1 /*
   2  * Copyright (c) 2001, 2017, 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 "prims/jvm.h"
  32 #include "runtime/mutexLocker.hpp"
  33 #include "runtime/safepoint.hpp"
  34 #include "runtime/thread.hpp"
  35 #include "runtime/threadSMR.hpp"
  36 #include "runtime/vmThread.hpp"
  37 
  38 SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent) :
  39   // SATB queues are only active during marking cycles. We create
  40   // them with their active field set to false. If a thread is
  41   // created during a cycle and its SATB queue needs to be activated
  42   // before the thread starts running, we'll need to set its active
  43   // field to true. This is done in JavaThread::initialize_queues().
  44   PtrQueue(qset, permanent, false /* active */)
  45 { }
  46 
  47 void SATBMarkQueue::flush() {
  48   // Filter now to possibly save work later.  If filtering empties the
  49   // buffer then flush_impl can deallocate the buffer.
  50   filter();
  51   flush_impl();
  52 }
  53 
  54 // Return true if a SATB buffer entry refers to an object that
  55 // requires marking.
  56 //
  57 // The entry must point into the G1 heap.  In particular, it must not
  58 // be a NULL pointer.  NULL pointers are pre-filtered and never
  59 // inserted into a SATB buffer.
  60 //
  61 // An entry that is below the NTAMS pointer for the containing heap
  62 // region requires marking. Such an entry must point to a valid object.
  63 //
  64 // An entry that is at least the NTAMS pointer for the containing heap
  65 // region might be any of the following, none of which should be marked.
  66 //
  67 // * A reference to an object allocated since marking started.
  68 //   According to SATB, such objects are implicitly kept live and do
  69 //   not need to be dealt with via SATB buffer processing.
  70 //
  71 // * A reference to a young generation object. Young objects are
  72 //   handled separately and are not marked by concurrent marking.
  73 //
  74 // * A stale reference to a young generation object. If a young
  75 //   generation object reference is recorded and not filtered out
  76 //   before being moved by a young collection, the reference becomes
  77 //   stale.
  78 //
  79 // * A stale reference to an eagerly reclaimed humongous object.  If a
  80 //   humongous object is recorded and then reclaimed, the reference
  81 //   becomes stale.
  82 //
  83 // The stale reference cases are implicitly handled by the NTAMS
  84 // comparison. Because of the possibility of stale references, buffer
  85 // processing must be somewhat circumspect and not assume entries
  86 // in an unfiltered buffer refer to valid objects.
  87 
  88 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
  89   // Includes rejection of NULL pointers.
  90   assert(heap->is_in_reserved(entry),
  91          "Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry));
  92 
  93   HeapRegion* region = heap->heap_region_containing(entry);
  94   assert(region != NULL, "No region for " PTR_FORMAT, p2i(entry));
  95   if (entry >= region->next_top_at_mark_start()) {
  96     return false;
  97   }
  98 
  99   assert(oopDesc::is_oop(oop(entry), true /* ignore mark word */),
 100          "Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry));
 101 
 102   return true;
 103 }
 104 
 105 inline bool retain_entry(const void* entry, G1CollectedHeap* heap) {
 106   return requires_marking(entry, heap) && !heap->isMarkedNext((oop)entry);
 107 }
 108 
 109 // This method removes entries from a SATB buffer that will not be
 110 // useful to the concurrent marking threads.  Entries are retained if
 111 // they require marking and are not already marked. Retained entries
 112 // are compacted toward the top of the buffer.
 113 
 114 void SATBMarkQueue::filter() {
 115   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 116   void** buf = _buf;
 117 
 118   if (buf == NULL) {
 119     // nothing to do
 120     return;
 121   }
 122 
 123   // Two-fingered compaction toward the end.
 124   void** src = &buf[index()];
 125   void** dst = &buf[capacity()];
 126   assert(src <= dst, "invariant");
 127   for ( ; src < dst; ++src) {
 128     // Search low to high for an entry to keep.
 129     void* entry = *src;
 130     if (retain_entry(entry, g1h)) {
 131       // Found keeper.  Search high to low for an entry to discard.
 132       while (src < --dst) {
 133         if (!retain_entry(*dst, g1h)) {
 134           *dst = entry;         // Replace discard with keeper.
 135           break;
 136         }
 137       }
 138       // If discard search failed (src == dst), the outer loop will also end.
 139     }
 140   }
 141   // dst points to the lowest retained entry, or the end of the buffer
 142   // if all the entries were filtered out.
 143   set_index(dst - buf);
 144 }
 145 
 146 // This method will first apply the above filtering to the buffer. If
 147 // post-filtering a large enough chunk of the buffer has been cleared
 148 // we can re-use the buffer (instead of enqueueing it) and we can just
 149 // allow the mutator to carry on executing using the same buffer
 150 // instead of replacing it.
 151 
 152 bool SATBMarkQueue::should_enqueue_buffer() {
 153   assert(_lock == NULL || _lock->owned_by_self(),
 154          "we should have taken the lock before calling this");
 155 
 156   // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
 157 
 158   // This method should only be called if there is a non-NULL buffer
 159   // that is full.
 160   assert(index() == 0, "pre-condition");
 161   assert(_buf != NULL, "pre-condition");
 162 
 163   filter();
 164 
 165   size_t cap = capacity();
 166   size_t percent_used = ((cap - index()) * 100) / cap;
 167   bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
 168   return should_enqueue;
 169 }
 170 
 171 void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
 172   assert(SafepointSynchronize::is_at_safepoint(),
 173          "SATB queues must only be processed at safepoints");
 174   if (_buf != NULL) {
 175     cl->do_buffer(&_buf[index()], size());
 176     reset();
 177   }
 178 }
 179 
 180 #ifndef PRODUCT
 181 // Helpful for debugging
 182 
 183 static void print_satb_buffer(const char* name,
 184                               void** buf,
 185                               size_t index,
 186                               size_t capacity) {
 187   tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT
 188                 " capacity: " SIZE_FORMAT,
 189                 name, p2i(buf), index, capacity);
 190 }
 191 
 192 void SATBMarkQueue::print(const char* name) {
 193   print_satb_buffer(name, _buf, index(), capacity());
 194 }
 195 
 196 #endif // PRODUCT
 197 
 198 SATBMarkQueueSet::SATBMarkQueueSet() :
 199   PtrQueueSet(),
 200   _shared_satb_queue(this, true /* permanent */) { }
 201 
 202 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
 203                                   int process_completed_threshold,
 204                                   Mutex* lock) {
 205   PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
 206   _shared_satb_queue.set_lock(lock);
 207 }
 208 
 209 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
 210   t->satb_mark_queue().handle_zero_index();
 211 }
 212 
 213 #ifdef ASSERT
 214 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
 215   log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");
 216   log_error(gc, verify)("Actual SATB active states:");
 217   log_error(gc, verify)("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
 218   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 219     log_error(gc, verify)("  Thread \"%s\" queue: %s", t->name(), t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");
 220   }
 221   log_error(gc, verify)("  Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
 222 }
 223 
 224 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
 225   // Verify queue set state
 226   if (is_active() != expected_active) {
 227     dump_active_states(expected_active);
 228     guarantee(false, "SATB queue set has an unexpected active state");
 229   }
 230 
 231   // Verify thread queue states
 232   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 233     if (t->satb_mark_queue().is_active() != expected_active) {
 234       dump_active_states(expected_active);
 235       guarantee(false, "Thread SATB queue has an unexpected active state");
 236     }
 237   }
 238 
 239   // Verify shared queue state
 240   if (shared_satb_queue()->is_active() != expected_active) {
 241     dump_active_states(expected_active);
 242     guarantee(false, "Shared SATB queue has an unexpected active state");
 243   }
 244 }
 245 #endif // ASSERT
 246 
 247 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
 248   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 249 #ifdef ASSERT
 250   verify_active_states(expected_active);
 251 #endif // ASSERT
 252   _all_active = active;
 253   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 254     t->satb_mark_queue().set_active(active);
 255   }
 256   shared_satb_queue()->set_active(active);
 257 }
 258 
 259 void SATBMarkQueueSet::filter_thread_buffers() {
 260   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 261     t->satb_mark_queue().filter();
 262   }
 263   shared_satb_queue()->filter();
 264 }
 265 
 266 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
 267   BufferNode* nd = NULL;
 268   {
 269     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 270     if (_completed_buffers_head != NULL) {
 271       nd = _completed_buffers_head;
 272       _completed_buffers_head = nd->next();
 273       if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
 274       _n_completed_buffers--;
 275       if (_n_completed_buffers == 0) _process_completed = false;
 276     }
 277   }
 278   if (nd != NULL) {
 279     void **buf = BufferNode::make_buffer_from_node(nd);
 280     size_t index = nd->index();
 281     size_t size = buffer_size();
 282     assert(index <= size, "invariant");
 283     cl->do_buffer(buf + index, size - index);
 284     deallocate_buffer(nd);
 285     return true;
 286   } else {
 287     return false;
 288   }
 289 }
 290 
 291 #ifndef PRODUCT
 292 // Helpful for debugging
 293 
 294 #define SATB_PRINTER_BUFFER_SIZE 256
 295 
 296 void SATBMarkQueueSet::print_all(const char* msg) {
 297   char buffer[SATB_PRINTER_BUFFER_SIZE];
 298   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 299 
 300   tty->cr();
 301   tty->print_cr("SATB BUFFERS [%s]", msg);
 302 
 303   BufferNode* nd = _completed_buffers_head;
 304   int i = 0;
 305   while (nd != NULL) {
 306     void** buf = BufferNode::make_buffer_from_node(nd);
 307     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
 308     print_satb_buffer(buffer, buf, nd->index(), buffer_size());
 309     nd = nd->next();
 310     i += 1;
 311   }
 312 
 313   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 314     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
 315     t->satb_mark_queue().print(buffer);
 316   }
 317 
 318   shared_satb_queue()->print("Shared");
 319 
 320   tty->cr();
 321 }
 322 #endif // PRODUCT
 323 
 324 void SATBMarkQueueSet::abandon_partial_marking() {
 325   BufferNode* buffers_to_delete = NULL;
 326   {
 327     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 328     while (_completed_buffers_head != NULL) {
 329       BufferNode* nd = _completed_buffers_head;
 330       _completed_buffers_head = nd->next();
 331       nd->set_next(buffers_to_delete);
 332       buffers_to_delete = nd;
 333     }
 334     _completed_buffers_tail = NULL;
 335     _n_completed_buffers = 0;
 336     DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
 337   }
 338   while (buffers_to_delete != NULL) {
 339     BufferNode* nd = buffers_to_delete;
 340     buffers_to_delete = nd->next();
 341     deallocate_buffer(nd);
 342   }
 343   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 344   // So we can safely manipulate these queues.
 345   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 346     t->satb_mark_queue().reset();
 347   }
 348   shared_satb_queue()->reset();
 349 }