improve rescheduling

src/rt/runtime.rs

@@ -50,6 +50,16 @@ struct Scheduler {
     machines: Vec<Arc<Machine>>,
 }
 
+impl Scheduler {
+    /// Get the next machine that has no work yet, if there is any.
+    fn next_idle_machine(&self) -> Option<Arc<Machine>> {
+        self.machines
+            .iter()
+            .find(|m| !m.has_work())
+            .map(|m| m.clone())
+    }
+}
+
 struct ThreadState {
     unparker: Unparker,
     parked: Arc<atomic::AtomicBool>,
@@ -258,8 +268,23 @@ impl Runtime {
                                         // run it
                                         m.run(self);
 
-                                        // when run ends, go into parked mode again
+                                        // when run ends
                                         {
+                                            // see if there are any available processors 
+                                            let mut sched = self.sched.lock().unwrap();
+                                            if let Some(p) = sched.processors.pop() {
+                                                // get a machine
+                                                if let Some(m) = sched.next_idle_machine(){
+                                                    *m.processor.lock() = Some(p);
+                                                    MACHINE.with(|machine| {
+                                                        machine.borrow_mut().replace(m);
+                                                    });
+                                                    continue;
+                                                }
+                                            }
+                                            drop(sched);
+
+                                            // go into parked mode, no work
                                             MACHINE.with(|machine| {
                                                 *machine.borrow_mut() = None;
                                             });
@@ -314,9 +339,8 @@ impl Runtime {
             #[cfg(feature = "tracing")]
             self.poll_count.fetch_add(1, Ordering::Relaxed);
             // if !sched.progress {
-
             if let Some(p) = sched.processors.pop() {
-                if let Some(m) = sched.machines.iter().find(|m| m.processor.lock().is_none()) {
+                if let Some(m) = sched.next_idle_machine() {
                     // find idle m
                     *m.processor.lock() = Some(p);
                     to_start.push(m.clone());
@@ -370,6 +394,15 @@ impl Machine {
         }
     }
 
+    fn has_work(&self) -> bool {
+        if let Some(p) = &*self.processor.lock() {
+            // TODO: is this the right check?
+            p.has_work()
+        } else {
+            false
+        }
+    }
+
     /// Schedules a task onto the machine.
     fn schedule(&self, rt: &Runtime, task: Runnable) {
         match self.processor.lock().as_mut() {
@@ -498,12 +531,7 @@ impl Machine {
             // If another thread is already blocked on the reactor, there is no point in keeping
             // the current thread around since there is too little work to do.
             if sched.polling {
-                if sched.machines.len() > MIN_MACHINES {
-                    break;
-                } else {
-                    // thread::sleep(Duration::from_micros(10));
-                    continue;
-                }
+                break;
             }
 
             // Take out the machine associated with the current thread.
@@ -566,6 +594,11 @@ impl Processor {
         }
     }
 
+    /// Is there any available work for this processor?
+    fn has_work(&self) -> bool {
+        self.slot.is_some() || !self.worker.is_empty()
+    }
+
     /// Schedules a task to run on this processor.
     fn schedule(&mut self, rt: &Runtime, task: Runnable) {
         match self.slot.replace(task) {