rt: rename internal runtime::Kind to Scheduler (#5017)

The `runtime::Kind` enum doesn't really represent the runtime flavor,
but is an enumeration of the different scheduler types. This patch
renames the enum to reflect this.

At a later time, it is likely the `Scheduler` enum will be moved to
`tokio::runtime::scheduler`, but that is punted to a later PR.

This rename is to make space for other enums

tokio/src/runtime/builder.rs

@@ -832,7 +832,7 @@ impl Builder {
     }
 
     fn build_current_thread_runtime(&mut self) -> io::Result<Runtime> {
-        use crate::runtime::{Config, CurrentThread, HandleInner, Kind};
+        use crate::runtime::{Config, CurrentThread, HandleInner, Scheduler};
         use std::sync::Arc;
 
         let (driver, resources) = driver::Driver::new(self.get_cfg())?;
@@ -869,7 +869,7 @@ impl Builder {
         });
 
         Ok(Runtime {
-            kind: Kind::CurrentThread(scheduler),
+            scheduler: Scheduler::CurrentThread(scheduler),
             handle: Handle { inner },
             blocking_pool,
         })
@@ -952,7 +952,7 @@ cfg_rt_multi_thread! {
     impl Builder {
         fn build_threaded_runtime(&mut self) -> io::Result<Runtime> {
             use crate::loom::sys::num_cpus;
-            use crate::runtime::{Config, HandleInner, Kind, MultiThread};
+            use crate::runtime::{Config, HandleInner, Scheduler, MultiThread};
             use std::sync::Arc;
 
             let core_threads = self.worker_threads.unwrap_or_else(num_cpus);
@@ -996,7 +996,7 @@ cfg_rt_multi_thread! {
             launch.launch();
 
             Ok(Runtime {
-                kind: Kind::MultiThread(scheduler),
+                scheduler: Scheduler::MultiThread(scheduler),
                 handle,
                 blocking_pool,
             })

tokio/src/runtime/mod.rs

@@ -297,8 +297,8 @@ cfg_rt! {
     /// [`Builder`]: struct@Builder
     #[derive(Debug)]
     pub struct Runtime {
-        /// Task executor
-        kind: Kind,
+        /// Task scheduler
+        scheduler: Scheduler,
 
         /// Handle to runtime, also contains driver handles
         handle: Handle,
@@ -307,9 +307,9 @@ cfg_rt! {
         blocking_pool: BlockingPool,
     }
 
-    /// The runtime executor is either a multi-thread or a current-thread executor.
+    /// The runtime scheduler is either a multi-thread or a current-thread executor.
     #[derive(Debug)]
-    enum Kind {
+    enum Scheduler {
         /// Execute all tasks on the current-thread.
         CurrentThread(CurrentThread),
 
@@ -491,10 +491,10 @@ cfg_rt! {
 
             let _enter = self.enter();
 
-            match &self.kind {
-                Kind::CurrentThread(exec) => exec.block_on(future),
+            match &self.scheduler {
+                Scheduler::CurrentThread(exec) => exec.block_on(future),
                 #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
-                Kind::MultiThread(exec) => exec.block_on(future),
+                Scheduler::MultiThread(exec) => exec.block_on(future),
             }
         }
 
@@ -609,8 +609,8 @@ cfg_rt! {
     #[allow(clippy::single_match)] // there are comments in the error branch, so we don't want if-let
     impl Drop for Runtime {
         fn drop(&mut self) {
-            match &mut self.kind {
-                Kind::CurrentThread(current_thread) => {
+            match &mut self.scheduler {
+                Scheduler::CurrentThread(current_thread) => {
                     // This ensures that tasks spawned on the current-thread
                     // runtime are dropped inside the runtime's context.
                     match self::context::try_enter(self.handle.clone()) {
@@ -624,7 +624,7 @@ cfg_rt! {
                     }
                 },
                 #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
-                Kind::MultiThread(_) => {
+                Scheduler::MultiThread(_) => {
                     // The threaded scheduler drops its tasks on its worker threads, which is
                     // already in the runtime's context.
                 },