rt: add missing Send bound (#3089)

tokio/Cargo.toml

@@ -98,7 +98,7 @@ bytes = { version = "0.6.0", optional = true }
 futures-core = { version = "0.3.0", optional = true }
 lazy_static = { version = "1.0.2", optional = true }
 memchr = { version = "2.2", optional = true }
-mio = { version = "0.7.3", optional = true }
+mio = { version = "0.7.5", optional = true }
 num_cpus = { version = "1.8.0", optional = true }
 parking_lot = { version = "0.11.0", optional = true } # Not in full
 slab = { version = "0.4.1", optional = true }
@@ -134,4 +134,4 @@ all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
 [package.metadata.playground]
-features = ["full"]
+features = ["full"]

tokio/src/runtime/blocking/pool.rs

@@ -70,6 +70,7 @@ const KEEP_ALIVE: Duration = Duration::from_secs(10);
 pub(crate) fn spawn_blocking<F, R>(func: F) -> JoinHandle<R>
 where
     F: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
 {
     let rt = context::current().expect("not currently running on the Tokio runtime.");
     rt.spawn_blocking(func)
@@ -79,6 +80,7 @@ where
 pub(crate) fn try_spawn_blocking<F, R>(func: F) -> Result<(), ()>
 where
     F: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
 {
     let rt = context::current().expect("not currently running on the Tokio runtime.");
 

tokio/src/runtime/blocking/task.rs

@@ -19,7 +19,8 @@ impl<T> Unpin for BlockingTask<T> {}
 
 impl<T, R> Future for BlockingTask<T>
 where
-    T: FnOnce() -> R,
+    T: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
 {
     type Output = R;
 

tokio/src/runtime/handle.rs

@@ -45,6 +45,7 @@ impl Handle {
     pub(crate) fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R>
     where
         F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
     {
         #[cfg(feature = "tracing")]
         let func = {

tokio/src/runtime/mod.rs

@@ -392,6 +392,7 @@ cfg_rt! {
         pub fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R>
         where
             F: FnOnce() -> R + Send + 'static,
+            R: Send + 'static,
         {
             self.handle.spawn_blocking(func)
         }