12243d2279
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. |
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