1 /*
   2  * Copyright (c) 2001, 2015, 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/g1CollectedHeap.inline.hpp"
  27 #include "gc/g1/satbQueue.hpp"
  28 #include "gc/shared/collectedHeap.hpp"
  29 #include "memory/allocation.inline.hpp"
  30 #include "oops/oop.inline.hpp"
  31 #include "runtime/mutexLocker.hpp"
  32 #include "runtime/safepoint.hpp"
  33 #include "runtime/thread.hpp"
  34 #include "runtime/vmThread.hpp"
  35 
  36 void ObjPtrQueue::flush() {
  37   // Filter now to possibly save work later.  If filtering empties the
  38   // buffer then flush_impl can deallocate the buffer.
  39   filter();
  40   flush_impl();
  41 }
  42 
  43 // Return true if a SATB buffer entry refers to an object that
  44 // requires marking.
  45 //
  46 // The entry must point into the G1 heap.  In particular, it must not
  47 // be a NULL pointer.  NULL pointers are pre-filtered and never
  48 // inserted into a SATB buffer.
  49 //
  50 // An entry that is below the NTAMS pointer for the containing heap
  51 // region requires marking. Such an entry must point to a valid object.
  52 //
  53 // An entry that is at least the NTAMS pointer for the containing heap
  54 // region might be any of the following, none of which should be marked.
  55 //
  56 // * A reference to an object allocated since marking started.
  57 //   According to SATB, such objects are implicitly kept live and do
  58 //   not need to be dealt with via SATB buffer processing.
  59 //
  60 // * A reference to a young generation object. Young objects are
  61 //   handled separately and are not marked by concurrent marking.
  62 //
  63 // * A stale reference to a young generation object. If a young
  64 //   generation object reference is recorded and not filtered out
  65 //   before being moved by a young collection, the reference becomes
  66 //   stale.
  67 //
  68 // * A stale reference to an eagerly reclaimed humongous object.  If a
  69 //   humongous object is recorded and then reclaimed, the reference
  70 //   becomes stale.
  71 //
  72 // The stale reference cases are implicitly handled by the NTAMS
  73 // comparison. Because of the possibility of stale references, buffer
  74 // processing must be somewhat circumspect and not assume entries
  75 // in an unfiltered buffer refer to valid objects.
  76 
  77 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
  78   // Includes rejection of NULL pointers.
  79   assert(heap->is_in_reserved(entry),
  80          "Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry));
  81 
  82   HeapRegion* region = heap->heap_region_containing_raw(entry);
  83   assert(region != NULL, "No region for " PTR_FORMAT, p2i(entry));
  84   if (entry >= region->next_top_at_mark_start()) {
  85     return false;
  86   }
  87 
  88   assert(((oop)entry)->is_oop(true /* ignore mark word */),
  89          "Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry));
  90 
  91   return true;
  92 }
  93 
  94 // This method removes entries from a SATB buffer that will not be
  95 // useful to the concurrent marking threads.  Entries are retained if
  96 // they require marking and are not already marked. Retained entries
  97 // are compacted toward the top of the buffer.
  98 
  99 void ObjPtrQueue::filter() {
 100   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 101   void** buf = _buf;
 102   size_t sz = _sz;
 103 
 104   if (buf == NULL) {
 105     // nothing to do
 106     return;
 107   }
 108 
 109   // Used for sanity checking at the end of the loop.
 110   debug_only(size_t entries = 0; size_t retained = 0;)
 111 
 112   size_t i = sz;
 113   size_t new_index = sz;
 114 
 115   while (i > _index) {
 116     assert(i > 0, "we should have at least one more entry to process");
 117     i -= oopSize;
 118     debug_only(entries += 1;)
 119     void** p = &buf[byte_index_to_index((int) i)];
 120     void* entry = *p;
 121     // NULL the entry so that unused parts of the buffer contain NULLs
 122     // at the end. If we are going to retain it we will copy it to its
 123     // final place. If we have retained all entries we have visited so
 124     // far, we'll just end up copying it to the same place.
 125     *p = NULL;
 126 
 127     if (requires_marking(entry, g1h) && !g1h->isMarkedNext((oop)entry)) {
 128       assert(new_index > 0, "we should not have already filled up the buffer");
 129       new_index -= oopSize;
 130       assert(new_index >= i,
 131              "new_index should never be below i, as we always compact 'up'");
 132       void** new_p = &buf[byte_index_to_index((int) new_index)];
 133       assert(new_p >= p, "the destination location should never be below "
 134              "the source as we always compact 'up'");
 135       assert(*new_p == NULL,
 136              "we should have already cleared the destination location");
 137       *new_p = entry;
 138       debug_only(retained += 1;)
 139     }
 140   }
 141 
 142 #ifdef ASSERT
 143   size_t entries_calc = (sz - _index) / oopSize;
 144   assert(entries == entries_calc, "the number of entries we counted "
 145          "should match the number of entries we calculated");
 146   size_t retained_calc = (sz - new_index) / oopSize;
 147   assert(retained == retained_calc, "the number of retained entries we counted "
 148          "should match the number of retained entries we calculated");
 149 #endif // ASSERT
 150 
 151   _index = new_index;
 152 }
 153 
 154 // This method will first apply the above filtering to the buffer. If
 155 // post-filtering a large enough chunk of the buffer has been cleared
 156 // we can re-use the buffer (instead of enqueueing it) and we can just
 157 // allow the mutator to carry on executing using the same buffer
 158 // instead of replacing it.
 159 
 160 bool ObjPtrQueue::should_enqueue_buffer() {
 161   assert(_lock == NULL || _lock->owned_by_self(),
 162          "we should have taken the lock before calling this");
 163 
 164   // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
 165 
 166   // This method should only be called if there is a non-NULL buffer
 167   // that is full.
 168   assert(_index == 0, "pre-condition");
 169   assert(_buf != NULL, "pre-condition");
 170 
 171   filter();
 172 
 173   size_t sz = _sz;
 174   size_t all_entries = sz / oopSize;
 175   size_t retained_entries = (sz - _index) / oopSize;
 176   size_t perc = retained_entries * 100 / all_entries;
 177   bool should_enqueue = perc > (size_t) G1SATBBufferEnqueueingThresholdPercent;
 178   return should_enqueue;
 179 }
 180 
 181 void ObjPtrQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
 182   assert(SafepointSynchronize::is_at_safepoint(),
 183          "SATB queues must only be processed at safepoints");
 184   if (_buf != NULL) {
 185     assert(_index % sizeof(void*) == 0, "invariant");
 186     assert(_sz % sizeof(void*) == 0, "invariant");
 187     assert(_index <= _sz, "invariant");
 188     cl->do_buffer(_buf + byte_index_to_index((int)_index),
 189                   byte_index_to_index((int)(_sz - _index)));
 190     _index = _sz;
 191   }
 192 }
 193 
 194 #ifndef PRODUCT
 195 // Helpful for debugging
 196 
 197 void ObjPtrQueue::print(const char* name) {
 198   print(name, _buf, _index, _sz);
 199 }
 200 
 201 void ObjPtrQueue::print(const char* name,
 202                         void** buf, size_t index, size_t sz) {
 203   gclog_or_tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " "
 204                          "index: " SIZE_FORMAT " sz: " SIZE_FORMAT,
 205                          name, p2i(buf), index, sz);
 206 }
 207 #endif // PRODUCT
 208 
 209 #ifdef _MSC_VER // the use of 'this' below gets a warning, make it go away
 210 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 211 #endif // _MSC_VER
 212 
 213 SATBMarkQueueSet::SATBMarkQueueSet() :
 214   PtrQueueSet(),
 215   _shared_satb_queue(this, true /*perm*/) { }
 216 
 217 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
 218                                   int process_completed_threshold,
 219                                   Mutex* lock) {
 220   PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
 221   _shared_satb_queue.set_lock(lock);
 222 }
 223 
 224 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
 225   t->satb_mark_queue().handle_zero_index();
 226 }
 227 
 228 #ifdef ASSERT
 229 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
 230   gclog_or_tty->print_cr("Expected SATB active state: %s",
 231                          expected_active ? "ACTIVE" : "INACTIVE");
 232   gclog_or_tty->print_cr("Actual SATB active states:");
 233   gclog_or_tty->print_cr("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
 234   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 235     gclog_or_tty->print_cr("  Thread \"%s\" queue: %s", t->name(),
 236                            t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");
 237   }
 238   gclog_or_tty->print_cr("  Shared queue: %s",
 239                          shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
 240 }
 241 
 242 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
 243   // Verify queue set state
 244   if (is_active() != expected_active) {
 245     dump_active_states(expected_active);
 246     guarantee(false, "SATB queue set has an unexpected active state");
 247   }
 248 
 249   // Verify thread queue states
 250   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 251     if (t->satb_mark_queue().is_active() != expected_active) {
 252       dump_active_states(expected_active);
 253       guarantee(false, "Thread SATB queue has an unexpected active state");
 254     }
 255   }
 256 
 257   // Verify shared queue state
 258   if (shared_satb_queue()->is_active() != expected_active) {
 259     dump_active_states(expected_active);
 260     guarantee(false, "Shared SATB queue has an unexpected active state");
 261   }
 262 }
 263 #endif // ASSERT
 264 
 265 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
 266   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 267 #ifdef ASSERT
 268   verify_active_states(expected_active);
 269 #endif // ASSERT
 270   _all_active = active;
 271   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 272     t->satb_mark_queue().set_active(active);
 273   }
 274   shared_satb_queue()->set_active(active);
 275 }
 276 
 277 void SATBMarkQueueSet::filter_thread_buffers() {
 278   for(JavaThread* t = Threads::first(); t; t = t->next()) {
 279     t->satb_mark_queue().filter();
 280   }
 281   shared_satb_queue()->filter();
 282 }
 283 
 284 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
 285   BufferNode* nd = NULL;
 286   {
 287     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 288     if (_completed_buffers_head != NULL) {
 289       nd = _completed_buffers_head;
 290       _completed_buffers_head = nd->next();
 291       if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
 292       _n_completed_buffers--;
 293       if (_n_completed_buffers == 0) _process_completed = false;
 294     }
 295   }
 296   if (nd != NULL) {
 297     void **buf = BufferNode::make_buffer_from_node(nd);
 298     // Skip over NULL entries at beginning (e.g. push end) of buffer.
 299     // Filtering can result in non-full completed buffers; see
 300     // should_enqueue_buffer.
 301     assert(_sz % sizeof(void*) == 0, "invariant");
 302     size_t limit = ObjPtrQueue::byte_index_to_index((int)_sz);
 303     for (size_t i = 0; i < limit; ++i) {
 304       if (buf[i] != NULL) {
 305         // Found the end of the block of NULLs; process the remainder.
 306         cl->do_buffer(buf + i, limit - i);
 307         break;
 308       }
 309     }
 310     deallocate_buffer(buf);
 311     return true;
 312   } else {
 313     return false;
 314   }
 315 }
 316 
 317 #ifndef PRODUCT
 318 // Helpful for debugging
 319 
 320 #define SATB_PRINTER_BUFFER_SIZE 256
 321 
 322 void SATBMarkQueueSet::print_all(const char* msg) {
 323   char buffer[SATB_PRINTER_BUFFER_SIZE];
 324   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 325 
 326   gclog_or_tty->cr();
 327   gclog_or_tty->print_cr("SATB BUFFERS [%s]", msg);
 328 
 329   BufferNode* nd = _completed_buffers_head;
 330   int i = 0;
 331   while (nd != NULL) {
 332     void** buf = BufferNode::make_buffer_from_node(nd);
 333     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
 334     ObjPtrQueue::print(buffer, buf, 0, _sz);
 335     nd = nd->next();
 336     i += 1;
 337   }
 338 
 339   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 340     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
 341     t->satb_mark_queue().print(buffer);
 342   }
 343 
 344   shared_satb_queue()->print("Shared");
 345 
 346   gclog_or_tty->cr();
 347 }
 348 #endif // PRODUCT
 349 
 350 void SATBMarkQueueSet::abandon_partial_marking() {
 351   BufferNode* buffers_to_delete = NULL;
 352   {
 353     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 354     while (_completed_buffers_head != NULL) {
 355       BufferNode* nd = _completed_buffers_head;
 356       _completed_buffers_head = nd->next();
 357       nd->set_next(buffers_to_delete);
 358       buffers_to_delete = nd;
 359     }
 360     _completed_buffers_tail = NULL;
 361     _n_completed_buffers = 0;
 362     DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
 363   }
 364   while (buffers_to_delete != NULL) {
 365     BufferNode* nd = buffers_to_delete;
 366     buffers_to_delete = nd->next();
 367     deallocate_buffer(BufferNode::make_buffer_from_node(nd));
 368   }
 369   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 370   // So we can safely manipulate these queues.
 371   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 372     t->satb_mark_queue().reset();
 373   }
 374  shared_satb_queue()->reset();
 375 }