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 *
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.
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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 "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 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_concurrent() 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 // An in-progress delete_empty_blocks_concurrent() operation can contend with
75 // the start of a concurrent iteration over the _active_mutex. Since both are
76 // under GC control, that potential contention can be eliminated by never
77 // scheduling both operations to run at the same time.
78 //
79 // ParState<concurrent, is_const>
80 // concurrent must be true if iteration may be concurrent with the
81 // mutators.
82 //
83 // is_const must be true if the iteration is over a constant storage
84 // object, false if the iteration may modify the storage object.
85 //
86 // ParState([const] OopStorage* storage)
87 // Construct an object for managing an iteration over storage. For a
88 // concurrent ParState, empty block deletion for the associated storage
89 // is inhibited for the life of the ParState.
90 //
91 // template<typename F> void iterate(F f)
92 // Repeatedly claims a block from the associated storage that has
93 // not been processed by this iteration (possibly by other threads),
94 // and applies f to each entry in the claimed block. Assume p is of
95 // type const oop* or oop*, according to is_const. Then f(p) must be
96 // a valid expression whose value is ignored. Concurrent uses must
97 // be prepared for an entry's value to change at any time, due to
98 // mutator activity.
99 //
100 // template<typename Closure> void oops_do(Closure* cl)
101 // Wrapper around iterate, providing an adaptation layer allowing
102 // the use of OopClosures and similar objects for iteration. Assume
103 // p is of type const oop* or oop*, according to is_const. Then
104 // cl->do_oop(p) must be a valid expression whose value is ignored.
105 // Concurrent uses must be prepared for the entry's value to change
106 // at any time, due to mutator activity.
107 //
108 // Optional operations, provided only if !concurrent && !is_const.
109 // These are not provided when is_const, because the storage object
110 // may be modified by the iteration infrastructure, even if the
111 // provided closure doesn't modify the storage object. These are not
112 // provided when concurrent because any pre-filtering behavior by the
113 // iteration infrastructure is inappropriate for concurrent iteration;
114 // modifications of the storage by the mutator could result in the
115 // pre-filtering being applied (successfully or not) to objects that
116 // are unrelated to what the closure finds in the entry.
117 //
118 // template<typename Closure> void weak_oops_do(Closure* cl)
119 // template<typename IsAliveClosure, typename Closure>
120 // void weak_oops_do(IsAliveClosure* is_alive, Closure* cl)
121 // Wrappers around iterate, providing an adaptation layer allowing
122 // the use of is-alive closures and OopClosures for iteration.
123 // Assume p is of type oop*. Then
124 //
125 // - cl->do_oop(p) must be a valid expression whose value is ignored.
126 //
127 // - is_alive->do_object_b(*p) must be a valid expression whose value
128 // is convertible to bool.
129 //
130 // If *p == NULL then neither is_alive nor cl will be invoked for p.
131 // If is_alive->do_object_b(*p) is false, then cl will not be
132 // invoked on p.
133
134 class OopStorage::BasicParState {
135 const OopStorage* _storage;
136 ActiveArray* _active_array;
137 size_t _block_count;
138 volatile size_t _next_block;
139 uint _estimated_thread_count;
140 bool _concurrent;
141
142 // Noncopyable.
143 BasicParState(const BasicParState&);
144 BasicParState& operator=(const BasicParState&);
145
146 struct IterationData;
147
148 void update_concurrent_iteration_count(int value);
149 bool claim_next_segment(IterationData* data);
150 bool finish_iteration(const IterationData* data) const;
151
152 // Wrapper for iteration handler; ignore handler result and return true.
153 template<typename F> class AlwaysTrueFn;
154
155 public:
156 BasicParState(const OopStorage* storage,
157 uint estimated_thread_count,
158 bool concurrent);
159 ~BasicParState();
160
161 template<bool is_const, typename F> void iterate(F f);
162
163 static uint default_estimated_thread_count(bool concurrent);
164 };
165
166 template<bool concurrent, bool is_const>
167 class OopStorage::ParState {
168 BasicParState _basic_state;
169
170 typedef typename Conditional<is_const,
171 const OopStorage*,
172 OopStorage*>::type StoragePtr;
173
174 public:
175 ParState(StoragePtr storage,
176 uint estimated_thread_count = BasicParState::default_estimated_thread_count(concurrent)) :
177 _basic_state(storage, estimated_thread_count, concurrent)
178 {}
179
180 template<typename F> void iterate(F f);
181 template<typename Closure> void oops_do(Closure* cl);
182 };
183
184 template<>
185 class OopStorage::ParState<false, false> {
186 BasicParState _basic_state;
187
188 public:
189 ParState(OopStorage* storage,
190 uint estimated_thread_count = BasicParState::default_estimated_thread_count(false)) :
191 _basic_state(storage, estimated_thread_count, false)
192 {}
193
194 template<typename F> void iterate(F f);
195 template<typename Closure> void oops_do(Closure* cl);
196 template<typename Closure> void weak_oops_do(Closure* cl);
197 template<typename IsAliveClosure, typename Closure>
198 void weak_oops_do(IsAliveClosure* is_alive, Closure* cl);
199 };
200
201 #endif // SHARE_GC_SHARED_OOPSTORAGEPARSTATE_HPP