Expose GC end timestamp

1 files changed, 18 insertions, 3 deletions

diff --git a/src/GHC/GC_Hook.hs b/src/GHC/GC_Hook.hs
index ea1586c..44826c9 100644
--- a/src/GHC/GC_Hook.hs
+++ b/src/GHC/GC_Hook.hs
@@ -3,6 +3,7 @@
 module GHC.GC_Hook (
   setGCHook,
   getGCLog,
+  Details(..),
 ) where
 
 import Control.Monad ((>=>))
@@ -11,14 +12,23 @@ import Foreign.C.Types (CChar, CSize(..))
 import Foreign.Marshal.Alloc (alloca, allocaBytes)
 import Foreign.Ptr (Ptr, castPtr, plusPtr)
 import Foreign.Storable (peek)
+import qualified System.Clock as Clock
 
 foreign import ccall "set_gchook" c_set_gchook
   :: IO ()
 foreign import ccall "copy_log_to_buffer" c_copy_log_to_buffer
   :: CSize -> Ptr CChar -> Ptr CSize -> Ptr CSize -> IO ()
 
+-- | GC details as given to the GC hook installed by 'setGCHook'. The only
+-- field that is not contained in `GCDetails_` provided by the GHC RTS is
+-- 'detTimestamp', which is the time at which the GC was finished. The GC start
+-- time can probably be computed by subtracting 'detElapsedNs' from this.
 data Details = Details
-  { -- | The generation number of this GC
+  { -- | The timestamp at which the GC was finished (i.e. `gcDoneHook` was
+    -- called). Note: this is recorded using the 'Clock.Monotonic' clock.
+    detTimestamp :: Clock.TimeSpec
+
+  , -- | The generation number of this GC
     detGen :: Word32
   , -- | Number of threads used in this GC
     detThreads :: Word32
@@ -76,12 +86,15 @@ data Details = Details
   deriving (Show)
 
 zeroDetails :: Details
-zeroDetails = Details 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
+zeroDetails = Details (Clock.fromNanoSecs 0) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
 
+-- | Initialise the GC hook.
 setGCHook :: IO ()
 setGCHook = do
   c_set_gchook
 
+-- | Get the log of 'Details' structures up until now; also clears the log. You
+-- will never get the same structure twice.
 getGCLog :: IO [Details]
 getGCLog =
   let bufferCapacity = 2048
@@ -105,7 +118,9 @@ peekDetails unitsize startptr =
   where
     fields :: [(Int, Ptr a -> Details -> IO Details)]
     fields =
-      [(4, peekModify $ \d x -> d { detGen = x })
+      [(8, peekModify $ \d x -> d { detTimestamp = (detTimestamp d) { Clock.sec = x } })
+      ,(8, peekModify $ \d x -> d { detTimestamp = (detTimestamp d) { Clock.nsec = x } })
+      ,(4, peekModify $ \d x -> d { detGen = x })
       ,(4, peekModify $ \d x -> d { detThreads = x })
       ,(8, peekModify $ \d x -> d { detAllocatedBytes = x })
       ,(8, peekModify $ \d x -> d { detLiveBytes = x })