Re: [PATCH stable-2.15] Fixup compatibility with GHC 7.4/base 4.5

['Brian Foley' via ganeti-devel]

On Fri, Jun 10, 2016 at 01:51:56PM +0200, 'Iustin Pop' via ganeti-devel wrote:
> It looks like commit c429dd26 introduced the use of
> atomicModifyIORef', which is only present in base 4.6 (GHC 7.6).
> Let's fix that by importing the actual implementation of said function
> from base 4.6 in case we're running with earlier versions.
> 
> Signed-off-by: Iustin Pop 

LGTM. Thanks!

[PATCH stable-2.15] Fixup compatibility with GHC 7.4/base 4.5

['Iustin Pop' via ganeti-devel]

It looks like commit c429dd26 introduced the use of
atomicModifyIORef', which is only present in base 4.6 (GHC 7.6).
Let's fix that by importing the actual implementation of said function
from base 4.6 in case we're running with earlier versions.

Signed-off-by: Iustin Pop 
---
 src/Ganeti/Compat.hs  | 14 ++
 src/Ganeti/JQScheduler.hs |  3 ++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/Ganeti/Compat.hs b/src/Ganeti/Compat.hs
index e5276d1..8e002e7 100644
--- a/src/Ganeti/Compat.hs
+++ b/src/Ganeti/Compat.hs
@@ -41,10 +41,12 @@ module Ganeti.Compat
   ( rwhnf
   , Control.Parallel.Strategies.parMap
   , finiteBitSize
+  , atomicModifyIORef'
   ) where
 
 import qualified Control.Parallel.Strategies
 import qualified Data.Bits
+import qualified Data.IORef
 
 -- | Wrapper over the function exported from
 -- "Control.Parallel.Strategies".
@@ -67,3 +69,15 @@ finiteBitSize :: (Data.Bits.FiniteBits a) => a -> Int
 finiteBitSize = Data.Bits.finiteBitSize
 #endif
 {-# INLINE finiteBitSize #-}
+
+-- FIXME: remove this when dropping support for GHC 7.4.
+atomicModifyIORef' :: Data.IORef.IORef a -> (a -> (a, b)) -> IO b
+#if MIN_VERSION_base(4,6,0)
+atomicModifyIORef' = Data.IORef.atomicModifyIORef'
+#else
+atomicModifyIORef' ref f = do
+b <- Data.IORef.atomicModifyIORef ref $ \a ->
+case f a of
+v@(a',_) -> a' `seq` v
+b `seq` return b
+#endif
diff --git a/src/Ganeti/JQScheduler.hs b/src/Ganeti/JQScheduler.hs
index 4f18f47..3a46934 100644
--- a/src/Ganeti/JQScheduler.hs
+++ b/src/Ganeti/JQScheduler.hs
@@ -56,7 +56,7 @@ import Control.Monad
 import Control.Monad.IO.Class
 import Data.Function (on)
 import Data.Functor ((<$))
-import Data.IORef
+import Data.IORef (IORef, atomicModifyIORef, newIORef, readIORef)
 import Data.List
 import Data.Maybe
 import qualified Data.Map as Map
@@ -66,6 +66,7 @@ import qualified Data.Set as S
 import System.INotify
 
 import Ganeti.BasicTypes
+import Ganeti.Compat
 import Ganeti.Constants as C
 import Ganeti.Errors
 import Ganeti.JQScheduler.Filtering (applyingFilter, jobFiltering)
-- 
2.8.0.rc3.226.g39d4020