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 ObjPtrQueue::ObjPtrQueue(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 ObjPtrQueue::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_raw(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 // This method removes entries from a SATB buffer that will not be
 104 // useful to the concurrent marking threads.  Entries are retained if
 105 // they require marking and are not already marked. Retained entries
 106 // are compacted toward the top of the buffer.
 107 
 108 void ObjPtrQueue::filter() {
 109   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 110   void** buf = _buf;
 111 
 112   if (buf == NULL) {
 113     // nothing to do
 114     return;
 115   }
 116 
 117   // Used for sanity checking at the end of the loop.
 118   DEBUG_ONLY(size_t entries = 0; size_t retained = 0;)
 119 
 120   assert(_index <= _sz, "invariant");
 121   void** limit = &buf[byte_index_to_index(_index)];
 122   void** src = &buf[byte_index_to_index(_sz)];
 123   void** dst = src;
 124 
 125   while (limit < src) {
 126     DEBUG_ONLY(entries += 1;)
 127     --src;
 128     void* entry = *src;
 129     // NULL the entry so that unused parts of the buffer contain NULLs
 130     // at the end. If we are going to retain it we will copy it to its
 131     // final place. If we have retained all entries we have visited so
 132     // far, we'll just end up copying it to the same place.
 133     *src = NULL;
 134 
 135     if (requires_marking(entry, g1h) && !g1h->isMarkedNext((oop)entry)) {
 136       --dst;
 137       assert(*dst == NULL, "filtering destination should be clear");
 138       *dst = entry;
 139       DEBUG_ONLY(retained += 1;);
 140     }
 141   }
 142   size_t new_index = pointer_delta(dst, buf, 1);
 143 
 144 #ifdef ASSERT
 145   size_t entries_calc = (_sz - _index) / sizeof(void*);
 146   assert(entries == entries_calc, "the number of entries we counted "
 147          "should match the number of entries we calculated");
 148   size_t retained_calc = (_sz - new_index) / sizeof(void*);
 149   assert(retained == retained_calc, "the number of retained entries we counted "
 150          "should match the number of retained entries we calculated");
 151 #endif // ASSERT
 152 
 153   _index = new_index;
 154 }
 155 
 156 // This method will first apply the above filtering to the buffer. If
 157 // post-filtering a large enough chunk of the buffer has been cleared
 158 // we can re-use the buffer (instead of enqueueing it) and we can just
 159 // allow the mutator to carry on executing using the same buffer
 160 // instead of replacing it.
 161 
 162 bool ObjPtrQueue::should_enqueue_buffer() {
 163   assert(_lock == NULL || _lock->owned_by_self(),
 164          "we should have taken the lock before calling this");
 165 
 166   // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
 167 
 168   // This method should only be called if there is a non-NULL buffer
 169   // that is full.
 170   assert(_index == 0, "pre-condition");
 171   assert(_buf != NULL, "pre-condition");
 172 
 173   filter();
 174 
 175   size_t percent_used = ((_sz - _index) * 100) / _sz;
 176   bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
 177   return should_enqueue;
 178 }
 179 
 180 void ObjPtrQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
 181   assert(SafepointSynchronize::is_at_safepoint(),
 182          "SATB queues must only be processed at safepoints");
 183   if (_buf != NULL) {
 184     assert(_index % sizeof(void*) == 0, "invariant");
 185     assert(_sz % sizeof(void*) == 0, "invariant");
 186     assert(_index <= _sz, "invariant");
 187     cl->do_buffer(_buf + byte_index_to_index(_index),
 188                   byte_index_to_index(_sz - _index));
 189     _index = _sz;
 190   }
 191 }
 192 
 193 #ifndef PRODUCT
 194 // Helpful for debugging
 195 
 196 void ObjPtrQueue::print(const char* name) {
 197   print(name, _buf, _index, _sz);
 198 }
 199 
 200 void ObjPtrQueue::print(const char* name,
 201                         void** buf, size_t index, size_t sz) {
 202   tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " "
 203                          "index: " SIZE_FORMAT " sz: " SIZE_FORMAT,
 204                          name, p2i(buf), index, sz);
 205 }
 206 #endif // PRODUCT
 207 
 208 SATBMarkQueueSet::SATBMarkQueueSet() :
 209   PtrQueueSet(),
 210   _shared_satb_queue(this, true /* permanent */) { }
 211 
 212 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
 213                                   int process_completed_threshold,
 214                                   Mutex* lock) {
 215   PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
 216   _shared_satb_queue.set_lock(lock);
 217 }
 218 
 219 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
 220   t->satb_mark_queue().handle_zero_index();
 221 }
 222 
 223 #ifdef ASSERT
 224 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
 225   log_info(gc, verify)("Expected SATB active state: %s",
 226                        expected_active ? "ACTIVE" : "INACTIVE");
 227   log_info(gc, verify)("Actual SATB active states:");
 228   log_info(gc, verify)("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
 229   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 230     log_info(gc, verify)("  Thread \"%s\" queue: %s", t->name(),
 231                          t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");
 232   }
 233   log_info(gc, verify)("  Shared queue: %s",
 234                          shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
 235 }
 236 
 237 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
 238   // Verify queue set state
 239   if (is_active() != expected_active) {
 240     dump_active_states(expected_active);
 241     guarantee(false, "SATB queue set has an unexpected active state");
 242   }
 243 
 244   // Verify thread queue states
 245   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 246     if (t->satb_mark_queue().is_active() != expected_active) {
 247       dump_active_states(expected_active);
 248       guarantee(false, "Thread SATB queue has an unexpected active state");
 249     }
 250   }
 251 
 252   // Verify shared queue state
 253   if (shared_satb_queue()->is_active() != expected_active) {
 254     dump_active_states(expected_active);
 255     guarantee(false, "Shared SATB queue has an unexpected active state");
 256   }
 257 }
 258 #endif // ASSERT
 259 
 260 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
 261   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 262 #ifdef ASSERT
 263   verify_active_states(expected_active);
 264 #endif // ASSERT
 265   _all_active = active;
 266   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 267     t->satb_mark_queue().set_active(active);
 268   }
 269   shared_satb_queue()->set_active(active);
 270 }
 271 
 272 void SATBMarkQueueSet::filter_thread_buffers() {
 273   for(JavaThread* t = Threads::first(); t; t = t->next()) {
 274     t->satb_mark_queue().filter();
 275   }
 276   shared_satb_queue()->filter();
 277 }
 278 
 279 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
 280   BufferNode* nd = NULL;
 281   {
 282     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 283     if (_completed_buffers_head != NULL) {
 284       nd = _completed_buffers_head;
 285       _completed_buffers_head = nd->next();
 286       if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
 287       _n_completed_buffers--;
 288       if (_n_completed_buffers == 0) _process_completed = false;
 289     }
 290   }
 291   if (nd != NULL) {
 292     void **buf = BufferNode::make_buffer_from_node(nd);
 293     // Skip over NULL entries at beginning (e.g. push end) of buffer.
 294     // Filtering can result in non-full completed buffers; see
 295     // should_enqueue_buffer.
 296     assert(_sz % sizeof(void*) == 0, "invariant");
 297     size_t limit = ObjPtrQueue::byte_index_to_index(_sz);
 298     for (size_t i = 0; i < limit; ++i) {
 299       if (buf[i] != NULL) {
 300         // Found the end of the block of NULLs; process the remainder.
 301         cl->do_buffer(buf + i, limit - i);
 302         break;
 303       }
 304     }
 305     deallocate_buffer(buf);
 306     return true;
 307   } else {
 308     return false;
 309   }
 310 }
 311 
 312 #ifndef PRODUCT
 313 // Helpful for debugging
 314 
 315 #define SATB_PRINTER_BUFFER_SIZE 256
 316 
 317 void SATBMarkQueueSet::print_all(const char* msg) {
 318   char buffer[SATB_PRINTER_BUFFER_SIZE];
 319   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 320 
 321   tty->cr();
 322   tty->print_cr("SATB BUFFERS [%s]", msg);
 323 
 324   BufferNode* nd = _completed_buffers_head;
 325   int i = 0;
 326   while (nd != NULL) {
 327     void** buf = BufferNode::make_buffer_from_node(nd);
 328     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
 329     ObjPtrQueue::print(buffer, buf, 0, _sz);
 330     nd = nd->next();
 331     i += 1;
 332   }
 333 
 334   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 335     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
 336     t->satb_mark_queue().print(buffer);
 337   }
 338 
 339   shared_satb_queue()->print("Shared");
 340 
 341   tty->cr();
 342 }
 343 #endif // PRODUCT
 344 
 345 void SATBMarkQueueSet::abandon_partial_marking() {
 346   BufferNode* buffers_to_delete = NULL;
 347   {
 348     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 349     while (_completed_buffers_head != NULL) {
 350       BufferNode* nd = _completed_buffers_head;
 351       _completed_buffers_head = nd->next();
 352       nd->set_next(buffers_to_delete);
 353       buffers_to_delete = nd;
 354     }
 355     _completed_buffers_tail = NULL;
 356     _n_completed_buffers = 0;
 357     DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
 358   }
 359   while (buffers_to_delete != NULL) {
 360     BufferNode* nd = buffers_to_delete;
 361     buffers_to_delete = nd->next();
 362     deallocate_buffer(BufferNode::make_buffer_from_node(nd));
 363   }
 364   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 365   // So we can safely manipulate these queues.
 366   for (JavaThread* t = Threads::first(); t; t = t->next()) {
 367     t->satb_mark_queue().reset();
 368   }
 369  shared_satb_queue()->reset();
 370 }