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From Jeff Trawick <traw...@gmail.com>
Subject Re: Why does apr_file_read() with !APR_XTHREAD use mutexes on Windows
Date Tue, 27 Apr 2010 11:03:21 GMT
On Tue, Apr 27, 2010 at 5:47 AM, Bert Huijben <bert@qqmail.nl> wrote:
>
>
>> -----Original Message-----
>> From: Jeff Trawick [mailto:trawick@gmail.com]
>> Sent: maandag 26 april 2010 23:14
>> To: APR Developer List
>> Cc: Bert Huijben
>> Subject: Re: Why does apr_file_read() with !APR_XTHREAD use mutexes on
>> Windows
>>
>> On Mon, Apr 26, 2010 at 4:38 PM, William A. Rowe Jr.
>> <wrowe@rowe-clan.net> wrote:
>> > On 4/26/2010 2:19 PM, Jeff Trawick wrote:
>> >>
>> >> So I don't think there's any hidden "reason" why a mutex should always
>> >> be obtained on Windows.  I too wouldn't be surprised if the fix breaks
>> >> some app code somewhere.
>> >
>> > Keep in mind fd-based operations are atomic on Unix, but not so on
>> windows.
>>
>> Since these are buffered files, it doesn't even come down to
>> differences in OS file operations; operations on the buffer would be
>> the expected failure point.
>>
>> So the question is whether or not APR expects multi-threaded apps
>> sharing a buffered file to turn on the XTHREAD flag.
>
> Another thing I was thinking about is how the append mode is used. I can
> imagine that is used to write to a single logfile in a multithreaded
> application. (But if we don't enable the mutex on other operating systems,
> it should probably be fixed in the application)

Append is special, in that POSIX has an append flag on open() which
handles atomicity of seek-to-end+write; so that mutex isn't needed on
all operating systems.  This is a case where Windows needs a mutex but
Unix doesn't.

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