Mon, 03 May 2010 10:24:51 -0700
6948537: CMS: BOT walkers observe out-of-thin-air zeros on sun4v sparc/CMT
Summary: On sun4v/CMT avoid use of memset() in BOT updates so as to prevent concurrent BOT readers from seeing the phantom zeros arising from memset()'s use of BIS.
Reviewed-by: jmasa, johnc, minqi, poonam, tonyp
1 /*
2 * Copyright (c) 2007 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 */
25 class CardTableRS; // fwd decl
26 class ConcurrentMarkSweepGeneration;
28 // A PermGen implemented with a CMS space, collected by a CMS collector.
29 class CMSPermGen: public PermGen {
30 friend class VMStructs;
32 protected:
33 // The "generation" view.
34 ConcurrentMarkSweepGeneration* _gen;
36 public:
37 CMSPermGen(ReservedSpace rs, size_t initial_byte_size,
38 CardTableRS* ct, FreeBlockDictionary::DictionaryChoice);
40 HeapWord* mem_allocate(size_t size);
42 void compute_new_size();
44 Generation* as_gen() const { return _gen; }
45 };
47 // This is the "generation" view of a CMSPermGen.
48 class CMSPermGenGen: public ConcurrentMarkSweepGeneration {
49 // Abstractly, this is a subtype that gets access to protected fields.
50 friend class CMSPermGen;
51 public:
52 CMSPermGenGen(ReservedSpace rs, size_t initial_byte_size,
53 int level, CardTableRS* ct):
54 // See comments in the constructor for CompactibleFreeListSpace
55 // regarding not using adaptive free lists for a perm gen.
56 ConcurrentMarkSweepGeneration(rs, initial_byte_size, // MinPermHeapExapnsion
57 level, ct, false /* use adaptive freelists */,
58 (FreeBlockDictionary::DictionaryChoice)CMSDictionaryChoice)
59 {}
61 void initialize_performance_counters();
63 const char* name() const {
64 return "concurrent-mark-sweep perm gen";
65 }
67 const char* short_name() const {
68 return "CMS Perm";
69 }
71 bool must_be_youngest() const { return false; }
72 bool must_be_oldest() const { return false; }
73 };