[PATCH] user32: Make functions use display dc thread-safe

[吕果]

Some functions in sysparams.c invoke get_display_dc to get display dc and
  then use it without lock mechanism. it will cause condition race in multi-thread.

PS:
  I dont't kown how to make a test than can stably run into this problem, but
  call GetSystemMetrics(SM_CXSCREEN) within a tight loop in different thread
  will get zero finally.

[Nikolay Sivov]

On 1/12/2018 8:39 AM, 吕果 wrote:
> Some functions in sysparams.c invoke get_display_dc to get display dc and
>   then use it without lock mechanism. it will cause condition race in multi-thread.
>
> PS:
>   I dont't kown how to make a test than can stably run into this problem, but
>   call GetSystemMetrics(SM_CXSCREEN) within a tight loop in different thread
>   will get zero finally.

Hi.

If the issue is get_display_dc() alone, you can use single
compare-exchange call to set static variable safely.

[Guo Lv]

The problem is not in get_display_dc() but use the value returned(HDC) without lock.

------------------ Original ------------------
From:  "Nikolay Sivov";
Date:  Fri, Jan 12, 2018 03:56 PM
To:  "吕果"; "wine-devel";
Subject:  Re: [PATCH] user32: Make functions use display dc thread-safe

On 1/12/2018 8:39 AM, 吕果 wrote:
> Some functions in sysparams.c invoke get_display_dc to get display dc and
>   then use it without lock mechanism. it will cause condition race in multi-thread.
>
> PS:
>   I dont't kown how to make a test than can stably run into this problem, but
>   call GetSystemMetrics(SM_CXSCREEN) within a tight loop in different thread
>   will get zero finally.

Hi.

If the issue is get_display_dc() alone, you can use single
compare-exchange call to set static variable safely.

[Alexandre Julliard]

Nikolay Sivov  writes:
> On 1/12/2018 8:39 AM, 吕果 wrote:
> > Some functions in sysparams.c invoke get_display_dc to get display dc and
> >   then use it without lock mechanism. it will cause condition race in multi-thread.
> >
> > PS:
> >   I dont't kown how to make a test than can stably run into this problem, but
> >   call GetSystemMetrics(SM_CXSCREEN) within a tight loop in different thread
> >   will get zero finally.
>
> Hi.
>
> If the issue is get_display_dc() alone, you can use single
> compare-exchange call to set static variable safely.

I expect that the issue is that you can't use the same DC from different
threads at the same time.