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Bug 4196

Summary: _ReadWriteBarrier is deprecated, use atomic_thread_fence instead
Product: SDL Reporter: Coriiander <coriiander>
Component: atomicAssignee: Sam Lantinga <slouken>
Status: RESOLVED WONTFIX QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2    
Version: don't know   
Hardware: All   
OS: Windows (All)   

Description Coriiander 2018-06-09 04:37:56 UTC 
Hello,

This message is with regards to compiler/memory barriers for the Windows platform.

In various parts throughout the SDL-code the _ReadWriteBarrier intrinsic is used. (e.g. in SDL_atomic.h, SDL_atomic.c and SDL_spinlock.c) Either through _ReadWriteBarrier or through various macros that evaluate to _ReadWriteBarrier (e.g. SDL_CompilerBarrier, SDL_MemoryBarrierAcquire and SDL_MemoryBarrierRelease).

I would like to point out that the _ReadWriteBarrier intrinsic has been deprecated for quite a while now and should not be used. To quote from MSDN:

The _ReadBarrier, _WriteBarrier, and _ReadWriteBarrier compiler intrinsics and the MemoryBarrier macro are all deprecated and should not be used. For inter-thread communication, use mechanisms such as atomic_thread_fence and std::atomic<T>, which are defined in the C++ Standard Library. For hardware access, use the /volatile:iso compiler option together with the volatile keyword.

MSDN-link:
https://msdn.microsoft.com/en-us/library/f20w0x5e.aspx?f=255&MSPPError=-2147217396



Cheers,
Cor Schols, alias Coriiander
Comment 1 Sam Lantinga 2019-06-12 15:29:38 UTC 
SDL is a C library, are there equivalent mechanisms for C libraries?
Comment 2 Sam Lantinga 2019-06-12 15:31:36 UTC 
Sorry, to be clear, SDL supports building without any C runtime to avoid C runtime issues on Windows. Is there a way to use atomic_thread_fence in this configuration?
Comment 3 Coriiander 2019-06-13 01:05:10 UTC 
(In reply to Sam Lantinga from comment #2)
> Sorry, to be clear, SDL supports building without any C runtime to avoid C
> runtime issues on Windows. Is there a way to use atomic_thread_fence in this
> configuration?

Yes, that's clear and a core value for SDL. Unfortuntely I don't know of a Microsoft-provided replacement for the deprecated APIs for C. It is an evergrowing problem with the provided Microsoft APIs, as in they're moving evermore away from providing usable C-interfaces.

Alternatives would be:
- keep using deprecated intrinsics;
- use build-time opt-in C++ implementation with custom public C interface;
- use generic fallback logic;
- provide architecture-specific assembler implementations (probably a no go);

As I cannot bring in a solution, I perhaps should not have filed the ticket. It's just that building forth upon deprecated matter feels wrong.
Comment 4 Sam Lantinga 2019-06-14 00:09:43 UTC 
I agree. It sounds like for now, continuing to use the intrinsics is our best option. Feel free to reopen this bug if you have more ideas.