1/*
2 * Copyright (c) 2018, 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#ifndef SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP
26#define SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP
27
28#include "gc/shared/oopStorage.hpp"
29#include "utilities/macros.hpp"
30
31//////////////////////////////////////////////////////////////////////////////
32// Support for parallel and optionally concurrent state iteration.
33//
34// Concurrent Iteration
35//
36// Iteration involves the _active_array (an ActiveArray), which contains all
37// of the blocks owned by a storage object.
38//
39// A concurrent ParState increments the associated storage's
40// _concurrent_iteration_count when the state is constructed, and
41// decrements it when the state is destroyed. These assignments are made with
42// _active_mutex locked. Meanwhile, empty block deletion is not done while
43// _concurrent_iteration_count is non-zero. The counter check and the dependent
44// removal of a block from the _active_array is performed with _active_mutex
45// locked. This prevents concurrent iteration and empty block deletion from
46// interfering with with each other.
47//
48// Both allocate() and delete_empty_blocks() lock the
49// _allocation_mutex while performing their respective list and array
50// manipulations, preventing them from interfering with each other.
51//
52// When allocate() creates a new block, it is added to the end of the
53// _active_array. Then _active_array's _block_count is incremented to account
54// for the new block. When concurrent iteration is started (by a parallel
55// worker thread calling the state's iterate() function), the current
56// _active_array and its _block_count are captured for use by the iteration,
57// with iteration processing all blocks in that array up to that block count.
58//
59// As a result, the sequence over which concurrent iteration operates is
60// stable. However, once the iteration is started, later allocations may add
61// blocks to the end of the array that won't be examined by the iteration.
62// An allocation may even require expansion of the array, so the iteration is
63// no longer processing the current array, but rather the previous one.
64// And while the sequence is stable, concurrent allocate() and release()
65// operations may change the set of allocated entries in a block at any time
66// during the iteration.
67//
68// As a result, a concurrent iteration handler must accept that some
69// allocations and releases that occur after the iteration started will not be
70// seen by the iteration. Further, some may overlap examination by the
71// iteration. To help with this, allocate() and release() have an invariant
72// that an entry's value must be NULL when it is not in use.
73//
74// ParState<concurrent, is_const>
75// concurrent must be true if iteration may be concurrent with the
76// mutators.
77//
78// is_const must be true if the iteration is over a constant storage
79// object, false if the iteration may modify the storage object.
80//
81// ParState([const] OopStorage* storage)
82// Construct an object for managing an iteration over storage. For a
83// concurrent ParState, empty block deletion for the associated storage
84// is inhibited for the life of the ParState.
85//
86// template<typename F> void iterate(F f)
87// Repeatedly claims a block from the associated storage that has
88// not been processed by this iteration (possibly by other threads),
89// and applies f to each entry in the claimed block. Assume p is of
90// type const oop* or oop*, according to is_const. Then f(p) must be
91// a valid expression whose value is ignored. Concurrent uses must
92// be prepared for an entry's value to change at any time, due to
93// mutator activity.
94//
95// template<typename Closure> void oops_do(Closure* cl)
96// Wrapper around iterate, providing an adaptation layer allowing
97// the use of OopClosures and similar objects for iteration. Assume
98// p is of type const oop* or oop*, according to is_const. Then
99// cl->do_oop(p) must be a valid expression whose value is ignored.
100// Concurrent uses must be prepared for the entry's value to change
101// at any time, due to mutator activity.
102//
103// Optional operations, provided only if !concurrent && !is_const.
104// These are not provided when is_const, because the storage object
105// may be modified by the iteration infrastructure, even if the
106// provided closure doesn't modify the storage object. These are not
107// provided when concurrent because any pre-filtering behavior by the
108// iteration infrastructure is inappropriate for concurrent iteration;
109// modifications of the storage by the mutator could result in the
110// pre-filtering being applied (successfully or not) to objects that
111// are unrelated to what the closure finds in the entry.
112//
113// template<typename Closure> void weak_oops_do(Closure* cl)
114// template<typename IsAliveClosure, typename Closure>
115// void weak_oops_do(IsAliveClosure* is_alive, Closure* cl)
116// Wrappers around iterate, providing an adaptation layer allowing
117// the use of is-alive closures and OopClosures for iteration.
118// Assume p is of type oop*. Then
119//
120// - cl->do_oop(p) must be a valid expression whose value is ignored.
121//
122// - is_alive->do_object_b(*p) must be a valid expression whose value
123// is convertible to bool.
124//
125// If *p == NULL then neither is_alive nor cl will be invoked for p.
126// If is_alive->do_object_b(*p) is false, then cl will not be
127// invoked on p.
128
129class OopStorage::BasicParState {
130 const OopStorage* _storage;
131 ActiveArray* _active_array;
132 size_t _block_count;
133 volatile size_t _next_block;
134 uint _estimated_thread_count;
135 bool _concurrent;
136
137 // Noncopyable.
138 BasicParState(const BasicParState&);
139 BasicParState& operator=(const BasicParState&);
140
141 struct IterationData;
142
143 void update_concurrent_iteration_count(int value);
144 bool claim_next_segment(IterationData* data);
145 bool finish_iteration(const IterationData* data) const;
146
147 // Wrapper for iteration handler; ignore handler result and return true.
148 template<typename F> class AlwaysTrueFn;
149
150public:
151 BasicParState(const OopStorage* storage,
152 uint estimated_thread_count,
153 bool concurrent);
154 ~BasicParState();
155
156 template<bool is_const, typename F> void iterate(F f);
157
158 static uint default_estimated_thread_count(bool concurrent);
159};
160
161template<bool concurrent, bool is_const>
162class OopStorage::ParState {
163 BasicParState _basic_state;
164
165 typedef typename Conditional<is_const,
166 const OopStorage*,
167 OopStorage*>::type StoragePtr;
168
169public:
170 ParState(StoragePtr storage,
171 uint estimated_thread_count = BasicParState::default_estimated_thread_count(concurrent)) :
172 _basic_state(storage, estimated_thread_count, concurrent)
173 {}
174
175 template<typename F> void iterate(F f);
176 template<typename Closure> void oops_do(Closure* cl);
177};
178
179template<>
180class OopStorage::ParState<false, false> {
181 BasicParState _basic_state;
182
183public:
184 ParState(OopStorage* storage,
185 uint estimated_thread_count = BasicParState::default_estimated_thread_count(false)) :
186 _basic_state(storage, estimated_thread_count, false)
187 {}
188
189 template<typename F> void iterate(F f);
190 template<typename Closure> void oops_do(Closure* cl);
191 template<typename Closure> void weak_oops_do(Closure* cl);
192 template<typename IsAliveClosure, typename Closure>
193 void weak_oops_do(IsAliveClosure* is_alive, Closure* cl);
194};
195
196#endif // SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP
197