From 19c6265ed5b475754216dca801408b833c293bc6 Mon Sep 17 00:00:00 2001
From: Yifan Wu <shinbokuow@163.com>
Date: Thu, 8 Jul 2021 18:15:52 +0800
Subject: [PATCH] RefCell->UPSafeCell

---
 os/src/batch.rs    | 56 +++++++++++++++++++++-------------------------
 os/src/main.rs     |  1 +
 os/src/sync/mod.rs |  3 +++
 os/src/sync/up.rs  | 27 ++++++++++++++++++++++
 4 files changed, 57 insertions(+), 30 deletions(-)
 create mode 100644 os/src/sync/mod.rs
 create mode 100644 os/src/sync/up.rs

diff --git a/os/src/batch.rs b/os/src/batch.rs
index a17346ed..7a29c9a1 100644
--- a/os/src/batch.rs
+++ b/os/src/batch.rs
@@ -1,6 +1,6 @@
-use core::cell::RefCell;
 use lazy_static::*;
 use crate::trap::TrapContext;
+use crate::sync::UPSafeCell;
 
 const USER_STACK_SIZE: usize = 4096 * 2;
 const KERNEL_STACK_SIZE: usize = 4096 * 2;
@@ -39,16 +39,12 @@ impl UserStack {
 }
 
 struct AppManager {
-    inner: RefCell<AppManagerInner>,
-}
-struct AppManagerInner {
     num_app: usize,
     current_app: usize,
     app_start: [usize; MAX_APP_NUM + 1],
 }
-unsafe impl Sync for AppManager {}
 
-impl AppManagerInner {
+impl AppManager {
     pub fn print_app_info(&self) {
         println!("[kernel] num_app = {}", self.num_app);
         for i in 0..self.num_app {
@@ -64,9 +60,10 @@ impl AppManagerInner {
         // clear icache
         llvm_asm!("fence.i" :::: "volatile");
         // clear app area
-        (APP_BASE_ADDRESS..APP_BASE_ADDRESS + APP_SIZE_LIMIT).for_each(|addr| {
-            (addr as *mut u8).write_volatile(0);
-        });
+        core::slice::from_raw_parts_mut(
+            APP_BASE_ADDRESS as *mut u8,
+            APP_SIZE_LIMIT
+        ).fill(0);
         let app_src = core::slice::from_raw_parts(
             self.app_start[app_id] as *const u8,
             self.app_start[app_id + 1] - self.app_start[app_id]
@@ -86,23 +83,21 @@ impl AppManagerInner {
 }
 
 lazy_static! {
-    static ref APP_MANAGER: AppManager = AppManager {
-        inner: RefCell::new({
-            extern "C" { fn _num_app(); }
-            let num_app_ptr = _num_app as usize as *const usize;
-            let num_app = unsafe { num_app_ptr.read_volatile() };
-            let mut app_start: [usize; MAX_APP_NUM + 1] = [0; MAX_APP_NUM + 1];
-            let app_start_raw: &[usize] = unsafe {
-                core::slice::from_raw_parts(num_app_ptr.add(1), num_app + 1)
-            };
-            app_start[..=num_app].copy_from_slice(app_start_raw);
-            AppManagerInner {
-                num_app,
-                current_app: 0,
-                app_start,
-            }
-        }),
-    };
+    static ref APP_MANAGER: UPSafeCell<AppManager> = unsafe { UPSafeCell::new({
+        extern "C" { fn _num_app(); }
+        let num_app_ptr = _num_app as usize as *const usize;
+        let num_app = num_app_ptr.read_volatile();
+        let mut app_start: [usize; MAX_APP_NUM + 1] = [0; MAX_APP_NUM + 1];
+        let app_start_raw: &[usize] =  core::slice::from_raw_parts(
+            num_app_ptr.add(1), num_app + 1
+        );
+        app_start[..=num_app].copy_from_slice(app_start_raw);
+        AppManager {
+            num_app,
+            current_app: 0,
+            app_start,
+        }
+    })};
 }
 
 pub fn init() {
@@ -110,15 +105,16 @@ pub fn init() {
 }
 
 pub fn print_app_info() {
-    APP_MANAGER.inner.borrow().print_app_info();
+    APP_MANAGER.upsafe_access().print_app_info();
 }
 
 pub fn run_next_app() -> ! {
-    let current_app = APP_MANAGER.inner.borrow().get_current_app();
+    let app_manager = APP_MANAGER.upsafe_access();
+    let current_app = app_manager.get_current_app();
     unsafe {
-        APP_MANAGER.inner.borrow().load_app(current_app);
+        app_manager.load_app(current_app);
     }
-    APP_MANAGER.inner.borrow_mut().move_to_next_app();
+    app_manager.move_to_next_app();
     extern "C" { fn __restore(cx_addr: usize); }
     unsafe {
         __restore(KERNEL_STACK.push_context(
diff --git a/os/src/main.rs b/os/src/main.rs
index 8f8fdeb7..b43c79ad 100644
--- a/os/src/main.rs
+++ b/os/src/main.rs
@@ -11,6 +11,7 @@ mod sbi;
 mod syscall;
 mod trap;
 mod batch;
+mod sync;
 
 global_asm!(include_str!("entry.asm"));
 global_asm!(include_str!("link_app.S"));
diff --git a/os/src/sync/mod.rs b/os/src/sync/mod.rs
new file mode 100644
index 00000000..77295248
--- /dev/null
+++ b/os/src/sync/mod.rs
@@ -0,0 +1,3 @@
+mod up;
+
+pub use up::UPSafeCell;
\ No newline at end of file
diff --git a/os/src/sync/up.rs b/os/src/sync/up.rs
new file mode 100644
index 00000000..849ac4bc
--- /dev/null
+++ b/os/src/sync/up.rs
@@ -0,0 +1,27 @@
+/// Wrap a static data structure inside it so that we are 
+/// able to access it without any `unsafe`.
+///
+/// We should only use it in uniprocessor.
+///
+/// In order to get mutable reference of inner data, call 
+/// `upsafe_access`. 
+pub struct UPSafeCell<T> {
+    /// inner data
+    data: T,
+}
+
+unsafe impl<T> Sync for UPSafeCell<T> {}
+
+impl<T> UPSafeCell<T> {
+    /// User is responsible to guarantee that inner struct is only used in
+    /// uniprocessor.
+    pub unsafe fn new(value: T) -> Self {
+        Self { data: value, }
+    }
+    /// Mention that user should hold exactly one &mut T at a time. 
+    pub fn upsafe_access(&self) -> &mut T {
+        unsafe {
+            &mut *(&self.data as *const _ as usize as *mut T)
+        }
+    }
+}
\ No newline at end of file