wip

hbs2-storage-simple/lib/HBS2/Storage/Compact.hs

@@ -77,9 +77,9 @@ data Header =
 data CompactStorage =
   CompactStorage
   { csHandle     :: MVar Handle
-  , csHandleSem  :: TSem
-  , csHeaderOff  :: TVar EntryOffset
-  , csKeys       :: TVar (HashMap ByteString (Either IndexEntry ByteString))
+  , csHeaderOff  :: IORef EntryOffset
+  , csSeq        :: IORef Integer
+  , csKeys       :: IORef (HashMap ByteString (Either (IndexEntry,Integer) (ByteString,Integer)))
   }
 
 type ForCompactStorage m = MonadIO m
@@ -104,18 +104,17 @@ compactStorageOpen _ fp = do
   sz <- hFileSize ha
   mha <- newMVar ha
 
-  hoff0 <- newTVarIO 0
-  keys0 <- newTVarIO mempty
-
-  sem <- atomically $ newTSem 1
+  hoff0 <- newIORef 0
+  keys0 <- newIORef mempty
+  ss   <- newIORef 0
 
   if sz == 0 then
-    pure $ CompactStorage mha sem hoff0 keys0
+    pure $ CompactStorage mha hoff0 ss keys0
   else do
     (p,header) <- readHeader mha Nothing >>= maybe (throwIO InvalidHeader) pure
     traceM (show ("HEADER",header))
-    hoff <- newTVarIO p
-    let sto = CompactStorage mha sem hoff keys0
+    hoff <- newIORef p
+    let sto = CompactStorage mha hoff ss keys0
     readIndex sto (hdrIndexOffset header) (hdrIndexEntries header)
 
     flip fix (hdrPrev header) $ \next -> \case
@@ -162,17 +161,16 @@ readIndex sto offset num = liftIO do
     when (rn /= num) do
       throwIO BrokenIndex
 
-    atomically do
-      let new = HM.fromList [ (k,Left e) | e@(IndexEntry _ _ _ _ k) <- entries ]
+    let new = HM.fromList [ (idxEntryKey e,Left (e,0)) | e <- entries ]
       -- readIndex from newer to older
       -- so we keep only the newer values in map
-      modifyTVar (csKeys sto) (HM.unionWith (\_ b -> b) new)
+    modifyIORef' (csKeys sto) (HM.unionWith (\_ b -> b) new)
 
 compactStorageCommit :: ForCompactStorage m => CompactStorage -> m ()
 compactStorageCommit sto = liftIO do
   withMVar (csHandle sto) $ \ha -> do
     hSeek ha SeekFromEnd 0
-    kv <- readTVarIO (csKeys sto) <&> HM.toList
+    kv <- readIORef (csKeys sto) <&> HM.toList
 
     let items = [ (k, v) | (k, Right v) <- kv ]
 
@@ -183,20 +181,20 @@ compactStorageCommit sto = liftIO do
       idxEntries <- flip fix (off0, items, mempty) $ \next (off, what, idx) -> do
          case what of
           [] -> pure idx
-          ((k,v):rest) -> do
+          ((k,(v,i)):rest) -> do
             BS.hPut ha v
             let sz = fromIntegral $ BS.length v
-            next (off + sz, rest, IndexEntry (fromIntegral off) (fromIntegral sz) 0 False k : idx)
+            next (off + sz, rest, (IndexEntry (fromIntegral off) (fromIntegral sz) 0 False k,i) : idx)
 
       offIdx0 <- hTell ha <&> fromIntegral
 
-      for_ idxEntries $ \e -> do
+      for_ idxEntries $ \(e,_) -> do
         let lbs = serialise e
         LBS.hPut ha (B.toLazyByteString $
                         word16BE (fromIntegral $ LBS.length lbs)
                         <> B.lazyByteString lbs)
 
-      offPrev <- readTVarIO (csHeaderOff sto)
+      offPrev <- readIORef (csHeaderOff sto)
 
       -- FIXME: maybe-slow-length-calc
       appendHeader ha (Just offPrev) offIdx0 (fromIntegral $ length idxEntries)
@@ -206,24 +204,32 @@ compactStorageCommit sto = liftIO do
 
       offLast <- hTell ha <&> fromIntegral
 
-      let es = HM.fromList [ (idxEntryKey e, Left e) | e <- idxEntries ]
+      -- atomically do
+      atomicWriteIORef (csHeaderOff sto) (offLast - headerSize 1)
+      atomicModifyIORef' (csKeys sto) $ \m -> do
+        let new = foldl merge m idxEntries
+        (new, ())
 
-      atomically do
-        writeTVar (csHeaderOff sto) (offLast - headerSize 1)
-        modifyTVar (csKeys sto) (`mappend` es)
+      where
+        merge m (el,i) = HM.insertWith mergeEl (idxEntryKey el) (Left (el,i)) m
+        mergeEl new old = if getSeq new >= getSeq old then new else old
+        getSeq = \case
+          Left (_,i) -> i
+          Right (_,i) -> i
 
 compactStoragePut :: ForCompactStorage m => CompactStorage -> ByteString -> ByteString -> m ()
 compactStoragePut sto k v = do
   -- TODO: ASAP-do-not-write-value-if-not-changed
-  atomically $ modifyTVar (csKeys sto) (HM.insert k (Right v))
+  c <- atomicModifyIORef' (csSeq sto) (\n -> (n+1,n))
+  atomicModifyIORef' (csKeys sto) (\m -> (HM.insert k (Right (v,c)) m, ()))
 
 compactStorageGet :: ForCompactStorage m => CompactStorage -> ByteString -> m (Maybe ByteString)
 compactStorageGet sto key = do
-  val <- readTVarIO (csKeys sto) <&> HM.lookup key
+  val <- readIORef (csKeys sto) <&> HM.lookup key
   case val of
     Nothing -> pure Nothing
-    Just (Right s) -> pure (Just s)
-    Just (Left e)  -> liftIO do
+    Just (Right (s,_)) -> pure (Just s)
+    Just (Left (e,_))  -> liftIO do
       r <- withMVar (csHandle sto) $ \ha -> do
              try @_ @IOException do
                   hSeek ha AbsoluteSeek (fromIntegral $ idxEntryOffset e)