Add Absorb::drop_second

Author: jonhoo

evmap/src/write.rs

@@ -542,14 +542,19 @@ where
     fn drop_first(self: Box<Self>) {
         // since the two copies are exactly equal, we need to make sure that we *don't* call the
         // destructors of any of the values that are in our map, as they'll all be called when the
-        // last read handle goes out of scope. to do so, we first clear w_handle, which won't drop
-        // any elements since its values are kept as ManuallyDrop:
+        // last read handle goes out of scope.
         //
         // Safety: ManuallyDrop<T> has the same layout as T.
         let inner =
             unsafe { Box::from_raw(Box::into_raw(self) as *mut Inner<K, ManuallyDrop<V>, M, S>) };
         drop(inner);
     }
+
+    fn drop_second(self: Box<Self>) {
+        // when the second copy is dropped is where we want to _actually_ drop all the values in
+        // the map. this happens automatically.
+        drop(self);
+    }
 }
 
 impl<K, V, M, S> Extend<(K, V)> for WriteHandle<K, V, M, S>

left-right/src/lib.rs

@@ -232,6 +232,11 @@ pub trait Absorb<O> {
     ///
     /// Defaults to calling `Self::drop`.
     fn drop_first(self: Box<Self>) {}
+
+    /// Drop the second of the two copies.
+    ///
+    /// Defaults to calling `Self::drop`.
+    fn drop_second(self: Box<Self>) {}
 }
 
 /// Construct a new write and read handle pair from an empty data structure.

left-right/src/write.rs

@@ -103,8 +103,8 @@ where
         // this is safe, since we know that no readers are using this pointer
         // anymore (due to the .wait() following swapping the pointer with NULL).
         //
-        // safety: w_handle was initially crated from a `Box`, and is no longer aliased.
-        drop(unsafe { Box::from_raw(r_handle) });
+        // safety: r_handle was initially crated from a `Box`, and is no longer aliased.
+        Absorb::drop_second(unsafe { Box::from_raw(r_handle) });
     }
 }