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Please try the latest snapshot [Re: 1.7.8: write fails with EAGAIN]
On Mon, Mar 07, 2011 at 11:38:49AM -0500, Christopher Faylor wrote:
>On Mon, Mar 07, 2011 at 10:37:08AM -0500, Christopher Faylor wrote:
>>On Mon, Mar 07, 2011 at 11:39:51AM +0100, Corinna Vinschen wrote:
>>>On Mar 5 21:12, Robert Wruck wrote:
>>>> recently, I found that cygwin-git was not able to 'cat-file' files
>>>> that exceeded some size (in my case about 80MB).
>>>> I tracked this down to the cygwin implementation of write() that
>>>> behaves quite odd in some cases.
>>>> I wrote a small program (source attached) that mmaps a given file
>>>> and tries to write it to another file or stdout.
>>>> The results vary:
>>>> If the destination is a file (`writetest infile outfile` or
>>>> `writetest infile > outfile`), the write succeeds in a single call.
>>>> If the destination is a pipe (`writetest infile | cat > outfile`),
>>>> the write succeeds in most cases. BUT:
>>>> Under WinXP (XP Service Pack 2, 32bit), the call returns -1 and
>>>> errno=EAGAIN. Nevertheless, SOME data is written to the pipe (in my
>>>> case 4096 byte for each call).
>>>> This breaks git since it does an infinite loop while errno=EAGAIN.
>>>Hang on, you are saying that a *blocking* write(2) to a pipe returns
>>>with EAGAIN? Are you sure? It would be quite a surprise if git would
>>>actually do that. EAGAIN is only an expected error for non-blocking
>>>I/O, so applications which use blocking I/O usually only test for EINTR.
>>I can barely convince myself that there's a pathological case where an
>>EAGAIN could leak out. I'm investigating now.
>Actually, in this case, it looks like the problem is that Windows
>doesn't like sending a huge buffer to a pipe. The errno in this case
>should probably be something like EFBIG rather than EAGAIN.
>Does git deal with this type of errno gracefully or does it just abort
>if the write() fails for any reason? I'd rather just fail and let the
>caller deal with it than complicate Cygwin's code by trying to loop
>writing smaller amount of data to the pipe so I'd prefer just changing
>the errno if that solves the problem.
I've just uploaded a snapshot which attempts to work around this
problem. I ended up making some fairly substantial changes to the
pipe handling so this needs some serious testing, especially on
different platforms, e.g., XP, XP64, Windows 2008, etc.
Please try the latest snapshot at:
Problem reports: http://cygwin.com/problems.html
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