shotgun/lib/object_memory-barrier.h

   1 /*
   2
   3  We need to have a write barrier that performs checks whenever a reference
   4  is written. This allows the new generation to collected without collecting
   5  the old generation too.
   6
   7  The idea is that if +target+ is on object in the old generation, and +val+
   8  is an object in the new generation, we need to add +target+ to the remember
   9  set of new generation so that when we go to collect the new generation,
  10  we are sure that +val+ survives.
  11
  12  The flag is so that we don't put the object into the remember set
  13  more than once.
  14  */
  15
  16
  17 /* TODO: This routine MUST be optimized because it's hit constantly. */
  18
  19 #include <assert.h>
  20
  21 static inline void object_memory_write_barrier(object_memory om, OBJECT target, OBJECT val) {
  22   gc_zone tz, vz;
  23   if(!REFERENCE_P(val)) return;
  24
  25   tz = target->gc_zone;
  26   vz = val->gc_zone;
  27
  28   assert(tz > 0);
  29   assert(vz > 0);
  30   xassert(val->klass != Qnil);
  31
  32   /* if the target is in a higher numbered zone than val, then
  33      that means it needs to be in the remember set. */
  34   if(tz < vz) {
  35     object_memory_update_rs(om, target, val);
  36   }
  37 }