Re: BUG #16685: The ecpg thread/descriptor test fails sometimes on Windows - Mailing list pgsql-bugs

From Alexander Lakhin
Subject Re: BUG #16685: The ecpg thread/descriptor test fails sometimes on Windows
Date
Msg-id dedbf623-ae82-5635-a639-944395697799@gmail.com
Whole thread Raw
In response to Re: BUG #16685: The ecpg thread/descriptor test fails sometimes on Windows  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: BUG #16685: The ecpg thread/descriptor test fails sometimes on Windows  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-bugs
24.10.2020 19:54, Tom Lane wrote:
> I'm forced to the conclusion that there's something wrong with
> ECPG's emulation of pthread_once ...
>
> ... and now that I look at it, it seems just as obvious what
> is wrong there:
>
> void
> win32_pthread_once(volatile pthread_once_t *once, void (*fn) (void))
> {
>     if (!*once)
>     {
>         pthread_mutex_lock(&win32_pthread_once_lock);
>         if (!*once)
>         {
>             *once = true;
>             fn();
>         }
>         pthread_mutex_unlock(&win32_pthread_once_lock);
>     }
> }
>
> We should not set *once until AFTER we execute fn().
> Otherwise, other threads passing through pthread_once()
> will mistakenly fall through, expecting the initialization
> to be done already.
>
> (So in this view, adding a sleep just before fn() would
> make the failure more reproducible.)
Yes, adding "pg_usleep(1000L);" just before fn() leads to 15 of 100
tests failed (without the delay more than 100 iterations could pass
successfully).
And the reverse test construction:
            fn();
            pg_usleep(1000L);
            *once = true;
Makes all the tests (I ran 30x100 iterations) pass just fine.
Thank you for looking into this!

Best regards,
Alexander



pgsql-bugs by date:

Previous
From: Tom Lane
Date:
Subject: Re: BUG #16678: The ecpg connect/test5 test sometimes fails on Windows
Next
From: Tom Lane
Date:
Subject: Re: BUG #16685: The ecpg thread/descriptor test fails sometimes on Windows