task: add tokio::task::join_set::Builder::spawn_blocking (#6578)

Signed-off-by: hi-rustin <[email protected]>

tokio/src/task/join_set.rs

@@ -308,7 +308,7 @@ impl<T: 'static> JoinSet<T> {
 
     /// Tries to join one of the tasks in the set that has completed and return its output.
     ///
-    /// Returns `None` if the set is empty.    
+    /// Returns `None` if the set is empty.
     pub fn try_join_next(&mut self) -> Option<Result<T, JoinError>> {
         // Loop over all notified `JoinHandle`s to find one that's ready, or until none are left.
         loop {
@@ -623,6 +623,51 @@ impl<'a, T: 'static> Builder<'a, T> {
         Ok(self.joinset.insert(self.builder.spawn_on(future, handle)?))
     }
 
+    /// Spawn the blocking code on the blocking threadpool with this builder's
+    /// settings, and store it in the [`JoinSet`].
+    ///
+    /// # Returns
+    ///
+    /// An [`AbortHandle`] that can be used to remotely cancel the task.
+    ///
+    /// # Panics
+    ///
+    /// This method panics if called outside of a Tokio runtime.
+    ///
+    /// [`JoinSet`]: crate::task::JoinSet
+    /// [`AbortHandle`]: crate::task::AbortHandle
+    #[track_caller]
+    pub fn spawn_blocking<F>(self, f: F) -> std::io::Result<AbortHandle>
+    where
+        F: FnOnce() -> T,
+        F: Send + 'static,
+        T: Send,
+    {
+        Ok(self.joinset.insert(self.builder.spawn_blocking(f)?))
+    }
+
+    /// Spawn the blocking code on the blocking threadpool of the provided
+    /// runtime handle with this builder's settings, and store it in the
+    /// [`JoinSet`].
+    ///
+    /// # Returns
+    ///
+    /// An [`AbortHandle`] that can be used to remotely cancel the task.
+    ///
+    /// [`JoinSet`]: crate::task::JoinSet
+    /// [`AbortHandle`]: crate::task::AbortHandle
+    #[track_caller]
+    pub fn spawn_blocking_on<F>(self, f: F, handle: &Handle) -> std::io::Result<AbortHandle>
+    where
+        F: FnOnce() -> T,
+        F: Send + 'static,
+        T: Send,
+    {
+        Ok(self
+            .joinset
+            .insert(self.builder.spawn_blocking_on(f, handle)?))
+    }
+
     /// Spawn the provided task on the current [`LocalSet`] with this builder's
     /// settings, and store it in the [`JoinSet`].
     ///