[Mesa-dev] [PATCH v2 0/3] asynchronous pbo transfer with glthread

[Nicolai Hähnle]

On 01.04.2017 11:42, Gregory Hainaut wrote:
> Hello,
>
> Please find a new version to handle invalid buffer handles.
>
> Allow to handle this kind of case:
>    genBuffer(&pbo);
>    DeleteBuffer(pbo);
>    BindBuffer(pbo)
>    TexSubImage2D(user_memory_pointer); // Data transfer will be synchronous
>
> There are various subtely to handle multi threaded shared context. In order to
> keep the code sane, I've considered a buffer invalid when it is deleted by a
> context even it is still bound to others contexts. It will force a synchronous
> transfer which is always safe.

Thanks! I think you're right that tracking pointers is not actually 
needed as long as Create/Delete are synchronous. It's less accurate, but 
the inaccuracy doesn't necessarily lead to correctness problems.

Still, I believe there is the following bug in the series:

glGenBuffers(1, &pbo);
glBindBuffer(..., pbo);
glDeleteBuffers(1, &pbo);
glTexSubImage2D(...); // will be asynchronous, but refers to user memory 
because the pbo was implicitly unbound

Once you fix this bug by updating the current context's bindings in 
glDeleteBuffers, you'll have the following multi-context situation, 
which is sub-optimal but not a bug -- and applications which do that are 
crazy anyway, so let's not worry about them. I'm just mentioning it for 
completeness:

Ctx A: glGenBuffers(1, &pbo);
Ctx A: glBindBuffer(PIXEL_UNPACK_BUFFER, pbo);
Ctx B: glDeleteBuffers(1, &pbo);
Ctx A: glGenBuffers(1, &pbo); // assume that this gets the same buffer name
Ctx A: glDeleteBuffers(1, &pbo);
Ctx A: glTexSubImage2D(...); // will be synchronous, even though it 
_could_ be asynchronous (because the PBO that was generated first is 
still bound!)

Cheers,
Nicolai


>
> Gregory Hainaut (3):
>   mesa/glthread: track buffer creation/destruction
>   mesa/glthread: add tracking of PBO binding
>   mapi/glthread: generate asynchronous code for PBO transfer
>
>  src/mapi/glapi/gen/ARB_direct_state_access.xml |  18 +--
>  src/mapi/glapi/gen/ARB_robustness.xml          |   2 +-
>  src/mapi/glapi/gen/gl_API.dtd                  |  10 +-
>  src/mapi/glapi/gen/gl_API.xml                  |  32 +++---
>  src/mapi/glapi/gen/gl_marshal.py               |  23 +++-
>  src/mapi/glapi/gen/marshal_XML.py              |  19 +++-
>  src/mesa/main/glthread.h                       |  10 ++
>  src/mesa/main/marshal.c                        | 149 ++++++++++++++++++++++++-
>  src/mesa/main/marshal.h                        |  24 ++++
>  src/mesa/main/mtypes.h                         |   5 +
>  src/mesa/main/shared.c                         |   4 +
>  11 files changed, 257 insertions(+), 39 deletions(-)
>


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