1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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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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_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/lockFreeStack.hpp"
32 #include "utilities/sizes.hpp"
33
34 class Mutex;
35
36 // There are various techniques that require threads to be able to log
37 // addresses. For example, a generational write barrier might log
38 // the addresses of modified old-generation objects. This type supports
39 // this operation.
40
41 class BufferNode;
42 class PtrQueueSet;
43 class PtrQueue {
44 friend class VMStructs;
45
46 // Noncopyable - not defined.
47 PtrQueue(const PtrQueue&);
48 PtrQueue& operator=(const 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 // If true, the queue is permanent, and doesn't need to deallocate
57 // its buffer in the destructor (since that obtains a lock which may not
58 // be legally locked by then.
59 const bool _permanent;
60
61 // The (byte) index at which an object was last enqueued. Starts at
62 // capacity_in_bytes (indicating an empty buffer) and goes towards zero.
63 // Value is always pointer-size aligned.
64 size_t _index;
65
66 // Size of the current buffer, in bytes.
67 // Value is always pointer-size aligned.
68 size_t _capacity_in_bytes;
69
70 static const size_t _element_size = sizeof(void*);
71
72 // Get the capacity, in bytes. The capacity must have been set.
73 size_t capacity_in_bytes() const {
74 assert(_capacity_in_bytes > 0, "capacity not set");
75 return _capacity_in_bytes;
76 }
77
78 void set_capacity(size_t entries) {
79 size_t byte_capacity = index_to_byte_index(entries);
80 assert(_capacity_in_bytes == 0 || _capacity_in_bytes == byte_capacity,
81 "changing capacity " SIZE_FORMAT " -> " SIZE_FORMAT,
82 _capacity_in_bytes, byte_capacity);
83 _capacity_in_bytes = byte_capacity;
84 }
85
86 static size_t byte_index_to_index(size_t ind) {
87 assert(is_aligned(ind, _element_size), "precondition");
88 return ind / _element_size;
89 }
90
91 static size_t index_to_byte_index(size_t ind) {
92 return ind * _element_size;
93 }
94
95 protected:
96 // The buffer.
97 void** _buf;
98
99 size_t index() const {
100 return byte_index_to_index(_index);
101 }
102
103 void set_index(size_t new_index) {
104 size_t byte_index = index_to_byte_index(new_index);
105 assert(byte_index <= capacity_in_bytes(), "precondition");
106 _index = byte_index;
107 }
108
109 size_t capacity() const {
110 return byte_index_to_index(capacity_in_bytes());
111 }
112
113 // If there is a lock associated with this buffer, this is that lock.
114 Mutex* _lock;
115
116 PtrQueueSet* qset() { return _qset; }
117 bool is_permanent() const { return _permanent; }
118
119 // Process queue entries and release resources.
120 void flush_impl();
121
122 // Initialize this queue to contain a null buffer, and be part of the
123 // given PtrQueueSet.
124 PtrQueue(PtrQueueSet* qset, bool permanent = false, bool active = false);
125
126 // Requires queue flushed or permanent.
127 ~PtrQueue();
128
129 public:
130
131 // Associate a lock with a ptr queue.
132 void set_lock(Mutex* lock) { _lock = lock; }
133
134 // Forcibly set empty.
135 void reset() {
136 if (_buf != NULL) {
137 _index = capacity_in_bytes();
138 }
139 }
140
141 void enqueue(volatile void* ptr) {
142 enqueue((void*)(ptr));
143 }
144
145 // Enqueues the given "obj".
146 void enqueue(void* ptr) {
147 if (!_active) return;
148 else enqueue_known_active(ptr);
149 }
150
151 // This method is called when we're doing the zero index handling
152 // and gives a chance to the queues to do any pre-enqueueing
153 // processing they might want to do on the buffer. It should return
154 // true if the buffer should be enqueued, or false if enough
155 // entries were cleared from it so that it can be re-used. It should
156 // not return false if the buffer is still full (otherwise we can
157 // get into an infinite loop).
158 virtual bool should_enqueue_buffer() { return true; }
159 void handle_zero_index();
160
161 void enqueue_known_active(void* ptr);
162
163 // Return the size of the in-use region.
164 size_t size() const {
165 size_t result = 0;
166 if (_buf != NULL) {
167 assert(_index <= capacity_in_bytes(), "Invariant");
168 result = byte_index_to_index(capacity_in_bytes() - _index);
169 }
170 return result;
171 }
172
173 bool is_empty() const {
174 return _buf == NULL || capacity_in_bytes() == _index;
175 }
176
177 // Set the "active" property of the queue to "b". An enqueue to an
178 // inactive thread is a no-op. Setting a queue to inactive resets its
179 // log to the empty state.
180 void set_active(bool b) {
181 _active = b;
182 if (!b && _buf != NULL) {
183 reset();
184 } else if (b && _buf != NULL) {
185 assert(index() == capacity(),
186 "invariant: queues are empty when activated.");
187 }
188 }
189
190 bool is_active() const { return _active; }
191
192 // To support compiler.
193
194 protected:
195 template<typename Derived>
196 static ByteSize byte_offset_of_index() {
197 return byte_offset_of(Derived, _index);
198 }
199
200 static ByteSize byte_width_of_index() { return in_ByteSize(sizeof(size_t)); }
201
202 template<typename Derived>
203 static ByteSize byte_offset_of_buf() {
204 return byte_offset_of(Derived, _buf);
205 }
206
207 static ByteSize byte_width_of_buf() { return in_ByteSize(_element_size); }
208
209 template<typename Derived>
210 static ByteSize byte_offset_of_active() {
211 return byte_offset_of(Derived, _active);
212 }
213
214 static ByteSize byte_width_of_active() { return in_ByteSize(sizeof(bool)); }
215
216 };
217
218 class BufferNode {
219 size_t _index;
220 BufferNode* volatile _next;
221 void* _buffer[1]; // Pseudo flexible array member.
222
223 BufferNode() : _index(0), _next(NULL) { }
224 ~BufferNode() { }
225
226 static size_t buffer_offset() {
227 return offset_of(BufferNode, _buffer);
228 }
229
230 static BufferNode* volatile* next_ptr(BufferNode& bn) { return &bn._next; }
231
232 AIX_ONLY(public:) // xlC 12 on AIX doesn't implement C++ DR45.
233 // Allocate a new BufferNode with the "buffer" having size elements.
234 static BufferNode* allocate(size_t size);
235
236 // Free a BufferNode.
237 static void deallocate(BufferNode* node);
238
239 public:
240 typedef LockFreeStack<BufferNode, &next_ptr> Stack;
241
242 BufferNode* next() const { return _next; }
243 void set_next(BufferNode* n) { _next = n; }
244 size_t index() const { return _index; }
245 void set_index(size_t i) { _index = i; }
246
247 // Return the BufferNode containing the buffer, after setting its index.
248 static BufferNode* make_node_from_buffer(void** buffer, size_t index) {
249 BufferNode* node =
250 reinterpret_cast<BufferNode*>(
251 reinterpret_cast<char*>(buffer) - buffer_offset());
252 node->set_index(index);
253 return node;
254 }
255
256 // Return the buffer for node.
257 static void** make_buffer_from_node(BufferNode *node) {
258 // &_buffer[0] might lead to index out of bounds warnings.
259 return reinterpret_cast<void**>(
260 reinterpret_cast<char*>(node) + buffer_offset());
261 }
262
263 class Allocator; // Free-list based allocator.
264 class TestSupport; // Unit test support.
265 };
266
267 // Allocation is based on a lock-free free list of nodes, linked through
268 // BufferNode::_next (see BufferNode::Stack). To solve the ABA problem,
269 // popping a node from the free list is performed within a GlobalCounter
270 // critical section, and pushing nodes onto the free list is done after
271 // a GlobalCounter synchronization associated with the nodes to be pushed.
272 // This is documented behavior so that other parts of the node life-cycle
273 // can depend on and make use of it too.
274 class BufferNode::Allocator {
275 friend class TestSupport;
276
277 // Since we don't expect many instances, and measured >15% speedup
278 // on stress gtest, padding seems like a good tradeoff here.
279 #define DECLARE_PADDED_MEMBER(Id, Type, Name) \
280 Type Name; DEFINE_PAD_MINUS_SIZE(Id, DEFAULT_CACHE_LINE_SIZE, sizeof(Type))
281
282 const size_t _buffer_size;
283 char _name[DEFAULT_CACHE_LINE_SIZE - sizeof(size_t)]; // Use name as padding.
284 DECLARE_PADDED_MEMBER(1, Stack, _pending_list);
285 DECLARE_PADDED_MEMBER(2, Stack, _free_list);
286 DECLARE_PADDED_MEMBER(3, volatile size_t, _pending_count);
287 DECLARE_PADDED_MEMBER(4, volatile size_t, _free_count);
288 DECLARE_PADDED_MEMBER(5, volatile bool, _transfer_lock);
289
290 #undef DECLARE_PADDED_MEMBER
291
292 void delete_list(BufferNode* list);
293 bool try_transfer_pending();
294
295 public:
296 Allocator(const char* name, size_t buffer_size);
297 ~Allocator();
298
299 const char* name() const { return _name; }
300 size_t buffer_size() const { return _buffer_size; }
301 size_t free_count() const;
302 BufferNode* allocate();
303 void release(BufferNode* node);
304
305 // Deallocate some of the available buffers. remove_goal is the target
306 // number to remove. Returns the number actually deallocated, which may
307 // be less than the goal if there were fewer available.
308 size_t reduce_free_list(size_t remove_goal);
309 };
310
311 // A PtrQueueSet represents resources common to a set of pointer queues.
312 // In particular, the individual queues allocate buffers from this shared
313 // set, and return completed buffers to the set.
314 class PtrQueueSet {
315 BufferNode::Allocator* _allocator;
316
317 Monitor* _cbl_mon; // Protects the fields below.
318 BufferNode* _completed_buffers_head;
319 BufferNode* _completed_buffers_tail;
320 size_t _n_completed_buffers;
321
322 size_t _process_completed_buffers_threshold;
323 volatile bool _process_completed_buffers;
324
325 // If true, notify_all on _cbl_mon when the threshold is reached.
326 bool _notify_when_complete;
327
328 // Maximum number of elements allowed on completed queue: after that,
329 // enqueuer does the work itself.
330 size_t _max_completed_buffers;
331 size_t _completed_buffers_padding;
332
333 void assert_completed_buffers_list_len_correct_locked() NOT_DEBUG_RETURN;
334
335 protected:
336 bool _all_active;
337
338 // A mutator thread does the the work of processing a buffer.
339 // Returns "true" iff the work is complete (and the buffer may be
340 // deallocated).
341 virtual bool mut_process_buffer(BufferNode* node) {
342 ShouldNotReachHere();
343 return false;
344 }
345
346 // Create an empty ptr queue set.
347 PtrQueueSet(bool notify_when_complete = false);
348 ~PtrQueueSet();
349
350 // Because of init-order concerns, we can't pass these as constructor
351 // arguments.
352 void initialize(Monitor* cbl_mon, BufferNode::Allocator* allocator);
353
354 // For (unlocked!) iteration over the completed buffers.
355 BufferNode* completed_buffers_head() const { return _completed_buffers_head; }
356
357 // Deallocate all of the completed buffers.
358 void abandon_completed_buffers();
359
360 public:
361
362 // Return the buffer for a BufferNode of size buffer_size().
363 void** allocate_buffer();
364
365 // Return an empty buffer to the free list. The node is required
366 // to have been allocated with a size of buffer_size().
367 void deallocate_buffer(BufferNode* node);
368
369 // A completed buffer is a buffer the mutator is finished with, and
370 // is ready to be processed by the collector. It need not be full.
371
372 // Adds node to the completed buffer list.
373 void enqueue_completed_buffer(BufferNode* node);
374
375 // If the number of completed buffers is > stop_at, then remove and
376 // return a completed buffer from the list. Otherwise, return NULL.
377 BufferNode* get_completed_buffer(size_t stop_at = 0);
378
379 // To be invoked by the mutator.
380 bool process_or_enqueue_completed_buffer(BufferNode* node);
381
382 bool process_completed_buffers() { return _process_completed_buffers; }
383 void set_process_completed_buffers(bool x) { _process_completed_buffers = x; }
384
385 bool is_active() { return _all_active; }
386
387 size_t buffer_size() const {
388 return _allocator->buffer_size();
389 }
390
391 // Get/Set the number of completed buffers that triggers log processing.
392 // Log processing should be done when the number of buffers exceeds the
393 // threshold.
394 void set_process_completed_buffers_threshold(size_t sz) {
395 _process_completed_buffers_threshold = sz;
396 }
397 size_t process_completed_buffers_threshold() const {
398 return _process_completed_buffers_threshold;
399 }
400 static const size_t ProcessCompletedBuffersThresholdNever = ~size_t(0);
401
402 size_t completed_buffers_num() const { return _n_completed_buffers; }
403
404 void merge_bufferlists(PtrQueueSet* src);
405
406 void set_max_completed_buffers(size_t m) {
407 _max_completed_buffers = m;
408 }
409 size_t max_completed_buffers() const {
410 return _max_completed_buffers;
411 }
412 static const size_t MaxCompletedBuffersUnlimited = ~size_t(0);
413
414 void set_completed_buffers_padding(size_t padding) {
415 _completed_buffers_padding = padding;
416 }
417 size_t completed_buffers_padding() const {
418 return _completed_buffers_padding;
419 }
420
421 // Notify the consumer if the number of buffers crossed the threshold
422 void notify_if_necessary();
423 };
424
425 #endif // SHARE_GC_SHARED_PTRQUEUE_HPP