Apply 1 suggestion(s) to 1 file(s)

libraries/base/Control/Exception/Base.hs

@@ -214,13 +214,21 @@ onException io what = io `catch` \e -> do _ <- what
 --
 -- > withFile name mode = bracket (openFile name mode) hClose
 --
--- Implementation of bracket is using 'mask', which means that the release
--- handler should be uninterruptible to run to completion in presence of
--- asynchronous exceptions. 'hClose' is uninterruptible if used
--- non-concurrently, closing a socket (from \"network\" package) is
--- uninterruptible as well, an example of interruptible close handler is
--- 'killThread' which should be wrapped using 'uninterruptibleMask_' when used
--- with 'bracket'. Comments in 'uninterruptibleMask' still aply.
+-- Bracket wraps the release action with 'mask', which is sufficient to ensure
+-- that the release action executes to completion when it does not invoke any
+-- interruptible actions, even in the presence of asynchronous exceptions.  For
+-- example, `hClose` is uninterruptible when it is not racing other uses of the
+-- handle.  Similarly, closing a socket (from \"network\" package) is also
+-- uninterruptible under similar conditions.  An example of an interruptible
+-- action is 'killThread'.  Completion of interruptible release actions can be
+-- ensured by wrapping them in in 'uninterruptibleMask_', but this risks making
+-- the program non-responsive to @Control-C@, or timeouts.  Another option is to
+-- run the release action asynchronously in its own thread:
+--
+-- > void $ uninterruptibleMask_ $ forkIO $ do { ... }
+--
+-- The resource will be released as soon as possible, but the thread that invoked
+-- bracket will not block in an uninterruptible state.
 --
 bracket
         :: IO a         -- ^ computation to run first (\"acquire resource\")