1 /*
2 * Copyright (c) 2001, 2020, 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 *
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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23 */
24
25 #ifndef SHARE_GC_SHARED_PTRQUEUE_HPP
26 #define SHARE_GC_SHARED_PTRQUEUE_HPP
27
28 #include "memory/padded.hpp"
29 #include "utilities/align.hpp"
30 #include "utilities/debug.hpp"
31 #include "utilities/globalDefinitions.hpp"
32 #include "utilities/lockFreeStack.hpp"
33 #include "utilities/sizes.hpp"
34
35 class Mutex;
36 class Monitor;
37
38 // There are various techniques that require threads to be able to log
39 // addresses. For example, a generational write barrier might log
40 // the addresses of modified old-generation objects. This type supports
41 // this operation.
42
43 class BufferNode;
44 class PtrQueueSet;
45 class PtrQueue {
46 friend class VMStructs;
47
48 NONCOPYABLE(PtrQueue);
49
50 // The ptr queue set to which this queue belongs.
51 PtrQueueSet* const _qset;
52
53 // Whether updates should be logged.
54 bool _active;
55
56 // The (byte) index at which an object was last enqueued. Starts at
57 // capacity_in_bytes (indicating an empty buffer) and goes towards zero.
58 // Value is always pointer-size aligned.
59 size_t _index;
60
61 // Size of the current buffer, in bytes.
62 // Value is always pointer-size aligned.
63 size_t _capacity_in_bytes;
64
65 static const size_t _element_size = sizeof(void*);
66
67 // Get the capacity, in bytes. The capacity must have been set.
68 size_t capacity_in_bytes() const {
69 assert(_capacity_in_bytes > 0, "capacity not set");
70 return _capacity_in_bytes;
71 }
72
73 static size_t byte_index_to_index(size_t ind) {
74 assert(is_aligned(ind, _element_size), "precondition");
75 return ind / _element_size;
76 }
77
78 static size_t index_to_byte_index(size_t ind) {
79 return ind * _element_size;
80 }
81
82 protected:
83 // The buffer.
84 void** _buf;
85
86 size_t index() const {
87 return byte_index_to_index(_index);
88 }
89
90 void set_index(size_t new_index) {
91 size_t byte_index = index_to_byte_index(new_index);
92 assert(byte_index <= capacity_in_bytes(), "precondition");
93 _index = byte_index;
94 }
95
96 size_t capacity() const {
97 return byte_index_to_index(capacity_in_bytes());
98 }
99
100 PtrQueueSet* qset() const { return _qset; }
101
102 // Process queue entries and release resources.
103 void flush_impl();
104
105 // Process (some of) the buffer and leave it in place for further use,
106 // or enqueue the buffer and allocate a new one.
107 virtual void handle_completed_buffer() = 0;
108
109 void allocate_buffer();
110
111 // Enqueue the current buffer in the qset and allocate a new buffer.
112 void enqueue_completed_buffer();
113
114 // Initialize this queue to contain a null buffer, and be part of the
115 // given PtrQueueSet.
116 PtrQueue(PtrQueueSet* qset, bool active = false);
117
118 // Requires queue flushed.
119 ~PtrQueue();
120
121 public:
122
123 // Forcibly set empty.
124 void reset() {
125 if (_buf != NULL) {
126 _index = capacity_in_bytes();
127 }
128 }
129
130 void enqueue(volatile void* ptr) {
131 enqueue((void*)(ptr));
132 }
133
134 // Enqueues the given "obj".
135 void enqueue(void* ptr) {
136 if (!_active) return;
137 else enqueue_known_active(ptr);
138 }
139
140 void handle_zero_index();
141
142 void enqueue_known_active(void* ptr);
143
144 // Return the size of the in-use region.
145 size_t size() const {
146 size_t result = 0;
147 if (_buf != NULL) {
148 assert(_index <= capacity_in_bytes(), "Invariant");
149 result = byte_index_to_index(capacity_in_bytes() - _index);
150 }
151 return result;
152 }
153
154 bool is_empty() const {
155 return _buf == NULL || capacity_in_bytes() == _index;
156 }
157
158 // Set the "active" property of the queue to "b". An enqueue to an
159 // inactive thread is a no-op. Setting a queue to inactive resets its
160 // log to the empty state.
161 void set_active(bool b) {
162 _active = b;
163 if (!b && _buf != NULL) {
164 reset();
165 } else if (b && _buf != NULL) {
166 assert(index() == capacity(),
167 "invariant: queues are empty when activated.");
168 }
169 }
170
171 bool is_active() const { return _active; }
172
173 // To support compiler.
174
175 protected:
176 template<typename Derived>
177 static ByteSize byte_offset_of_index() {
178 return byte_offset_of(Derived, _index);
179 }
180
181 static ByteSize byte_width_of_index() { return in_ByteSize(sizeof(size_t)); }
182
183 template<typename Derived>
184 static ByteSize byte_offset_of_buf() {
185 return byte_offset_of(Derived, _buf);
186 }
187
188 static ByteSize byte_width_of_buf() { return in_ByteSize(_element_size); }
189
190 template<typename Derived>
191 static ByteSize byte_offset_of_active() {
192 return byte_offset_of(Derived, _active);
193 }
194
195 static ByteSize byte_width_of_active() { return in_ByteSize(sizeof(bool)); }
196
197 };
198
199 class BufferNode {
200 size_t _index;
201 BufferNode* volatile _next;
202 void* _buffer[1]; // Pseudo flexible array member.
203
204 BufferNode() : _index(0), _next(NULL) { }
205 ~BufferNode() { }
206
207 NONCOPYABLE(BufferNode);
208
209 static size_t buffer_offset() {
210 return offset_of(BufferNode, _buffer);
211 }
212
213 // Allocate a new BufferNode with the "buffer" having size elements.
214 static BufferNode* allocate(size_t size);
215
216 // Free a BufferNode.
217 static void deallocate(BufferNode* node);
218
219 public:
220 static BufferNode* volatile* next_ptr(BufferNode& bn) { return &bn._next; }
221 typedef LockFreeStack<BufferNode, &next_ptr> Stack;
222
223 BufferNode* next() const { return _next; }
224 void set_next(BufferNode* n) { _next = n; }
225 size_t index() const { return _index; }
226 void set_index(size_t i) { _index = i; }
227
228 // Return the BufferNode containing the buffer, after setting its index.
229 static BufferNode* make_node_from_buffer(void** buffer, size_t index) {
230 BufferNode* node =
231 reinterpret_cast<BufferNode*>(
232 reinterpret_cast<char*>(buffer) - buffer_offset());
233 node->set_index(index);
234 return node;
235 }
236
237 // Return the buffer for node.
238 static void** make_buffer_from_node(BufferNode *node) {
239 // &_buffer[0] might lead to index out of bounds warnings.
240 return reinterpret_cast<void**>(
241 reinterpret_cast<char*>(node) + buffer_offset());
242 }
243
244 class Allocator; // Free-list based allocator.
245 class TestSupport; // Unit test support.
246 };
247
248 // Allocation is based on a lock-free free list of nodes, linked through
249 // BufferNode::_next (see BufferNode::Stack). To solve the ABA problem,
250 // popping a node from the free list is performed within a GlobalCounter
251 // critical section, and pushing nodes onto the free list is done after
252 // a GlobalCounter synchronization associated with the nodes to be pushed.
253 // This is documented behavior so that other parts of the node life-cycle
254 // can depend on and make use of it too.
255 class BufferNode::Allocator {
256 friend class TestSupport;
257
258 // Since we don't expect many instances, and measured >15% speedup
259 // on stress gtest, padding seems like a good tradeoff here.
260 #define DECLARE_PADDED_MEMBER(Id, Type, Name) \
261 Type Name; DEFINE_PAD_MINUS_SIZE(Id, DEFAULT_CACHE_LINE_SIZE, sizeof(Type))
262
263 const size_t _buffer_size;
264 char _name[DEFAULT_CACHE_LINE_SIZE - sizeof(size_t)]; // Use name as padding.
265 DECLARE_PADDED_MEMBER(1, Stack, _pending_list);
266 DECLARE_PADDED_MEMBER(2, Stack, _free_list);
267 DECLARE_PADDED_MEMBER(3, volatile size_t, _pending_count);
268 DECLARE_PADDED_MEMBER(4, volatile size_t, _free_count);
269 DECLARE_PADDED_MEMBER(5, volatile bool, _transfer_lock);
270
271 #undef DECLARE_PADDED_MEMBER
272
273 void delete_list(BufferNode* list);
274 bool try_transfer_pending();
275
276 NONCOPYABLE(Allocator);
277
278 public:
279 Allocator(const char* name, size_t buffer_size);
280 ~Allocator();
281
282 const char* name() const { return _name; }
283 size_t buffer_size() const { return _buffer_size; }
284 size_t free_count() const;
285 BufferNode* allocate();
286 void release(BufferNode* node);
287
288 // Deallocate some of the available buffers. remove_goal is the target
289 // number to remove. Returns the number actually deallocated, which may
290 // be less than the goal if there were fewer available.
291 size_t reduce_free_list(size_t remove_goal);
292 };
293
294 // A PtrQueueSet represents resources common to a set of pointer queues.
295 // In particular, the individual queues allocate buffers from this shared
296 // set, and return completed buffers to the set.
297 class PtrQueueSet {
298 BufferNode::Allocator* _allocator;
299
300 NONCOPYABLE(PtrQueueSet);
301
302 protected:
303 bool _all_active;
304
305 // Create an empty ptr queue set.
306 PtrQueueSet(BufferNode::Allocator* allocator);
307 ~PtrQueueSet();
308
309 public:
310
311 // Return the associated BufferNode allocator.
312 BufferNode::Allocator* allocator() const { return _allocator; }
313
314 // Return the buffer for a BufferNode of size buffer_size().
315 void** allocate_buffer();
316
317 // Return an empty buffer to the free list. The node is required
318 // to have been allocated with a size of buffer_size().
319 void deallocate_buffer(BufferNode* node);
320
321 // A completed buffer is a buffer the mutator is finished with, and
322 // is ready to be processed by the collector. It need not be full.
323
324 // Adds node to the completed buffer list.
325 virtual void enqueue_completed_buffer(BufferNode* node) = 0;
326
327 bool is_active() { return _all_active; }
328
329 size_t buffer_size() const {
330 return _allocator->buffer_size();
331 }
332 };
333
334 #endif // SHARE_GC_SHARED_PTRQUEUE_HPP