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