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author | Niklas Hambüchen <mail@nh2.me> | 2019-02-14 16:52:17 -0500 |
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committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2019-02-19 06:20:13 -0500 |
commit | 76ac103f5021cba5cd000293c7cb8c2bd3148e7a (patch) | |
tree | f5b48d9ad3877beb62f223a6d96fea6a714b78d9 | |
parent | 7833cf407d1f608bebb1d38bb99d3035d8d735e6 (diff) | |
download | haskell-76ac103f5021cba5cd000293c7cb8c2bd3148e7a.tar.gz |
base: Document errno behaviour in haddocks.
Also add an implementation comment for details.
-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 |