Optimize dumpsym maximum memory usage

This took ages to track down. Turns out GHC keeps references to all
loaded ModIfaces in the PackageInterfaceTable in ExternalPackageState
for caching. ExternalPackageState is in an IORef in HscEnv so
overwriting that with a copy from right after init improves things a
bit. Next I use unsafeInterleaveIO to load the ModIfaces as we serialize
the symbol table rather than before thus reducing the amount of memory
needed even more.

Language/Haskell/GhcMod/Find.hs

@@ -1,4 +1,4 @@
-{-# LANGUAGE CPP, BangPatterns, DoAndIfThenElse #-}
+{-# LANGUAGE CPP, BangPatterns, DoAndIfThenElse, TupleSections #-}
 
 module Language.Haskell.GhcMod.Find
 #ifndef SPEC
@@ -18,6 +18,20 @@ module Language.Haskell.GhcMod.Find
 #endif
   where
 
+import Control.Applicative
+import Control.Monad
+import Control.Exception
+import Control.Concurrent
+import Data.List
+import Data.Binary
+import Data.ByteString (ByteString)
+import Data.IORef
+import qualified Data.ByteString.Lazy as LBS
+import qualified GHC as G
+import FastString
+import Module
+import OccName
+import HscTypes
 import Language.Haskell.GhcMod.Convert
 import Language.Haskell.GhcMod.Gap
 import Language.Haskell.GhcMod.Monad
@@ -26,35 +40,36 @@ import Language.Haskell.GhcMod.PathsAndFiles
 import Language.Haskell.GhcMod.Types
 import Language.Haskell.GhcMod.Utils
 import Language.Haskell.GhcMod.World
+import Language.Haskell.GhcMod.Target
+import Language.Haskell.GhcMod.LightGhc
 
-import qualified GHC as G
-import Name
-import Module
 import Exception
 
-import Control.Applicative
-import Control.Monad
 import Control.Monad.Trans.Control
-import Control.Concurrent
 import Data.Function
-import Data.List
-import Data.Map (Map)
-import qualified Data.Map as M
 import System.Directory
 import System.Directory.ModTime
 import System.FilePath ((</>))
 import System.IO
+import System.IO.Unsafe (unsafeInterleaveIO)
 import Prelude
 
+import Data.Map.Strict (Map)
+import qualified Data.Map.Strict as M
+import Data.Set (Set)
+import qualified Data.Set as S
+
 ----------------------------------------------------------------
 
 -- | Type of function and operation names.
-type Symbol = String
+type Symbol = ByteString
+type ModuleNameBS = ByteString
+
 -- | Database from 'Symbol' to \['ModuleString'\].
 data SymbolDb = SymbolDb
-  { table             :: Map Symbol [ModuleString]
+  { table             :: Map Symbol [ModuleNameBS]
   , symbolDbCachePath :: FilePath
-  } deriving (Show)
+  }
 
 isOutdated :: IOish m => SymbolDb -> GhcModT m Bool
 isOutdated db =
@@ -64,18 +79,18 @@ isOutdated db =
 
 -- | Looking up 'SymbolDb' with 'Symbol' to \['ModuleString'\]
 --   which will be concatenated. 'loadSymbolDb' is called internally.
-findSymbol :: IOish m => Symbol -> GhcModT m String
+findSymbol :: IOish m => String -> GhcModT m String
 findSymbol sym = do
   tmpdir <- cradleTempDir <$> cradle
   loadSymbolDb tmpdir >>= lookupSymbol sym
 
 -- | Looking up 'SymbolDb' with 'Symbol' to \['ModuleString'\]
 --   which will be concatenated.
-lookupSymbol :: IOish m => Symbol -> SymbolDb -> GhcModT m String
+lookupSymbol :: IOish m => String -> SymbolDb -> GhcModT m String
-lookupSymbol sym db = convert' $ lookupSym sym db
+lookupSymbol sym db = convert' $ lookupSym (fastStringToByteString $ mkFastString sym) db
 
 lookupSym :: Symbol -> SymbolDb -> [ModuleString]
-lookupSym sym db = M.findWithDefault [] sym $ table db
+lookupSym sym db = map (ModuleString . unpackFS . mkFastStringByteString) $ M.findWithDefault [] sym $ table db
 
 ---------------------------------------------------------------
 
@@ -85,14 +100,12 @@ loadSymbolDb dir = do
   ghcMod <- liftIO ghcModExecutable
   readProc <- gmReadProcess
   file   <- liftIO $ chop <$> readProc ghcMod ["dumpsym", dir] ""
-  !db    <- M.fromAscList . map conv . lines <$> liftIO (readFile file)
+  !db    <- M.fromList . decode <$> liftIO (LBS.readFile file)
   return $ SymbolDb
     { table             = db
     , symbolDbCachePath = file
     }
   where
-    conv :: String -> (Symbol, [ModuleString])
-    conv = read
     chop :: String -> String
     chop "" = ""
     chop xs = init xs
@@ -107,19 +120,21 @@ loadSymbolDb dir = do
 dumpSymbol :: IOish m => FilePath -> GhcModT m String
 dumpSymbol dir = do
   create <- (liftIO . isOlderThan cache) =<< timedPackageCaches
-  runGmPkgGhc $ do
+  pkgOpts <- packageGhcOptions
-    when create $
+  when create $ liftIO $ do
-      liftIO . writeSymbolCache cache =<< getGlobalSymbolTable
+    withLightHscEnv pkgOpts $ \env -> do
-    return $ unlines [cache]
+      writeSymbolCache cache =<< getGlobalSymbolTable env
+
+  return $ unlines [cache]
   where
     cache = dir </> symbolCacheFile
 
 writeSymbolCache :: FilePath
-                 -> [(Symbol, [ModuleString])]
+                 -> Map Symbol (Set ModuleNameBS)
                  -> IO ()
 writeSymbolCache cache sm =
   void . withFile cache WriteMode $ \hdl ->
-    mapM (hPrint hdl) sm
+    LBS.hPutStr hdl (encode sm)
 
 -- | Check whether given file is older than any file from the given set.
 -- Returns True if given file does not exist.
@@ -133,28 +148,30 @@ isOlderThan cache files = do
     return $ any (tCache <=) $ map tfTime files -- including equal just in case
 
 -- | Browsing all functions in all system modules.
-getGlobalSymbolTable :: LightGhc [(Symbol, [ModuleString])]
+getGlobalSymbolTable :: HscEnv -> IO (Map Symbol (Set ModuleNameBS))
-getGlobalSymbolTable = do
+getGlobalSymbolTable hsc_env =
-  df  <- G.getSessionDynFlags
+  foldM (extend hsc_env) M.empty $ listVisibleModules $ hsc_dflags hsc_env
-  let mods = listVisibleModules df
-  moduleInfos <- mapM G.getModuleInfo mods
-  return $ collectModules
-         $ extractBindings `concatMap` (moduleInfos `zip` mods)
 
-extractBindings :: (Maybe G.ModuleInfo, G.Module)
+extend :: HscEnv
-                -> [(Symbol, ModuleString)]
+       -> Map Symbol (Set ModuleNameBS)
-extractBindings (Nothing,  _)   = []
+       -> Module
-extractBindings (Just inf, mdl) =
+       -> IO (Map Symbol (Set ModuleNameBS))
-  map (\name -> (getOccString name, modStr)) names
+extend hsc_env mm mdl = do
-  where
+  eps <- readIORef $ hsc_EPS hsc_env
-    names  = G.modInfoExports inf
+  modinfo <- unsafeInterleaveIO $ runLightGhc hsc_env $ do
-    modStr = ModuleString $ moduleNameString $ moduleName mdl
+    G.getModuleInfo mdl <* liftIO (writeIORef (hsc_EPS hsc_env) eps)
 
-collectModules :: [(Symbol, ModuleString)]
+  return $ M.unionWith S.union mm $ extractBindings modinfo mdl
-               -> [(Symbol, [ModuleString])]
+
-collectModules = map tieup . groupBy ((==) `on` fst) . sort
+extractBindings :: Maybe G.ModuleInfo
-  where
+                -> G.Module
-    tieup x = (head (map fst x), map snd x)
+                -> Map Symbol (Set ModuleNameBS)
+extractBindings Nothing  _   = M.empty
+extractBindings (Just inf) mdl = M.fromList $ do
+  name <- G.modInfoExports inf
+  let sym = fastStringToByteString $ occNameFS $ G.getOccName name
+      mdls = S.singleton $ fastStringToByteString $ moduleNameFS $ moduleName mdl
+  return (sym, mdls)
 
 ----------------------------------------------------------------