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Re: 1.7.8: write fails with EAGAIN
On Mon, Mar 07, 2011 at 11:39:51AM +0100, Corinna Vinschen wrote:
>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.
I can barely convince myself that there's a pathological case where an
EAGAIN could leak out. I'm investigating now.
cgf
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