1 /*
  2  * Copyright (c) 2015, 2019, Red Hat, Inc. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 12  * version 2 for more details (a copy is included in the LICENSE file that
 13  * accompanied this code).
 14  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP
 26 #define SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP
 27 
 28 #include "gc/shenandoah/shenandoahForwarding.hpp"
 29 
 30 #include "gc/shenandoah/shenandoahAsserts.hpp"
 31 #include "oops/markWord.hpp"
 32 #include "runtime/thread.hpp"
 33 
 34 inline oop ShenandoahForwarding::get_forwardee_raw(oop obj) {
 35   shenandoah_assert_in_heap(NULL, obj);
 36   return get_forwardee_raw_unchecked(obj);
 37 }
 38 
 39 inline oop ShenandoahForwarding::get_forwardee_raw_unchecked(oop obj) {
 40   // JVMTI and JFR code use mark words for marking objects for their needs.
 41   // On this path, we can encounter the "marked" object, but with NULL
 42   // fwdptr. That object is still not forwarded, and we need to return
 43   // the object itself.
 44   markWord mark = obj->mark();
 45   if (mark.is_marked()) {
 46     HeapWord* fwdptr = (HeapWord*) mark.clear_lock_bits().to_pointer();
 47     if (fwdptr != NULL) {
 48       return cast_to_oop(fwdptr);
 49     }
 50   }
 51   return obj;
 52 }
 53 
 54 inline oop ShenandoahForwarding::get_forwardee_mutator(oop obj) {
 55   // Same as above, but mutator thread cannot ever see NULL forwardee.
 56   shenandoah_assert_correct(NULL, obj);
 57   assert(Thread::current()->is_Java_thread(), "Must be a mutator thread");
 58 
 59   markWord mark = obj->mark();
 60   if (mark.is_marked()) {
 61     HeapWord* fwdptr = (HeapWord*) mark.clear_lock_bits().to_pointer();
 62     assert(fwdptr != NULL, "Forwarding pointer is never null here");
 63     return cast_to_oop(fwdptr);
 64   } else {
 65     return obj;
 66   }
 67 }
 68 
 69 inline oop ShenandoahForwarding::get_forwardee(oop obj) {
 70   shenandoah_assert_correct(NULL, obj);
 71   return get_forwardee_raw_unchecked(obj);
 72 }
 73 
 74 inline bool ShenandoahForwarding::is_forwarded(oop obj) {
 75   return obj->mark().is_marked();
 76 }
 77 
 78 inline oop ShenandoahForwarding::try_update_forwardee(oop obj, oop update) {
 79 
 80   markWord old_mark = ObjectSynchronizer::read_stable_mark(obj);
 81   assert(!old_mark.is_being_inflated(), "must not see INFLATING marker here");
 82 
 83   if (old_mark.is_marked()) {
 84     return cast_to_oop(old_mark.clear_lock_bits().to_pointer());
 85   }
 86 
 87   // Ensure that the copy has the correct mark-word, in case it happened to copy with
 88   // INFLATING marker.
 89   update->set_mark(old_mark);
 90 
 91   markWord new_mark = markWord::encode_pointer_as_mark(update);
 92   while (true) {
 93     markWord prev_mark = obj->cas_set_mark(new_mark, old_mark, memory_order_conservative);
 94     if (prev_mark == old_mark) {
 95       return update;
 96     } else if (prev_mark == markWord::INFLATING()) {
 97       // This happens when we encounter a stack-locked object in from-space.
 98       // Busy-wait for completion.
 99       SpinPause();
100     } else {
101       assert(prev_mark.is_marked(), "must be forwarded");
102       return cast_to_oop(prev_mark.clear_lock_bits().to_pointer());
103     }
104   }
105 }
106 
107 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP