1 /*
   2  * Copyright (c) 2001, 2019, 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/shared/collectedHeap.hpp"
  28 #include "memory/allocation.inline.hpp"
  29 #include "oops/oop.inline.hpp"
  30 #include "runtime/mutexLocker.hpp"
  31 #include "runtime/safepoint.hpp"
  32 #include "runtime/thread.hpp"
  33 #include "runtime/threadSMR.hpp"
  34 #include "runtime/vmThread.hpp"
  35 #include "utilities/macros.hpp"
  36 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  37 #include "gc/shenandoah/shenandoahSATBMarkQueue.hpp"
  38 #include "gc/shenandoah/shenandoahThreadLocalData.hpp"
  39 
  40 ShenandoahSATBMarkQueue::ShenandoahSATBMarkQueue(ShenandoahSATBMarkQueueSet* qset, bool permanent) :
  41   // SATB queues are only active during marking cycles. We create
  42   // them with their active field set to false. If a thread is
  43   // created during a cycle and its SATB queue needs to be activated
  44   // before the thread starts running, we'll need to set its active
  45   // field to true. This is done in G1SBarrierSet::on_thread_attach().
  46   PtrQueue(qset, permanent, false /* active */)
  47 { }
  48 
  49 void ShenandoahSATBMarkQueue::flush() {
  50   // Filter now to possibly save work later.  If filtering empties the
  51   // buffer then flush_impl can deallocate the buffer.
  52   filter();
  53   flush_impl();
  54 }
  55 
  56 // Return true if a SATB buffer entry refers to an object that
  57 // requires marking.
  58 //
  59 // The entry must point into the Shenandoah heap.  In particular, it must not
  60 // be a NULL pointer.  NULL pointers are pre-filtered and never
  61 // inserted into a SATB buffer.
  62 //
  63 // An entry that is below the NTAMS pointer for the containing heap
  64 // region requires marking. Such an entry must point to a valid object.
  65 //
  66 // An entry that is at least the NTAMS pointer for the containing heap
  67 // region might be any of the following, none of which should be marked.
  68 //
  69 // * A reference to an object allocated since marking started.
  70 //   According to SATB, such objects are implicitly kept live and do
  71 //   not need to be dealt with via SATB buffer processing.
  72 //
  73 // * A reference to a young generation object. Young objects are
  74 //   handled separately and are not marked by concurrent marking.
  75 //
  76 // * A stale reference to a young generation object. If a young
  77 //   generation object reference is recorded and not filtered out
  78 //   before being moved by a young collection, the reference becomes
  79 //   stale.
  80 //
  81 // * A stale reference to an eagerly reclaimed humongous object.  If a
  82 //   humongous object is recorded and then reclaimed, the reference
  83 //   becomes stale.
  84 //
  85 // The stale reference cases are implicitly handled by the NTAMS
  86 // comparison. Because of the possibility of stale references, buffer
  87 // processing must be somewhat circumspect and not assume entries
  88 // in an unfiltered buffer refer to valid objects.
  89 
  90 inline bool retain_entry(const void* entry, ShenandoahHeap* heap) {
  91   return heap->requires_marking(entry);
  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 ShenandoahSATBMarkQueue::filter() {
 100   ShenandoahHeap* heap = ShenandoahHeap::heap();
 101   void** buf = _buf;
 102 
 103   if (buf == NULL) {
 104     // nothing to do
 105     return;
 106   }
 107 
 108   // Two-fingered compaction toward the end.
 109   void** src = &buf[index()];
 110   void** dst = &buf[capacity()];
 111   assert(src <= dst, "invariant");
 112   for ( ; src < dst; ++src) {
 113     // Search low to high for an entry to keep.
 114     void* entry = *src;
 115     if (retain_entry(entry, heap)) {
 116       // Found keeper.  Search high to low for an entry to discard.
 117       while (src < --dst) {
 118         if (!retain_entry(*dst, heap)) {
 119           *dst = entry;         // Replace discard with keeper.
 120           break;
 121         }
 122       }
 123       // If discard search failed (src == dst), the outer loop will also end.
 124     }
 125   }
 126   // dst points to the lowest retained entry, or the end of the buffer
 127   // if all the entries were filtered out.
 128   set_index(dst - buf);
 129 }
 130 
 131 // This method will first apply the above filtering to the buffer. If
 132 // post-filtering a large enough chunk of the buffer has been cleared
 133 // we can re-use the buffer (instead of enqueueing it) and we can just
 134 // allow the mutator to carry on executing using the same buffer
 135 // instead of replacing it.
 136 
 137 bool ShenandoahSATBMarkQueue::should_enqueue_buffer() {
 138   assert(_lock == NULL || _lock->owned_by_self(),
 139          "we should have taken the lock before calling this");
 140 
 141   // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
 142 
 143   // This method should only be called if there is a non-NULL buffer
 144   // that is full.
 145   assert(index() == 0, "pre-condition");
 146   assert(_buf != NULL, "pre-condition");
 147 
 148   filter();
 149 
 150   size_t cap = capacity();
 151   size_t percent_used = ((cap - index()) * 100) / cap;
 152   bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
 153 
 154   Thread* t = Thread::current();
 155   if (ShenandoahThreadLocalData::is_force_satb_flush(t)) {
 156     if (!should_enqueue && cap != index()) {
 157       // Non-empty buffer is compacted, and we decided not to enqueue it.
 158       // We still want to know about leftover work in that buffer eventually.
 159       // This avoid dealing with these leftovers during the final-mark, after
 160       // the buffers are drained completely. See JDK-8205353 for more discussion.
 161       should_enqueue = true;
 162     }
 163     ShenandoahThreadLocalData::set_force_satb_flush(t, false);
 164   }
 165   return should_enqueue;
 166 }
 167 
 168 void ShenandoahSATBMarkQueue::apply_closure_and_empty(ShenandoahSATBBufferClosure* cl) {
 169   assert(SafepointSynchronize::is_at_safepoint(),
 170          "SATB queues must only be processed at safepoints");
 171   if (_buf != NULL) {
 172     cl->do_buffer(&_buf[index()], size());
 173     reset();
 174   }
 175 }
 176 
 177 #ifndef PRODUCT
 178 // Helpful for debugging
 179 
 180 static void print_satb_buffer(const char* name,
 181                               void** buf,
 182                               size_t index,
 183                               size_t capacity) {
 184   tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT
 185                 " capacity: " SIZE_FORMAT,
 186                 name, p2i(buf), index, capacity);
 187 }
 188 
 189 void ShenandoahSATBMarkQueue::print(const char* name) {
 190   print_satb_buffer(name, _buf, index(), capacity());
 191 }
 192 
 193 #endif // PRODUCT
 194 
 195 ShenandoahSATBMarkQueueSet::ShenandoahSATBMarkQueueSet() :
 196   PtrQueueSet(),
 197   _shared_satb_queue(this, true /* permanent */) { }
 198 
 199 void ShenandoahSATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
 200                                             int process_completed_threshold,
 201                                             Mutex* lock) {
 202   PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
 203   _shared_satb_queue.set_lock(lock);
 204 }
 205 
 206 #ifdef ASSERT
 207 void ShenandoahSATBMarkQueueSet::dump_active_states(bool expected_active) {
 208   log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");
 209   log_error(gc, verify)("Actual SATB active states:");
 210   log_error(gc, verify)("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
 211   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 212     log_error(gc, verify)("  Thread \"%s\" queue: %s", t->name(), satb_queue_for_thread(t).is_active() ? "ACTIVE" : "INACTIVE");
 213   }
 214   log_error(gc, verify)("  Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
 215 }
 216 
 217 void ShenandoahSATBMarkQueueSet::verify_active_states(bool expected_active) {
 218   // Verify queue set state
 219   if (is_active() != expected_active) {
 220     dump_active_states(expected_active);
 221     guarantee(false, "SATB queue set has an unexpected active state");
 222   }
 223 
 224   // Verify thread queue states
 225   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 226     if (satb_queue_for_thread(t).is_active() != expected_active) {
 227       dump_active_states(expected_active);
 228       guarantee(false, "Thread SATB queue has an unexpected active state");
 229     }
 230   }
 231 
 232   // Verify shared queue state
 233   if (shared_satb_queue()->is_active() != expected_active) {
 234     dump_active_states(expected_active);
 235     guarantee(false, "Shared SATB queue has an unexpected active state");
 236   }
 237 }
 238 #endif // ASSERT
 239 
 240 void ShenandoahSATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
 241   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 242 #ifdef ASSERT
 243   verify_active_states(expected_active);
 244 #endif // ASSERT
 245   _all_active = active;
 246   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 247     satb_queue_for_thread(t).set_active(active);
 248   }
 249   shared_satb_queue()->set_active(active);
 250 }
 251 
 252 void ShenandoahSATBMarkQueueSet::filter_thread_buffers() {
 253   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 254     satb_queue_for_thread(t).filter();
 255   }
 256   shared_satb_queue()->filter();
 257 }
 258 
 259 bool ShenandoahSATBMarkQueueSet::apply_closure_to_completed_buffer(ShenandoahSATBBufferClosure* cl) {
 260   BufferNode* nd = NULL;
 261   {
 262     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 263     if (_completed_buffers_head != NULL) {
 264       nd = _completed_buffers_head;
 265       _completed_buffers_head = nd->next();
 266       if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
 267       _n_completed_buffers--;
 268       if (_n_completed_buffers == 0) _process_completed = false;
 269     }
 270   }
 271   if (nd != NULL) {
 272     void **buf = BufferNode::make_buffer_from_node(nd);
 273     size_t index = nd->index();
 274     size_t size = buffer_size();
 275     assert(index <= size, "invariant");
 276     cl->do_buffer(buf + index, size - index);
 277     deallocate_buffer(nd);
 278     return true;
 279   } else {
 280     return false;
 281   }
 282 }
 283 
 284 #ifndef PRODUCT
 285 // Helpful for debugging
 286 
 287 #define SATB_PRINTER_BUFFER_SIZE 256
 288 
 289 void ShenandoahSATBMarkQueueSet::print_all(const char* msg) {
 290   char buffer[SATB_PRINTER_BUFFER_SIZE];
 291   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 292 
 293   tty->cr();
 294   tty->print_cr("SATB BUFFERS [%s]", msg);
 295 
 296   BufferNode* nd = _completed_buffers_head;
 297   int i = 0;
 298   while (nd != NULL) {
 299     void** buf = BufferNode::make_buffer_from_node(nd);
 300     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
 301     print_satb_buffer(buffer, buf, nd->index(), buffer_size());
 302     nd = nd->next();
 303     i += 1;
 304   }
 305 
 306   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 307     jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
 308     satb_queue_for_thread(t).print(buffer);
 309   }
 310 
 311   shared_satb_queue()->print("Shared");
 312 
 313   tty->cr();
 314 }
 315 #endif // PRODUCT
 316 
 317 void ShenandoahSATBMarkQueueSet::abandon_partial_marking() {
 318   BufferNode* buffers_to_delete = NULL;
 319   {
 320     MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
 321     while (_completed_buffers_head != NULL) {
 322       BufferNode* nd = _completed_buffers_head;
 323       _completed_buffers_head = nd->next();
 324       nd->set_next(buffers_to_delete);
 325       buffers_to_delete = nd;
 326     }
 327     _completed_buffers_tail = NULL;
 328     _n_completed_buffers = 0;
 329     DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
 330   }
 331   while (buffers_to_delete != NULL) {
 332     BufferNode* nd = buffers_to_delete;
 333     buffers_to_delete = nd->next();
 334     deallocate_buffer(nd);
 335   }
 336   assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
 337   // So we can safely manipulate these queues.
 338   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
 339     satb_queue_for_thread(t).reset();
 340   }
 341   shared_satb_queue()->reset();
 342 }
 343 
 344 ShenandoahSATBMarkQueue& ShenandoahSATBMarkQueueSet::satb_queue_for_thread(Thread* t) {
 345   return ShenandoahThreadLocalData::satb_mark_queue(t);
 346 }
 347