From f2bab47aa4bdd04f79e608debe64e3ddcea07702 Mon Sep 17 00:00:00 2001
From: Jorge Aparicio <japaricious@gmail.com>
Date: Fri, 7 Apr 2017 18:14:48 -0500
Subject: allow returns from checked::Resource.lock{,mut}

also add compiler barriers
---
 src/checked.rs | 18 ++++++++++++------
 src/lib.rs     | 14 ++++++++++++++
 2 files changed, 26 insertions(+), 6 deletions(-)

(limited to 'src')

diff --git a/src/checked.rs b/src/checked.rs
index fbdf692..4c91c05 100644
--- a/src/checked.rs
+++ b/src/checked.rs
@@ -51,27 +51,33 @@ where
 
     /// Locks the resource, blocking tasks with priority equal or smaller than
     /// the ceiling `C`
-    pub fn lock<F>(&'static self, f: F)
+    pub fn lock<R, F>(&'static self, f: F) -> R
     where
-        F: FnOnce(&T),
+        F: FnOnce(&T) -> R,
     {
         unsafe {
             let old_basepri = acquire(&self.locked, C::ceiling());
-            f(&*self.data.get());
+            ::compiler_barrier();
+            let ret = f(&*self.data.get());
+            ::compiler_barrier();
             release(&self.locked, old_basepri);
+            ret
         }
     }
 
     /// Mutably locks the resource, blocking tasks with priority equal or
     /// smaller than the ceiling `C`
-    pub fn lock_mut<F>(&'static self, f: F)
+    pub fn lock_mut<R, F>(&'static self, f: F) -> R
         where
-        F: FnOnce(&mut T),
+        F: FnOnce(&mut T) -> R,
     {
         unsafe {
             let old_basepri = acquire(&self.locked, C::ceiling());
-            f(&mut *self.data.get());
+            ::compiler_barrier();
+            let ret = f(&mut *self.data.get());
+            ::compiler_barrier();
             release(&self.locked, old_basepri);
+            ret
         }
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 95aa8ba..7cd0ff6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -105,7 +105,9 @@ where
     lock_check(ceiling);
     let old_basepri = basepri::read();
     basepri_max::write(ceiling);
+    compiler_barrier();
     let ret = f(&*res, ptr::read(0 as *const _));
+    compiler_barrier();
     basepri::write(old_basepri);
     ret
 }
@@ -121,11 +123,23 @@ where
     lock_check(ceiling);
     let old_basepri = basepri::read();
     basepri_max::write(ceiling);
+    compiler_barrier();
     let ret = f(&mut *res, ptr::read(0 as *const _));
+    compiler_barrier();
     basepri::write(old_basepri);
     ret
 }
 
+fn compiler_barrier() {
+    unsafe {
+        asm!(""
+             :
+             :
+             : "memory"
+             : "volatile");
+    }
+}
+
 /// A peripheral as a resource
 pub struct ResourceP<P, Ceiling>
 where
-- 
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