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/g1CollectedHeap.inline.hpp"
  27 #include "gc/g1/satbMarkQueue.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 SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent) :
  37   // SATB queues are only active during marking cycles. We create
  38   // them with their active field set to false. If a thread is
  39   // created during a cycle and its SATB queue needs to be activated
  40   // before the thread starts running, we'll need to set its active
  41   // field to true. This is done in JavaThread::initialize_queues().
  42   PtrQueue(qset, permanent, false /* active */)
  43 { }
  44 
  45 void SATBMarkQueue::flush() {
  46   // Filter now to possibly save work later.  If filtering empties the
  47   // buffer then flush_impl can deallocate the buffer.
  48   filter();
  49   flush_impl();
  50 }
  51 
  52 // Return true if a SATB buffer entry refers to an object that
  53 // requires marking.
  54 //
  55 // The entry must point into the G1 heap.  In particular, it must not
  56 // be a NULL pointer.  NULL pointers are pre-filtered and never
  57 // inserted into a SATB buffer.
  58 //
  59 // An entry that is below the NTAMS pointer for the containing heap
  60 // region requires marking. Such an entry must point to a valid object.
  61 //
  62 // An entry that is at least the NTAMS pointer for the containing heap
  63 // region might be any of the following, none of which should be marked.
  64 //
  65 // * A reference to an object allocated since marking started.
  66 //   According to SATB, such objects are implicitly kept live and do
  67 //   not need to be dealt with via SATB buffer processing.
  68 //
  69 // * A reference to a young generation object. Young objects are
  70 //   handled separately and are not marked by concurrent marking.
  71 //
  72 // * A stale reference to a young generation object. If a young
  73 //   generation object reference is recorded and not filtered out
  74 //   before being moved by a young collection, the reference becomes
  75 //   stale.
  76 //
  77 // * A stale reference to an eagerly reclaimed humongous object.  If a
  78 //   humongous object is recorded and then reclaimed, the reference
  79 //   becomes stale.
  80 //
  81 // The stale reference cases are implicitly handled by the NTAMS
  82 // comparison. Because of the possibility of stale references, buffer
  83 // processing must be somewhat circumspect and not assume entries
  84 // in an unfiltered buffer refer to valid objects.
  85 
  86 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
  87   // Includes rejection of NULL pointers.
  88   assert(heap->is_in_reserved(entry),
  89          "Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry));
  90 
  91   HeapRegion* region = heap->heap_region_containing(entry);
  92   assert(region != NULL, "No region for " PTR_FORMAT, p2i(entry));
  93   if (entry >= region->next_top_at_mark_start()) {
  94     return false;
  95   }
  96 
  97   assert(((oop)entry)->is_oop(true /* ignore mark word */),
  98          "Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry));
  99 
 100   return true;
 101 }
 102 
 103 inline bool retain_entry(const void* entry, G1CollectedHeap* heap) {
 104   return requires_marking(entry, heap) && !heap->isMarkedNext((oop)entry);
 105 }
 106 
 107 // This method removes entries from a SATB buffer that will not be
 108 // useful to the concurrent marking threads.  Entries are retained if
 109 // they require marking and are not already marked. Retained entries
 110 // are compacted toward the top of the buffer.
 111 
 112 void SATBMarkQueue::filter() {
 113   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 114   void** buf = _buf;
 115 
 116   if (buf == NULL) {
 117     // nothing to do
 118     return;
 119   }
 120 
 121   assert(_index <= _sz, "invariant");
 122 
 123   // Two-fingered compaction toward the end.
 124   void** src = &buf[byte_index_to_index(_index)];
 125   void** dst = &buf[byte_index_to_index(_sz)];
 126   for ( ; src < dst; ++src) {
 127     // Search low to high for an entry to keep.
 128     void* entry = *src;
 129     if (retain_entry(entry, g1h)) {
 130       // Found keeper.  Search high to low for an entry to discard.
 131       while (src < --dst) {
 132         if (!retain_entry(*dst, g1h)) {
 133           *dst = entry;         // Replace discard with keeper.
 134           break;
 135         }
 136       }
 137       // If discard search failed (src == dst), the outer loop will also end.
 138     }
 139   }
 140   // dst points to the lowest retained entry, or the end of the buffer
 141   // if all the entries were filtered out.
 142   _index = pointer_delta(dst, buf, 1);
 143 }
 144 
 145 // This method will first apply the above filtering to the buffer. If
 146 // post-filtering a large enough chunk of the buffer has been cleared
 147 // we can re-use the buffer (instead of enqueueing it) and we can just
 148 // allow the mutator to carry on executing using the same buffer
 149 // instead of replacing it.
 150 
 151 bool SATBMarkQueue::should_enqueue_buffer() {
 152   assert(_lock == NULL || _lock->owned_by_self(),
 153          "we should have taken the lock before calling this");
 154 
 155   // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
 156 
 157   // This method should only be called if there is a non-NULL buffer
 158   // that is full.
 159   assert(_index == 0, "pre-condition");
 160   assert(_buf != NULL, "pre-condition");
 161 
 162   filter();
 163 
 164   size_t percent_used = ((_sz - _index) * 100) / _sz;
 165   bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
 166   return should_enqueue;
 167 }
 168 
 169 void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
 170   assert(SafepointSynchronize::is_at_safepoint(),
 171          "SATB queues must only be processed at safepoints");
 172   if (_buf != NULL) {
 173     assert(_index % sizeof(void*) == 0, "invariant");
 174     assert(_sz % sizeof(void*) == 0, "invariant");
 175     assert(_index <= _sz, "invariant");
 176     cl->do_buffer(_buf + byte_index_to_index(_index),
 177                   byte_index_to_index(_sz - _index));
 178     _index = _sz;
 179   }
 180 }
 181 
 182 #ifndef PRODUCT
 183 // Helpful for debugging
 184 
 185 void SATBMarkQueue::print(const char* name) {
 186   print(name, _buf, _index, _sz);
 187 }
 188 
 189 void SATBMarkQueue::print(const char* name,
 190                           void** buf, size_t index, size_t sz) {
 191   tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT " sz: " SIZE_FORMAT,
 192                 name, p2i(buf), index, sz);
 193 }
 194 #endif // PRODUCT
 195 
 196 SATBMarkQueueSet::SATBMarkQueueSet() :
 197   PtrQueueSet(),
 198   _shared_satb_queue(this, true /* permanent */) { }
 199 
 200 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
 201                                   int process_completed_threshold,
 202                                   Mutex* lock) {
 203   PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
 204   _shared_satb_queue.set_lock(lock);
 205 }
 206 
 207 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
 208   t->satb_mark_queue().handle_zero_index();
 209 }
 210 
 211 #ifdef ASSERT
 212 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
 213   log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");
 214   log_error(gc, verify)("Actual SATB active states:");
 215   log_error(gc, verify)("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
 216   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 217     log_error(gc, verify)("  Thread \"%s\" queue: %s", t->name(), t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");
 218   }
 219   log_error(gc, verify)("  Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
 220 }
 221 
 222 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
 223   // Verify queue set state
 224   if (is_active() != expected_active) {
 225     dump_active_states(expected_active);
 226     guarantee(false, "SATB queue set has an unexpected active state");
 227   }
 228 
 229   // Verify thread queue states
 230   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 231     if (t->satb_mark_queue().is_active() != expected_active) {
 232       dump_active_states(expected_active);
 233       guarantee(false, "Thread SATB queue has an unexpected active state");
 234     }
 235   }
 236 
 237   // Verify shared queue state
 238   if (shared_satb_queue()->is_active() != expected_active) {
 239     dump_active_states(expected_active);
 240     guarantee(false, "Shared SATB queue has an unexpected active state");
 241   }
 242 }
 243 #endif // ASSERT
 244 
 245 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
 246   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 247 #ifdef ASSERT
 248   verify_active_states(expected_active);
 249 #endif // ASSERT
 250   _all_active = active;
 251   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 252     t->satb_mark_queue().set_active(active);
 253   }
 254   shared_satb_queue()->set_active(active);
 255 }
 256 
 257 void SATBMarkQueueSet::filter_thread_buffers() {
 258   for(JavaThread* t = Threads::first(); t; t = t->next()) {
 259     t->satb_mark_queue().filter();
 260   }
 261   shared_satb_queue()->filter();
 262 }
 263 
 264 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
 265   BufferNode* nd = NULL;
 266   {
 267     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 268     if (_completed_buffers_head != NULL) {
 269       nd = _completed_buffers_head;
 270       _completed_buffers_head = nd->next();
 271       if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
 272       _n_completed_buffers--;
 273       if (_n_completed_buffers == 0) _process_completed = false;
 274     }
 275   }
 276   if (nd != NULL) {
 277     void **buf = BufferNode::make_buffer_from_node(nd);
 278     size_t index = SATBMarkQueue::byte_index_to_index(nd->index());
 279     size_t size = SATBMarkQueue::byte_index_to_index(_sz);
 280     assert(index <= size, "invariant");
 281     cl->do_buffer(buf + index, size - index);
 282     deallocate_buffer(nd);
 283     return true;
 284   } else {
 285     return false;
 286   }
 287 }
 288 
 289 #ifndef PRODUCT
 290 // Helpful for debugging
 291 
 292 #define SATB_PRINTER_BUFFER_SIZE 256
 293 
 294 void SATBMarkQueueSet::print_all(const char* msg) {
 295   char buffer[SATB_PRINTER_BUFFER_SIZE];
 296   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 297 
 298   tty->cr();
 299   tty->print_cr("SATB BUFFERS [%s]", msg);
 300 
 301   BufferNode* nd = _completed_buffers_head;
 302   int i = 0;
 303   while (nd != NULL) {
 304     void** buf = BufferNode::make_buffer_from_node(nd);
 305     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
 306     SATBMarkQueue::print(buffer, buf, 0, _sz);
 307     nd = nd->next();
 308     i += 1;
 309   }
 310 
 311   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 312     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
 313     t->satb_mark_queue().print(buffer);
 314   }
 315 
 316   shared_satb_queue()->print("Shared");
 317 
 318   tty->cr();
 319 }
 320 #endif // PRODUCT
 321 
 322 void SATBMarkQueueSet::abandon_partial_marking() {
 323   BufferNode* buffers_to_delete = NULL;
 324   {
 325     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 326     while (_completed_buffers_head != NULL) {
 327       BufferNode* nd = _completed_buffers_head;
 328       _completed_buffers_head = nd->next();
 329       nd->set_next(buffers_to_delete);
 330       buffers_to_delete = nd;
 331     }
 332     _completed_buffers_tail = NULL;
 333     _n_completed_buffers = 0;
 334     DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
 335   }
 336   while (buffers_to_delete != NULL) {
 337     BufferNode* nd = buffers_to_delete;
 338     buffers_to_delete = nd->next();
 339     deallocate_buffer(nd);
 340   }
 341   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 342   // So we can safely manipulate these queues.
 343   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 344     t->satb_mark_queue().reset();
 345   }
 346  shared_satb_queue()->reset();
 347 }