-
Notifications
You must be signed in to change notification settings - Fork 224
/
jfrTraceIdLoadBarrier.hpp
87 lines (82 loc) · 4.15 KB
/
jfrTraceIdLoadBarrier.hpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
/*
* Copyright (c) 2020, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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_JFR_RECORDER_CHECKPOINT_TYPES_TRACEID_JFRTRACEIDLOADBARRIER_HPP
#define SHARE_JFR_RECORDER_CHECKPOINT_TYPES_TRACEID_JFRTRACEIDLOADBARRIER_HPP
#include "jfr/utilities/jfrTypes.hpp"
#include "memory/allocation.hpp"
class ClassLoaderData;
class Klass;
class Method;
class ModuleEntry;
class PackageEntry;
/*
* The JFR equivalent of a 'GC Load Barrier' where, instead of tracking object accesses on the heap,
* we track accesses to JVM internal objects in native memory iff it stand in a relation to JFR events.
*
* Events can have fields referring to VM internal objects, for example Klass*, Method*, ClassLoaderData*, etc.
* At an event site, objects, or more specifically pointers to objects, are stored into the event just before
* the event is committed. As part of committing the event to the recording stream, instead of serializing these
* pointers directly, the writer mechanism writes a unique value of type traceid used by JFR to represent it.
* Conceptually, this is very similar to representing a reference using a foreign key.
*
* After this relation has been established, the JFR system must have a way to later locate the object in order to
* serialize the information it represents, i.e to produce "tables" containing information related to foreign keys.
* The information in these tables then materialize as constants in the recording stream delivered as part of Checkpoint events,
* letting events containing references become resolvable.
*
* The 'load barrier' is a means to accomplish this: it intercepts loading of traceid values from JVM internal objects,
* allowing JFR to keep track.
*
* Once intercepted, this tracking is implemented using two mechanisms:
*
* 'Tagging':
* ----------
* The barrier determines if the object needs to be marked, or tagged, and if so in what way.
* Tagging is a function of the current epoch and is implemented as a bit pattern installed into the traceid field of the object.
*
* 'Root set' of Klasses:
* ----------
* JFR collects the set of tagged JVM internal objects at certain intervals. This set is derived from a subset, or 'root set',
* consisting of incrementally tagged klasses for the epoch. The barrier enqueues a newly tagged klass, as a root, to an epoch-relative,
* distributed queue. The collection step will use the queue to process the root set, from which most artifacts tagged can be discovered.
*
*/
class JfrTraceIdLoadBarrier : AllStatic {
friend class JfrCheckpointManager;
private:
static bool initialize();
static void clear();
static void destroy();
static void enqueue(const Klass* klass);
public:
static traceid load(const ClassLoaderData* cld);
static traceid load(const Klass* klass);
static traceid load(const Klass* klass, const Method* method);
static traceid load(const Method* method);
static traceid load(const ModuleEntry* module);
static traceid load(const PackageEntry* package);
static traceid load_leakp(const Klass* klass, const Method* method); // leak profiler
static void do_klasses(void f(Klass*), bool previous_epoch = false);
};
#endif // SHARE_JFR_RECORDER_CHECKPOINT_TYPES_TRACEID_JFRTRACEIDLOADBARRIER_HPP