diff options
| -rw-r--r-- | libraries/base/GHC/IO/Unsafe.hs | 26 |
1 files changed, 5 insertions, 21 deletions
diff --git a/libraries/base/GHC/IO/Unsafe.hs b/libraries/base/GHC/IO/Unsafe.hs index 2a5a87f7bc..0d98d7050b 100644 --- a/libraries/base/GHC/IO/Unsafe.hs +++ b/libraries/base/GHC/IO/Unsafe.hs @@ -108,33 +108,17 @@ unsafeDupablePerformIO (IO m) = case runRW# m of (# _, a #) -> a When passed a value of type @IO a@, the 'IO' will only be performed when the value of the @a@ is demanded. This is used to implement lazy file reading, see 'System.IO.hGetContents'. + +@ unsafeInterleaveIO m === pure (unsafePerformIO m) @ -} {-# INLINE unsafeInterleaveIO #-} unsafeInterleaveIO :: IO a -> IO a -unsafeInterleaveIO m = unsafeDupableInterleaveIO (noDuplicate >> m) +unsafeInterleaveIO m = pure (unsafePerformIO m) --- We used to believe that INLINE on unsafeInterleaveIO was safe, --- because the state from this IO thread is passed explicitly to the --- interleaved IO, so it cannot be floated out and shared. --- --- HOWEVER, if the compiler figures out that r is used strictly here, --- then it will eliminate the thunk and the side effects in m will no --- longer be shared in the way the programmer was probably expecting, --- but can be performed many times. In #5943, this broke our --- definition of fixIO, which contains --- --- ans <- unsafeInterleaveIO (takeMVar m) --- --- after inlining, we lose the sharing of the takeMVar, so the second --- time 'ans' was demanded we got a deadlock. We could fix this with --- a readMVar, but it seems wrong for unsafeInterleaveIO to sometimes --- share and sometimes not (plus it probably breaks the noDuplicate). --- So now, we do not inline unsafeDupableInterleaveIO. +-- | @ unsafeDupableInterleaveIO m = pure (unsafeDupablePerformIO m) @ {-# INLINE unsafeDupableInterleaveIO #-} unsafeDupableInterleaveIO :: IO a -> IO a -unsafeDupableInterleaveIO (IO m) - = IO ( \ s -> - (# s, runRW# (\s2 -> case m s2 of (# _, res #) -> res) #)) +unsafeDupableInterleaveIO m = pure (unsafeDupablePerformIO m) {-| Ensures that the suspensions under evaluation by the current thread |