Draft: Add BWoS-queue backend to tokio

tokio/Cargo.toml

@@ -24,7 +24,7 @@ keywords = ["io", "async", "non-blocking", "futures"]
 [features]
 # Include nothing by default
 default = []
-
+bwos = []
 # enable everything
 full = [
   "fs",
@@ -37,6 +37,7 @@ full = [
   "rt",
   "rt-multi-thread",
   "signal",
+  "stats",
   "sync",
   "time",
 ]
@@ -72,6 +73,7 @@ process = [
 # Includes basic task execution capabilities
 rt = []
 rt-multi-thread = [
+  "bwos",
   "num_cpus",
   "rt",
 ]

tokio/src/macros/cfg.rs

@@ -196,7 +196,7 @@ macro_rules! cfg_metrics {
         $(
             // For now, metrics is only disabled in loom tests.
             // When stabilized, it might have a dedicated feature flag.
-            #[cfg(all(tokio_unstable, not(loom)))]
+            #[cfg(all(tokio_unstable, not(loom), feature="stats"))]
             #[cfg_attr(docsrs, doc(cfg(tokio_unstable)))]
             $item
         )*
@@ -206,15 +206,15 @@ macro_rules! cfg_metrics {
 macro_rules! cfg_not_metrics {
     ($($item:item)*) => {
         $(
-            #[cfg(not(all(tokio_unstable, not(loom))))]
+            #[cfg(not(all(tokio_unstable, not(loom), feature = "stats")))]
             $item
         )*
     }
 }
 
 macro_rules! cfg_not_rt_and_metrics_and_net {
     ($($item:item)*) => {
-        $( #[cfg(not(all(feature = "net", feature = "rt", all(tokio_unstable, not(loom)))))]$item )*
+        $( #[cfg(not(all(feature = "net", feature = "rt", all(tokio_unstable, not(loom), feature = "stats"))))]$item )*
     }
 }
 
@@ -373,6 +373,21 @@ macro_rules! cfg_not_rt_multi_thread {
     }
 }
 
+macro_rules! cfg_rt_multi_thread_bwos {
+    ($($item:item)*) => {
+        $(
+            #[cfg(all(
+                tokio_unstable,
+                feature = "rt-multi-thread",
+                feature = "bwos",
+                not(tokio_wasi)
+            ))]
+            #[cfg_attr(docsrs, doc(cfg(feature = "bwos")))]
+            $item
+        )*
+    }
+}
+
 macro_rules! cfg_taskdump {
     ($($item:item)*) => {
         $(

tokio/src/runtime/builder.rs

@@ -188,11 +188,25 @@ cfg_unstable! {
 
 pub(crate) type ThreadNameFn = std::sync::Arc<dyn Fn() -> String + Send + Sync + 'static>;
 
+cfg_rt_multi_thread!(
+    #[derive(Clone, Copy)]
+    #[allow(dead_code)]
+    pub(crate) enum MultiThreadFlavor {
+        /// The default multithreaded tokio runqueue, based on the golang runqueue.
+        Default,
+        // There may be more (sub-) variants in the future influencing e.g. queue size
+        // or stealing strategy
+        /// A Block-based workstealing queue offering better performance
+        //#[cfg(all(tokio_unstable, feature = "bwos"))]
+        Bwos,
+    }
+);
+
 #[derive(Clone, Copy)]
 pub(crate) enum Kind {
     CurrentThread,
     #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
-    MultiThread,
+    MultiThread(MultiThreadFlavor),
 }
 
 impl Builder {
@@ -214,15 +228,23 @@ impl Builder {
         Builder::new(Kind::CurrentThread, 31, EVENT_INTERVAL)
     }
 
-    cfg_not_wasi! {
+    cfg_rt_multi_thread! {
         /// Returns a new builder with the multi thread scheduler selected.
         ///
         /// Configuration methods can be chained on the return value.
-        #[cfg(feature = "rt-multi-thread")]
-        #[cfg_attr(docsrs, doc(cfg(feature = "rt-multi-thread")))]
         pub fn new_multi_thread() -> Builder {
             // The number `61` is fairly arbitrary. I believe this value was copied from golang.
-            Builder::new(Kind::MultiThread, 61, 61)
+            Builder::new(Kind::MultiThread(MultiThreadFlavor::Bwos), 61, 61)
+        }
+    }
+
+    cfg_rt_multi_thread_bwos! {
+        /// Returns a new builder with the BWoS multi thread scheduler selected.
+        ///
+        /// Configuration methods can be chained on the return value.
+        pub fn new_multi_thread_bwos() -> Builder {
+            // The number `61` is copied from `new_multi_thread()`.
+            Builder::new(Kind::MultiThread(MultiThreadFlavor::Bwos), 61, 61)
         }
     }
 
@@ -649,7 +671,7 @@ impl Builder {
         match &self.kind {
             Kind::CurrentThread => self.build_current_thread_runtime(),
             #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
-            Kind::MultiThread => self.build_threaded_runtime(),
+            Kind::MultiThread(flavor) => self.build_threaded_runtime(*flavor),
         }
     }
 
@@ -658,7 +680,7 @@ impl Builder {
             enable_pause_time: match self.kind {
                 Kind::CurrentThread => true,
                 #[cfg(all(feature = "rt-multi-thread", not(tokio_wasi)))]
-                Kind::MultiThread => false,
+                Kind::MultiThread(_) => false,
             },
             enable_io: self.enable_io,
             enable_time: self.enable_time,
@@ -1163,7 +1185,7 @@ cfg_test_util! {
 
 cfg_rt_multi_thread! {
     impl Builder {
-        fn build_threaded_runtime(&mut self) -> io::Result<Runtime> {
+        fn build_threaded_runtime(&mut self, flavor: MultiThreadFlavor) -> io::Result<Runtime> {
             use crate::loom::sys::num_cpus;
             use crate::runtime::{Config, runtime::Scheduler};
             use crate::runtime::scheduler::{self, MultiThread};
@@ -1183,6 +1205,7 @@ cfg_rt_multi_thread! {
 
             let (scheduler, handle, launch) = MultiThread::new(
                 core_threads,
+                flavor,
                 driver,
                 driver_handle,
                 blocking_spawner,

tokio/src/runtime/scheduler/multi_thread/mod.rs

@@ -14,6 +14,8 @@ pub(crate) use park::{Parker, Unparker};
 
 pub(crate) mod queue;
 
+//pub(crate) mod queue;
+
 mod worker;
 pub(crate) use worker::{Context, Launch};
 
@@ -27,6 +29,7 @@ use crate::runtime::{
 };
 use crate::util::RngSeedGenerator;
 
+use crate::runtime::builder::MultiThreadFlavor;
 use std::fmt;
 use std::future::Future;
 
@@ -38,6 +41,7 @@ pub(crate) struct MultiThread;
 impl MultiThread {
     pub(crate) fn new(
         size: usize,
+        flavor: MultiThreadFlavor,
         driver: Driver,
         driver_handle: driver::Handle,
         blocking_spawner: blocking::Spawner,
@@ -47,6 +51,7 @@ impl MultiThread {
         let parker = Parker::new(driver);
         let (handle, launch) = worker::create(
             size,
+            flavor,
             parker,
             driver_handle,
             blocking_spawner,