Add Sync impl for spinlock/mutex guards.

Author: m-ou-se

src/ch4_spin_lock/s3_guard.rs

@@ -14,6 +14,8 @@ pub struct Guard<'a, T> {
     lock: &'a SpinLock<T>,
 }
 
+unsafe impl<T> Sync for Guard<'_, T> where T: Sync {}
+
 impl<T> SpinLock<T> {
     pub const fn new(value: T) -> Self {
         Self {

src/ch9_locks/mutex_1.rs

@@ -17,6 +17,8 @@ pub struct MutexGuard<'a, T> {
     mutex: &'a Mutex<T>,
 }
 
+unsafe impl<T> Sync for MutexGuard<'_, T> where T: Sync {}
+
 impl<T> Deref for MutexGuard<'_, T> {
     type Target = T;
     fn deref(&self) -> &T {

src/ch9_locks/mutex_2.rs

@@ -18,6 +18,8 @@ pub struct MutexGuard<'a, T> {
     mutex: &'a Mutex<T>,
 }
 
+unsafe impl<T> Sync for MutexGuard<'_, T> where T: Sync {}
+
 impl<T> Deref for MutexGuard<'_, T> {
     type Target = T;
     fn deref(&self) -> &T {

src/ch9_locks/mutex_3.rs

@@ -18,6 +18,8 @@ pub struct MutexGuard<'a, T> {
     pub(crate) mutex: &'a Mutex<T>,
 }
 
+unsafe impl<T> Sync for MutexGuard<'_, T> where T: Sync {}
+
 impl<T> Deref for MutexGuard<'_, T> {
     type Target = T;
     fn deref(&self) -> &T {