markOop.cpp revision 1039:987e948ebbc8 
1/*
2 * Copyright 1997-2008 Sun Microsystems, 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
24
25# include "incls/_precompiled.incl"
26# include "incls/_markOop.cpp.incl"
27
28
29void markOopDesc::print_on(outputStream* st) const {
30  if (is_locked()) {
31    st->print("locked(0x%lx)->", value());
32    markOop(*(markOop*)value())->print_on(st);
33  } else {
34    assert(is_unlocked() || has_bias_pattern(), "just checking");
35    st->print("mark(");
36    if (has_bias_pattern())  st->print("biased,");
37    st->print("hash %#lx,", hash());
38    st->print("age %d)", age());
39  }
40}
41
42
43// Give advice about whether the oop that contains this markOop
44// should be cached or not.
45bool markOopDesc::should_not_be_cached() const {
46  // the cast is because decode_pointer() isn't marked const
47  if (is_marked() && ((markOopDesc *)this)->decode_pointer() != NULL) {
48    // If the oop containing this markOop is being forwarded, then
49    // we are in the middle of GC and we do not want the containing
50    // oop to be added to a cache. We have no way of knowing whether
51    // the cache has already been visited by the current GC phase so
52    // we don't know whether the forwarded oop will be properly
53    // processed in this phase. If the forwarded oop is not properly
54    // processed, then we'll see strange crashes or asserts during
55    // the next GC run because the markOop will contain an unexpected
56    // value.
57    //
58    // This situation has been seen when we are GC'ing a methodOop
59    // because we use the methodOop while we're GC'ing it. Scary
60    // stuff. Some of the uses the methodOop cause the methodOop to
61    // be added to the OopMapCache in the instanceKlass as a side
62    // effect. This check lets the cache maintainer know when a
63    // cache addition would not be safe.
64    return true;
65  }
66
67  // caching the containing oop should be just fine
68  return false;
69}
70