rev 59534 : 8245961: Shenandoah: move some root marking to concurrent phase

   1 /*
   2  * Copyright (c) 2019, 2020, Red Hat, Inc. 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 
  27 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
  28 #include "gc/shenandoah/shenandoahConcurrentRoots.hpp"
  29 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  30 #include "gc/shenandoah/shenandoahNMethod.inline.hpp"
  31 #include "memory/resourceArea.hpp"
  32 
  33 ShenandoahNMethod::ShenandoahNMethod(nmethod* nm, GrowableArray<oop*>& oops, bool non_immediate_oops) :
  34   _nm(nm), _oops(NULL), _oops_count(0), _unregistered(false) {
  35 
  36   if (!oops.is_empty()) {
  37     _oops_count = oops.length();
  38     _oops = NEW_C_HEAP_ARRAY(oop*, _oops_count, mtGC);
  39     for (int c = 0; c < _oops_count; c++) {
  40       _oops[c] = oops.at(c);
  41     }
  42   }
  43   _has_non_immed_oops = non_immediate_oops;
  44 
  45   assert_same_oops();
  46 }
  47 
  48 ShenandoahNMethod::~ShenandoahNMethod() {
  49   if (_oops != NULL) {
  50     FREE_C_HEAP_ARRAY(oop*, _oops);
  51   }
  52 }
  53 
  54 class ShenandoahHasCSetOopClosure : public OopClosure {
  55 private:
  56   ShenandoahHeap* const _heap;
  57   bool                  _has_cset_oops;
  58 
  59 public:
  60   ShenandoahHasCSetOopClosure(ShenandoahHeap *heap) :
  61     _heap(heap),
  62     _has_cset_oops(false) {
  63   }
  64 
  65   bool has_cset_oops() const {
  66     return _has_cset_oops;
  67   }
  68 
  69   void do_oop(oop* p) {
  70     oop value = RawAccess<>::oop_load(p);
  71     if (!_has_cset_oops && _heap->in_collection_set(value)) {
  72       _has_cset_oops = true;
  73     }
  74   }
  75 
  76   void do_oop(narrowOop* p) {
  77     ShouldNotReachHere();
  78   }
  79 };
  80 
  81 bool ShenandoahNMethod::has_cset_oops(ShenandoahHeap *heap) {
  82   ShenandoahHasCSetOopClosure cl(heap);
  83   oops_do(&cl);
  84   return cl.has_cset_oops();
  85 }
  86 
  87 void ShenandoahNMethod::update() {
  88   ResourceMark rm;
  89   bool non_immediate_oops = false;
  90   GrowableArray<oop*> oops;
  91 
  92   detect_reloc_oops(nm(), oops, non_immediate_oops);
  93   if (oops.length() != _oops_count) {
  94     if (_oops != NULL) {
  95       FREE_C_HEAP_ARRAY(oop*, _oops);
  96       _oops = NULL;
  97     }
  98 
  99     _oops_count = oops.length();
 100     if (_oops_count > 0) {
 101       _oops = NEW_C_HEAP_ARRAY(oop*, _oops_count, mtGC);
 102     }
 103   }
 104 
 105   for (int index = 0; index < _oops_count; index ++) {
 106     _oops[index] = oops.at(index);
 107   }
 108   _has_non_immed_oops = non_immediate_oops;
 109 
 110   assert_same_oops();
 111 }
 112 
 113 void ShenandoahNMethod::detect_reloc_oops(nmethod* nm, GrowableArray<oop*>& oops, bool& has_non_immed_oops) {
 114   has_non_immed_oops = false;
 115   // Find all oops relocations
 116   RelocIterator iter(nm);
 117   while (iter.next()) {
 118     if (iter.type() != relocInfo::oop_type) {
 119       // Not an oop
 120       continue;
 121     }
 122 
 123     oop_Relocation* r = iter.oop_reloc();
 124     if (!r->oop_is_immediate()) {
 125       // Non-immediate oop found
 126       has_non_immed_oops = true;
 127       continue;
 128     }
 129 
 130     oop value = r->oop_value();
 131     if (value != NULL) {
 132       oop* addr = r->oop_addr();
 133       shenandoah_assert_correct(addr, value);
 134       shenandoah_assert_not_in_cset_except(addr, value, ShenandoahHeap::heap()->cancelled_gc());
 135       shenandoah_assert_not_forwarded(addr, value);
 136       // Non-NULL immediate oop found. NULL oops can safely be
 137       // ignored since the method will be re-registered if they
 138       // are later patched to be non-NULL.
 139       oops.push(addr);
 140     }
 141   }
 142 }
 143 
 144 ShenandoahNMethod* ShenandoahNMethod::for_nmethod(nmethod* nm) {
 145   ResourceMark rm;
 146   bool non_immediate_oops = false;
 147   GrowableArray<oop*> oops;
 148 
 149   detect_reloc_oops(nm, oops, non_immediate_oops);
 150 
 151   // No embedded oops
 152   if(!ShenandoahConcurrentRoots::can_do_concurrent_class_unloading() &&
 153     oops.is_empty() && nm->oops_begin() >= nm->oops_end()) {
 154     return NULL;
 155   }
 156 
 157   return new ShenandoahNMethod(nm, oops, non_immediate_oops);
 158 }
 159 
 160 template <bool HAS_FWD>
 161 class ShenandoahKeepNMethodMetadataAliveClosure : public OopClosure {
 162 private:
 163   ShenandoahBarrierSet* const _bs;
 164 public:
 165   ShenandoahKeepNMethodMetadataAliveClosure() :
 166     _bs(static_cast<ShenandoahBarrierSet*>(BarrierSet::barrier_set())) {
 167   }
 168 
 169   virtual void do_oop(oop* p) {
 170     oop obj = RawAccess<>::oop_load(p);
 171     if (!CompressedOops::is_null(obj)) {
 172       if (HAS_FWD) {
 173         obj = ShenandoahBarrierSet::resolve_forwarded_not_null(obj);
 174       }
 175       _bs->enqueue(obj);
 176     }
 177   }
 178 
 179   virtual void do_oop(narrowOop* p) {
 180     ShouldNotReachHere();
 181   }
 182 };
 183 
 184 void ShenandoahNMethod::heal_nmethod(nmethod* nm) {
 185   ShenandoahNMethod* data = gc_data(nm);
 186   assert(data != NULL, "Sanity");
 187   assert(data->lock()->owned_by_self(), "Must hold the lock");
 188 
 189   ShenandoahHeap* const heap = ShenandoahHeap::heap();
 190   if (heap->is_concurrent_mark_in_progress()) {
 191     if (heap->has_forwarded_objects()) {
 192       ShenandoahKeepNMethodMetadataAliveClosure<true> cl;
 193       data->oops_do(&cl);
 194     } else {
 195       ShenandoahKeepNMethodMetadataAliveClosure<false> cl;
 196       data->oops_do(&cl);
 197     }
 198   } else if (heap->is_concurrent_weak_root_in_progress()) {
 199     ShenandoahEvacOOMScope evac_scope;
 200     heal_nmethod_metadata(data);
 201   } else {
 202     // There is possibility that GC is cancelled when it arrives final mark.
 203     // In this case, concurrent root phase is skipped and degenerated GC should be
 204     // followed, where nmethods are disarmed.
 205     assert(heap->cancelled_gc(), "What else?");
 206   }
 207 }
 208 
 209 #ifdef ASSERT
 210 void ShenandoahNMethod::assert_alive_and_correct() {
 211   assert(_nm->is_alive(), "only alive nmethods here");
 212   ShenandoahHeap* heap = ShenandoahHeap::heap();
 213   for (int c = 0; c < _oops_count; c++) {
 214     oop *loc = _oops[c];
 215     assert(_nm->code_contains((address) loc) || _nm->oops_contains(loc), "nmethod should contain the oop*");
 216     oop o = RawAccess<>::oop_load(loc);
 217     shenandoah_assert_correct_except(loc, o, o == NULL || heap->is_full_gc_move_in_progress());
 218   }
 219 
 220   oop* const begin = _nm->oops_begin();
 221   oop* const end = _nm->oops_end();
 222   for (oop* p = begin; p < end; p++) {
 223     if (*p != Universe::non_oop_word()) {
 224       oop o = RawAccess<>::oop_load(p);
 225       shenandoah_assert_correct_except(p, o, o == NULL || heap->is_full_gc_move_in_progress());
 226     }
 227   }
 228 }
 229 
 230 class ShenandoahNMethodOopDetector : public OopClosure {
 231 private:
 232   ResourceMark rm; // For growable array allocation below.
 233   GrowableArray<oop*> _oops;
 234 
 235 public:
 236   ShenandoahNMethodOopDetector() : _oops(10) {};
 237 
 238   void do_oop(oop* o) {
 239     _oops.append(o);
 240   }
 241   void do_oop(narrowOop* o) {
 242     fatal("NMethods should not have compressed oops embedded.");
 243   }
 244 
 245   GrowableArray<oop*>* oops() {
 246     return &_oops;
 247   }
 248 
 249   bool has_oops() {
 250     return !_oops.is_empty();
 251   }
 252 };
 253 
 254 void ShenandoahNMethod::assert_same_oops(bool allow_dead) {
 255   ShenandoahNMethodOopDetector detector;
 256   nm()->oops_do(&detector, allow_dead);
 257 
 258   GrowableArray<oop*>* oops = detector.oops();
 259 
 260   int count = _oops_count;
 261   for (int index = 0; index < _oops_count; index ++) {
 262     assert(oops->contains(_oops[index]), "Must contain this oop");
 263   }
 264 
 265   for (oop* p = nm()->oops_begin(); p < nm()->oops_end(); p ++) {
 266     if (*p == Universe::non_oop_word()) continue;
 267     count++;
 268     assert(oops->contains(p), "Must contain this oop");
 269   }
 270 
 271   if (oops->length() < count) {
 272     stringStream debug_stream;
 273     debug_stream.print_cr("detected locs: %d", oops->length());
 274     for (int i = 0; i < oops->length(); i++) {
 275       debug_stream.print_cr("-> " PTR_FORMAT, p2i(oops->at(i)));
 276     }
 277     debug_stream.print_cr("recorded oops: %d", _oops_count);
 278     for (int i = 0; i < _oops_count; i++) {
 279       debug_stream.print_cr("-> " PTR_FORMAT, p2i(_oops[i]));
 280     }
 281     GrowableArray<oop*> check;
 282     bool non_immed;
 283     detect_reloc_oops(nm(), check, non_immed);
 284     debug_stream.print_cr("check oops: %d", check.length());
 285     for (int i = 0; i < check.length(); i++) {
 286       debug_stream.print_cr("-> " PTR_FORMAT, p2i(check.at(i)));
 287     }
 288     fatal("Must match #detected: %d, #recorded: %d, #total: %d, begin: " PTR_FORMAT ", end: " PTR_FORMAT "\n%s",
 289           oops->length(), _oops_count, count, p2i(nm()->oops_begin()), p2i(nm()->oops_end()), debug_stream.as_string());
 290   }
 291 }
 292 
 293 void ShenandoahNMethod::assert_no_oops(nmethod* nm, bool allow_dead) {
 294   ShenandoahNMethodOopDetector detector;
 295   nm->oops_do(&detector, allow_dead);
 296   assert(detector.oops()->length() == 0, "Should not have oops");
 297 }
 298 #endif
 299 
 300 ShenandoahNMethodTable::ShenandoahNMethodTable() :
 301   _heap(ShenandoahHeap::heap()),
 302   _index(0),
 303   _itr_cnt(0) {
 304   _list = new ShenandoahNMethodList(minSize);
 305 }
 306 
 307 ShenandoahNMethodTable::~ShenandoahNMethodTable() {
 308   assert(_list != NULL, "Sanity");
 309   _list->release();
 310 }
 311 
 312 void ShenandoahNMethodTable::register_nmethod(nmethod* nm) {
 313   assert(CodeCache_lock->owned_by_self(), "Must have CodeCache_lock held");
 314   assert(_index >= 0 && _index <= _list->size(), "Sanity");
 315 
 316   ShenandoahNMethod* data = ShenandoahNMethod::gc_data(nm);
 317   ShenandoahReentrantLocker data_locker(data != NULL ? data->lock() : NULL);
 318 
 319   if (data != NULL) {
 320     assert(contain(nm), "Must have been registered");
 321     assert(nm == data->nm(), "Must be same nmethod");
 322     data->update();
 323   } else {
 324     data = ShenandoahNMethod::for_nmethod(nm);
 325     if (data == NULL) {
 326       assert(!ShenandoahConcurrentRoots::can_do_concurrent_class_unloading(),
 327              "Only possible when concurrent class unloading is off");
 328       return;
 329     }
 330     ShenandoahNMethod::attach_gc_data(nm, data);
 331     ShenandoahLocker locker(&_lock);
 332     log_register_nmethod(nm);
 333     append(data);
 334   }
 335   // Disarm new nmethod
 336   ShenandoahNMethod::disarm_nmethod(nm);
 337 }
 338 
 339 void ShenandoahNMethodTable::unregister_nmethod(nmethod* nm) {
 340   assert_locked_or_safepoint(CodeCache_lock);
 341 
 342   ShenandoahNMethod* data = ShenandoahNMethod::gc_data(nm);
 343   if (data == NULL) {
 344     assert(!ShenandoahConcurrentRoots::can_do_concurrent_class_unloading(),
 345            "Only possible when concurrent class unloading is off");
 346     ShenandoahNMethod::assert_no_oops(nm, true /*allow_dead*/);
 347     return;
 348   }
 349 
 350   if (Thread::current()->is_Code_cache_sweeper_thread()) {
 351     wait_until_concurrent_iteration_done();
 352   }
 353   log_unregister_nmethod(nm);
 354   ShenandoahLocker locker(&_lock);
 355   assert(contain(nm), "Must have been registered");
 356 
 357   ShenandoahReentrantLocker data_locker(data->lock());
 358   data->mark_unregistered();
 359 }
 360 
 361 void ShenandoahNMethodTable::flush_nmethod(nmethod* nm) {
 362   assert(CodeCache_lock->owned_by_self(), "Must have CodeCache_lock held");
 363   assert(Thread::current()->is_Code_cache_sweeper_thread(), "Must from Sweep thread");
 364   ShenandoahNMethod* data = ShenandoahNMethod::gc_data(nm);
 365   assert(data != NULL || !ShenandoahConcurrentRoots::can_do_concurrent_class_unloading(),
 366          "Only possible when concurrent class unloading is off");
 367   if (data == NULL) {
 368     ShenandoahNMethod::assert_no_oops(nm, true /*allow_dead*/);
 369     return;
 370   }
 371 
 372   // Can not alter the array when iteration is in progress
 373   wait_until_concurrent_iteration_done();
 374   log_flush_nmethod(nm);
 375 
 376   ShenandoahLocker locker(&_lock);
 377   int idx = index_of(nm);
 378   assert(idx >= 0 && idx < _index, "Invalid index");
 379   ShenandoahNMethod::attach_gc_data(nm, NULL);
 380   remove(idx);
 381 }
 382 
 383 bool ShenandoahNMethodTable::contain(nmethod* nm) const {
 384   return index_of(nm) != -1;
 385 }
 386 
 387 ShenandoahNMethod* ShenandoahNMethodTable::at(int index) const {
 388   assert(index >= 0 && index < _index, "Out of bound");
 389   return _list->at(index);
 390 }
 391 
 392 int ShenandoahNMethodTable::index_of(nmethod* nm) const {
 393   for (int index = 0; index < length(); index ++) {
 394     if (at(index)->nm() == nm) {
 395       return index;
 396     }
 397   }
 398   return -1;
 399 }
 400 
 401 void ShenandoahNMethodTable::remove(int idx) {
 402   shenandoah_assert_locked_or_safepoint(CodeCache_lock);
 403   assert(!iteration_in_progress(), "Can not happen");
 404   assert(_index >= 0 && _index <= _list->size(), "Sanity");
 405 
 406   assert(idx >= 0 && idx < _index, "Out of bound");
 407   ShenandoahNMethod* snm = _list->at(idx);
 408   ShenandoahNMethod* tmp = _list->at(_index - 1);
 409   _list->set(idx, tmp);
 410   _index --;
 411 
 412   delete snm;
 413 }
 414 
 415 void ShenandoahNMethodTable::wait_until_concurrent_iteration_done() {
 416   assert(CodeCache_lock->owned_by_self(), "Lock must be held");
 417   while (iteration_in_progress()) {
 418     CodeCache_lock->wait_without_safepoint_check();
 419   }
 420 }
 421 
 422 void ShenandoahNMethodTable::append(ShenandoahNMethod* snm) {
 423   if (is_full()) {
 424     int new_size = 2 * _list->size();
 425     // Rebuild table and replace current one
 426     rebuild(new_size);
 427   }
 428 
 429   _list->set(_index++,  snm);
 430   assert(_index >= 0 && _index <= _list->size(), "Sanity");
 431 }
 432 
 433 void ShenandoahNMethodTable::rebuild(int size) {
 434   ShenandoahNMethodList* new_list = new ShenandoahNMethodList(size);
 435   new_list->transfer(_list, _index);
 436 
 437   // Release old list
 438   _list->release();
 439   _list = new_list;
 440 }
 441 
 442 ShenandoahNMethodTableSnapshot* ShenandoahNMethodTable::snapshot_for_iteration() {
 443   _itr_cnt++;
 444   return new ShenandoahNMethodTableSnapshot(this);
 445 }
 446 
 447 void ShenandoahNMethodTable::finish_iteration(ShenandoahNMethodTableSnapshot* snapshot) {
 448   assert(iteration_in_progress(), "Why we here?");
 449   assert(snapshot != NULL, "No snapshot");
 450   _itr_cnt--;
 451 
 452   delete snapshot;
 453 }
 454 
 455 void ShenandoahNMethodTable::log_register_nmethod(nmethod* nm) {
 456   LogTarget(Debug, gc, nmethod) log;
 457   if (!log.is_enabled()) {
 458     return;
 459   }
 460 
 461   ResourceMark rm;
 462   log.print("Register NMethod: %s.%s [" PTR_FORMAT "] (%s)",
 463             nm->method()->method_holder()->external_name(),
 464             nm->method()->name()->as_C_string(),
 465             p2i(nm),
 466             nm->compiler_name());
 467 }
 468 
 469 void ShenandoahNMethodTable::log_unregister_nmethod(nmethod* nm) {
 470   LogTarget(Debug, gc, nmethod) log;
 471   if (!log.is_enabled()) {
 472     return;
 473   }
 474 
 475   ResourceMark rm;
 476   log.print("Unregister NMethod: %s.%s [" PTR_FORMAT "]",
 477             nm->method()->method_holder()->external_name(),
 478             nm->method()->name()->as_C_string(),
 479             p2i(nm));
 480 }
 481 
 482 void ShenandoahNMethodTable::log_flush_nmethod(nmethod* nm) {
 483   LogTarget(Debug, gc, nmethod) log;
 484   if (!log.is_enabled()) {
 485     return;
 486   }
 487 
 488   ResourceMark rm;
 489   log.print("Flush NMethod: (" PTR_FORMAT ")", p2i(nm));
 490 }
 491 
 492 #ifdef ASSERT
 493 void ShenandoahNMethodTable::assert_nmethods_alive_and_correct() {
 494   assert_locked_or_safepoint(CodeCache_lock);
 495 
 496   for (int index = 0; index < length(); index ++) {
 497     ShenandoahNMethod* m = _list->at(index);
 498     // Concurrent unloading may have dead nmethods to be cleaned by sweeper
 499     if (m->is_unregistered()) continue;
 500     m->assert_alive_and_correct();
 501   }
 502 }
 503 #endif
 504 
 505 
 506 ShenandoahNMethodList::ShenandoahNMethodList(int size) :
 507   _size(size), _ref_count(1) {
 508   _list = NEW_C_HEAP_ARRAY(ShenandoahNMethod*, size, mtGC);
 509 }
 510 
 511 ShenandoahNMethodList::~ShenandoahNMethodList() {
 512   assert(_list != NULL, "Sanity");
 513   assert(_ref_count == 0, "Must be");
 514   FREE_C_HEAP_ARRAY(ShenandoahNMethod*, _list);
 515 }
 516 
 517 void ShenandoahNMethodList::transfer(ShenandoahNMethodList* const list, int limit) {
 518   assert(limit <= size(), "Sanity");
 519   ShenandoahNMethod** old_list = list->list();
 520   for (int index = 0; index < limit; index++) {
 521     _list[index] = old_list[index];
 522   }
 523 }
 524 
 525 ShenandoahNMethodList* ShenandoahNMethodList::acquire() {
 526   assert(CodeCache_lock->owned_by_self(), "Lock must be held");
 527   _ref_count++;
 528   return this;
 529 }
 530 
 531 void ShenandoahNMethodList::release() {
 532   assert(CodeCache_lock->owned_by_self(), "Lock must be held");
 533   _ref_count--;
 534   if (_ref_count == 0) {
 535     delete this;
 536   }
 537 }
 538 
 539 ShenandoahNMethodTableSnapshot::ShenandoahNMethodTableSnapshot(ShenandoahNMethodTable* table) :
 540   _heap(ShenandoahHeap::heap()), _list(table->_list->acquire()), _limit(table->_index), _claimed(0) {
 541 }
 542 
 543 ShenandoahNMethodTableSnapshot::~ShenandoahNMethodTableSnapshot() {
 544   _list->release();
 545 }
 546 
 547 void ShenandoahNMethodTableSnapshot::parallel_blobs_do(CodeBlobClosure *f) {
 548   size_t stride = 256; // educated guess
 549 
 550   ShenandoahNMethod** const list = _list->list();
 551 
 552   size_t max = (size_t)_limit;
 553   while (_claimed < max) {
 554     size_t cur = Atomic::fetch_and_add(&_claimed, stride);
 555     size_t start = cur;
 556     size_t end = MIN2(cur + stride, max);
 557     if (start >= max) break;
 558 
 559     for (size_t idx = start; idx < end; idx++) {
 560       ShenandoahNMethod* nmr = list[idx];
 561       assert(nmr != NULL, "Sanity");
 562       if (nmr->is_unregistered()) {
 563         continue;
 564       }
 565 
 566       nmr->assert_alive_and_correct();
 567       f->do_code_blob(nmr->nm());
 568     }
 569   }
 570 }
 571 
 572 void ShenandoahNMethodTableSnapshot::concurrent_nmethods_do(NMethodClosure* cl) {
 573   size_t stride = 256; // educated guess
 574 
 575   ShenandoahNMethod** list = _list->list();
 576   size_t max = (size_t)_limit;
 577   while (_claimed < max) {
 578     size_t cur = Atomic::fetch_and_add(&_claimed, stride);
 579     size_t start = cur;
 580     size_t end = MIN2(cur + stride, max);
 581     if (start >= max) break;
 582 
 583     for (size_t idx = start; idx < end; idx++) {
 584       ShenandoahNMethod* data = list[idx];
 585       assert(data != NULL, "Should not be NULL");
 586       if (!data->is_unregistered()) {
 587         cl->do_nmethod(data->nm());
 588       }
 589     }
 590   }
 591 }
 592 
 593 ShenandoahConcurrentNMethodIterator::ShenandoahConcurrentNMethodIterator(ShenandoahNMethodTable* table) :
 594   _table(table), _table_snapshot(NULL) {
 595 }
 596 
 597 void ShenandoahConcurrentNMethodIterator::nmethods_do_begin() {
 598   assert(CodeCache_lock->owned_by_self(), "Lock must be held");
 599   assert(ShenandoahConcurrentRoots::can_do_concurrent_class_unloading(),
 600          "Only for concurrent class unloading");
 601   _table_snapshot = _table->snapshot_for_iteration();
 602 }
 603 
 604 void ShenandoahConcurrentNMethodIterator::nmethods_do(NMethodClosure* cl) {
 605   assert(_table_snapshot != NULL, "Must first call nmethod_do_begin()");
 606   _table_snapshot->concurrent_nmethods_do(cl);
 607 }
 608 
 609 void ShenandoahConcurrentNMethodIterator::nmethods_do_end() {
 610   assert(CodeCache_lock->owned_by_self(), "Lock must be held");
 611   assert(ShenandoahConcurrentRoots::can_do_concurrent_class_unloading(),
 612          "Only for concurrent class unloading");
 613   _table->finish_iteration(_table_snapshot);
 614   CodeCache_lock->notify_all();
 615 }
--- EOF ---