From a93451b3df8b67e3dc16b107ff8cfc4140cf0c69 Mon Sep 17 00:00:00 2001
From: zhangxinyu <840317537@qq.com>
Date: Wed, 17 May 2023 17:09:46 +0800
Subject: [PATCH] =?UTF-8?q?=E8=87=AA=E5=B7=B1=E5=B0=81=E8=A3=85=E4=B8=80?=
 =?UTF-8?q?=E4=B8=AArefcell?=
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---
 ch2/os/src/sync/mod.rs |  4 ++++
 ch2/os/src/sync/up.rs  | 31 +++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)
 create mode 100644 ch2/os/src/sync/mod.rs
 create mode 100644 ch2/os/src/sync/up.rs

diff --git a/ch2/os/src/sync/mod.rs b/ch2/os/src/sync/mod.rs
new file mode 100644
index 0000000..1ccdd2e
--- /dev/null
+++ b/ch2/os/src/sync/mod.rs
@@ -0,0 +1,4 @@
+//! Synchronization and interior mutability primitives
+
+mod up;
+pub use up::UPSafeCell;
diff --git a/ch2/os/src/sync/up.rs b/ch2/os/src/sync/up.rs
new file mode 100644
index 0000000..e8ba20c
--- /dev/null
+++ b/ch2/os/src/sync/up.rs
@@ -0,0 +1,31 @@
+//! Uniprocessor interior mutability primitives
+
+use core::cell::{RefCell, RefMut};
+
+/// 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
+/// `exclusive_access`.
+pub struct UPSafeCell<T> {
+    /// inner data
+    inner: RefCell<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 {
+            inner: RefCell::new(value),
+        }
+    }
+    /// Exclusive access inner data in UPSafeCell. Panic if the data has been borrowed.
+    pub fn exclusive_access(&self) -> RefMut<'_, T> {
+        self.inner.borrow_mut()
+    }
+}