[project @ 1999-02-02 14:40:46 by simonm]

Mention 'finalise' and 'mkWeakNoFinaliser'.

diff --git a/ghc/docs/libraries/Weak.sgml b/ghc/docs/libraries/Weak.sgml
index 0f223f4..80ba68b 100644 (file)
--- a/ghc/docs/libraries/Weak.sgml
+++ b/ghc/docs/libraries/Weak.sgml
@@ -19,15 +19,16 @@ module Weak (
        -- instance Eq (Weak v)  
 
        mkWeak,                 -- :: k -> v -> IO () -> IO (Weak v)
-       deRefWeak               -- :: Weak v -> IO (Maybe v)
+       deRefWeak,              -- :: Weak v -> IO (Maybe v)
+       finalise,               -- :: Weak v -> IO ()
 
        -- Not yet implemented
-       -- finalise             -- :: Weak v -> IO ()
        -- replaceFinaliser     -- :: Weak v -> IO () -> IO ()
 
-       mkWeakPtr               -- :: k -> IO () -> IO (Weak k)
-       mkWeakPair              -- :: k -> v -> IO () -> IO (Weak (k,v))
-       addFinaliser            -- :: k -> IO () -> IO ()
+       mkWeakPtr,              -- :: k -> IO () -> IO (Weak k)
+       mkWeakPair,             -- :: k -> v -> IO () -> IO (Weak (k,v))
+       mkWeakNoFinaliser,      -- :: k -> v -> IO (Weak v)
+       addFinaliser,           -- :: k -> IO () -> IO ()
        addForeignFinaliser     -- :: ForeignObj -> IO () -> IO ()
    ) where
 </verb></tscreen>
@@ -188,6 +189,26 @@ weak pointers:
 These more general weak pointers are enough to implement memo
 tables properly.
 
+A weak pointer can be finalised early, using the <tt/finalise/ operation:
+
+<tscreen><verb>
+finalise :: Weak v -> IO ()
+</verb></tscreen>
+
+When you don't need a finaliser, we provide the following operation:
+
+<tscreen><verb>
+mkWeakNoFinaliser :: k -> v -> IO (Weak v)
+mkWeakNoFinaliser k v = mkWeak k v (return ())
+</verb></tscreen>
+
+Which creates a weak pointer with a null finaliser.  Lots of null
+finalisers can be expensive, because each one runs in a separate
+thread, so the intention is that <tt/mkWeakNoFinaliser> avoids all the
+extra costs by generating a special kind of weak pointer without a
+finaliser.  So although the semantics of mkWeakNoFinaliser is as given
+above, its actual implementation is somewhat different.
+
 <sect1> A precise semantics
 <p>
 The above informal specification is fine for simple situations,