Added method to unpoison poisoned RWARCs

src/libextra/arc.rs

@@ -48,6 +48,7 @@ use core::cast;
 use core::unstable::sync::UnsafeAtomicRcBox;
 use core::task;
 use core::borrow;
+use core::util;
 
 /// As sync::condvar, a mechanism for unlock-and-descheduling and signaling.
 pub struct Condvar<'self> {
@@ -332,6 +333,28 @@ impl<T:Const + Owned> RWARC<T> {
         }
     }
 
+    /// As write(), but unpoisons poisoned ARCs.
+    #[inline]
+    pub fn unpoison<U>(&self, blk: &fn() -> (T, U)) -> U {
+        unsafe {
+            let state = self.x.get();
+            do (*borrow_rwlock(state)).write {
+                let _z = PoisonOnFail(&mut (*state).failed);
+
+                let mut (writevalue, result) = blk();
+
+                util::swap(&mut (*state).data, &mut writevalue);
+                if (*state).failed {
+                    // Might be uninitialized so is unsafe to destroy
+                    cast::forget(writevalue)
+                }
+                (*state).failed = false;
+
+                result
+            }
+        }
+    }
+
     /// As write(), but with a condvar, as sync::rwlock.write_cond().
     #[inline]
     pub fn write_cond<'x, 'c, U>(&self,
@@ -736,6 +759,24 @@ mod tests {
         }
     }
     #[test]
+    fn test_rw_arc_unpoison() {
+        let arc = RWARC(0);
+
+        // Poison the arc
+        let arc_clone = arc.clone();
+        do task::spawn_unlinked {
+            do arc_clone.write |_| {
+                fail!()
+            }
+        }
+
+        do arc.unpoison { (0, ()) }
+
+        do arc.read |_| {
+            // Should succeed at reading the now unpoisoned value
+        }
+    }
+    #[test]
     fn test_rw_downgrade() {
         // (1) A downgrader gets in write mode and does cond.wait.
         // (2) A writer gets in write mode, sets state to 42, and does signal.