rt: clean up arguments passed to basic scheduler (#4767)

Extracts the refactor from #4518.

The basic scheduler takes many configuration options as arguments to the
constructor. This cleans it up a bit by defining a `Config` struct and
using that to pass arguments to the constructor.

tokio/src/runtime/basic_scheduler.rs

@@ -57,12 +57,6 @@ struct Core {
 
     /// Metrics batch
     metrics: MetricsBatch,
-
-    /// How many ticks before pulling a task from the global/remote queue?
-    global_queue_interval: u32,
-
-    /// How many ticks before yielding to the driver for timer and I/O events?
-    event_interval: u32,
 }
 
 #[derive(Clone)]
@@ -70,6 +64,20 @@ pub(crate) struct Spawner {
     shared: Arc<Shared>,
 }
 
+pub(crate) struct Config {
+    /// How many ticks before pulling a task from the global/remote queue?
+    pub(crate) global_queue_interval: u32,
+
+    /// How many ticks before yielding to the driver for timer and I/O events?
+    pub(crate) event_interval: u32,
+
+    /// Callback for a worker parking itself
+    pub(crate) before_park: Option<Callback>,
+
+    /// Callback for a worker unparking itself
+    pub(crate) after_unpark: Option<Callback>,
+}
+
 /// Scheduler state shared between threads.
 struct Shared {
     /// Remote run queue. None if the `Runtime` has been dropped.
@@ -87,11 +95,8 @@ struct Shared {
     /// Handle to I/O driver, timer, blocking pool, ...
     handle_inner: HandleInner,
 
-    /// Callback for a worker parking itself
+    /// Scheduler configuration options
-    before_park: Option<Callback>,
+    config: Config,
-
-    /// Callback for a worker unparking itself
-    after_unpark: Option<Callback>,
 
     /// Keeps track of various runtime metrics.
     scheduler_metrics: SchedulerMetrics,
@@ -117,14 +122,7 @@ const INITIAL_CAPACITY: usize = 64;
 scoped_thread_local!(static CURRENT: Context);
 
 impl BasicScheduler {
-    pub(crate) fn new(
+    pub(crate) fn new(driver: Driver, handle_inner: HandleInner, config: Config) -> BasicScheduler {
-        driver: Driver,
-        handle_inner: HandleInner,
-        before_park: Option<Callback>,
-        after_unpark: Option<Callback>,
-        global_queue_interval: u32,
-        event_interval: u32,
-    ) -> BasicScheduler {
         let unpark = driver.unpark();
 
         let spawner = Spawner {
@@ -134,8 +132,7 @@ impl BasicScheduler {
                 unpark,
                 woken: AtomicBool::new(false),
                 handle_inner,
-                before_park,
+                config,
-                after_unpark,
                 scheduler_metrics: SchedulerMetrics::new(),
                 worker_metrics: WorkerMetrics::new(),
             }),
@@ -147,8 +144,6 @@ impl BasicScheduler {
             tick: 0,
             driver: Some(driver),
             metrics: MetricsBatch::new(),
-            global_queue_interval,
-            event_interval,
         })));
 
         BasicScheduler {
@@ -302,7 +297,7 @@ impl Context {
     fn park(&self, mut core: Box<Core>) -> Box<Core> {
         let mut driver = core.driver.take().expect("driver missing");
 
-        if let Some(f) = &self.spawner.shared.before_park {
+        if let Some(f) = &self.spawner.shared.config.before_park {
             // Incorrect lint, the closures are actually different types so `f`
             // cannot be passed as an argument to `enter`.
             #[allow(clippy::redundant_closure)]
@@ -325,7 +320,7 @@ impl Context {
             core.metrics.returned_from_park();
         }
 
-        if let Some(f) = &self.spawner.shared.after_unpark {
+        if let Some(f) = &self.spawner.shared.config.after_unpark {
             // Incorrect lint, the closures are actually different types so `f`
             // cannot be passed as an argument to `enter`.
             #[allow(clippy::redundant_closure)]
@@ -515,12 +510,12 @@ impl CoreGuard<'_> {
                     }
                 }
 
-                for _ in 0..core.event_interval {
+                for _ in 0..core.spawner.shared.config.event_interval {
                     // Get and increment the current tick
                     let tick = core.tick;
                     core.tick = core.tick.wrapping_add(1);
 
-                    let entry = if tick % core.global_queue_interval == 0 {
+                    let entry = if tick % core.spawner.shared.config.global_queue_interval == 0 {
                         core.spawner.pop().or_else(|| core.tasks.pop_front())
                     } else {
                         core.tasks.pop_front().or_else(|| core.spawner.pop())

tokio/src/runtime/builder.rs

@@ -632,6 +632,7 @@ impl Builder {
     }
 
     fn build_basic_runtime(&mut self) -> io::Result<Runtime> {
+        use crate::runtime::basic_scheduler::Config;
         use crate::runtime::{BasicScheduler, HandleInner, Kind};
 
         let (driver, resources) = driver::Driver::new(self.get_cfg())?;
@@ -655,10 +656,12 @@ impl Builder {
         let scheduler = BasicScheduler::new(
             driver,
             handle_inner,
-            self.before_park.clone(),
+            Config {
-            self.after_unpark.clone(),
+                before_park: self.before_park.clone(),
-            self.global_queue_interval,
+                after_unpark: self.after_unpark.clone(),
-            self.event_interval,
+                global_queue_interval: self.global_queue_interval,
+                event_interval: self.event_interval,
+            },
         );
         let spawner = Spawner::Basic(scheduler.spawner().clone());