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use crate::io::*;
use crate::proc::task::*;
use alloc::collections::VecDeque;
use lazy_static::lazy_static;
use spin::Mutex;
// the global scheduler takes a spinlock (will change later). Must be extra
// careful with it: never do context swap before releasing the lock on scheduler,
// otherwise the next task won't be able to aquire the lock again.
lazy_static! {
pub static ref SCHEDULER: Mutex<Scheduler> = Mutex::new(Scheduler::new());
}
// TODO the lifetime here is pretty much broken. Fix this later
// the scheduler should be a per-cpu instance and it shall not lock.
// Because the `do_schedule` does not return to release the lock
pub struct Scheduler {
pub run_queue: VecDeque<TaskId>,
}
impl Scheduler {
pub const MIN_TASK_CAP: usize = 16;
pub fn new() -> Self {
Self {
// btw. try_with_capacity is an unstable feature.
run_queue: VecDeque::try_with_capacity(16).unwrap(),
}
}
// maybe we reject inserting existing tasks?
pub fn insert_task(&mut self, tid: TaskId) {
self.run_queue.push_back(tid);
}
pub fn try_remove(&mut self, _tid: TaskId) {
// try to remove all occurence of tid in the run_queue maybe do
// something special if the task is in the wait queue but we are not
// there yet.
todo!("not implemented");
}
// pop front, push back
pub fn do_schedule() {
// TODO: remove this spinlock, because we should protect the scheduler
// with irq_save/restore
if SCHEDULER.is_locked() {
panic!("scheduler lock has been taken, something wrong");
}
let mut lock_guard = SCHEDULER.lock();
let next_tid = lock_guard
.run_queue
.pop_front()
.expect("empty run queue, how?");
let next_task = next_tid.get_task_ref_mut();
let me = Task::current().unwrap();
lock_guard.run_queue.push_back(next_tid);
if me.pid == next_task.pid {
return;
}
// make sure we release the scheduler lock before doing context
// swap
drop(lock_guard);
unsafe {
context_swap(
&(me.context) as *const _ as u64,
&(next_task.context) as *const _ as u64,
);
}
}
// like do_schedule but we there is no running context to save
pub fn kickoff() {
if SCHEDULER.is_locked() {
panic!("scheduler lock has been taken, something wrong");
}
let mut lock_guard = SCHEDULER.lock();
let t = lock_guard
.run_queue
.pop_front()
.expect("run queue empty, can't start");
let first_task = t.get_task_ref_mut();
lock_guard.run_queue.push_back(t);
drop(lock_guard);
unsafe {
context_swap_to(&(first_task.context) as *const _ as u64);
}
}
}
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