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_OOPSTORAGE_HPP
26 #define SHARE_GC_SHARED_OOPSTORAGE_HPP
27
28 #include "memory/allocation.hpp"
29 #include "oops/oop.hpp"
30 #include "utilities/globalDefinitions.hpp"
31 #include "utilities/macros.hpp"
32
33 class Mutex;
34 class outputStream;
35
36 // OopStorage supports management of off-heap references to objects allocated
37 // in the Java heap. An OopStorage object provides a set of Java object
38 // references (oop values), which clients refer to via oop* handles to the
39 // associated OopStorage entries. Clients allocate entries to create a
40 // (possibly weak) reference to a Java object, use that reference, and release
41 // the reference when no longer needed.
42 //
43 // The garbage collector must know about all OopStorage objects and their
44 // reference strength. OopStorage provides the garbage collector with support
45 // for iteration over all the allocated entries.
46 //
47 // There are several categories of interaction with an OopStorage object.
48 //
49 // (1) allocation and release of entries, by the mutator or the VM.
50 // (2) iteration by the garbage collector, possibly concurrent with mutator.
51 // (3) iteration by other, non-GC, tools (only at safepoints).
52 // (4) cleanup of unused internal storage, possibly concurrent with mutator.
53 //
54 // A goal of OopStorage is to make these interactions thread-safe, while
55 // minimizing potential lock contention issues within and between these
56 // categories. In particular, support for concurrent iteration by the garbage
57 // collector, under certain restrictions, is required. Further, it must not
58 // block nor be blocked by other operations for long periods.
59 //
60 // Internally, OopStorage is a set of Block objects, from which entries are
61 // allocated and released. A block contains an oop[] and a bitmask indicating
62 // which entries are in use (have been allocated and not yet released). New
63 // blocks are constructed and added to the storage object when an entry
64 // allocation request is made and there are no blocks with unused entries.
65 // Blocks may be removed and deleted when empty.
66 //
67 // There are two important (and somewhat intertwined) protocols governing
68 // concurrent access to a storage object. These are the Concurrent Iteration
69 // Protocol and the Allocation Protocol. See the ParState class for a
70 // discussion of concurrent iteration and the management of thread
71 // interactions for this protocol. Similarly, see the allocate() function for
72 // a discussion of allocation.
73
74 class OopStorage : public CHeapObj<mtGC> {
75 public:
76 OopStorage(const char* name, Mutex* allocate_mutex, Mutex* active_mutex);
77 ~OopStorage();
78
79 // These count and usage accessors are racy unless at a safepoint.
80
81 // The number of allocated and not yet released entries.
82 size_t allocation_count() const;
83
84 // The number of blocks of entries. Useful for sizing parallel iteration.
85 size_t block_count() const;
86
87 // Total number of blocks * memory allocation per block, plus
88 // bookkeeping overhead, including this storage object.
89 size_t total_memory_usage() const;
90
91 enum EntryStatus {
92 INVALID_ENTRY,
93 UNALLOCATED_ENTRY,
94 ALLOCATED_ENTRY
95 };
96
97 // Locks _allocate_mutex.
98 // precondition: ptr != NULL.
99 EntryStatus allocation_status(const oop* ptr) const;
100
101 // Allocates and returns a new entry. Returns NULL if memory allocation
102 // failed. Locks _allocate_mutex.
103 // postcondition: *result == NULL.
104 oop* allocate();
105
106 // Deallocates ptr. No locking.
107 // precondition: ptr is a valid allocated entry.
108 // precondition: *ptr == NULL.
109 void release(const oop* ptr);
110
111 // Releases all the ptrs. Possibly faster than individual calls to
112 // release(oop*). Best if ptrs is sorted by address. No locking.
113 // precondition: All elements of ptrs are valid allocated entries.
114 // precondition: *ptrs[i] == NULL, for i in [0,size).
115 void release(const oop* const* ptrs, size_t size);
116
117 // Applies f to each allocated entry's location. f must be a function or
118 // function object. Assume p is either a const oop* or an oop*, depending
119 // on whether the associated storage is const or non-const, respectively.
120 // Then f(p) must be a valid expression. The result of invoking f(p) must
121 // be implicitly convertible to bool. Iteration terminates and returns
122 // false if any invocation of f returns false. Otherwise, the result of
123 // iteration is true.
124 // precondition: at safepoint.
125 template<typename F> inline bool iterate_safepoint(F f);
126 template<typename F> inline bool iterate_safepoint(F f) const;
127
128 // oops_do and weak_oops_do are wrappers around iterate_safepoint, providing
129 // an adaptation layer allowing the use of existing is-alive closures and
130 // OopClosures. Assume p is either const oop* or oop*, depending on whether
131 // the associated storage is const or non-const, respectively. Then
132 //
133 // - closure->do_oop(p) must be a valid expression whose value is ignored.
134 //
135 // - is_alive->do_object_b(*p) must be a valid expression whose value is
136 // convertible to bool.
137 //
138 // For weak_oops_do, if *p == NULL then neither is_alive nor closure will be
139 // invoked for p. If is_alive->do_object_b(*p) is false, then closure will
140 // not be invoked on p, and *p will be set to NULL.
141
142 template<typename Closure> inline void oops_do(Closure* closure);
143 template<typename Closure> inline void oops_do(Closure* closure) const;
144 template<typename Closure> inline void weak_oops_do(Closure* closure);
145
146 template<typename IsAliveClosure, typename Closure>
147 inline void weak_oops_do(IsAliveClosure* is_alive, Closure* closure);
148
149 // Parallel iteration is for the exclusive use of the GC.
150 // Other clients must use serial iteration.
151 template<bool concurrent, bool is_const> class ParState;
152
153 // Block cleanup functions are for the exclusive use of the GC.
154 // Both stop deleting if there is an in-progress concurrent iteration.
155 // Concurrent deletion locks both the allocate_mutex and the active_mutex.
156 void delete_empty_blocks_safepoint();
157 void delete_empty_blocks_concurrent();
158
159 // Debugging and logging support.
160 const char* name() const;
161 void print_on(outputStream* st) const PRODUCT_RETURN;
162
163 // Provides access to storage internals, for unit testing.
164 // Declare, but not define, the public class OopStorage::TestAccess.
165 // That class is defined as part of the unit-test. It "exports" the needed
166 // private types by providing public typedefs for them.
167 class TestAccess;
168
169 // xlC on AIX can't compile test_oopStorage.cpp with following private
170 // classes. C++03 introduced access for nested classes with DR45, but xlC
171 // version 12 rejects it.
172 NOT_AIX( private: )
173 class Block; // Forward decl; defined in .inline.hpp file.
174 class BlockList; // Forward decl for BlockEntry friend decl.
175
176 class BlockEntry {
177 friend class BlockList;
178
179 // Members are mutable, and we deal exclusively with pointers to
180 // const, to make const blocks easier to use; a block being const
181 // doesn't prevent modifying its list state.
182 mutable const Block* _prev;
183 mutable const Block* _next;
184
185 // Noncopyable.
186 BlockEntry(const BlockEntry&);
187 BlockEntry& operator=(const BlockEntry&);
188
189 public:
190 BlockEntry();
191 ~BlockEntry();
192 };
193
194 class BlockList {
195 const Block* _head;
196 const Block* _tail;
197 const BlockEntry& (*_get_entry)(const Block& block);
198
199 // Noncopyable.
200 BlockList(const BlockList&);
201 BlockList& operator=(const BlockList&);
202
203 public:
204 BlockList(const BlockEntry& (*get_entry)(const Block& block));
205 ~BlockList();
206
207 Block* head();
208 const Block* chead() const;
209 const Block* ctail() const;
210
211 Block* prev(Block& block);
212 Block* next(Block& block);
213
214 const Block* prev(const Block& block) const;
215 const Block* next(const Block& block) const;
216
217 void push_front(const Block& block);
218 void push_back(const Block& block);
219 void unlink(const Block& block);
220 };
221
222 private:
223 const char* _name;
224 BlockList _active_list;
225 BlockList _allocate_list;
226 Block* volatile _active_head;
227 Block* volatile _deferred_updates;
228
229 Mutex* _allocate_mutex;
230 Mutex* _active_mutex;
231
232 // Counts are volatile for racy unlocked accesses.
233 volatile size_t _allocation_count;
234 volatile size_t _block_count;
235 // mutable because this gets set even for const iteration.
236 mutable bool _concurrent_iteration_active;
237
238 Block* find_block_or_null(const oop* ptr) const;
239 void delete_empty_block(const Block& block);
240 bool reduce_deferred_updates();
241
242 template<typename F, typename Storage>
243 static bool iterate_impl(F f, Storage* storage);
244
245 // Implementation support for parallel iteration
246 class BasicParState;
247
248 // Wrapper for OopClosure-style function, so it can be used with
249 // iterate. Assume p is of type oop*. Then cl->do_oop(p) must be a
250 // valid expression whose value may be ignored.
251 template<typename Closure> class OopFn;
252 template<typename Closure> static OopFn<Closure> oop_fn(Closure* cl);
253
254 // Wrapper for BoolObjectClosure + iteration handler pair, so they
255 // can be used with iterate.
256 template<typename IsAlive, typename F> class IfAliveFn;
257 template<typename IsAlive, typename F>
258 static IfAliveFn<IsAlive, F> if_alive_fn(IsAlive* is_alive, F f);
259
260 // Wrapper for iteration handler, automatically skipping NULL entries.
261 template<typename F> class SkipNullFn;
262 template<typename F> static SkipNullFn<F> skip_null_fn(F f);
263 };
264
265 #endif // include guard