1 /*
2 * Copyright (c) 2001, 2019, 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 #include "precompiled.hpp"
26 #include "gc/shared/ptrQueue.hpp"
27 #include "logging/log.hpp"
28 #include "memory/allocation.hpp"
29 #include "memory/allocation.inline.hpp"
30 #include "runtime/atomic.hpp"
31 #include "runtime/mutex.hpp"
32 #include "runtime/mutexLocker.hpp"
33 #include "runtime/orderAccess.hpp"
34 #include "runtime/thread.inline.hpp"
35 #include "utilities/globalCounter.inline.hpp"
36
37 #include <new>
38
39 PtrQueue::PtrQueue(PtrQueueSet* qset, bool active) :
40 _qset(qset),
41 _active(active),
42 _index(0),
43 _capacity_in_bytes(0),
44 _buf(NULL)
45 {}
46
47 PtrQueue::~PtrQueue() {
48 assert(_buf == NULL, "queue must be flushed before delete");
49 }
50
51 void PtrQueue::flush_impl() {
52 if (_buf != NULL) {
53 BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
54 if (is_empty()) {
55 // No work to do.
56 qset()->deallocate_buffer(node);
57 } else {
58 qset()->enqueue_completed_buffer(node);
59 }
60 _buf = NULL;
61 set_index(0);
62 }
63 }
64
65 void PtrQueue::enqueue_known_active(void* ptr) {
66 while (_index == 0) {
67 handle_zero_index();
68 }
69
70 assert(_buf != NULL, "postcondition");
71 assert(index() > 0, "postcondition");
72 assert(index() <= capacity(), "invariant");
73 _index -= _element_size;
74 _buf[index()] = ptr;
75 }
76
77 void PtrQueue::handle_zero_index() {
78 assert(index() == 0, "precondition");
79
80 if (_buf != NULL) {
81 handle_completed_buffer();
82 } else {
83 // Bootstrapping kludge; lazily initialize capacity. The initial
84 // thread's queues are constructed before the second phase of the
85 // two-phase initialization of the associated qsets. As a result,
86 // we can't initialize _capacity_in_bytes in the queue constructor.
87 if (_capacity_in_bytes == 0) {
88 _capacity_in_bytes = index_to_byte_index(qset()->buffer_size());
89 }
90 allocate_buffer();
91 }
92 }
93
94 void PtrQueue::allocate_buffer() {
95 _buf = qset()->allocate_buffer();
96 reset();
97 }
98
99 void PtrQueue::enqueue_completed_buffer() {
100 assert(_buf != NULL, "precondition");
101 BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
102 qset()->enqueue_completed_buffer(node);
103 allocate_buffer();
104 }
105
106 BufferNode* BufferNode::allocate(size_t size) {
107 size_t byte_size = size * sizeof(void*);
108 void* data = NEW_C_HEAP_ARRAY(char, buffer_offset() + byte_size, mtGC);
109 return new (data) BufferNode;
110 }
111
112 void BufferNode::deallocate(BufferNode* node) {
113 node->~BufferNode();
114 FREE_C_HEAP_ARRAY(char, node);
115 }
116
117 BufferNode::Allocator::Allocator(const char* name, size_t buffer_size) :
118 _buffer_size(buffer_size),
119 _pending_list(),
120 _free_list(),
121 _pending_count(0),
122 _free_count(0),
123 _transfer_lock(false)
124 {
125 strncpy(_name, name, sizeof(_name) - 1);
126 _name[sizeof(_name) - 1] = '\0';
127 }
128
129 BufferNode::Allocator::~Allocator() {
130 delete_list(_free_list.pop_all());
131 delete_list(_pending_list.pop_all());
132 }
133
134 void BufferNode::Allocator::delete_list(BufferNode* list) {
135 while (list != NULL) {
136 BufferNode* next = list->next();
137 DEBUG_ONLY(list->set_next(NULL);)
138 BufferNode::deallocate(list);
139 list = next;
140 }
141 }
142
143 size_t BufferNode::Allocator::free_count() const {
144 return Atomic::load(&_free_count);
145 }
146
147 BufferNode* BufferNode::Allocator::allocate() {
148 BufferNode* node;
149 {
150 // Protect against ABA; see release().
151 GlobalCounter::CriticalSection cs(Thread::current());
152 node = _free_list.pop();
153 }
154 if (node == NULL) {
155 node = BufferNode::allocate(_buffer_size);
156 } else {
157 // Decrement count after getting buffer from free list. This, along
158 // with incrementing count before adding to free list, ensures count
159 // never underflows.
160 size_t count = Atomic::sub(1u, &_free_count);
161 assert((count + 1) != 0, "_free_count underflow");
162 }
163 return node;
164 }
165
166 // To solve the ABA problem for lock-free stack pop, allocate does the
167 // pop inside a critical section, and release synchronizes on the
168 // critical sections before adding to the _free_list. But we don't
169 // want to make every release have to do a synchronize. Instead, we
170 // initially place released nodes on the _pending_list, and transfer
171 // them to the _free_list in batches. Only one transfer at a time is
172 // permitted, with a lock bit to control access to that phase. A
173 // transfer takes all the nodes from the _pending_list, synchronizes on
174 // the _free_list pops, and then adds the former pending nodes to the
175 // _free_list. While that's happening, other threads might be adding
176 // other nodes to the _pending_list, to be dealt with by some later
177 // transfer.
178 void BufferNode::Allocator::release(BufferNode* node) {
179 assert(node != NULL, "precondition");
180 assert(node->next() == NULL, "precondition");
181
182 // Desired minimum transfer batch size. There is relatively little
183 // importance to the specific number. It shouldn't be too big, else
184 // we're wasting space when the release rate is low. If the release
185 // rate is high, we might accumulate more than this before being
186 // able to start a new transfer, but that's okay. Also note that
187 // the allocation rate and the release rate are going to be fairly
188 // similar, due to how the buffers are used.
189 const size_t trigger_transfer = 10;
190
191 // Add to pending list. Update count first so no underflow in transfer.
192 size_t pending_count = Atomic::add(1u, &_pending_count);
193 _pending_list.push(*node);
194 if (pending_count > trigger_transfer) {
195 try_transfer_pending();
196 }
197 }
198
199 // Try to transfer nodes from _pending_list to _free_list, with a
200 // synchronization delay for any in-progress pops from the _free_list,
201 // to solve ABA there. Return true if performed a (possibly empty)
202 // transfer, false if blocked from doing so by some other thread's
203 // in-progress transfer.
204 bool BufferNode::Allocator::try_transfer_pending() {
205 // Attempt to claim the lock.
206 if (Atomic::load(&_transfer_lock) || // Skip CAS if likely to fail.
207 Atomic::cmpxchg(true, &_transfer_lock, false)) {
208 return false;
209 }
210 // Have the lock; perform the transfer.
211
212 // Claim all the pending nodes.
213 BufferNode* first = _pending_list.pop_all();
214 if (first != NULL) {
215 // Prepare to add the claimed nodes, and update _pending_count.
216 BufferNode* last = first;
217 size_t count = 1;
218 for (BufferNode* next = first->next(); next != NULL; next = next->next()) {
219 last = next;
220 ++count;
221 }
222 Atomic::sub(count, &_pending_count);
223
224 // Wait for any in-progress pops, to avoid ABA for them.
225 GlobalCounter::write_synchronize();
226
227 // Add synchronized nodes to _free_list.
228 // Update count first so no underflow in allocate().
229 Atomic::add(count, &_free_count);
230 _free_list.prepend(*first, *last);
231 log_trace(gc, ptrqueue, freelist)
232 ("Transferred %s pending to free: " SIZE_FORMAT, name(), count);
233 }
234 OrderAccess::release_store(&_transfer_lock, false);
235 return true;
236 }
237
238 size_t BufferNode::Allocator::reduce_free_list(size_t remove_goal) {
239 try_transfer_pending();
240 size_t removed = 0;
241 for ( ; removed < remove_goal; ++removed) {
242 BufferNode* node = _free_list.pop();
243 if (node == NULL) break;
244 BufferNode::deallocate(node);
245 }
246 size_t new_count = Atomic::sub(removed, &_free_count);
247 log_debug(gc, ptrqueue, freelist)
248 ("Reduced %s free list by " SIZE_FORMAT " to " SIZE_FORMAT,
249 name(), removed, new_count);
250 return removed;
251 }
252
253 PtrQueueSet::PtrQueueSet() :
254 _allocator(NULL),
255 _all_active(false)
256 {}
257
258 PtrQueueSet::~PtrQueueSet() {}
259
260 void PtrQueueSet::initialize(BufferNode::Allocator* allocator) {
261 assert(allocator != NULL, "Init order issue?");
262 _allocator = allocator;
263 }
264
265 void** PtrQueueSet::allocate_buffer() {
266 BufferNode* node = _allocator->allocate();
267 return BufferNode::make_buffer_from_node(node);
268 }
269
270 void PtrQueueSet::deallocate_buffer(BufferNode* node) {
271 _allocator->release(node);
272 }
273