 +41,12 @@ pub trait EventsLoopExt {
 impl EventsLoopExt for EventsLoop {
     #[inline]
     fn new_x11() -> Result<Self, XNotSupported> {
-        LinuxEventsLoop::new_x11().map(|ev| EventsLoop { events_loop: ev })
+        LinuxEventsLoop::new_x11().map(|ev|
+            EventsLoop {
+                events_loop: ev,
+                _marker: ::std::marker::PhantomData,
+            }
+        )
     }
 
     #[inline]
@@ -50,7 +55,8 @@ impl EventsLoopExt for EventsLoop {
             events_loop: match LinuxEventsLoop::new_wayland() {
                 Ok(e) => e,
                 Err(_) => panic!()      // TODO: propagate
-            }
+            },
+            _marker: ::std::marker::PhantomData,
         }
     }
 
diff --git a/tests/events_loop_proxy_send.rs b/tests/events_loop_proxy_send.rs
deleted file mode 100644
index 5c44aa13..00000000
--- a/tests/events_loop_proxy_send.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-extern crate winit;
-
-#[test]
-fn events_loop_proxy_send() {
-    // ensures that `winit::EventsLoopProxy` implements `Send`
-    fn needs_send<T:Send>() {}
-    needs_send::<winit::EventsLoopProxy>();
-}
diff --git a/tests/send_objects.rs b/tests/send_objects.rs
new file mode 100644
index 00000000..f3328c10
--- /dev/null
+++ b/tests/send_objects.rs
@@ -0,0 +1,23 @@
+extern crate winit;
+
+fn needs_send<T:Send>() {}
+
+#[test]
+fn events_loop_proxy_send() {
+    // ensures that `winit::EventsLoopProxy` implements `Send`
+    needs_send::<winit::EventsLoopProxy>();
+}
+
+#[test]
+fn window_send() {
+    // ensures that `winit::Window` implements `Send`
+    needs_send::<winit::Window>();
+}
+
+#[test]
+fn ids_send() {
+    // ensures that the various `..Id` types implement `Send`
+    needs_send::<winit::WindowId>();
+    needs_send::<winit::DeviceId>();
+    needs_send::<winit::MonitorId>();
+}