src/share/vm/gc_implementation/g1/heapRegionSet.cpp - platform/external/jetbrains/jdk8u_hotspot - Git at Google

 /*
  * Copyright (c) 2011, 2014, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */

 #include "precompiled.hpp"
 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
 #include "gc_implementation/g1/heapRegionRemSet.hpp"
 #include "gc_implementation/g1/heapRegionSet.inline.hpp"

 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC

 uint FreeRegionList::_unrealistically_long_length = 0;

 void HeapRegionSetBase::fill_in_ext_msg(hrs_ext_msg* msg, const char* message) {
   msg->append("[%s] %s ln: %u cy: "SIZE_FORMAT,
               name(), message, length(), total_capacity_bytes());
   fill_in_ext_msg_extra(msg);
 }

 #ifndef PRODUCT
 void HeapRegionSetBase::verify_region(HeapRegion* hr) {
   assert(hr->containing_set() == this, err_msg("Inconsistent containing set for %u", hr->hrm_index()));
   assert(!hr->is_young(), err_msg("Adding young region %u", hr->hrm_index())); // currently we don't use these sets for young regions
   assert(hr->isHumongous() == regions_humongous(), err_msg("Wrong humongous state for region %u and set %s", hr->hrm_index(), name()));
   assert(hr->is_free() == regions_free(), err_msg("Wrong free state for region %u and set %s", hr->hrm_index(), name()));
   assert(!hr->is_free() || hr->is_empty(), err_msg("Free region %u is not empty for set %s", hr->hrm_index(), name()));
   assert(!hr->is_empty() || hr->is_free(), err_msg("Empty region %u is not free for set %s", hr->hrm_index(), name()));
   assert(hr->rem_set()->verify_ready_for_par_iteration(), err_msg("Wrong iteration state %u", hr->hrm_index()));
 }
 #endif

 void HeapRegionSetBase::verify() {
   // It's important that we also observe the MT safety protocol even
   // for the verification calls. If we do verification without the
   // appropriate locks and the set changes underneath our feet
   // verification might fail and send us on a wild goose chase.
   check_mt_safety();

   guarantee(( is_empty() && length() == 0 && total_capacity_bytes() == 0) ||
             (!is_empty() && length() >= 0 && total_capacity_bytes() >= 0),
             hrs_ext_msg(this, "invariant"));
 }

 void HeapRegionSetBase::verify_start() {
   // See comment in verify() about MT safety and verification.
   check_mt_safety();
   assert(!_verify_in_progress,
          hrs_ext_msg(this, "verification should not be in progress"));

   // Do the basic verification first before we do the checks over the regions.
   HeapRegionSetBase::verify();

   _verify_in_progress = true;
 }

 void HeapRegionSetBase::verify_end() {
   // See comment in verify() about MT safety and verification.
   check_mt_safety();
   assert(_verify_in_progress,
          hrs_ext_msg(this, "verification should be in progress"));

   _verify_in_progress = false;
 }

 void HeapRegionSetBase::print_on(outputStream* out, bool print_contents) {
   out->cr();
   out->print_cr("Set: %s ("PTR_FORMAT")", name(), this);
   out->print_cr("  Region Assumptions");
   out->print_cr("    humongous         : %s", BOOL_TO_STR(regions_humongous()));
   out->print_cr("    free              : %s", BOOL_TO_STR(regions_free()));
   out->print_cr("  Attributes");
   out->print_cr("    length            : %14u", length());
   out->print_cr("    total capacity    : "SIZE_FORMAT_W(14)" bytes",
                 total_capacity_bytes());
 }

 HeapRegionSetBase::HeapRegionSetBase(const char* name, bool humongous, bool free, HRSMtSafeChecker* mt_safety_checker)
   : _name(name), _verify_in_progress(false),
     _is_humongous(humongous), _is_free(free), _mt_safety_checker(mt_safety_checker),
     _count()
 { }

 void FreeRegionList::set_unrealistically_long_length(uint len) {
   guarantee(_unrealistically_long_length == 0, "should only be set once");
   _unrealistically_long_length = len;
 }

 void FreeRegionList::fill_in_ext_msg_extra(hrs_ext_msg* msg) {
   msg->append(" hd: "PTR_FORMAT" tl: "PTR_FORMAT, _head, _tail);
 }

 void FreeRegionList::remove_all() {
   check_mt_safety();
   verify_optional();

   HeapRegion* curr = _head;
   while (curr != NULL) {
     verify_region(curr);

     HeapRegion* next = curr->next();
     curr->set_next(NULL);
     curr->set_prev(NULL);
     curr->set_containing_set(NULL);
     curr = next;
   }
   clear();

   verify_optional();
 }

 void FreeRegionList::add_ordered(FreeRegionList* from_list) {
   check_mt_safety();
   from_list->check_mt_safety();

   verify_optional();
   from_list->verify_optional();

   if (from_list->is_empty()) {
     return;
   }

   #ifdef ASSERT
   FreeRegionListIterator iter(from_list);
   while (iter.more_available()) {
     HeapRegion* hr = iter.get_next();
     // In set_containing_set() we check that we either set the value
     // from NULL to non-NULL or vice versa to catch bugs. So, we have
     // to NULL it first before setting it to the value.
     hr->set_containing_set(NULL);
     hr->set_containing_set(this);
   }
   #endif // ASSERT

   if (is_empty()) {
     assert(length() == 0 && _tail == NULL, hrs_ext_msg(this, "invariant"));
     _head = from_list->_head;
     _tail = from_list->_tail;
   } else {
     HeapRegion* curr_to = _head;
     HeapRegion* curr_from = from_list->_head;

     while (curr_from != NULL) {
       while (curr_to != NULL && curr_to->hrm_index() < curr_from->hrm_index()) {
         curr_to = curr_to->next();
       }

       if (curr_to == NULL) {
         // The rest of the from list should be added as tail
         _tail->set_next(curr_from);
         curr_from->set_prev(_tail);
         curr_from = NULL;
       } else {
         HeapRegion* next_from = curr_from->next();

         curr_from->set_next(curr_to);
         curr_from->set_prev(curr_to->prev());
         if (curr_to->prev() == NULL) {
           _head = curr_from;
         } else {
           curr_to->prev()->set_next(curr_from);
         }
         curr_to->set_prev(curr_from);

         curr_from = next_from;
       }
     }

     if (_tail->hrm_index() < from_list->_tail->hrm_index()) {
       _tail = from_list->_tail;
     }
   }

   _count.increment(from_list->length(), from_list->total_capacity_bytes());
   from_list->clear();

   verify_optional();
   from_list->verify_optional();
 }

 void FreeRegionList::remove_starting_at(HeapRegion* first, uint num_regions) {
   check_mt_safety();
   assert(num_regions >= 1, hrs_ext_msg(this, "pre-condition"));
   assert(!is_empty(), hrs_ext_msg(this, "pre-condition"));

   verify_optional();
   DEBUG_ONLY(uint old_length = length();)

   HeapRegion* curr = first;
   uint count = 0;
   while (count < num_regions) {
     verify_region(curr);
     HeapRegion* next = curr->next();
     HeapRegion* prev = curr->prev();

     assert(count < num_regions,
            hrs_err_msg("[%s] should not come across more regions "
                        "pending for removal than num_regions: %u",
                        name(), num_regions));

     if (prev == NULL) {
       assert(_head == curr, hrs_ext_msg(this, "invariant"));
       _head = next;
     } else {
       assert(_head != curr, hrs_ext_msg(this, "invariant"));
       prev->set_next(next);
     }
     if (next == NULL) {
       assert(_tail == curr, hrs_ext_msg(this, "invariant"));
       _tail = prev;
     } else {
       assert(_tail != curr, hrs_ext_msg(this, "invariant"));
       next->set_prev(prev);
     }
     if (_last = curr) {
       _last = NULL;
     }

     curr->set_next(NULL);
     curr->set_prev(NULL);
     remove(curr);

     count++;
     curr = next;
   }

   assert(count == num_regions,
          hrs_err_msg("[%s] count: %u should be == num_regions: %u",
                      name(), count, num_regions));
   assert(length() + num_regions == old_length,
          hrs_err_msg("[%s] new length should be consistent "
                      "new length: %u old length: %u num_regions: %u",
                      name(), length(), old_length, num_regions));

   verify_optional();
 }

 void FreeRegionList::verify() {
   // See comment in HeapRegionSetBase::verify() about MT safety and
   // verification.
   check_mt_safety();

   // This will also do the basic verification too.
   verify_start();

   verify_list();

   verify_end();
 }

 void FreeRegionList::clear() {
   _count = HeapRegionSetCount();
   _head = NULL;
   _tail = NULL;
   _last = NULL;
 }

 void FreeRegionList::print_on(outputStream* out, bool print_contents) {
   HeapRegionSetBase::print_on(out, print_contents);
   out->print_cr("  Linking");
   out->print_cr("    head              : "PTR_FORMAT, _head);
   out->print_cr("    tail              : "PTR_FORMAT, _tail);

   if (print_contents) {
     out->print_cr("  Contents");
     FreeRegionListIterator iter(this);
     while (iter.more_available()) {
       HeapRegion* hr = iter.get_next();
       hr->print_on(out);
     }
   }

   out->cr();
 }

 void FreeRegionList::verify_list() {
   HeapRegion* curr = _head;
   HeapRegion* prev1 = NULL;
   HeapRegion* prev0 = NULL;
   uint count = 0;
   size_t capacity = 0;
   uint last_index = 0;

   guarantee(_head == NULL || _head->prev() == NULL, "_head should not have a prev");
   while (curr != NULL) {
     verify_region(curr);

     count++;
     guarantee(count < _unrealistically_long_length,
         hrs_err_msg("[%s] the calculated length: %u seems very long, is there maybe a cycle? curr: "PTR_FORMAT" prev0: "PTR_FORMAT" " "prev1: "PTR_FORMAT" length: %u", name(), count, curr, prev0, prev1, length()));

     if (curr->next() != NULL) {
       guarantee(curr->next()->prev() == curr, "Next or prev pointers messed up");
     }
     guarantee(curr->hrm_index() == 0 || curr->hrm_index() > last_index, "List should be sorted");
     last_index = curr->hrm_index();

     capacity += curr->capacity();

     prev1 = prev0;
     prev0 = curr;
     curr = curr->next();
   }

   guarantee(_tail == prev0, err_msg("Expected %s to end with %u but it ended with %u.", name(), _tail->hrm_index(), prev0->hrm_index()));
   guarantee(_tail == NULL || _tail->next() == NULL, "_tail should not have a next");
   guarantee(length() == count, err_msg("%s count mismatch. Expected %u, actual %u.", name(), length(), count));
   guarantee(total_capacity_bytes() == capacity, err_msg("%s capacity mismatch. Expected " SIZE_FORMAT ", actual " SIZE_FORMAT,
       name(), total_capacity_bytes(), capacity));
 }

 // Note on the check_mt_safety() methods below:
 //
 // Verification of the "master" heap region sets / lists that are
 // maintained by G1CollectedHeap is always done during a STW pause and
 // by the VM thread at the start / end of the pause. The standard
 // verification methods all assert check_mt_safety(). This is
 // important as it ensures that verification is done without
 // concurrent updates taking place at the same time. It follows, that,
 // for the "master" heap region sets / lists, the check_mt_safety()
 // method should include the VM thread / STW case.

 void MasterFreeRegionListMtSafeChecker::check() {
   // Master Free List MT safety protocol:
   // (a) If we're at a safepoint, operations on the master free list
   // should be invoked by either the VM thread (which will serialize
   // them) or by the GC workers while holding the
   // FreeList_lock.
   // (b) If we're not at a safepoint, operations on the master free
   // list should be invoked while holding the Heap_lock.

   if (SafepointSynchronize::is_at_safepoint()) {
     guarantee(Thread::current()->is_VM_thread() ||
               FreeList_lock->owned_by_self(), "master free list MT safety protocol at a safepoint");
   } else {
     guarantee(Heap_lock->owned_by_self(), "master free list MT safety protocol outside a safepoint");
   }
 }

 void SecondaryFreeRegionListMtSafeChecker::check() {
   // Secondary Free List MT safety protocol:
   // Operations on the secondary free list should always be invoked
   // while holding the SecondaryFreeList_lock.

   guarantee(SecondaryFreeList_lock->owned_by_self(), "secondary free list MT safety protocol");
 }

 void OldRegionSetMtSafeChecker::check() {
   // Master Old Set MT safety protocol:
   // (a) If we're at a safepoint, operations on the master old set
   // should be invoked:
   // - by the VM thread (which will serialize them), or
   // - by the GC workers while holding the FreeList_lock, if we're
   //   at a safepoint for an evacuation pause (this lock is taken
   //   anyway when an GC alloc region is retired so that a new one
   //   is allocated from the free list), or
   // - by the GC workers while holding the OldSets_lock, if we're at a
   //   safepoint for a cleanup pause.
   // (b) If we're not at a safepoint, operations on the master old set
   // should be invoked while holding the Heap_lock.

   if (SafepointSynchronize::is_at_safepoint()) {
     guarantee(Thread::current()->is_VM_thread()
         || FreeList_lock->owned_by_self() || OldSets_lock->owned_by_self(),
         "master old set MT safety protocol at a safepoint");
   } else {
     guarantee(Heap_lock->owned_by_self(), "master old set MT safety protocol outside a safepoint");
   }
 }

 void HumongousRegionSetMtSafeChecker::check() {
   // Humongous Set MT safety protocol:
   // (a) If we're at a safepoint, operations on the master humongous
   // set should be invoked by either the VM thread (which will
   // serialize them) or by the GC workers while holding the
   // OldSets_lock.
   // (b) If we're not at a safepoint, operations on the master
   // humongous set should be invoked while holding the Heap_lock.

   if (SafepointSynchronize::is_at_safepoint()) {
     guarantee(Thread::current()->is_VM_thread() ||
               OldSets_lock->owned_by_self(),
               "master humongous set MT safety protocol at a safepoint");
   } else {
     guarantee(Heap_lock->owned_by_self(),
               "master humongous set MT safety protocol outside a safepoint");
   }
 }

 void FreeRegionList_test() {
   FreeRegionList l("test");

   const uint num_regions_in_test = 5;
   // Create a fake heap. It does not need to be valid, as the HeapRegion constructor
   // does not access it.
   MemRegion heap(NULL, num_regions_in_test * HeapRegion::GrainWords);
   // Allocate a fake BOT because the HeapRegion constructor initializes
   // the BOT.
   size_t bot_size = G1BlockOffsetSharedArray::compute_size(heap.word_size());
   HeapWord* bot_data = NEW_C_HEAP_ARRAY(HeapWord, bot_size, mtGC);
   ReservedSpace bot_rs(G1BlockOffsetSharedArray::compute_size(heap.word_size()));
   G1RegionToSpaceMapper* bot_storage =
     G1RegionToSpaceMapper::create_mapper(bot_rs,
                                          bot_rs.size(),
                                          os::vm_page_size(),
                                          HeapRegion::GrainBytes,
                                          G1BlockOffsetSharedArray::N_bytes,
                                          mtGC);
   G1BlockOffsetSharedArray oa(heap, bot_storage);
   bot_storage->commit_regions(0, num_regions_in_test);
   HeapRegion hr0(0, &oa, heap);
   HeapRegion hr1(1, &oa, heap);
   HeapRegion hr2(2, &oa, heap);
   HeapRegion hr3(3, &oa, heap);
   HeapRegion hr4(4, &oa, heap);
   l.add_ordered(&hr1);
   l.add_ordered(&hr0);
   l.add_ordered(&hr3);
   l.add_ordered(&hr4);
   l.add_ordered(&hr2);
   assert(l.length() == num_regions_in_test, "wrong length");
   l.verify_list();

   bot_storage->uncommit_regions(0, num_regions_in_test);
   delete bot_storage;
   FREE_C_HEAP_ARRAY(HeapWord, bot_data, mtGC);
 }
	/*
	* Copyright (c) 2011, 2014, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*
	*/

	#include "precompiled.hpp"
	#include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
	#include "gc_implementation/g1/heapRegionRemSet.hpp"
	#include "gc_implementation/g1/heapRegionSet.inline.hpp"

	PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC

	uint FreeRegionList::_unrealistically_long_length = 0;

	void HeapRegionSetBase::fill_in_ext_msg(hrs_ext_msg* msg, const char* message) {
	msg->append("[%s] %s ln: %u cy: "SIZE_FORMAT,
	name(), message, length(), total_capacity_bytes());
	fill_in_ext_msg_extra(msg);
	}

	#ifndef PRODUCT
	void HeapRegionSetBase::verify_region(HeapRegion* hr) {
	assert(hr->containing_set() == this, err_msg("Inconsistent containing set for %u", hr->hrm_index()));
	assert(!hr->is_young(), err_msg("Adding young region %u", hr->hrm_index())); // currently we don't use these sets for young regions
	assert(hr->isHumongous() == regions_humongous(), err_msg("Wrong humongous state for region %u and set %s", hr->hrm_index(), name()));
	assert(hr->is_free() == regions_free(), err_msg("Wrong free state for region %u and set %s", hr->hrm_index(), name()));
	assert(!hr->is_free() \|\| hr->is_empty(), err_msg("Free region %u is not empty for set %s", hr->hrm_index(), name()));
	assert(!hr->is_empty() \|\| hr->is_free(), err_msg("Empty region %u is not free for set %s", hr->hrm_index(), name()));
	assert(hr->rem_set()->verify_ready_for_par_iteration(), err_msg("Wrong iteration state %u", hr->hrm_index()));
	}
	#endif

	void HeapRegionSetBase::verify() {
	// It's important that we also observe the MT safety protocol even
	// for the verification calls. If we do verification without the
	// appropriate locks and the set changes underneath our feet
	// verification might fail and send us on a wild goose chase.
	check_mt_safety();

	guarantee(( is_empty() && length() == 0 && total_capacity_bytes() == 0) \|\|
	(!is_empty() && length() >= 0 && total_capacity_bytes() >= 0),
	hrs_ext_msg(this, "invariant"));
	}

	void HeapRegionSetBase::verify_start() {
	// See comment in verify() about MT safety and verification.
	check_mt_safety();
	assert(!_verify_in_progress,
	hrs_ext_msg(this, "verification should not be in progress"));

	// Do the basic verification first before we do the checks over the regions.
	HeapRegionSetBase::verify();

	_verify_in_progress = true;
	}

	void HeapRegionSetBase::verify_end() {
	// See comment in verify() about MT safety and verification.
	check_mt_safety();
	assert(_verify_in_progress,
	hrs_ext_msg(this, "verification should be in progress"));

	_verify_in_progress = false;
	}

	void HeapRegionSetBase::print_on(outputStream* out, bool print_contents) {
	out->cr();
	out->print_cr("Set: %s ("PTR_FORMAT")", name(), this);
	out->print_cr(" Region Assumptions");
	out->print_cr(" humongous : %s", BOOL_TO_STR(regions_humongous()));
	out->print_cr(" free : %s", BOOL_TO_STR(regions_free()));
	out->print_cr(" Attributes");
	out->print_cr(" length : %14u", length());
	out->print_cr(" total capacity : "SIZE_FORMAT_W(14)" bytes",
	total_capacity_bytes());
	}

	HeapRegionSetBase::HeapRegionSetBase(const char* name, bool humongous, bool free, HRSMtSafeChecker* mt_safety_checker)
	: _name(name), _verify_in_progress(false),
	_is_humongous(humongous), _is_free(free), _mt_safety_checker(mt_safety_checker),
	_count()
	{ }

	void FreeRegionList::set_unrealistically_long_length(uint len) {
	guarantee(_unrealistically_long_length == 0, "should only be set once");
	_unrealistically_long_length = len;
	}

	void FreeRegionList::fill_in_ext_msg_extra(hrs_ext_msg* msg) {
	msg->append(" hd: "PTR_FORMAT" tl: "PTR_FORMAT, _head, _tail);
	}

	void FreeRegionList::remove_all() {
	check_mt_safety();
	verify_optional();

	HeapRegion* curr = _head;
	while (curr != NULL) {
	verify_region(curr);

	HeapRegion* next = curr->next();
	curr->set_next(NULL);
	curr->set_prev(NULL);
	curr->set_containing_set(NULL);
	curr = next;
	}
	clear();

	verify_optional();
	}

	void FreeRegionList::add_ordered(FreeRegionList* from_list) {
	check_mt_safety();
	from_list->check_mt_safety();

	verify_optional();
	from_list->verify_optional();

	if (from_list->is_empty()) {
	return;
	}

	#ifdef ASSERT
	FreeRegionListIterator iter(from_list);
	while (iter.more_available()) {
	HeapRegion* hr = iter.get_next();
	// In set_containing_set() we check that we either set the value
	// from NULL to non-NULL or vice versa to catch bugs. So, we have
	// to NULL it first before setting it to the value.
	hr->set_containing_set(NULL);
	hr->set_containing_set(this);
	}
	#endif // ASSERT

	if (is_empty()) {
	assert(length() == 0 && _tail == NULL, hrs_ext_msg(this, "invariant"));
	_head = from_list->_head;
	_tail = from_list->_tail;
	} else {
	HeapRegion* curr_to = _head;
	HeapRegion* curr_from = from_list->_head;

	while (curr_from != NULL) {
	while (curr_to != NULL && curr_to->hrm_index() < curr_from->hrm_index()) {
	curr_to = curr_to->next();
	}

	if (curr_to == NULL) {
	// The rest of the from list should be added as tail
	_tail->set_next(curr_from);
	curr_from->set_prev(_tail);
	curr_from = NULL;
	} else {
	HeapRegion* next_from = curr_from->next();

	curr_from->set_next(curr_to);
	curr_from->set_prev(curr_to->prev());
	if (curr_to->prev() == NULL) {
	_head = curr_from;
	} else {
	curr_to->prev()->set_next(curr_from);
	}
	curr_to->set_prev(curr_from);

	curr_from = next_from;
	}
	}

	if (_tail->hrm_index() < from_list->_tail->hrm_index()) {
	_tail = from_list->_tail;
	}
	}

	_count.increment(from_list->length(), from_list->total_capacity_bytes());
	from_list->clear();

	verify_optional();
	from_list->verify_optional();
	}

	void FreeRegionList::remove_starting_at(HeapRegion* first, uint num_regions) {
	check_mt_safety();
	assert(num_regions >= 1, hrs_ext_msg(this, "pre-condition"));
	assert(!is_empty(), hrs_ext_msg(this, "pre-condition"));

	verify_optional();
	DEBUG_ONLY(uint old_length = length();)

	HeapRegion* curr = first;
	uint count = 0;
	while (count < num_regions) {
	verify_region(curr);
	HeapRegion* next = curr->next();
	HeapRegion* prev = curr->prev();

	assert(count < num_regions,
	hrs_err_msg("[%s] should not come across more regions "
	"pending for removal than num_regions: %u",
	name(), num_regions));

	if (prev == NULL) {
	assert(_head == curr, hrs_ext_msg(this, "invariant"));
	_head = next;
	} else {
	assert(_head != curr, hrs_ext_msg(this, "invariant"));
	prev->set_next(next);
	}
	if (next == NULL) {
	assert(_tail == curr, hrs_ext_msg(this, "invariant"));
	_tail = prev;
	} else {
	assert(_tail != curr, hrs_ext_msg(this, "invariant"));
	next->set_prev(prev);
	}
	if (_last = curr) {
	_last = NULL;
	}

	curr->set_next(NULL);
	curr->set_prev(NULL);
	remove(curr);

	count++;
	curr = next;
	}

	assert(count == num_regions,
	hrs_err_msg("[%s] count: %u should be == num_regions: %u",
	name(), count, num_regions));
	assert(length() + num_regions == old_length,
	hrs_err_msg("[%s] new length should be consistent "
	"new length: %u old length: %u num_regions: %u",
	name(), length(), old_length, num_regions));

	verify_optional();
	}

	void FreeRegionList::verify() {
	// See comment in HeapRegionSetBase::verify() about MT safety and
	// verification.
	check_mt_safety();

	// This will also do the basic verification too.
	verify_start();

	verify_list();

	verify_end();
	}

	void FreeRegionList::clear() {
	_count = HeapRegionSetCount();
	_head = NULL;
	_tail = NULL;
	_last = NULL;
	}

	void FreeRegionList::print_on(outputStream* out, bool print_contents) {
	HeapRegionSetBase::print_on(out, print_contents);
	out->print_cr(" Linking");
	out->print_cr(" head : "PTR_FORMAT, _head);
	out->print_cr(" tail : "PTR_FORMAT, _tail);

	if (print_contents) {
	out->print_cr(" Contents");
	FreeRegionListIterator iter(this);
	while (iter.more_available()) {
	HeapRegion* hr = iter.get_next();
	hr->print_on(out);
	}
	}

	out->cr();
	}

	void FreeRegionList::verify_list() {
	HeapRegion* curr = _head;
	HeapRegion* prev1 = NULL;
	HeapRegion* prev0 = NULL;
	uint count = 0;
	size_t capacity = 0;
	uint last_index = 0;

	guarantee(_head == NULL \|\| _head->prev() == NULL, "_head should not have a prev");
	while (curr != NULL) {
	verify_region(curr);

	count++;
	guarantee(count < _unrealistically_long_length,
	hrs_err_msg("[%s] the calculated length: %u seems very long, is there maybe a cycle? curr: "PTR_FORMAT" prev0: "PTR_FORMAT" " "prev1: "PTR_FORMAT" length: %u", name(), count, curr, prev0, prev1, length()));

	if (curr->next() != NULL) {
	guarantee(curr->next()->prev() == curr, "Next or prev pointers messed up");
	}
	guarantee(curr->hrm_index() == 0 \|\| curr->hrm_index() > last_index, "List should be sorted");
	last_index = curr->hrm_index();

	capacity += curr->capacity();

	prev1 = prev0;
	prev0 = curr;
	curr = curr->next();
	}

	guarantee(_tail == prev0, err_msg("Expected %s to end with %u but it ended with %u.", name(), _tail->hrm_index(), prev0->hrm_index()));
	guarantee(_tail == NULL \|\| _tail->next() == NULL, "_tail should not have a next");
	guarantee(length() == count, err_msg("%s count mismatch. Expected %u, actual %u.", name(), length(), count));
	guarantee(total_capacity_bytes() == capacity, err_msg("%s capacity mismatch. Expected " SIZE_FORMAT ", actual " SIZE_FORMAT,
	name(), total_capacity_bytes(), capacity));
	}

	// Note on the check_mt_safety() methods below:
	//
	// Verification of the "master" heap region sets / lists that are
	// maintained by G1CollectedHeap is always done during a STW pause and
	// by the VM thread at the start / end of the pause. The standard
	// verification methods all assert check_mt_safety(). This is
	// important as it ensures that verification is done without
	// concurrent updates taking place at the same time. It follows, that,
	// for the "master" heap region sets / lists, the check_mt_safety()
	// method should include the VM thread / STW case.

	void MasterFreeRegionListMtSafeChecker::check() {
	// Master Free List MT safety protocol:
	// (a) If we're at a safepoint, operations on the master free list
	// should be invoked by either the VM thread (which will serialize
	// them) or by the GC workers while holding the
	// FreeList_lock.
	// (b) If we're not at a safepoint, operations on the master free
	// list should be invoked while holding the Heap_lock.

	if (SafepointSynchronize::is_at_safepoint()) {
	guarantee(Thread::current()->is_VM_thread() \|\|
	FreeList_lock->owned_by_self(), "master free list MT safety protocol at a safepoint");
	} else {
	guarantee(Heap_lock->owned_by_self(), "master free list MT safety protocol outside a safepoint");
	}
	}

	void SecondaryFreeRegionListMtSafeChecker::check() {
	// Secondary Free List MT safety protocol:
	// Operations on the secondary free list should always be invoked
	// while holding the SecondaryFreeList_lock.

	guarantee(SecondaryFreeList_lock->owned_by_self(), "secondary free list MT safety protocol");
	}

	void OldRegionSetMtSafeChecker::check() {
	// Master Old Set MT safety protocol:
	// (a) If we're at a safepoint, operations on the master old set
	// should be invoked:
	// - by the VM thread (which will serialize them), or
	// - by the GC workers while holding the FreeList_lock, if we're
	// at a safepoint for an evacuation pause (this lock is taken
	// anyway when an GC alloc region is retired so that a new one
	// is allocated from the free list), or
	// - by the GC workers while holding the OldSets_lock, if we're at a
	// safepoint for a cleanup pause.
	// (b) If we're not at a safepoint, operations on the master old set
	// should be invoked while holding the Heap_lock.

	if (SafepointSynchronize::is_at_safepoint()) {
	guarantee(Thread::current()->is_VM_thread()
	\|\| FreeList_lock->owned_by_self() \|\| OldSets_lock->owned_by_self(),
	"master old set MT safety protocol at a safepoint");
	} else {
	guarantee(Heap_lock->owned_by_self(), "master old set MT safety protocol outside a safepoint");
	}
	}

	void HumongousRegionSetMtSafeChecker::check() {
	// Humongous Set MT safety protocol:
	// (a) If we're at a safepoint, operations on the master humongous
	// set should be invoked by either the VM thread (which will
	// serialize them) or by the GC workers while holding the
	// OldSets_lock.
	// (b) If we're not at a safepoint, operations on the master
	// humongous set should be invoked while holding the Heap_lock.

	if (SafepointSynchronize::is_at_safepoint()) {
	guarantee(Thread::current()->is_VM_thread() \|\|
	OldSets_lock->owned_by_self(),
	"master humongous set MT safety protocol at a safepoint");
	} else {
	guarantee(Heap_lock->owned_by_self(),
	"master humongous set MT safety protocol outside a safepoint");
	}
	}

	void FreeRegionList_test() {
	FreeRegionList l("test");

	const uint num_regions_in_test = 5;
	// Create a fake heap. It does not need to be valid, as the HeapRegion constructor
	// does not access it.
	MemRegion heap(NULL, num_regions_in_test * HeapRegion::GrainWords);
	// Allocate a fake BOT because the HeapRegion constructor initializes
	// the BOT.
	size_t bot_size = G1BlockOffsetSharedArray::compute_size(heap.word_size());
	HeapWord* bot_data = NEW_C_HEAP_ARRAY(HeapWord, bot_size, mtGC);
	ReservedSpace bot_rs(G1BlockOffsetSharedArray::compute_size(heap.word_size()));
	G1RegionToSpaceMapper* bot_storage =
	G1RegionToSpaceMapper::create_mapper(bot_rs,
	bot_rs.size(),
	os::vm_page_size(),
	HeapRegion::GrainBytes,
	G1BlockOffsetSharedArray::N_bytes,
	mtGC);
	G1BlockOffsetSharedArray oa(heap, bot_storage);
	bot_storage->commit_regions(0, num_regions_in_test);
	HeapRegion hr0(0, &oa, heap);
	HeapRegion hr1(1, &oa, heap);
	HeapRegion hr2(2, &oa, heap);
	HeapRegion hr3(3, &oa, heap);
	HeapRegion hr4(4, &oa, heap);
	l.add_ordered(&hr1);
	l.add_ordered(&hr0);
	l.add_ordered(&hr3);
	l.add_ordered(&hr4);
	l.add_ordered(&hr2);
	assert(l.length() == num_regions_in_test, "wrong length");
	l.verify_list();

	bot_storage->uncommit_regions(0, num_regions_in_test);
	delete bot_storage;
	FREE_C_HEAP_ARRAY(HeapWord, bot_data, mtGC);
	}