diff --git a/os/src/main.rs b/os/src/main.rs
index 145f50a1..0f04c1fe 100644
--- a/os/src/main.rs
+++ b/os/src/main.rs
@@ -43,10 +43,18 @@ pub fn rust_main() -> ! {
     mm::init();
     println!("[kernel] back to world!");
     mm::remap_test();
+
+    // add apps
+    let num_app = loader::get_num_app();
+    println!("num_app={}", num_app);
+    for i in 0..num_app {
+        println!("i={}", i);
+        task::add_application(loader::get_app_data(i), i);
+    }
     trap::init();
-    //trap::enable_interrupt();
     trap::enable_timer_interrupt();
     timer::set_next_trigger();
-    task::run_first_task();
+    println!("before task::run_tasks!");
+    task::run_tasks();
     panic!("Unreachable in rust_main!");
 }
\ No newline at end of file
diff --git a/os/src/task/manager.rs b/os/src/task/manager.rs
new file mode 100644
index 00000000..1b9a5ad8
--- /dev/null
+++ b/os/src/task/manager.rs
@@ -0,0 +1,34 @@
+use super::TaskControlBlock;
+use alloc::collections::VecDeque;
+use alloc::sync::Arc;
+use spin::Mutex;
+use lazy_static::*;
+
+pub struct TaskManager {
+    ready_queue: VecDeque<Arc<Mutex<TaskControlBlock>>>,
+}
+
+/// A simple FIFO scheduler.
+impl TaskManager {
+    pub fn new() -> Self {
+        Self { ready_queue: VecDeque::new(), }
+    }
+    pub fn add(&mut self, task: Arc<Mutex<TaskControlBlock>>) {
+        self.ready_queue.push_back(task);
+    }
+    pub fn fetch(&mut self) -> Option<Arc<Mutex<TaskControlBlock>>> {
+        self.ready_queue.pop_front()
+    }
+}
+
+lazy_static! {
+    pub static ref TASK_MANAGER: Mutex<TaskManager> = Mutex::new(TaskManager::new());
+}
+
+pub fn add_task(task: Arc<Mutex<TaskControlBlock>>) {
+    TASK_MANAGER.lock().add(task);
+}
+
+pub fn fetch_task() -> Option<Arc<Mutex<TaskControlBlock>>> {
+    TASK_MANAGER.lock().fetch()
+}
\ No newline at end of file
diff --git a/os/src/task/mod.rs b/os/src/task/mod.rs
index 009829e7..eaf7ced2 100644
--- a/os/src/task/mod.rs
+++ b/os/src/task/mod.rs
@@ -1,6 +1,8 @@
 mod context;
 mod switch;
 mod task;
+mod manager;
+mod processor;
 
 use crate::loader::{get_num_app, get_app_data};
 use crate::trap::TrapContext;
@@ -9,141 +11,38 @@ use lazy_static::*;
 use switch::__switch;
 use task::{TaskControlBlock, TaskStatus};
 use alloc::vec::Vec;
+use alloc::sync::Arc;
+use spin::Mutex;
+use manager::fetch_task;
 
 pub use context::TaskContext;
-
-pub struct TaskManager {
-    num_app: usize,
-    inner: RefCell<TaskManagerInner>,
-}
-
-struct TaskManagerInner {
-    tasks: Vec<TaskControlBlock>,
-    current_task: usize,
-}
-
-unsafe impl Sync for TaskManager {}
-
-lazy_static! {
-    pub static ref TASK_MANAGER: TaskManager = {
-        println!("init TASK_MANAGER");
-        let num_app = get_num_app();
-        println!("num_app = {}", num_app);
-        let mut tasks: Vec<TaskControlBlock> = Vec::new();
-        for i in 0..num_app {
-            tasks.push(TaskControlBlock::new(
-                get_app_data(i),
-                i,
-            ));
-        }
-        TaskManager {
-            num_app,
-            inner: RefCell::new(TaskManagerInner {
-                tasks,
-                current_task: 0,
-            }),
-        }
-    };
-}
-
-impl TaskManager {
-    fn run_first_task(&self) {
-        self.inner.borrow_mut().tasks[0].task_status = TaskStatus::Running;
-        let next_task_cx = self.inner.borrow().tasks[0].get_task_cx_ptr2();
-        let _unused: usize = 0;
-        unsafe {
-            __switch(
-                &_unused as *const _,
-                next_task_cx,
-            );
-        }
-    }
-
-    fn mark_current_suspended(&self) {
-        let mut inner = self.inner.borrow_mut();
-        let current = inner.current_task;
-        inner.tasks[current].task_status = TaskStatus::Ready;
-    }
-
-    fn mark_current_exited(&self) {
-        let mut inner = self.inner.borrow_mut();
-        let current = inner.current_task;
-        inner.tasks[current].task_status = TaskStatus::Exited;
-    }
-
-    fn find_next_task(&self) -> Option<usize> {
-        let inner = self.inner.borrow();
-        let current = inner.current_task;
-        (current + 1..current + self.num_app + 1)
-            .map(|id| id % self.num_app)
-            .find(|id| {
-                inner.tasks[*id].task_status == TaskStatus::Ready
-            })
-    }
-
-    fn get_current_token(&self) -> usize {
-        let inner = self.inner.borrow();
-        let current = inner.current_task;
-        inner.tasks[current].get_user_token()
-    }
-
-    fn get_current_trap_cx(&self) -> &mut TrapContext {
-        let inner = self.inner.borrow();
-        let current = inner.current_task;
-        inner.tasks[current].get_trap_cx()
-    }
-
-    fn run_next_task(&self) {
-        if let Some(next) = self.find_next_task() {
-            let mut inner = self.inner.borrow_mut();
-            let current = inner.current_task;
-            inner.tasks[next].task_status = TaskStatus::Running;
-            inner.current_task = next;
-            let current_task_cx = inner.tasks[current].get_task_cx_ptr2();
-            let next_task_cx = inner.tasks[next].get_task_cx_ptr2();
-            core::mem::drop(inner);
-            unsafe {
-                __switch(
-                    current_task_cx,
-                    next_task_cx,
-                );
-            }
-        } else {
-            panic!("All applications completed!");
-        }
-    }
-}
-
-pub fn run_first_task() {
-    TASK_MANAGER.run_first_task();
-}
-
-fn run_next_task() {
-    TASK_MANAGER.run_next_task();
-}
-
-fn mark_current_suspended() {
-    TASK_MANAGER.mark_current_suspended();
-}
-
-fn mark_current_exited() {
-    TASK_MANAGER.mark_current_exited();
-}
+pub use processor::{
+    run_tasks,
+    current_task,
+    current_user_token,
+    current_trap_cx,
+    take_current_task,
+    schedule,
+};
+pub use manager::add_task;
 
 pub fn suspend_current_and_run_next() {
-    mark_current_suspended();
-    run_next_task();
+    // There must be an application running.
+    let task = current_task().unwrap();
+    let task_cx_ptr = task.lock().get_task_cx_ptr2();
+    // Change status to Ready.
+    task.lock().task_status = TaskStatus::Ready;
+    // push back to ready queue.
+    add_task(task);
+    // jump to scheduling cycle
+    schedule(task_cx_ptr);
 }
 
 pub fn exit_current_and_run_next() {
-    mark_current_exited();
-    run_next_task();
+    // The resource recycle mechanism needs child processes. Now we just panic!
+    panic!("An application exited!");
 }
 
-pub fn current_user_token() -> usize {
-    TASK_MANAGER.get_current_token()
+pub fn add_application(elf_data: &[u8], app_id: usize) {
+    add_task(Arc::new(Mutex::new(TaskControlBlock::new(elf_data, app_id))));
 }
-
-pub fn current_trap_cx() -> &'static mut TrapContext {
-    TASK_MANAGER.get_current_trap_cx()
-}
\ No newline at end of file
diff --git a/os/src/task/processor.rs b/os/src/task/processor.rs
new file mode 100644
index 00000000..5551fb72
--- /dev/null
+++ b/os/src/task/processor.rs
@@ -0,0 +1,96 @@
+use super::TaskControlBlock;
+use alloc::sync::Arc;
+use spin::Mutex;
+use lazy_static::*;
+use super::{add_task, fetch_task};
+use super::__switch;
+use crate::trap::TrapContext;
+
+pub struct Processor {
+    inner: Mutex<ProcessorInner>,
+}
+
+unsafe impl Sync for Processor {}
+
+struct ProcessorInner {
+    current: Option<Arc<Mutex<TaskControlBlock>>>,
+    idle_task_cx_ptr: usize,
+}
+
+impl Processor {
+    pub fn new() -> Self {
+        Self {
+            inner: Mutex::new(ProcessorInner {
+                current: None,
+                idle_task_cx_ptr: 0,
+            }),
+        }
+    }
+    fn get_idle_task_cx_ptr2(&self) -> *const usize {
+        let inner = self.inner.lock();
+        &inner.idle_task_cx_ptr as *const usize
+    }
+    pub fn run(&self) {
+        //println!("into Processor::run");
+        loop {
+            if let Some(task) = fetch_task() {
+                //println!("found task!");
+                let idle_task_cx_ptr = self.get_idle_task_cx_ptr2();
+                let next_task_cx_ptr = task.lock().get_task_cx_ptr2();
+                //println!("next_task_cx_ptr={:p}", next_task_cx_ptr);
+                self.inner.lock().current = Some(task);
+                unsafe {
+                    __switch(
+                        idle_task_cx_ptr,
+                        next_task_cx_ptr,
+                    );
+                }
+            }
+        }
+    }
+    pub fn take_current(&self) -> Option<Arc<Mutex<TaskControlBlock>>> {
+        self.inner.lock().current.take()
+    }
+    pub fn current(&self) -> Option<Arc<Mutex<TaskControlBlock>>> {
+        self.inner.lock().current.as_ref().map(|task| task.clone())
+    }
+}
+
+lazy_static! {
+    pub static ref PROCESSOR: Processor = Processor::new();
+}
+
+pub fn run_tasks() {
+    PROCESSOR.run();
+}
+
+pub fn take_current_task() -> Option<Arc<Mutex<TaskControlBlock>>> {
+    PROCESSOR.take_current()
+}
+
+pub fn current_task() -> Option<Arc<Mutex<TaskControlBlock>>> {
+    //println!("into current_task!");
+    PROCESSOR.current()
+}
+
+pub fn current_user_token() -> usize {
+    //println!("into current_user_token!");
+    let task = current_task().unwrap();
+    //println!("Got task in current_user_token!");
+    let token = task.lock().get_user_token();
+    token
+}
+
+pub fn current_trap_cx() -> &'static mut TrapContext {
+    current_task().unwrap().as_ref().lock().get_trap_cx()
+}
+
+pub fn schedule(switched_task_cx_ptr2: *const usize) {
+    let idle_task_cx_ptr2 = PROCESSOR.get_idle_task_cx_ptr2();
+    unsafe {
+        __switch(
+            switched_task_cx_ptr2,
+            idle_task_cx_ptr2,
+        );
+    }
+}
diff --git a/os/src/task/task.rs b/os/src/task/task.rs
index 8e38635b..db1eea83 100644
--- a/os/src/task/task.rs
+++ b/os/src/task/task.rs
@@ -4,11 +4,14 @@ use crate::config::{TRAP_CONTEXT, kernel_stack_position};
 use super::TaskContext;
 
 pub struct TaskControlBlock {
+    // immutable
+    pub trap_cx_ppn: PhysPageNum,
+    pub base_size: usize,
+    //pub pid: usize,
+    // mutable
     pub task_cx_ptr: usize,
     pub task_status: TaskStatus,
     pub memory_set: MemorySet,
-    pub trap_cx_ppn: PhysPageNum,
-    pub base_size: usize,
 }
 
 impl TaskControlBlock {
@@ -65,4 +68,5 @@ pub enum TaskStatus {
     Ready,
     Running,
     Exited,
+    Zombie,
 }
\ No newline at end of file
diff --git a/os/src/trap/mod.rs b/os/src/trap/mod.rs
index 46e113bb..01d096f5 100644
--- a/os/src/trap/mod.rs
+++ b/os/src/trap/mod.rs
@@ -83,6 +83,7 @@ pub fn trap_handler() -> ! {
 
 #[no_mangle]
 pub fn trap_return() -> ! {
+    //println!("into trap_return!");
     set_user_trap_entry();
     let trap_cx_ptr = TRAP_CONTEXT;
     let user_satp = current_user_token();
@@ -91,6 +92,7 @@ pub fn trap_return() -> ! {
         fn __restore();
     }
     let restore_va = __restore as usize - __alltraps as usize + TRAMPOLINE;
+    //println!("before jr!");
     unsafe {
         llvm_asm!("jr $0" :: "r"(restore_va), "{a0}"(trap_cx_ptr), "{a1}"(user_satp) :: "volatile");
     }