rt: add a method to determine if the flavor of the runtime.

tokio/src/runtime/handle.rs

@@ -1,4 +1,4 @@
-use crate::runtime::scheduler;
+use crate::runtime::{scheduler, Flavor};
 
 /// Handle to the runtime.
 ///
@@ -101,6 +101,32 @@ impl Handle {
         }
     }
 
+    /// Returns the flavor of the current `Runtime`.
+    ///
+    /// ```
+    /// use tokio::runtime::{Handle, Flavor};
+    ///
+    /// #[tokio::main(flavor = "current_thread")]
+    /// async fn main() {
+    ///   assert_eq!(Flavor::CurrentThread, Handle::current().get_flavor());
+    /// }
+    /// ```
+    ///
+    /// ```
+    /// use tokio::runtime::{Handle, Flavor};
+    ///
+    /// #[tokio::main(flavor = "multi_thread", worker_threads = 4)]
+    /// async fn main() {
+    ///   assert_eq!(Flavor::MultiThread, Handle::current().get_flavor());
+    /// }
+    /// ```
+    pub fn get_flavor(&self) -> Flavor {
+        match self.inner {
+            scheduler::Handle::CurrentThread(_) => Flavor::CurrentThread,
+            scheduler::Handle::MultiThread(_) => Flavor::MultiThread,
+        }
+    }
+
     /// Returns a Handle view over the currently running Runtime
     ///
     /// Returns an error if no Runtime has been started

tokio/src/runtime/mod.rs

@@ -312,6 +312,15 @@ cfg_rt! {
         blocking_pool: BlockingPool,
     }
 
+    /// The flavor of the `Runtime`.
+    #[derive(Debug, PartialEq)]
+    pub enum Flavor {
+        /// The flavor that executes all tasks on the current thread.
+        CurrentThread,
+        /// The flavor that executes tasks across multiple threads.
+        MultiThread,
+    }
+
     /// The runtime scheduler is either a multi-thread or a current-thread executor.
     #[derive(Debug)]
     enum Scheduler {