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
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7 * published by the Free Software Foundation.
8 *
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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
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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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 "memory/allocation.hpp"
30 #include "utilities/macros.hpp"
31
32 #if INCLUDE_ALL_GCS
33
34 //////////////////////////////////////////////////////////////////////////////
35 // Support for parallel and optionally concurrent state iteration.
36 //
37 // Parallel iteration is for the exclusive use of the GC. Other iteration
38 // clients must use serial iteration.
39 //
40 // Concurrent Iteration
41 //
42 // Iteration involves the _active_list, which contains all of the blocks owned
43 // by a storage object. This is a doubly-linked list, linked through
44 // dedicated fields in the blocks.
45 //
46 // At most one concurrent ParState can exist at a time for a given storage
47 // object.
48 //
49 // A concurrent ParState sets the associated storage's
50 // _concurrent_iteration_active flag true when the state is constructed, and
51 // sets it false when the state is destroyed. These assignments are made with
52 // _active_mutex locked. Meanwhile, empty block deletion is not done while
53 // _concurrent_iteration_active is true. The flag check and the dependent
54 // removal of a block from the _active_list is performed with _active_mutex
55 // locked. This prevents concurrent iteration and empty block deletion from
56 // interfering with with each other.
57 //
58 // Both allocate() and delete_empty_blocks_concurrent() lock the
59 // _allocate_mutex while performing their respective list manipulations,
60 // preventing them from interfering with each other.
61 //
62 // When allocate() creates a new block, it is added to the front of the
63 // _active_list. Then _active_head is set to the new block. When concurrent
64 // iteration is started (by a parallel worker thread calling the state's
65 // iterate() function), the current _active_head is used as the initial block
66 // for the iteration, with iteration proceeding down the list headed by that
67 // block.
68 //
69 // As a result, the list over which concurrent iteration operates is stable.
70 // However, once the iteration is started, later allocations may add blocks to
71 // the front of the list that won't be examined by the iteration. And while
72 // the list is stable, concurrent allocate() and release() operations may
73 // change the set of allocated entries in a block at any time during the
74 // iteration.
75 //
76 // As a result, a concurrent iteration handler must accept that some
77 // allocations and releases that occur after the iteration started will not be
78 // seen by the iteration. Further, some may overlap examination by the
79 // iteration. To help with this, allocate() and release() have an invariant
80 // that an entry's value must be NULL when it is not in use.
81 //
82 // An in-progress delete_empty_blocks_concurrent() operation can contend with
83 // the start of a concurrent iteration over the _active_mutex. Since both are
84 // under GC control, that potential contention can be eliminated by never
85 // scheduling both operations to run at the same time.
86 //
87 // ParState<concurrent, is_const>
88 // concurrent must be true if iteration is concurrent with the
89 // mutator, false if iteration is at a safepoint.
90 //
91 // is_const must be true if the iteration is over a constant storage
92 // object, false if the iteration may modify the storage object.
93 //
94 // ParState([const] OopStorage* storage)
95 // Construct an object for managing an iteration over storage. For a
96 // concurrent ParState, empty block deletion for the associated storage
97 // is inhibited for the life of the ParState. There can be no more
98 // than one live concurrent ParState at a time for a given storage object.
99 //
100 // template<typename F> void iterate(F f)
101 // Repeatedly claims a block from the associated storage that has
102 // not been processed by this iteration (possibly by other threads),
103 // and applies f to each entry in the claimed block. Assume p is of
104 // type const oop* or oop*, according to is_const. Then f(p) must be
105 // a valid expression whose value is ignored. Concurrent uses must
106 // be prepared for an entry's value to change at any time, due to
107 // mutator activity.
108 //
109 // template<typename Closure> void oops_do(Closure* cl)
110 // Wrapper around iterate, providing an adaptation layer allowing
111 // the use of OopClosures and similar objects for iteration. Assume
112 // p is of type const oop* or oop*, according to is_const. Then
113 // cl->do_oop(p) must be a valid expression whose value is ignored.
114 // Concurrent uses must be prepared for the entry's value to change
115 // at any time, due to mutator activity.
116 //
117 // Optional operations, provided only if !concurrent && !is_const.
118 // These are not provided when is_const, because the storage object
119 // may be modified by the iteration infrastructure, even if the
120 // provided closure doesn't modify the storage object. These are not
121 // provided when concurrent because any pre-filtering behavior by the
122 // iteration infrastructure is inappropriate for concurrent iteration;
123 // modifications of the storage by the mutator could result in the
124 // pre-filtering being applied (successfully or not) to objects that
125 // are unrelated to what the closure finds in the entry.
126 //
127 // template<typename Closure> void weak_oops_do(Closure* cl)
128 // template<typename IsAliveClosure, typename Closure>
129 // void weak_oops_do(IsAliveClosure* is_alive, Closure* cl)
130 // Wrappers around iterate, providing an adaptation layer allowing
131 // the use of is-alive closures and OopClosures for iteration.
132 // Assume p is of type oop*. Then
133 //
134 // - cl->do_oop(p) must be a valid expression whose value is ignored.
135 //
136 // - is_alive->do_object_b(*p) must be a valid expression whose value
137 // is convertible to bool.
138 //
139 // If *p == NULL then neither is_alive nor cl will be invoked for p.
140 // If is_alive->do_object_b(*p) is false, then cl will not be
141 // invoked on p.
142
143 class OopStorage::BasicParState VALUE_OBJ_CLASS_SPEC {
144 OopStorage* _storage;
145 void* volatile _next_block;
146 bool _concurrent;
147
148 // Noncopyable.
149 BasicParState(const BasicParState&);
150 BasicParState& operator=(const BasicParState&);
151
152 void update_iteration_state(bool value);
153 void ensure_iteration_started();
154 Block* claim_next_block();
155
156 // Wrapper for iteration handler; ignore handler result and return true.
157 template<typename F> class AlwaysTrueFn;
158
159 public:
160 BasicParState(OopStorage* storage, bool concurrent);
161 ~BasicParState();
162
163 template<bool is_const, typename F> void iterate(F f);
164 };
165
166 template<bool concurrent, bool is_const>
167 class OopStorage::ParState VALUE_OBJ_CLASS_SPEC {
168 BasicParState _basic_state;
169
170 public:
171 ParState(const OopStorage* storage) :
172 // For simplicity, always recorded as non-const.
173 _basic_state(const_cast<OopStorage*>(storage), concurrent)
174 {}
175
176 template<typename F> void iterate(F f);
177 template<typename Closure> void oops_do(Closure* cl);
178 };
179
180 template<>
181 class OopStorage::ParState<false, false> VALUE_OBJ_CLASS_SPEC {
182 BasicParState _basic_state;
183
184 public:
185 ParState(OopStorage* storage) :
186 _basic_state(storage, 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 // INCLUDE_ALL_GCS
197
198 #endif // SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP