1 /*
   2  * Copyright (c) 2001, 2016, 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/g1/ptrQueue.hpp"
  27 #include "memory/allocation.hpp"
  28 #include "memory/allocation.inline.hpp"
  29 #include "runtime/mutex.hpp"
  30 #include "runtime/mutexLocker.hpp"
  31 #include "runtime/thread.inline.hpp"
  32 
  33 PtrQueue::PtrQueue(PtrQueueSet* qset, bool permanent, bool active) :
  34   _qset(qset), _buf(NULL), _index(0), _sz(0), _active(active),
  35   _permanent(permanent), _lock(NULL)
  36 {}
  37 
  38 PtrQueue::~PtrQueue() {
  39   assert(_permanent || (_buf == NULL), "queue must be flushed before delete");
  40 }
  41 
  42 void PtrQueue::flush_impl() {
  43   if (!_permanent && _buf != NULL) {
  44     if (_index == _sz) {
  45       // No work to do.
  46       qset()->deallocate_buffer(_buf);
  47     } else {
  48       // We must NULL out the unused entries, then enqueue.
  49       size_t limit = byte_index_to_index(_index);
  50       for (size_t i = 0; i < limit; ++i) {
  51         _buf[i] = NULL;
  52       }
  53       qset()->enqueue_complete_buffer(_buf);
  54     }
  55     _buf = NULL;
  56     _index = 0;
  57   }
  58 }
  59 
  60 
  61 void PtrQueue::enqueue_known_active(void* ptr) {
  62   assert(_index <= _sz, "Invariant.");
  63   assert(_index == 0 || _buf != NULL, "invariant");
  64 
  65   while (_index == 0) {
  66     handle_zero_index();
  67   }
  68 
  69   assert(_index > 0, "postcondition");
  70   _index -= sizeof(void*);
  71   _buf[byte_index_to_index(_index)] = ptr;
  72   assert(_index <= _sz, "Invariant.");
  73 }
  74 
  75 void PtrQueue::locking_enqueue_completed_buffer(void** buf) {
  76   assert(_lock->owned_by_self(), "Required.");
  77 
  78   // We have to unlock _lock (which may be Shared_DirtyCardQ_lock) before
  79   // we acquire DirtyCardQ_CBL_mon inside enqueue_complete_buffer as they
  80   // have the same rank and we may get the "possible deadlock" message
  81   _lock->unlock();
  82 
  83   qset()->enqueue_complete_buffer(buf);
  84   // We must relock only because the caller will unlock, for the normal
  85   // case.
  86   _lock->lock_without_safepoint_check();
  87 }
  88 
  89 
  90 PtrQueueSet::PtrQueueSet(bool notify_when_complete) :
  91   _max_completed_queue(0),
  92   _cbl_mon(NULL), _fl_lock(NULL),
  93   _notify_when_complete(notify_when_complete),
  94   _sz(0),
  95   _completed_buffers_head(NULL),
  96   _completed_buffers_tail(NULL),
  97   _n_completed_buffers(0),
  98   _process_completed_threshold(0), _process_completed(false),
  99   _buf_free_list(NULL), _buf_free_list_sz(0)
 100 {
 101   _fl_owner = this;
 102 }
 103 
 104 PtrQueueSet::~PtrQueueSet() {
 105   // There are presently only a couple (derived) instances ever
 106   // created, and they are permanent, so no harm currently done by
 107   // doing nothing here.
 108 }
 109 
 110 void PtrQueueSet::initialize(Monitor* cbl_mon,
 111                              Mutex* fl_lock,
 112                              size_t process_completed_threshold,
 113                              size_t max_completed_queue,
 114                              PtrQueueSet *fl_owner) {
 115   _max_completed_queue = max_completed_queue;
 116   _process_completed_threshold = process_completed_threshold;
 117   _completed_queue_padding = 0;
 118   assert(cbl_mon != NULL && fl_lock != NULL, "Init order issue?");
 119   _cbl_mon = cbl_mon;
 120   _fl_lock = fl_lock;
 121   _fl_owner = (fl_owner != NULL) ? fl_owner : this;
 122 }
 123 
 124 void** PtrQueueSet::allocate_buffer() {
 125   assert(_sz > 0, "Didn't set a buffer size.");
 126   MutexLockerEx x(_fl_owner->_fl_lock, Mutex::_no_safepoint_check_flag);
 127   if (_fl_owner->_buf_free_list != NULL) {
 128     void** res = BufferNode::make_buffer_from_node(_fl_owner->_buf_free_list);
 129     _fl_owner->_buf_free_list = _fl_owner->_buf_free_list->next();
 130     _fl_owner->_buf_free_list_sz--;
 131     return res;
 132   } else {
 133     // Allocate space for the BufferNode in front of the buffer.
 134     char *b =  NEW_C_HEAP_ARRAY(char, _sz + BufferNode::aligned_size(), mtGC);
 135     return BufferNode::make_buffer_from_block(b);
 136   }
 137 }
 138 
 139 void PtrQueueSet::deallocate_buffer(void** buf) {
 140   assert(_sz > 0, "Didn't set a buffer size.");
 141   MutexLockerEx x(_fl_owner->_fl_lock, Mutex::_no_safepoint_check_flag);
 142   BufferNode *node = BufferNode::make_node_from_buffer(buf);
 143   node->set_next(_fl_owner->_buf_free_list);
 144   _fl_owner->_buf_free_list = node;
 145   _fl_owner->_buf_free_list_sz++;
 146 }
 147 
 148 void PtrQueueSet::reduce_free_list() {
 149   assert(_fl_owner == this, "Free list reduction is allowed only for the owner");
 150   // For now we'll adopt the strategy of deleting half.
 151   MutexLockerEx x(_fl_lock, Mutex::_no_safepoint_check_flag);
 152   size_t n = _buf_free_list_sz / 2;
 153   while (n > 0) {
 154     assert(_buf_free_list != NULL, "_buf_free_list_sz must be wrong.");
 155     void* b = BufferNode::make_block_from_node(_buf_free_list);
 156     _buf_free_list = _buf_free_list->next();
 157     FREE_C_HEAP_ARRAY(char, b);
 158     _buf_free_list_sz --;
 159     n--;
 160   }
 161 }
 162 
 163 void PtrQueue::handle_zero_index() {
 164   assert(_index == 0, "Precondition.");
 165 
 166   // This thread records the full buffer and allocates a new one (while
 167   // holding the lock if there is one).
 168   if (_buf != NULL) {
 169     if (!should_enqueue_buffer()) {
 170       assert(_index > 0, "the buffer can only be re-used if it's not full");
 171       return;
 172     }
 173 
 174     if (_lock) {
 175       assert(_lock->owned_by_self(), "Required.");
 176 
 177       // The current PtrQ may be the shared dirty card queue and
 178       // may be being manipulated by more than one worker thread
 179       // during a pause. Since the enqueueing of the completed
 180       // buffer unlocks the Shared_DirtyCardQ_lock more than one
 181       // worker thread can 'race' on reading the shared queue attributes
 182       // (_buf and _index) and multiple threads can call into this
 183       // routine for the same buffer. This will cause the completed
 184       // buffer to be added to the CBL multiple times.
 185 
 186       // We "claim" the current buffer by caching value of _buf in
 187       // a local and clearing the field while holding _lock. When
 188       // _lock is released (while enqueueing the completed buffer)
 189       // the thread that acquires _lock will skip this code,
 190       // preventing the subsequent the multiple enqueue, and
 191       // install a newly allocated buffer below.
 192 
 193       void** buf = _buf;   // local pointer to completed buffer
 194       _buf = NULL;         // clear shared _buf field
 195 
 196       locking_enqueue_completed_buffer(buf);  // enqueue completed buffer
 197 
 198       // While the current thread was enqueueing the buffer another thread
 199       // may have a allocated a new buffer and inserted it into this pointer
 200       // queue. If that happens then we just return so that the current
 201       // thread doesn't overwrite the buffer allocated by the other thread
 202       // and potentially losing some dirtied cards.
 203 
 204       if (_buf != NULL) return;
 205     } else {
 206       if (qset()->process_or_enqueue_complete_buffer(_buf)) {
 207         // Recycle the buffer. No allocation.
 208         _sz = qset()->buffer_size();
 209         _index = _sz;
 210         return;
 211       }
 212     }
 213   }
 214   // Reallocate the buffer
 215   _buf = qset()->allocate_buffer();
 216   _sz = qset()->buffer_size();
 217   _index = _sz;
 218 }
 219 
 220 bool PtrQueueSet::process_or_enqueue_complete_buffer(void** buf) {
 221   if (Thread::current()->is_Java_thread()) {
 222     // We don't lock. It is fine to be epsilon-precise here.
 223     if (_max_completed_queue == 0 || _max_completed_queue > 0 &&
 224         _n_completed_buffers >= _max_completed_queue + _completed_queue_padding) {
 225       bool b = mut_process_buffer(buf);
 226       if (b) {
 227         // True here means that the buffer hasn't been deallocated and the caller may reuse it.
 228         return true;
 229       }
 230     }
 231   }
 232   // The buffer will be enqueued. The caller will have to get a new one.
 233   enqueue_complete_buffer(buf);
 234   return false;
 235 }
 236 
 237 void PtrQueueSet::enqueue_complete_buffer(void** buf, size_t index) {
 238   MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 239   BufferNode* cbn = BufferNode::new_from_buffer(buf);
 240   cbn->set_index(index);
 241   if (_completed_buffers_tail == NULL) {
 242     assert(_completed_buffers_head == NULL, "Well-formedness");
 243     _completed_buffers_head = cbn;
 244     _completed_buffers_tail = cbn;
 245   } else {
 246     _completed_buffers_tail->set_next(cbn);
 247     _completed_buffers_tail = cbn;
 248   }
 249   _n_completed_buffers++;
 250 
 251   if (!_process_completed && 
 252       _n_completed_buffers >= _process_completed_threshold) {
 253     _process_completed = true;
 254     if (_notify_when_complete) {
 255       _cbl_mon->notify();
 256     }
 257   }
 258   DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
 259 }
 260 
 261 size_t PtrQueueSet::completed_buffers_list_length() {
 262   size_t n = 0;
 263   BufferNode* cbn = _completed_buffers_head;
 264   while (cbn != NULL) {
 265     n++;
 266     cbn = cbn->next();
 267   }
 268   return n;
 269 }
 270 
 271 void PtrQueueSet::assert_completed_buffer_list_len_correct() {
 272   MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 273   assert_completed_buffer_list_len_correct_locked();
 274 }
 275 
 276 void PtrQueueSet::assert_completed_buffer_list_len_correct_locked() {
 277   guarantee(completed_buffers_list_length() ==  _n_completed_buffers,
 278             "Completed buffer length is wrong.");
 279 }
 280 
 281 void PtrQueueSet::set_buffer_size(size_t sz) {
 282   assert(_sz == 0 && sz > 0, "Should be called only once.");
 283   _sz = sz * sizeof(void*);
 284 }
 285 
 286 // Merge lists of buffers. Notify the processing threads.
 287 // The source queue is emptied as a result. The queues
 288 // must share the monitor.
 289 void PtrQueueSet::merge_bufferlists(PtrQueueSet *src) {
 290   assert(_cbl_mon == src->_cbl_mon, "Should share the same lock");
 291   MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 292   if (_completed_buffers_tail == NULL) {
 293     assert(_completed_buffers_head == NULL, "Well-formedness");
 294     _completed_buffers_head = src->_completed_buffers_head;
 295     _completed_buffers_tail = src->_completed_buffers_tail;
 296   } else {
 297     assert(_completed_buffers_head != NULL, "Well formedness");
 298     if (src->_completed_buffers_head != NULL) {
 299       _completed_buffers_tail->set_next(src->_completed_buffers_head);
 300       _completed_buffers_tail = src->_completed_buffers_tail;
 301     }
 302   }
 303   _n_completed_buffers += src->_n_completed_buffers;
 304 
 305   src->_n_completed_buffers = 0;
 306   src->_completed_buffers_head = NULL;
 307   src->_completed_buffers_tail = NULL;
 308 
 309   assert(_completed_buffers_head == NULL && _completed_buffers_tail == NULL ||
 310          _completed_buffers_head != NULL && _completed_buffers_tail != NULL,
 311          "Sanity");
 312 }
 313 
 314 void PtrQueueSet::notify_if_necessary() {
 315   MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 316   if (_n_completed_buffers >= _process_completed_threshold || _max_completed_queue == 0) {
 317     _process_completed = true;
 318     if (_notify_when_complete)
 319       _cbl_mon->notify();
 320   }
 321 }
--- EOF ---