src/hotspot/share/gc/shenandoah/shenandoahForwarding.inline.hpp

/*
 * Copyright (c) 2015, 2020, Red Hat, Inc. All rights reserved.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#ifndef SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP
#define SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP

#include "gc/shenandoah/shenandoahAsserts.hpp"
#include "gc/shenandoah/shenandoahForwarding.hpp"
#include "oops/markOop.inline.hpp"
#include "runtime/atomic.hpp"

inline HeapWord* ShenandoahForwarding::get_forwardee_raw(oop obj) {
  shenandoah_assert_in_heap(NULL, obj);
  return get_forwardee_raw_unchecked(obj);
}

inline HeapWord* ShenandoahForwarding::get_forwardee_raw_unchecked(oop obj) {
  // JVMTI and JFR code use mark words for marking objects for their needs.
  // On this path, we can encounter the "marked" object, but with NULL
  // fwdptr. That object is still not forwarded, and we need to return
  // the object itself.
  markOop mark = obj->mark_raw();
  if (mark.is_marked()) {
    HeapWord* fwdptr = (HeapWord*) mark.clear_lock_bits();
    if (fwdptr != NULL) {
      return fwdptr;
    }
  }
  return (HeapWord*)obj;
}

inline oop ShenandoahForwarding::get_forwardee_mutator(oop obj) {
  // Same as above, but mutator thread cannot ever see NULL forwardee.
  shenandoah_assert_correct(NULL, obj);
  assert(Thread::current()->is_Java_thread(), "Must be a mutator thread");

  markOop mark = obj->mark_raw();
  if (mark.is_marked()) {
    HeapWord* fwdptr = (HeapWord*)mark.clear_lock_bits();
    assert(fwdptr != NULL, "Forwarding pointer is never null here");
    return oop(fwdptr);
  } else {
    return obj;
  }
}

inline oop ShenandoahForwarding::get_forwardee(oop obj) {
  shenandoah_assert_correct(NULL, obj);
  return oop(get_forwardee_raw_unchecked(obj));
}

inline bool ShenandoahForwarding::is_forwarded(oop obj) {
  return obj->mark_raw().is_marked();
}

inline oop ShenandoahForwarding::try_update_forwardee(oop obj, oop update) {
  markOop old_mark = obj->mark_raw();
  if (old_mark.is_marked()) {
    return (oop) old_mark.clear_lock_bits();
  }

  markOop new_mark = markOop::encode_pointer_as_mark(update);
  markOop prev_mark = obj->cas_set_mark_raw(new_mark, old_mark);
  if (prev_mark == old_mark) {
    return update;
  } else {
    return (oop) prev_mark.clear_lock_bits();
  }
}

#endif // SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP