ObjectMonitor::is_busy() in src/hotspot/share/runtime/objectMonitor.hpp
returns intptr_t:

  intptr_t is_busy() const {
    // TODO-FIXME: assert _owner == null implies _recursions = 0
    intptr_t ret_code = _waiters | intptr_t(_cxq) | intptr_t(_EntryList);
    if (contentions() > 0) {
      ret_code |= contentions();
    }
    if (_owner != DEFLATER_MARKER) {
      ret_code |= intptr_t(_owner);
    }
    return ret_code;
  }

Generally, HotSpot style is that is_Foo() functions return bool
so ObjectMonitor::is_busy() is an anomaly.

This topic came during the discussion about:

    JDK-8253064 monitor list simplifications and getting rid of TSM