diff options
| -rw-r--r-- | libraries/base/Foreign/C/Error.hs | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/libraries/base/Foreign/C/Error.hs b/libraries/base/Foreign/C/Error.hs index 90b949b782..6d6c0cc0dd 100644 --- a/libraries/base/Foreign/C/Error.hs +++ b/libraries/base/Foreign/C/Error.hs @@ -255,11 +255,15 @@ isValidErrno (Errno errno) = errno /= -1 -- | Get the current value of @errno@ in the current thread. -- +-- On GHC, the runtime will ensure that any Haskell thread will only see "its own" +-- @errno@, by saving and restoring the value when Haskell threads are scheduled +-- across OS threads. getErrno :: IO Errno -- We must call a C function to get the value of errno in general. On -- threaded systems, errno is hidden behind a C macro so that each OS --- thread gets its own copy. +-- thread gets its own copy (`saved_errno`, which `rts/Schedule.c` restores +-- back into the thread-local `errno` when a Haskell thread is rescheduled). getErrno = do e <- get_errno; return (Errno e) foreign import ccall unsafe "HsBase.h __hscore_get_errno" get_errno :: IO CInt |