1 /*
   2  * Copyright (c) 2001, 2018, 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 "jvm.h"
  27 #include "gc/g1/g1CollectedHeap.inline.hpp"
  28 #include "gc/g1/g1ThreadLocalData.hpp"
  29 #include "gc/g1/satbMarkQueue.hpp"
  30 #include "gc/shared/collectedHeap.hpp"
  31 #include "memory/allocation.inline.hpp"
  32 #include "oops/oop.inline.hpp"
  33 #include "runtime/mutexLocker.hpp"
  34 #include "runtime/safepoint.hpp"
  35 #include "runtime/thread.hpp"
  36 #include "runtime/threadSMR.hpp"
  37 #include "runtime/vmThread.hpp"




  38 
  39 SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent) :
  40   // SATB queues are only active during marking cycles. We create
  41   // them with their active field set to false. If a thread is
  42   // created during a cycle and its SATB queue needs to be activated
  43   // before the thread starts running, we'll need to set its active
  44   // field to true. This is done in G1SBarrierSet::on_thread_attach().
  45   PtrQueue(qset, permanent, false /* active */)
  46 { }
  47 
  48 void SATBMarkQueue::flush() {
  49   // Filter now to possibly save work later.  If filtering empties the
  50   // buffer then flush_impl can deallocate the buffer.
  51   filter();
  52   flush_impl();
  53 }
  54 
  55 // Return true if a SATB buffer entry refers to an object that
  56 // requires marking.
  57 //
  58 // The entry must point into the G1 heap.  In particular, it must not
  59 // be a NULL pointer.  NULL pointers are pre-filtered and never
  60 // inserted into a SATB buffer.
  61 //
  62 // An entry that is below the NTAMS pointer for the containing heap
  63 // region requires marking. Such an entry must point to a valid object.
  64 //
  65 // An entry that is at least the NTAMS pointer for the containing heap
  66 // region might be any of the following, none of which should be marked.
  67 //
  68 // * A reference to an object allocated since marking started.
  69 //   According to SATB, such objects are implicitly kept live and do
  70 //   not need to be dealt with via SATB buffer processing.
  71 //
  72 // * A reference to a young generation object. Young objects are
  73 //   handled separately and are not marked by concurrent marking.
  74 //
  75 // * A stale reference to a young generation object. If a young
  76 //   generation object reference is recorded and not filtered out
  77 //   before being moved by a young collection, the reference becomes
  78 //   stale.
  79 //
  80 // * A stale reference to an eagerly reclaimed humongous object.  If a
  81 //   humongous object is recorded and then reclaimed, the reference
  82 //   becomes stale.
  83 //
  84 // The stale reference cases are implicitly handled by the NTAMS
  85 // comparison. Because of the possibility of stale references, buffer
  86 // processing must be somewhat circumspect and not assume entries
  87 // in an unfiltered buffer refer to valid objects.
  88 
  89 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
  90   // Includes rejection of NULL pointers.
  91   assert(heap->is_in_reserved(entry),
  92          "Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry));
  93 
  94   HeapRegion* region = heap->heap_region_containing(entry);
  95   assert(region != NULL, "No region for " PTR_FORMAT, p2i(entry));
  96   if (entry >= region->next_top_at_mark_start()) {
  97     return false;
  98   }
  99 
 100   assert(oopDesc::is_oop(oop(entry), true /* ignore mark word */),
 101          "Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry));
 102 
 103   return true;
 104 }
 105 
 106 inline bool retain_entry(const void* entry, G1CollectedHeap* heap) {
 107   return requires_marking(entry, heap) && !heap->is_marked_next((oop)entry);








 108 }
 109 
 110 // This method removes entries from a SATB buffer that will not be
 111 // useful to the concurrent marking threads.  Entries are retained if
 112 // they require marking and are not already marked. Retained entries
 113 // are compacted toward the top of the buffer.
 114 
 115 void SATBMarkQueue::filter() {
 116   G1CollectedHeap* g1h = G1CollectedHeap::heap();

 117   void** buf = _buf;
 118 
 119   if (buf == NULL) {
 120     // nothing to do
 121     return;
 122   }
 123 
 124   // Two-fingered compaction toward the end.
 125   void** src = &buf[index()];
 126   void** dst = &buf[capacity()];
 127   assert(src <= dst, "invariant");
 128   for ( ; src < dst; ++src) {
 129     // Search low to high for an entry to keep.
 130     void* entry = *src;
 131     if (retain_entry(entry, g1h)) {
 132       // Found keeper.  Search high to low for an entry to discard.
 133       while (src < --dst) {
 134         if (!retain_entry(*dst, g1h)) {
 135           *dst = entry;         // Replace discard with keeper.
 136           break;
 137         }
 138       }
 139       // If discard search failed (src == dst), the outer loop will also end.
 140     }
 141   }
 142   // dst points to the lowest retained entry, or the end of the buffer
 143   // if all the entries were filtered out.
 144   set_index(dst - buf);
 145 }
 146 
 147 // This method will first apply the above filtering to the buffer. If
 148 // post-filtering a large enough chunk of the buffer has been cleared
 149 // we can re-use the buffer (instead of enqueueing it) and we can just
 150 // allow the mutator to carry on executing using the same buffer
 151 // instead of replacing it.
 152 
 153 bool SATBMarkQueue::should_enqueue_buffer() {
 154   assert(_lock == NULL || _lock->owned_by_self(),
 155          "we should have taken the lock before calling this");
 156 
 157   // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
 158 
 159   // This method should only be called if there is a non-NULL buffer
 160   // that is full.
 161   assert(index() == 0, "pre-condition");
 162   assert(_buf != NULL, "pre-condition");
 163 
 164   filter();
 165 
 166   size_t cap = capacity();
 167   size_t percent_used = ((cap - index()) * 100) / cap;
 168   bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
 169   return should_enqueue;
 170 }
 171 
 172 void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
 173   assert(SafepointSynchronize::is_at_safepoint(),
 174          "SATB queues must only be processed at safepoints");
 175   if (_buf != NULL) {
 176     cl->do_buffer(&_buf[index()], size());
 177     reset();
 178   }
 179 }
 180 
 181 #ifndef PRODUCT
 182 // Helpful for debugging
 183 
 184 static void print_satb_buffer(const char* name,
 185                               void** buf,
 186                               size_t index,
 187                               size_t capacity) {
 188   tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT
 189                 " capacity: " SIZE_FORMAT,
 190                 name, p2i(buf), index, capacity);
 191 }
 192 
 193 void SATBMarkQueue::print(const char* name) {
 194   print_satb_buffer(name, _buf, index(), capacity());
 195 }
 196 
 197 #endif // PRODUCT
 198 
 199 SATBMarkQueueSet::SATBMarkQueueSet() :
 200   PtrQueueSet(),
 201   _shared_satb_queue(this, true /* permanent */) { }
 202 
 203 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
 204                                   int process_completed_threshold,
 205                                   Mutex* lock) {
 206   PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
 207   _shared_satb_queue.set_lock(lock);
 208 }
 209 
 210 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
 211   G1ThreadLocalData::satb_mark_queue(t).handle_zero_index();
 212 }
 213 
 214 #ifdef ASSERT
 215 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
 216   log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");
 217   log_error(gc, verify)("Actual SATB active states:");
 218   log_error(gc, verify)("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
 219   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 220     log_error(gc, verify)("  Thread \"%s\" queue: %s", t->name(), G1ThreadLocalData::satb_mark_queue(t).is_active() ? "ACTIVE" : "INACTIVE");
 221   }
 222   log_error(gc, verify)("  Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
 223 }
 224 
 225 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
 226   // Verify queue set state
 227   if (is_active() != expected_active) {
 228     dump_active_states(expected_active);
 229     guarantee(false, "SATB queue set has an unexpected active state");
 230   }
 231 
 232   // Verify thread queue states
 233   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 234     if (G1ThreadLocalData::satb_mark_queue(t).is_active() != expected_active) {
 235       dump_active_states(expected_active);
 236       guarantee(false, "Thread SATB queue has an unexpected active state");
 237     }
 238   }
 239 
 240   // Verify shared queue state
 241   if (shared_satb_queue()->is_active() != expected_active) {
 242     dump_active_states(expected_active);
 243     guarantee(false, "Shared SATB queue has an unexpected active state");
 244   }
 245 }
 246 #endif // ASSERT
 247 
 248 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
 249   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 250 #ifdef ASSERT
 251   verify_active_states(expected_active);
 252 #endif // ASSERT
 253   _all_active = active;
 254   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 255     G1ThreadLocalData::satb_mark_queue(t).set_active(active);
 256   }
 257   shared_satb_queue()->set_active(active);
 258 }
 259 
 260 void SATBMarkQueueSet::filter_thread_buffers() {
 261   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 262     G1ThreadLocalData::satb_mark_queue(t).filter();
 263   }
 264   shared_satb_queue()->filter();
 265 }
 266 
 267 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
 268   BufferNode* nd = NULL;
 269   {
 270     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 271     if (_completed_buffers_head != NULL) {
 272       nd = _completed_buffers_head;
 273       _completed_buffers_head = nd->next();
 274       if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
 275       _n_completed_buffers--;
 276       if (_n_completed_buffers == 0) _process_completed = false;
 277     }
 278   }
 279   if (nd != NULL) {
 280     void **buf = BufferNode::make_buffer_from_node(nd);
 281     size_t index = nd->index();
 282     size_t size = buffer_size();
 283     assert(index <= size, "invariant");
 284     cl->do_buffer(buf + index, size - index);
 285     deallocate_buffer(nd);
 286     return true;
 287   } else {
 288     return false;
 289   }
 290 }
 291 
 292 #ifndef PRODUCT
 293 // Helpful for debugging
 294 
 295 #define SATB_PRINTER_BUFFER_SIZE 256
 296 
 297 void SATBMarkQueueSet::print_all(const char* msg) {
 298   char buffer[SATB_PRINTER_BUFFER_SIZE];
 299   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 300 
 301   tty->cr();
 302   tty->print_cr("SATB BUFFERS [%s]", msg);
 303 
 304   BufferNode* nd = _completed_buffers_head;
 305   int i = 0;
 306   while (nd != NULL) {
 307     void** buf = BufferNode::make_buffer_from_node(nd);
 308     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
 309     print_satb_buffer(buffer, buf, nd->index(), buffer_size());
 310     nd = nd->next();
 311     i += 1;
 312   }
 313 
 314   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 315     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
 316     G1ThreadLocalData::satb_mark_queue(t).print(buffer);
 317   }
 318 
 319   shared_satb_queue()->print("Shared");
 320 
 321   tty->cr();
 322 }
 323 #endif // PRODUCT
 324 
 325 void SATBMarkQueueSet::abandon_partial_marking() {
 326   BufferNode* buffers_to_delete = NULL;
 327   {
 328     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 329     while (_completed_buffers_head != NULL) {
 330       BufferNode* nd = _completed_buffers_head;
 331       _completed_buffers_head = nd->next();
 332       nd->set_next(buffers_to_delete);
 333       buffers_to_delete = nd;
 334     }
 335     _completed_buffers_tail = NULL;
 336     _n_completed_buffers = 0;
 337     DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
 338   }
 339   while (buffers_to_delete != NULL) {
 340     BufferNode* nd = buffers_to_delete;
 341     buffers_to_delete = nd->next();
 342     deallocate_buffer(nd);
 343   }
 344   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 345   // So we can safely manipulate these queues.
 346   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 347     G1ThreadLocalData::satb_mark_queue(t).reset();
 348   }
 349   shared_satb_queue()->reset();
 350 }









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