relay log problem

[Ken Thomases]

On Jan 28, 2010, at 5:21 PM, Michael Stefaniuc wrote:

> On 01/28/2010 10:59 PM, Henri Verbeet wrote:
>> On 28 January 2010 22:39, Stefan Leichter<Stefan.Leichter at camline.com>  wrote:
>>> Is this a know problem? Is a work around available?
>>> 
>> Yeah, that's a known problem. As a workaround you can use ">>"
>> (append) instead of ">" to redirect to the file. You'll still need the
>> "2>&1" to redirect stderr to stdout, of course.
> That won't workaround the problem. The problem is that there are multiple threads/programs that write at the same time to stdout/stderr.
> I have seen it with fixme/err/warn messages too; even with crash dumps.

Using >> in the shell causes the stdout file descriptor to be opened with O_APPEND.  Using 2>&1 makes stderr dup the file descriptor, so it gets the same flag.

With O_APPEND, the kernel ensures that all writes append to the file.  Multiple threads or programs using an O_APPEND descriptor can't overwrite each other.  If the code uses multiple writes for a single line, then those multiple writes can be interleaved, but can't overwrite.  And, for the most part, Wine's debug logging uses single writes so it won't even interleave.

Regards,
Ken