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| author |  Joey Hess <joey@kitenet.net> | 2011-11-25 11:46:07 -0400 |
|---|---|---|
| committer | Joey Hess <joey@kitenet.net> | 2011-11-25 11:51:06 -0400 |
| commit | 12243d2279cae65ed163bdec1edb268817514265 (patch) | |
| tree | 9e8dfecb67c8e070a2e9d929d4ee9bf142bbc369 /Messages.hs | |
| parent | 566a5f4881ef036d748ebc55140358087aaae63c (diff) | |
Flush json output, avoiding a buffering problem that could result in doubled output.
The bug was that with --json, output lines were sometimes doubled. For
example, git annex init --json would output two lines, despite only running
one thing. Adding to the weirdness, this only occurred when the output
was redirected to a pipe or a file.
Strace showed two processes outputting the same buffered output.
The second process was this writer process (only needed to work around
bug #624389):
_ <- forkProcess $ do
hPutStr toh $ unlines paths
hClose toh
exitSuccess
The doubled output occurs when this process exits, and ghc flushes the
inherited stdout buffer. Why only when piping? I don't know, but ghc may
be behaving differently when stdout is not a terminal.
While this is quite possibly a ghc bug, there is a nice fix in git-annex.
Explicitly flushing after each chunk of json is output works around the
problem, and as a side effect, json is streamed rather than being output
all at the end when performing an expensive operaition.
However, note that this means all uses of putStr in git-annex must be
explicitly flushed. The others were, already.
Diffstat (limited to 'Messages.hs')
| -rw-r--r-- | Messages.hs | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/Messages.hs b/Messages.hs index 6ea347ca4..a7f14f485 100644 --- a/Messages.hs +++ b/Messages.hs @@ -129,7 +129,7 @@ handle json normal = Annex.getState Annex.output >>= go where go Annex.NormalOutput = liftIO normal go Annex.QuietOutput = q - go Annex.JSONOutput = liftIO json + go Annex.JSONOutput = liftIO $ flushed $ json q :: Monad m => m () q = return () |