diff --git a/crate/thread/src/lib.rs b/crate/thread/src/lib.rs
index af97063..242c984 100644
--- a/crate/thread/src/lib.rs
+++ b/crate/thread/src/lib.rs
@@ -2,7 +2,6 @@
 #![feature(alloc)]
 #![feature(const_fn)]
 #![feature(linkage)]
-#![feature(nll)]
 #![feature(vec_resize_default)]
 #![feature(asm)]
 #![feature(exact_size_is_empty)]
diff --git a/crate/thread/src/scheduler.rs b/crate/thread/src/scheduler.rs
deleted file mode 100644
index a73960d..0000000
--- a/crate/thread/src/scheduler.rs
+++ /dev/null
@@ -1,242 +0,0 @@
-use alloc::{collections::BinaryHeap, vec::Vec};
-use log::*;
-
-type Pid = usize;
-
-///
-pub trait Scheduler {
-    fn insert(&mut self, pid: Pid);
-    fn remove(&mut self, pid: Pid);
-    fn select(&mut self) -> Option<Pid>;
-    fn tick(&mut self, current: Pid) -> bool;   // need reschedule?
-    fn set_priority(&mut self, pid: Pid, priority: u8);
-    fn move_to_head(&mut self, pid: Pid);
-}
-
-pub use self::rr::RRScheduler;
-pub use self::stride::StrideScheduler;
-
-mod rr {
-    use super::*;
-
-    pub struct RRScheduler {
-        max_time_slice: usize,
-        infos: Vec<RRProcInfo>,
-    }
-
-    #[derive(Debug, Default, Copy, Clone)]
-    struct RRProcInfo {
-        present: bool,
-        rest_slice: usize,
-        prev: Pid,
-        next: Pid,
-    }
-
-    impl Scheduler for RRScheduler {
-        fn insert(&mut self, pid: Pid) {
-            let pid = pid + 1;
-            expand(&mut self.infos, pid);
-            {
-                let info = &mut self.infos[pid];
-                assert!(!info.present);
-                info.present = true;
-                if info.rest_slice == 0 {
-                    info.rest_slice = self.max_time_slice;
-                }
-            }
-            self._list_add_before(pid, 0);
-            trace!("rr insert {}", pid - 1);
-        }
-
-        fn remove(&mut self, pid: Pid) {
-            let pid = pid + 1;
-            assert!(self.infos[pid].present);
-            self.infos[pid].present = false;
-            self._list_remove(pid);
-            trace!("rr remove {}", pid - 1);
-        }
-
-        fn select(&mut self) -> Option<Pid> {
-            let ret = match self.infos[0].next {
-                0 => None,
-                i => Some(i - 1),
-            };
-            trace!("rr select {:?}", ret);
-            ret
-        }
-
-        fn tick(&mut self, current: Pid) -> bool {
-            let current = current + 1;
-            expand(&mut self.infos, current);
-            assert!(!self.infos[current].present);
-
-            let rest = &mut self.infos[current].rest_slice;
-            if *rest > 0 {
-                *rest -= 1;
-            } else {
-                warn!("current process rest_slice = 0, need reschedule")
-            }
-            *rest == 0
-        }
-
-        fn set_priority(&mut self, _pid: usize, _priority: u8) {
-        }
-
-        fn move_to_head(&mut self, pid: usize) {
-            let pid = pid + 1;
-            assert!(self.infos[pid].present);
-            self._list_remove(pid);
-            self._list_add_after(pid, 0);
-            trace!("rr move_to_head {}", pid - 1);
-        }
-    }
-
-    impl RRScheduler {
-        pub fn new(max_time_slice: usize) -> Self {
-            RRScheduler {
-                max_time_slice,
-                infos: Vec::default(),
-            }
-        }
-        fn _list_add_before(&mut self, i: Pid, at: Pid) {
-            let prev = self.infos[at].prev;
-            self.infos[i].next = at;
-            self.infos[i].prev = prev;
-            self.infos[prev].next = i;
-            self.infos[at].prev = i;
-        }
-        fn _list_add_after(&mut self, i: Pid, at: Pid) {
-            let next = self.infos[at].next;
-            self._list_add_before(i, next);
-        }
-        fn _list_remove(&mut self, i: Pid) {
-            let next = self.infos[i].next;
-            let prev = self.infos[i].prev;
-            self.infos[next].prev = prev;
-            self.infos[prev].next = next;
-            self.infos[i].next = 0;
-            self.infos[i].prev = 0;
-        }
-    }
-}
-
-mod stride {
-    use super::*;
-
-    pub struct StrideScheduler {
-        max_time_slice: usize,
-        infos: Vec<StrideProcInfo>,
-        queue: BinaryHeap<(Stride, Pid)>, // It's max heap, so pass < 0
-    }
-
-    #[derive(Debug, Default, Copy, Clone)]
-    struct StrideProcInfo {
-        present: bool,
-        rest_slice: usize,
-        stride: Stride,
-        priority: u8,
-    }
-
-    impl StrideProcInfo {
-        fn pass(&mut self) {
-            const BIG_STRIDE: Stride = 1 << 20;
-            let pass = if self.priority == 0 {
-                BIG_STRIDE
-            } else {
-                BIG_STRIDE / self.priority as Stride
-            };
-            // FIXME: overflowing_add is not working ???
-            // self.stride.overflowing_add(pass);
-            self.stride += pass;
-        }
-    }
-
-    type Stride = i32;
-
-    impl Scheduler for StrideScheduler {
-        fn insert(&mut self, pid: Pid) {
-            expand(&mut self.infos, pid);
-            let info = &mut self.infos[pid];
-            assert!(!info.present);
-            info.present = true;
-            if info.rest_slice == 0 {
-                info.rest_slice = self.max_time_slice;
-            }
-            self.queue.push((-info.stride, pid));
-            trace!("stride insert {}", pid);
-        }
-
-        fn remove(&mut self, pid: Pid) {
-            let info = &mut self.infos[pid];
-            assert!(info.present);
-            info.present = false;
-            if self.queue.peek().is_some() && self.queue.peek().unwrap().1 == pid {
-                self.queue.pop();
-            } else {
-                // BinaryHeap only support pop the top.
-                // So in order to remove an arbitrary element,
-                // we have to take all elements into a Vec,
-                // then push the rest back.
-                let rest: Vec<_> = self.queue.drain().filter(|&p| p.1 != pid).collect();
-                use core::iter::FromIterator;
-                self.queue = BinaryHeap::from_iter(rest.into_iter());
-            }
-            trace!("stride remove {}", pid);
-        }
-
-        fn select(&mut self) -> Option<Pid> {
-            let ret = self.queue.peek().map(|&(_, pid)| pid);
-            if let Some(pid) = ret {
-                let old_stride = self.infos[pid].stride;
-                self.infos[pid].pass();
-                let stride = self.infos[pid].stride;
-                trace!("stride {} {:#x} -> {:#x}", pid, old_stride, stride);
-            }
-            trace!("stride select {:?}", ret);
-            ret
-        }
-
-        fn tick(&mut self, current: Pid) -> bool {
-            expand(&mut self.infos, current);
-            assert!(!self.infos[current].present);
-
-            let rest = &mut self.infos[current].rest_slice;
-            if *rest > 0 {
-                *rest -= 1;
-            } else {
-                warn!("current process rest_slice = 0, need reschedule")
-            }
-            *rest == 0
-        }
-
-        fn set_priority(&mut self, pid: Pid, priority: u8) {
-            self.infos[pid].priority = priority;
-            trace!("stride {} priority = {}", pid, priority);
-        }
-
-        fn move_to_head(&mut self, pid: Pid) {
-            if self.queue.peek().is_some() {
-                let stride = -self.queue.peek().unwrap().0;
-                self.remove(pid);
-                self.infos[pid].stride = stride;
-                self.insert(pid);
-            }
-        }
-    }
-
-    impl StrideScheduler {
-        pub fn new(max_time_slice: usize) -> Self {
-            StrideScheduler {
-                max_time_slice,
-                infos: Vec::default(),
-                queue: BinaryHeap::default(),
-            }
-        }
-    }
-}
-
-fn expand<T: Default + Clone>(vec: &mut Vec<T>, id: usize) {
-    let len = vec.len();
-    vec.resize(len.max(id + 1), T::default());
-}
-
diff --git a/crate/thread/src/scheduler/mod.rs b/crate/thread/src/scheduler/mod.rs
new file mode 100644
index 0000000..04e56fd
--- /dev/null
+++ b/crate/thread/src/scheduler/mod.rs
@@ -0,0 +1,32 @@
+use alloc::{collections::BinaryHeap, vec::Vec};
+
+use log::*;
+use spin::Mutex;
+
+pub use self::rr::RRScheduler;
+pub use self::stride::StrideScheduler;
+
+mod rr;
+mod stride;
+
+type Pid = usize;
+
+/// The scheduler for a ThreadPool
+pub trait Scheduler: Sync + 'static {
+    /// Push a thread to the back of ready queue.
+    fn push(&self, pid: Pid);
+    /// Remove a thread from the ready queue.
+    fn remove(&self, pid: Pid);
+    /// Select a thread to run, pop it from the queue.
+    fn pop(&self) -> Option<Pid>;
+    /// Got a tick from CPU.
+    /// Return true if need reschedule.
+    fn tick(&self, current_pid: Pid) -> bool;
+    /// Set priority of a thread.
+    fn set_priority(&self, pid: Pid, priority: u8);
+}
+
+fn expand<T: Default + Clone>(vec: &mut Vec<T>, id: usize) {
+    let len = vec.len();
+    vec.resize(len.max(id + 1), T::default());
+}
diff --git a/crate/thread/src/scheduler/rr.rs b/crate/thread/src/scheduler/rr.rs
new file mode 100644
index 0000000..eb79b76
--- /dev/null
+++ b/crate/thread/src/scheduler/rr.rs
@@ -0,0 +1,118 @@
+use super::*;
+
+pub struct RRScheduler {
+    inner: Mutex<RRSchedulerInner>,
+}
+
+struct RRSchedulerInner {
+    max_time_slice: usize,
+    infos: Vec<RRProcInfo>,
+}
+
+#[derive(Debug, Default, Copy, Clone)]
+struct RRProcInfo {
+    present: bool,
+    rest_slice: usize,
+    prev: Pid,
+    next: Pid,
+}
+
+impl Scheduler for RRScheduler {
+    fn push(&self, pid: usize) {
+        self.inner.lock().push(pid);
+    }
+    fn remove(&self, pid: usize) {
+        self.inner.lock().remove(pid);
+    }
+    fn pop(&self) -> Option<usize> {
+        self.inner.lock().pop()
+    }
+    fn tick(&self, current_pid: usize) -> bool {
+        self.inner.lock().tick(current_pid)
+    }
+    fn set_priority(&self, _pid: usize, _priority: u8) {}
+}
+
+impl RRScheduler {
+    pub fn new(max_time_slice: usize) -> Self {
+        let inner = RRSchedulerInner {
+            max_time_slice,
+            infos: Vec::default(),
+        };
+        RRScheduler { inner: Mutex::new(inner) }
+    }
+}
+
+impl RRSchedulerInner {
+    fn push(&mut self, pid: Pid) {
+        let pid = pid + 1;
+        expand(&mut self.infos, pid);
+        {
+            let info = &mut self.infos[pid];
+            assert!(!info.present);
+            info.present = true;
+            if info.rest_slice == 0 {
+                info.rest_slice = self.max_time_slice;
+            }
+        }
+        self._list_add_before(pid, 0);
+        trace!("rr push {}", pid - 1);
+    }
+
+    fn remove(&mut self, pid: Pid) {
+        let pid = pid + 1;
+        assert!(self.infos[pid].present);
+        self.infos[pid].present = false;
+        self._list_remove(pid);
+        trace!("rr remove {}", pid - 1);
+    }
+
+    fn pop(&mut self) -> Option<Pid> {
+        let ret = match self.infos[0].next {
+            0 => None,
+            pid => {
+                self.infos[pid].present = false;
+                self._list_remove(pid);
+                Some(pid - 1)
+            },
+        };
+        trace!("rr pop {:?}", ret);
+        ret
+    }
+
+    fn tick(&mut self, current: Pid) -> bool {
+        let current = current + 1;
+        expand(&mut self.infos, current);
+        assert!(!self.infos[current].present);
+
+        let rest = &mut self.infos[current].rest_slice;
+        if *rest > 0 {
+            *rest -= 1;
+        } else {
+            warn!("current process rest_slice = 0, need reschedule")
+        }
+        *rest == 0
+    }
+}
+
+impl RRSchedulerInner {
+    fn _list_add_before(&mut self, i: Pid, at: Pid) {
+        let prev = self.infos[at].prev;
+        self.infos[i].next = at;
+        self.infos[i].prev = prev;
+        self.infos[prev].next = i;
+        self.infos[at].prev = i;
+    }
+    fn _list_add_after(&mut self, i: Pid, at: Pid) {
+        let next = self.infos[at].next;
+        self._list_add_before(i, next);
+    }
+    fn _list_remove(&mut self, i: Pid) {
+        let next = self.infos[i].next;
+        let prev = self.infos[i].prev;
+        self.infos[next].prev = prev;
+        self.infos[prev].next = next;
+        self.infos[i].next = 0;
+        self.infos[i].prev = 0;
+    }
+}
diff --git a/crate/thread/src/scheduler/stride.rs b/crate/thread/src/scheduler/stride.rs
new file mode 100644
index 0000000..12292a7
--- /dev/null
+++ b/crate/thread/src/scheduler/stride.rs
@@ -0,0 +1,126 @@
+use super::*;
+
+pub struct StrideScheduler {
+    inner: Mutex<StrideSchedulerInner>,
+}
+
+pub struct StrideSchedulerInner {
+    max_time_slice: usize,
+    infos: Vec<StrideProcInfo>,
+    queue: BinaryHeap<(Stride, Pid)>, // It's max heap, so pass < 0
+}
+
+#[derive(Debug, Default, Copy, Clone)]
+struct StrideProcInfo {
+    present: bool,
+    rest_slice: usize,
+    stride: Stride,
+    priority: u8,
+}
+
+impl StrideProcInfo {
+    fn pass(&mut self) {
+        const BIG_STRIDE: Stride = 1 << 20;
+        let pass = if self.priority == 0 {
+            BIG_STRIDE
+        } else {
+            BIG_STRIDE / self.priority as Stride
+        };
+        // FIXME: overflowing_add is not working ???
+        // self.stride.overflowing_add(pass);
+        self.stride += pass;
+    }
+}
+
+type Stride = i32;
+
+impl Scheduler for StrideScheduler {
+    fn push(&self, pid: usize) {
+        self.inner.lock().push(pid);
+    }
+    fn remove(&self, pid: usize) {
+        self.inner.lock().remove(pid);
+    }
+    fn pop(&self) -> Option<usize> {
+        self.inner.lock().pop()
+    }
+    fn tick(&self, current_pid: usize) -> bool {
+        self.inner.lock().tick(current_pid)
+    }
+    fn set_priority(&self, pid: usize, priority: u8) {
+        self.inner.lock().set_priority(pid, priority);
+    }
+}
+
+impl StrideScheduler {
+    pub fn new(max_time_slice: usize) -> Self {
+        let inner = StrideSchedulerInner {
+            max_time_slice,
+            infos: Vec::default(),
+            queue: BinaryHeap::default(),
+        };
+        StrideScheduler { inner: Mutex::new(inner) }
+    }
+}
+
+impl StrideSchedulerInner {
+    fn push(&mut self, pid: Pid) {
+        expand(&mut self.infos, pid);
+        let info = &mut self.infos[pid];
+        assert!(!info.present);
+        info.present = true;
+        if info.rest_slice == 0 {
+            info.rest_slice = self.max_time_slice;
+        }
+        self.queue.push((-info.stride, pid));
+        trace!("stride push {}", pid);
+    }
+
+    fn remove(&mut self, pid: Pid) {
+        let info = &mut self.infos[pid];
+        assert!(info.present);
+        info.present = false;
+        if self.queue.peek().is_some() && self.queue.peek().unwrap().1 == pid {
+            self.queue.pop();
+        } else {
+            // BinaryHeap only support pop the top.
+            // So in order to remove an arbitrary element,
+            // we have to take all elements into a Vec,
+            // then push the rest back.
+            let rest: Vec<_> = self.queue.drain().filter(|&p| p.1 != pid).collect();
+            use core::iter::FromIterator;
+            self.queue = BinaryHeap::from_iter(rest.into_iter());
+        }
+        trace!("stride remove {}", pid);
+    }
+
+    fn pop(&mut self) -> Option<Pid> {
+        let ret = self.queue.pop().map(|(_, pid)| pid);
+        if let Some(pid) = ret {
+            let old_stride = self.infos[pid].stride;
+            self.infos[pid].pass();
+            let stride = self.infos[pid].stride;
+            trace!("stride {} {:#x} -> {:#x}", pid, old_stride, stride);
+        }
+        trace!("stride pop {:?}", ret);
+        ret
+    }
+
+    fn tick(&mut self, current: Pid) -> bool {
+        expand(&mut self.infos, current);
+        assert!(!self.infos[current].present);
+
+        let rest = &mut self.infos[current].rest_slice;
+        if *rest > 0 {
+            *rest -= 1;
+        } else {
+            warn!("current process rest_slice = 0, need reschedule")
+        }
+        *rest == 0
+    }
+
+    fn set_priority(&mut self, pid: Pid, priority: u8) {
+        self.infos[pid].priority = priority;
+        trace!("stride {} priority = {}", pid, priority);
+    }
+}
diff --git a/crate/thread/src/thread_pool.rs b/crate/thread/src/thread_pool.rs
index 93d159f..487dc77 100644
--- a/crate/thread/src/thread_pool.rs
+++ b/crate/thread/src/thread_pool.rs
@@ -37,15 +37,15 @@ pub trait Context {
 
 pub struct ThreadPool {
     threads: Vec<Mutex<Option<Thread>>>,
-    scheduler: Mutex<Box<Scheduler>>,
+    scheduler: Box<Scheduler>,
     timer: Mutex<Timer<Event>>,
 }
 
 impl ThreadPool {
-    pub fn new(scheduler: Box<Scheduler>, max_proc_num: usize) -> Self {
+    pub fn new(scheduler: impl Scheduler, max_proc_num: usize) -> Self {
         ThreadPool {
             threads: new_vec_default(max_proc_num),
-            scheduler: Mutex::new(scheduler),
+            scheduler: Box::new(scheduler),
             timer: Mutex::new(Timer::new()),
         }
     }
@@ -69,7 +69,7 @@ impl ThreadPool {
             parent,
             children: Vec::new(),
         });
-        self.scheduler.lock().insert(tid);
+        self.scheduler.push(tid);
         self.threads[parent].lock().as_mut().expect("invalid parent proc")
             .children.push(tid);
         tid
@@ -89,24 +89,22 @@ impl ThreadPool {
             }
         }
         match tid {
-            Some(tid) => self.scheduler.lock().tick(tid),
+            Some(tid) => self.scheduler.tick(tid),
             None => false,
         }
     }
 
     /// Set the priority of process `tid`
     pub fn set_priority(&self, tid: Tid, priority: u8) {
-        self.scheduler.lock().set_priority(tid, priority);
+        self.scheduler.set_priority(tid, priority);
     }
 
     /// Called by Processor to get a process to run.
     /// The manager first mark it `Running`,
     /// then take out and return its Context.
     pub(crate) fn run(&self, cpu_id: usize) -> Option<(Tid, Box<Context>)> {
-        let mut scheduler = self.scheduler.lock();
-        scheduler.select()
+        self.scheduler.pop()
             .map(|tid| {
-                scheduler.remove(tid);
                 let mut proc_lock = self.threads[tid].lock();
                 let mut proc = proc_lock.as_mut().expect("process not exist");
                 proc.status = Status::Running(cpu_id);
@@ -123,7 +121,7 @@ impl ThreadPool {
         proc.status_after_stop = Status::Ready;
         proc.context = Some(context);
         match proc.status {
-            Status::Ready => self.scheduler.lock().insert(tid),
+            Status::Ready => self.scheduler.push(tid),
             Status::Exited(_) => self.exit_handler(tid, proc),
             _ => {}
         }
@@ -137,10 +135,10 @@ impl ThreadPool {
         trace!("process {} {:?} -> {:?}", tid, proc.status, status);
         match (&proc.status, &status) {
             (Status::Ready, Status::Ready) => return,
-            (Status::Ready, _) => self.scheduler.lock().remove(tid),
+            (Status::Ready, _) => self.scheduler.remove(tid),
             (Status::Exited(_), _) => panic!("can not set status for a exited process"),
             (Status::Sleeping, Status::Exited(_)) => self.timer.lock().stop(Event::Wakeup(tid)),
-            (_, Status::Ready) => self.scheduler.lock().insert(tid),
+            (_, Status::Ready) => self.scheduler.push(tid),
             _ => {}
         }
         match proc.status {
diff --git a/kernel/src/process/mod.rs b/kernel/src/process/mod.rs
index 7626841..72e94fa 100644
--- a/kernel/src/process/mod.rs
+++ b/kernel/src/process/mod.rs
@@ -11,7 +11,7 @@ mod abi;
 
 pub fn init() {
     // NOTE: max_time_slice <= 5 to ensure 'priority' test pass
-    let scheduler = Box::new(scheduler::RRScheduler::new(5));
+    let scheduler = scheduler::RRScheduler::new(5);
     let manager = Arc::new(ThreadPool::new(scheduler, MAX_PROCESS_NUM));
 
     unsafe {