NGX error logging - Race condition possible?
igor at sysoev.ru
Mon Sep 3 06:14:30 UTC 2018
> On 2 Sep 2018, at 21:44, Slawitscheck Stefan via nginx-devel <nginx-devel at nginx.org> wrote:
> Dear Development Team,
> I have one question about the logging mechanism of nginx with more worker processes under Windows.
> In ngx_log.c is the function ngx_write_console() which calls the systemcall WriteFile().
> How is do you ensures that there is no race condition while using this function to write into the error.log file with multiple working processes?
> From my understanding, each worker process writes into the error.log file by itself. So it could be that there are two processes (worker) trying to write at the same time?
> So usually you need some locking, semaphore, mutex or something like that?
> If you ensure that there will be no race condition, how do you guarantee it?
> I am looking forward to your answer.
It should be guaranteed by CreateFile options: FILE_APPEND_DATA | SYNCHRONIZE.
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