Re: BUG #16685: The ecpg thread/descriptor test fails sometimes on Windows

I wrote:
> I'll bet that the correct fix is

>  static void
>  set_descriptors(struct descriptor *value)
>  {
> +    pthread_once(&descriptor_once, descriptor_key_init);
>     pthread_setspecific(descriptor_key, value);
>  }

No, looking closer, there are only two calls of set_descriptors()
and each of them is preceded by a call to get_descriptors().
So it should not be possible to get here without descriptor_key
having been initialized.

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.)

            regards, tom lane