/*

 * Copyright (c) 2000, 2018, 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

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 * questions.

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 */

#include "precompiled.hpp"

#include "gc/shared/cardTableBarrierSetAssembler.hpp"

#include "gc/shared/cardTableBarrierSet.inline.hpp"

#include "gc/shared/collectedHeap.hpp"

#include "gc/shared/genCollectedHeap.hpp"

#include "gc/shared/space.inline.hpp"

#include "logging/log.hpp"

#include "memory/virtualspace.hpp"

#include "oops/oop.inline.hpp"

#include "runtime/thread.hpp"

#include "services/memTracker.hpp"

#include "utilities/align.hpp"

#include "utilities/macros.hpp"

// This kind of "BarrierSet" allows a "CollectedHeap" to detect and

// enumerate ref fields that have been modified (since the last

// enumeration.)

CardTableBarrierSet::CardTableBarrierSet(BarrierSetAssembler* barrier_set_assembler,

                                         CardTable* card_table,

                                         const BarrierSet::FakeRtti& fake_rtti) :

  ModRefBarrierSet(barrier_set_assembler,

                   fake_rtti.add_tag(BarrierSet::CardTableBarrierSet)),

  _defer_initial_card_mark(false),

  _card_table(card_table)

{}

CardTableBarrierSet::CardTableBarrierSet(CardTable* card_table) :

  ModRefBarrierSet(make_barrier_set_assembler<CardTableBarrierSetAssembler>(),

                   BarrierSet::FakeRtti(BarrierSet::CardTableBarrierSet)),

  _defer_initial_card_mark(false),

  _card_table(card_table)

{}

void CardTableBarrierSet::initialize() {

  initialize_deferred_card_mark_barriers();

}

CardTableBarrierSet::~CardTableBarrierSet() {

  delete _card_table;

}

void CardTableBarrierSet::write_ref_array_work(MemRegion mr) {

  _card_table->dirty_MemRegion(mr);

}

void CardTableBarrierSet::invalidate(MemRegion mr) {

  _card_table->invalidate(mr);

}

void CardTableBarrierSet::print_on(outputStream* st) const {

  _card_table->print_on(st);

}

// Helper for ReduceInitialCardMarks. For performance,

// compiled code may elide card-marks for initializing stores

// to a newly allocated object along the fast-path. We

// compensate for such elided card-marks as follows:

// (a) Generational, non-concurrent collectors, such as

//     GenCollectedHeap(ParNew,DefNew,Tenured) and

//     ParallelScavengeHeap(ParallelGC, ParallelOldGC)

//     need the card-mark if and only if the region is

//     in the old gen, and do not care if the card-mark

//     succeeds or precedes the initializing stores themselves,

//     so long as the card-mark is completed before the next

//     scavenge. For all these cases, we can do a card mark

//     at the point at which we do a slow path allocation

//     in the old gen, i.e. in this call.

// (b) GenCollectedHeap(ConcurrentMarkSweepGeneration) requires

//     in addition that the card-mark for an old gen allocated

//     object strictly follow any associated initializing stores.

//     In these cases, the memRegion remembered below is

//     used to card-mark the entire region either just before the next

//     slow-path allocation by this thread or just before the next scavenge or

//     CMS-associated safepoint, whichever of these events happens first.

//     (The implicit assumption is that the object has been fully

//     initialized by this point, a fact that we assert when doing the

//     card-mark.)

// (c) G1CollectedHeap(G1) uses two kinds of write barriers. When a

//     G1 concurrent marking is in progress an SATB (pre-write-)barrier

//     is used to remember the pre-value of any store. Initializing

//     stores will not need this barrier, so we need not worry about

//     compensating for the missing pre-barrier here. Turning now

//     to the post-barrier, we note that G1 needs a RS update barrier

//     which simply enqueues a (sequence of) dirty cards which may

//     optionally be refined by the concurrent update threads. Note

//     that this barrier need only be applied to a non-young write,

//     but, like in CMS, because of the presence of concurrent refinement

//     (much like CMS' precleaning), must strictly follow the oop-store.

//     Thus, using the same protocol for maintaining the intended

//     invariants turns out, serendepitously, to be the same for both

//     G1 and CMS.

//

// For any future collector, this code should be reexamined with

// that specific collector in mind, and the documentation above suitably

// extended and updated.

void CardTableBarrierSet::on_slowpath_allocation_exit(JavaThread* thread, oop new_obj) {

#if defined(COMPILER2) || INCLUDE_JVMCI

  if (!ReduceInitialCardMarks) {

    return;

  }

  // If a previous card-mark was deferred, flush it now.

  flush_deferred_card_mark_barrier(thread);

  if (new_obj->is_typeArray() || _card_table->is_in_young(new_obj)) {

    // Arrays of non-references don't need a post-barrier.

    // The deferred_card_mark region should be empty

    // following the flush above.

    assert(thread->deferred_card_mark().is_empty(), "Error");

  } else {

    MemRegion mr((HeapWord*)new_obj, new_obj->size());

    assert(!mr.is_empty(), "Error");

    if (_defer_initial_card_mark) {

      // Defer the card mark

      thread->set_deferred_card_mark(mr);

    } else {

      // Do the card mark

      invalidate(mr);

    }

  }

#endif // COMPILER2 || JVMCI

}

void CardTableBarrierSet::initialize_deferred_card_mark_barriers() {

  // Used for ReduceInitialCardMarks (when COMPILER2 or JVMCI is used);

  // otherwise remains unused.

#if defined(COMPILER2) || INCLUDE_JVMCI

  _defer_initial_card_mark = is_server_compilation_mode_vm() && ReduceInitialCardMarks && can_elide_tlab_store_barriers()

                             && (DeferInitialCardMark || card_mark_must_follow_store());

#else

  assert(_defer_initial_card_mark == false, "Who would set it?");

#endif

}

void CardTableBarrierSet::flush_deferred_card_mark_barrier(JavaThread* thread) {

#if defined(COMPILER2) || INCLUDE_JVMCI

  MemRegion deferred = thread->deferred_card_mark();

  if (!deferred.is_empty()) {

    assert(_defer_initial_card_mark, "Otherwise should be empty");

    {

      // Verify that the storage points to a parsable object in heap

      DEBUG_ONLY(oop old_obj = oop(deferred.start());)

      assert(!_card_table->is_in_young(old_obj),

             "Else should have been filtered in on_slowpath_allocation_exit()");

      assert(oopDesc::is_oop(old_obj, true), "Not an oop");

      assert(deferred.word_size() == (size_t)(old_obj->size()),

             "Mismatch: multiple objects?");

    }

    write_region(deferred);

    // "Clear" the deferred_card_mark field

    thread->set_deferred_card_mark(MemRegion());

  }

  assert(thread->deferred_card_mark().is_empty(), "invariant");

#else

  assert(!_defer_initial_card_mark, "Should be false");

  assert(thread->deferred_card_mark().is_empty(), "Should be empty");

#endif

}

void CardTableBarrierSet::on_thread_detach(JavaThread* thread) {

  // The deferred store barriers must all have been flushed to the

  // card-table (or other remembered set structure) before GC starts

  // processing the card-table (or other remembered set).

  flush_deferred_card_mark_barrier(thread);

}

bool CardTableBarrierSet::card_mark_must_follow_store() const {

 return _card_table->scanned_concurrently();

}