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Bug 4992

Summary: UWP/WinRT does not set thread priority when using SDL_SetThreadPriority
Product: SDL Reporter: Jeff Loiselle <jeff>
Component: *don't know*Assignee: Sam Lantinga <slouken>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: flibitijibibo
Version: 2.0.10Keywords: target-2.0.12
Hardware: x86   
OS: Windows 10   
Attachments: Patch to implement WinRT SetThreadPriority

Description Jeff Loiselle 2020-02-18 03:57:49 UTC 
Thread priorities aren't being set in UWP/WinRT builds.  This was not initially possible in WinRT/UWP, however it is now possible.  This is affecting time sensitive threads like audio.  

NOTE:
Not all thread priorities appear to be valid for UWP.  I was unable to set a thread to real time, however I was able to set a thread to high (Highest in MS land).  

Docs for SetThreadPriority function:
https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-setthreadpriority
Comment 1 Sam Lantinga 2020-02-18 05:54:49 UTC 
Do you have a tested patch for this? I know for earlier SDKs it was not possible to compile UWP code using SetThreadPriority.
Comment 2 Jeff Loiselle 2020-02-18 20:38:46 UTC 
I do not.  We've got a workaround for our version of SDL, but we're only using it for UWP.  However our patch does not clamp priorities, so we also changed a few calls to make SDL use Highest instead of Realtime.  It also does not use the return value of SetThreadPriority as it's non-zero for success, instead of non-zero for failure which I believe is what SDL assumes.  

Our code is below with the following caveats:
1. Not ifdef'd for WinRT
2. Priorities above High will not be set.  (Setting to real time for instance will cause thread to remain normal priority).
3. Return code is not using return code of SetThreadPriority.

extern "C"
int
SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
{
    SetThreadPriority(GetCurrentThread(), priority);
    return (0);
}
Comment 3 Ryan C. Gordon 2020-02-18 22:43:17 UTC 
We should bump this to 2.0.13.

--ryan.
Comment 4 Ethan Lee 2020-02-26 20:36:54 UTC 
Created attachment 4230 [details]
Patch to implement WinRT SetThreadPriority

Attached is a diff that I used to get SetThreadPriority working locally. I still have no idea what the minimum SDK version is since Microsoft never documented it, but it's worth pointing out that they're much more aggressive about using the latest VS and UWP SDK anyway (for example, an updated Xbox is no longer compatible with VS2017, and updates are required to have a network connection of any kind).
Comment 5 Sam Lantinga 2020-03-01 20:51:20 UTC 
Okay, Ethan, your patch is in for release.
https://hg.libsdl.org/SDL/rev/61b564f66050

Thanks!