1 /*
   2  * Copyright (c) 1997, 2010, Oracle and/or its affiliates. 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 #include "precompiled.hpp"
  26 #include "oops/markOop.hpp"
  27 #ifdef TARGET_OS_FAMILY_linux
  28 # include "thread_linux.inline.hpp"
  29 #endif
  30 #ifdef TARGET_OS_FAMILY_solaris
  31 # include "thread_solaris.inline.hpp"
  32 #endif
  33 #ifdef TARGET_OS_FAMILY_windows
  34 # include "thread_windows.inline.hpp"
  35 #endif
  36 #ifdef TARGET_OS_FAMILY_bsd
  37 # include "thread_bsd.inline.hpp"
  38 #endif
  39 
  40 
  41 void markOopDesc::print_on(outputStream* st) const {
  42   if (is_locked()) {
  43     st->print("locked(0x%lx)->", value());
  44     markOop(*(markOop*)value())->print_on(st);
  45   } else {
  46     assert(is_unlocked() || has_bias_pattern(), "just checking");
  47     st->print("mark(");
  48     if (has_bias_pattern())  st->print("biased,");
  49     st->print("hash %#lx,", hash());
  50     st->print("age %d)", age());
  51   }
  52 }
  53 
  54 
  55 // Give advice about whether the oop that contains this markOop
  56 // should be cached or not.
  57 bool markOopDesc::should_not_be_cached() const {
  58   // the cast is because decode_pointer() isn't marked const
  59   if (is_marked() && ((markOopDesc *)this)->decode_pointer() != NULL) {
  60     // If the oop containing this markOop is being forwarded, then
  61     // we are in the middle of GC and we do not want the containing
  62     // oop to be added to a cache. We have no way of knowing whether
  63     // the cache has already been visited by the current GC phase so
  64     // we don't know whether the forwarded oop will be properly
  65     // processed in this phase. If the forwarded oop is not properly
  66     // processed, then we'll see strange crashes or asserts during
  67     // the next GC run because the markOop will contain an unexpected
  68     // value.
  69     //
  70     // This situation has been seen when we are GC'ing a methodOop
  71     // because we use the methodOop while we're GC'ing it. Scary
  72     // stuff. Some of the uses the methodOop cause the methodOop to
  73     // be added to the OopMapCache in the instanceKlass as a side
  74     // effect. This check lets the cache maintainer know when a
  75     // cache addition would not be safe.
  76     return true;
  77   }
  78 
  79   // caching the containing oop should be just fine
  80   return false;
  81 }