Add a yield_now function and use it in idle thread

src/main.rs

@@ -74,6 +74,7 @@ fn kernel_main(boot_info: &'static BootInfo) -> ! {
 fn idle_thread() -> ! {
     loop {
         x86_64::instructions::hlt();
+        multitasking::yield_now();
     }
 }
 

src/multitasking/mod.rs

@@ -9,6 +9,7 @@ static SCHEDULER: spin::Mutex<Option<Scheduler>> = spin::Mutex::new(None);
 #[repr(u64)]
 pub enum SwitchReason {
     Paused,
+    Yield,
     Blocked,
     Exit,
 }
@@ -29,19 +30,22 @@ pub fn invoke_scheduler() {
 }
 
 pub fn exit_thread() -> ! {
+    synchronous_context_switch(SwitchReason::Exit).expect("can't exit last thread");
+    unreachable!("finished thread continued");
+}
+
+pub fn yield_now() {
+    let _ = synchronous_context_switch(SwitchReason::Yield);
+}
+
+fn synchronous_context_switch(reason: SwitchReason) -> Result<(), ()> {
     let next = with_scheduler(|s| s.schedule());
     match next {
-        Some((next_stack_pointer, prev_thread_id)) => {
-            unsafe {
-                context_switch::context_switch_to(
-                    next_stack_pointer,
-                    prev_thread_id,
-                    SwitchReason::Exit,
-                )
-            }
-            unreachable!("finished thread continued")
-        }
-        None => panic!("can't exit last thread"),
+        Some((next_stack_pointer, prev_thread_id)) => unsafe {
+            context_switch::context_switch_to(next_stack_pointer, prev_thread_id, reason);
+            Ok(())
+        },
+        None => Err(()),
     }
 }
 

src/multitasking/scheduler.rs

@@ -74,7 +74,9 @@ impl Scheduler {
             return; // do nothing
         }
         match switch_reason {
-            SwitchReason::Paused => self.paused_threads.push_back(paused_thread_id),
+            SwitchReason::Paused | SwitchReason::Yield => {
+                self.paused_threads.push_back(paused_thread_id)
+            }
             SwitchReason::Blocked => {
                 self.blocked_threads.insert(paused_thread_id);
                 self.check_for_wakeup(paused_thread_id);