void VM_DeoptimizeAll::doit() {

      DeoptimizationMarker dm;
      // deoptimize all java threads in the system
      if (DeoptimizeALot) {
        for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
          if (thread->has_last_Java_frame()) {
            thread->deoptimize();
          }
        }
      } else if (DeoptimizeRandom) {

        // Deoptimize some selected threads and frames
        int tnum = os::random() & 0x3;
        int fnum =  os::random() & 0x3;
        int tcount = 0;
        for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) {
          if (thread->has_last_Java_frame()) {
            if (tcount++ == tnum)  {
            tcount = 0;
              int fcount = 0;
              // Deoptimize some selected frames.
              // Biased llocking wants a updated register map
              for(StackFrameStream fst(thread, UseBiasedLocking); !fst.is_done(); fst.next()) {
                if (fst.current()->can_be_deoptimized()) {
                  if (fcount++ == fnum) {
                    fcount = 0;
                    Deoptimization::deoptimize(thread, *fst.current(), fst.register_map());
                  }
                }
              }
            }
          }
        }
      }
    }