Mail Archives: cygwin/2011/03/07/05:40:23
On Mar 5 21:12, Robert Wruck wrote:
> Hi,
>
> 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.
Where you able to reproduce the issue with the testcase you attached to
your mail? If so, you forgot to add a hint how to use it and an example
of the expected outcome. That would be quite helpful.
> Any ideas where to investigate further? EAGAIN is set for example in
> fhandler.cc, fhandler_base_overlapped::has_ongoing_io but I don't
> know whether that function is involved in my case.
It is. The overlapped io stuff is only used for pipes and fifos right
now.
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
Red Hat
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