gistfile1.cpp

static RADINLINE bool is_fence_pending(GDrawFence fence)
{
   U32 retired = get_gpu_fence();

   // everything between "retired" (exclusive) and "next_fence_counter"
   // (inclusive) is pending. everything else is definitely done.
   //
   // we need to be careful about this test since the "fence" value
   // coming in is, for all practical purposes, an arbitrary U32. our
   // fence counter might have wrapped around multiple times since we last
   // used a resource that gets freed, for instance! so if we report a
   // fence ID as pending that's not actually in flight, we might end up
   // with an infinite wait.
   // 
   // this is a bit subtle since it depends on unsigned wraparound for us
   // to do the right thing.

   // number of pending fences (next_fence_counter has, by definition, not been written yet)
   U32 num_pending = gdraw->next_fence_counter - retired;

   // position of the current fence in the "list of pending fences", counting
   // from end (i.e. the "youngest" fence that we haven't even issued yet)
   U32 pos_in_pending_list = gdraw->next_fence_counter - fence.uinteger;

   return pos_in_pending_list < num_pending;
}