[Mesa-dev] [PATCH] mesa: framebuffer refcounting with atomic ops

[Tapani Pälli]

On 08/15/2017 05:14 PM, Timothy Arceri wrote:
> We seem to revisit this every few months. Please search your email for 
> all the details but the short answer is this makes some race 
> conditions worse. You will need to address and follow the previous 
> suggestions to be able to improve locking here.
>

ok will take a look,

Thanks;

> On 15/08/17 23:04, Marek Olšák wrote:
>> Reviewed-by: Marek Olšák <marek.olsak at amd.com>
>>
>> Marek
>>
>> On Tue, Aug 15, 2017 at 2:03 PM, Tapani Pälli 
>> <tapani.palli at intel.com> wrote:
>>> Signed-off-by: Tapani Pälli <tapani.palli at intel.com>
>>> ---
>>>   src/mesa/main/framebuffer.c | 19 +++++--------------
>>>   1 file changed, 5 insertions(+), 14 deletions(-)
>>>
>>> Use atomic ops in same manner as for shader objects, IMO makes
>>> code easier to read.
>>>
>>> diff --git a/src/mesa/main/framebuffer.c b/src/mesa/main/framebuffer.c
>>> index 039762a074..69e28c8af7 100644
>>> --- a/src/mesa/main/framebuffer.c
>>> +++ b/src/mesa/main/framebuffer.c
>>> @@ -45,7 +45,7 @@
>>>   #include "texobj.h"
>>>   #include "glformats.h"
>>>   #include "state.h"
>>> -
>>> +#include "util/u_atomic.h"
>>>
>>>
>>>   /**
>>> @@ -243,25 +243,16 @@ _mesa_reference_framebuffer_(struct 
>>> gl_framebuffer **ptr,
>>>   {
>>>      if (*ptr) {
>>>         /* unreference old renderbuffer */
>>> -      GLboolean deleteFlag = GL_FALSE;
>>>         struct gl_framebuffer *oldFb = *ptr;
>>> -
>>> -      mtx_lock(&oldFb->Mutex);
>>> -      assert(oldFb->RefCount > 0);
>>> -      oldFb->RefCount--;
>>> -      deleteFlag = (oldFb->RefCount == 0);
>>> -      mtx_unlock(&oldFb->Mutex);
>>> -
>>> -      if (deleteFlag)
>>> -         oldFb->Delete(oldFb);
>>> +      assert(p_atomic_read(&oldFb->RefCount) > 0);
>>> +      if (p_atomic_dec_zero(&oldFb->RefCount))
>>> +          oldFb->Delete(oldFb);
>>>
>>>         *ptr = NULL;
>>>      }
>>>
>>>      if (fb) {
>>> -      mtx_lock(&fb->Mutex);
>>> -      fb->RefCount++;
>>> -      mtx_unlock(&fb->Mutex);
>>> +      p_atomic_inc(&fb->RefCount);
>>>         *ptr = fb;
>>>      }
>>>   }
>>> -- 
>>> 2.13.5
>>>
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