3 files changed, 9 insertions, 3 deletions

diff --git a/adjmix/Adjmix.hs b/adjmix/Adjmix.hs
index 645ac6a..94416ac 100644
--- a/adjmix/Adjmix.hs
+++ b/adjmix/Adjmix.hs
@@ -3,6 +3,7 @@
 import Options.Applicative
 
 import System.FilePath
+import System.FileLock
 
 import Data.Char
 
@@ -20,6 +21,7 @@ optionParser = Options
                                <> metavar "DIRECTORY"
                                <> value "/dev/shm/mix"
                                <> showDefault
+                               <> help "Base directory"
                              )
                <*> strOption ( long "target"
                                <> short 't'
@@ -35,16 +37,19 @@ optionParser = Options
                <*> ( ( Set <$> option auto ( long "set"
                                              <> short 'o'
                                              <> metavar "LEVEL"
+                                             <> help "Overwrite the current level"
                                            )
                      )
                      <|> ( Add <$> option auto ( long "add"
                                                  <> short 'a'
                                                  <> metavar "LEVEL"
+                                                 <> help "Add to the current level"
                                                )
                          )
                      <|> ( Sub <$> option auto ( long "sub"
                                                  <> short 's'
                                                  <> metavar "LEVEL"
+                                                 <> help "Subtract from the current level"
                                                )
                          )
                    )
@@ -59,7 +64,7 @@ main = execParser opts >>= adjmix
            )
 
 adjmix :: Options -> IO ()
-adjmix Options{..} = do
+adjmix Options{..} = withFileLock levelFile' Exclusive $ const $ do
   oldLevel <- readFile levelFile' >>= readIO . stripSpace
   let
     newLevel = oldLevel `doAdjustment` adjustment
diff --git a/trivmix.cabal b/trivmix.cabal
index 803c640..54aad76 100644
--- a/trivmix.cabal
+++ b/trivmix.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                trivmix
-version:             2.5.2
+version:             2.5.3
 -- synopsis:            
 -- description:         
 license:             PublicDomain
@@ -48,6 +48,7 @@ executable adjmix
   build-depends:       base >=4.7 && <4.8
                      , optparse-applicative >=0.11 && <1
                      , filepath >=1.3 && <2
+                     , filelock >=0.1 && <1
                      , trivmix
   hs-source-dirs:      adjmix
   default-language:    Haskell2010
diff --git a/trivmix.nix b/trivmix.nix
index 298174b..d29bb48 100644
--- a/trivmix.nix
+++ b/trivmix.nix
@@ -6,7 +6,7 @@
 
 cabal.mkDerivation (self: {
   pname = "trivmix";
-  version = "2.5.2";
+  version = "2.5.3";
   src = ./.;
   isLibrary = true;
   isExecutable = true;