/*

 * Copyright (c) 2007, 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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 */

#include "precompiled.hpp"

#include "gc/cms/cmsCardTable.hpp"

#include "gc/cms/cmsHeap.hpp"

#include "gc/shared/cardTableBarrierSet.hpp"

#include "gc/shared/cardTableRS.hpp"

#include "gc/shared/collectedHeap.hpp"

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

#include "memory/allocation.inline.hpp"

#include "memory/virtualspace.hpp"

#include "oops/oop.inline.hpp"

#include "runtime/java.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/orderAccess.hpp"

#include "runtime/vmThread.hpp"

CMSCardTable::CMSCardTable(MemRegion whole_heap) :

    CardTableRS(whole_heap, CMSPrecleaningEnabled /* scanned_concurrently */) {

}

// Returns the number of chunks necessary to cover "mr".

size_t CMSCardTable::chunks_to_cover(MemRegion mr) {

  return (size_t)(addr_to_chunk_index(mr.last()) -

                  addr_to_chunk_index(mr.start()) + 1);

}

// Returns the index of the chunk in a stride which

// covers the given address.

uintptr_t CMSCardTable::addr_to_chunk_index(const void* addr) {

  uintptr_t card = (uintptr_t) byte_for(addr);

  return card / ParGCCardsPerStrideChunk;

}

void CMSCardTable::

non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,

                                     OopsInGenClosure* cl,

                                     CardTableRS* ct,

                                     uint n_threads) {

  assert(n_threads > 0, "expected n_threads > 0");

  assert(n_threads <= ParallelGCThreads,

         "n_threads: %u > ParallelGCThreads: %u", n_threads, ParallelGCThreads);

  // Make sure the LNC array is valid for the space.

  get_LNC_array_for_space(sp, lowest_non_clean,

                          lowest_non_clean_base_chunk_index,

                          lowest_non_clean_chunk_size);

  uint n_strides = n_threads * ParGCStridesPerThread;

  SequentialSubTasksDone* pst = sp->par_seq_tasks();

  // Sets the condition for completion of the subtask (how many threads

  // need to finish in order to be done).

  pst->set_n_threads(n_threads);

  pst->set_n_tasks(n_strides);

  uint stride = 0;

  while (pst->try_claim_task(/* reference */ stride)) {

    process_stride(sp, mr, stride, n_strides,

                   cl, ct,

                   lowest_non_clean,

                   lowest_non_clean_base_chunk_index,

                   lowest_non_clean_chunk_size);

  }

  if (pst->all_tasks_completed()) {

    // Clear lowest_non_clean array for next time.

    intptr_t first_chunk_index = addr_to_chunk_index(mr.start());

    uintptr_t last_chunk_index  = addr_to_chunk_index(mr.last());

    for (uintptr_t ch = first_chunk_index; ch <= last_chunk_index; ch++) {

      intptr_t ind = ch - lowest_non_clean_base_chunk_index;

      assert(0 <= ind && ind < (intptr_t)lowest_non_clean_chunk_size,

             "Bounds error");

      lowest_non_clean[ind] = NULL;

    }

  }

}

void

CMSCardTable::

process_stride(Space* sp,

               MemRegion used,

               jint stride, int n_strides,

               OopsInGenClosure* cl,

               CardTableRS* ct,

               uintptr_t lowest_non_clean_base_chunk_index,

               size_t    lowest_non_clean_chunk_size) {

  // We go from higher to lower addresses here; it wouldn't help that much

  // because of the strided parallelism pattern used here.

  // Find the first card address of the first chunk in the stride that is

  // at least "bottom" of the used region.

  uintptr_t start_chunk = addr_to_chunk_index(used.start());

  uintptr_t start_chunk_stride_num = start_chunk % n_strides;

  if ((uintptr_t)stride >= start_chunk_stride_num) {

  } else {

    // Go ahead to the next chunk group boundary, then to the requested stride.

  }

  while (chunk_card_start < end_card) {

    // Even though we go from lower to higher addresses below, the

    // strided parallelism can interleave the actual processing of the

    // dirty pages in various ways. For a specific chunk within this

    // stride, we take care to avoid double scanning or missing a card

    // by suitably initializing the "min_done" field in process_chunk_boundaries()

    // below, together with the dirty region extension accomplished in

    // DirtyCardToOopClosure::do_MemRegion().

    // Invariant: chunk_mr should be fully contained within the "used" region.

    assert(chunk_mr.word_size() > 0, "[chunk_card_start > used_end)");

    assert(used.contains(chunk_mr), "chunk_mr should be subset of used");

    // This function is used by the parallel card table iteration.

    const bool parallel = true;

    DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(),

                                                     cl->gen_boundary(),

                                                     parallel);

    ClearNoncleanCardWrapper clear_cl(dcto_cl, ct, parallel);

    // Process the chunk.

    process_chunk_boundaries(sp,

                             dcto_cl,

                             chunk_mr,

                             used,

                             lowest_non_clean,

                             lowest_non_clean_base_chunk_index,

                             lowest_non_clean_chunk_size);

    // We want the LNC array updates above in process_chunk_boundaries

    // to be visible before any of the card table value changes as a

    // result of the dirty card iteration below.

    OrderAccess::storestore();

    // We want to clear the cards: clear_cl here does the work of finding

    // contiguous dirty ranges of cards to process and clear.

    clear_cl.do_MemRegion(chunk_mr);

    // Find the next chunk of the stride.

    chunk_card_start += ParGCCardsPerStrideChunk * n_strides;

  }

}

void

CMSCardTable::

process_chunk_boundaries(Space* sp,

                         DirtyCardToOopClosure* dcto_cl,

                         MemRegion chunk_mr,

                         MemRegion used,

                         uintptr_t lowest_non_clean_base_chunk_index,

                         size_t    lowest_non_clean_chunk_size)

{

  // We must worry about non-array objects that cross chunk boundaries,

  // because such objects are both precisely and imprecisely marked:

  // .. if the head of such an object is dirty, the entire object

  //    needs to be scanned, under the interpretation that this

  //    was an imprecise mark

  // .. if the head of such an object is not dirty, we can assume

  //    precise marking and it's efficient to scan just the dirty

  //    cards.

  // In either case, each scanned reference must be scanned precisely

  // once so as to avoid cloning of a young referent. For efficiency,

  // our closures depend on this property and do not protect against

  // double scans.

  uintptr_t start_chunk_index = addr_to_chunk_index(chunk_mr.start());

  assert(start_chunk_index >= lowest_non_clean_base_chunk_index, "Bounds error.");

  uintptr_t cur_chunk_index   = start_chunk_index - lowest_non_clean_base_chunk_index;

  // First, set "our" lowest_non_clean entry, which would be

  // used by the thread scanning an adjoining left chunk with

  // a non-array object straddling the mutual boundary.

  // Find the object that spans our boundary, if one exists.

  // first_block is the block possibly straddling our left boundary.

  HeapWord* first_block = sp->block_start(chunk_mr.start());

  assert((chunk_mr.start() != used.start()) || (first_block == chunk_mr.start()),

         "First chunk should always have a co-initial block");

  // Does the block straddle the chunk's left boundary, and is it

  // a non-array object?

  if (first_block < chunk_mr.start()        // first block straddles left bdry

      && sp->block_is_obj(first_block)      // first block is an object

      && !(oop(first_block)->is_objArray()  // first block is not an array (arrays are precisely dirtied)

           || oop(first_block)->is_typeArray())) {

    // Find our least non-clean card, so that a left neighbor

    // does not scan an object straddling the mutual boundary

    // too far to the right, and attempt to scan a portion of

    // that object twice.

        byte_for(first_block + sp->block_size(first_block) - 1);

    // Note that this does not need to go beyond our last card

    // if our first object completely straddles this chunk.

         cur <= last_card_to_check; cur++) {

      if (card_will_be_scanned(val)) {

      } else {

        assert(!card_may_have_been_dirty(val), "Error");

      }

    }

    if (first_dirty_card != NULL) {

      assert(cur_chunk_index < lowest_non_clean_chunk_size, "Bounds error.");

      assert(lowest_non_clean[cur_chunk_index] == NULL,

             "Write exactly once : value should be stable hereafter for this round");

      lowest_non_clean[cur_chunk_index] = first_dirty_card;

    }

  } else {

    // In this case we can help our neighbor by just asking them

    // to stop at our first card (even though it may not be dirty).

    assert(lowest_non_clean[cur_chunk_index] == NULL, "Write once : value should be stable hereafter");

    lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk;

  }

  // Next, set our own max_to_do, which will strictly/exclusively bound

  // the highest address that we will scan past the right end of our chunk.

  HeapWord* max_to_do = NULL;

  if (chunk_mr.end() < used.end()) {

    // This is not the last chunk in the used region.

    // What is our last block? We check the first block of

    // the next (right) chunk rather than strictly check our last block

    // because it's potentially more efficient to do so.

    HeapWord* const last_block = sp->block_start(chunk_mr.end());

    assert(last_block <= chunk_mr.end(), "In case this property changes.");

    if ((last_block == chunk_mr.end())     // our last block does not straddle boundary

        || !sp->block_is_obj(last_block)   // last_block isn't an object

        || oop(last_block)->is_objArray()  // last_block is an array (precisely marked)

        || oop(last_block)->is_typeArray()) {

      max_to_do = chunk_mr.end();

    } else {

      assert(last_block < chunk_mr.end(), "Tautology");

      // It is a non-array object that straddles the right boundary of this chunk.

      // last_obj_card is the card corresponding to the start of the last object

      // in the chunk.  Note that the last object may not start in

      // the chunk.

      if (!card_will_be_scanned(val)) {

        assert(!card_may_have_been_dirty(val), "Error");

        // The card containing the head is not dirty.  Any marks on

        // subsequent cards still in this chunk must have been made

        // precisely; we can cap processing at the end of our chunk.

        max_to_do = chunk_mr.end();

      } else {

        // The last object must be considered dirty, and extends onto the

        // following chunk.  Look for a dirty card in that chunk that will

        // bound our processing.

        const size_t last_block_size = sp->block_size(last_block);

          byte_for(last_block + last_block_size - 1);

        // This search potentially goes a long distance looking

        // for the next card that will be scanned, terminating

        // at the end of the last_block, if no earlier dirty card

        // is found.

        assert(byte_for(chunk_mr.end()) - byte_for(chunk_mr.start()) == ParGCCardsPerStrideChunk,

               "last card of next chunk may be wrong");

             cur <= last_card_of_last_obj; cur++) {

          if (card_will_be_scanned(val)) {

            limit_card = cur; break;

          } else {

            assert(!card_may_have_been_dirty(val), "Error: card can't be skipped");

          }

        }

        if (limit_card != NULL) {

          max_to_do = addr_for(limit_card);

          assert(limit_card != NULL && max_to_do != NULL, "Error");

        } else {

          // The following is a pessimistic value, because it's possible

          // that a dirty card on a subsequent chunk has been cleared by

          // the time we get to look at it; we'll correct for that further below,

          // using the LNC array which records the least non-clean card

          // before cards were cleared in a particular chunk.

          limit_card = last_card_of_last_obj;

          max_to_do = last_block + last_block_size;

          assert(limit_card != NULL && max_to_do != NULL, "Error");

        }

        assert(0 < cur_chunk_index+1 && cur_chunk_index+1 < lowest_non_clean_chunk_size,

               "Bounds error.");

        // It is possible that a dirty card for the last object may have been

        // cleared before we had a chance to examine it. In that case, the value

        // will have been logged in the LNC for that chunk.

        // We need to examine as many chunks to the right as this object

        // covers. However, we need to bound this checking to the largest

        // entry in the LNC array: this is because the heap may expand

        // after the LNC array has been created but before we reach this point,

        // and the last block in our chunk may have been expanded to include

        // the expansion delta (and possibly subsequently allocated from, so

        // it wouldn't be sufficient to check whether that last block was

        // or was not an object at this point).

        uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1)

                                              - lowest_non_clean_base_chunk_index;

        const uintptr_t last_chunk_index    = addr_to_chunk_index(used.last())

                                              - lowest_non_clean_base_chunk_index;

        if (last_chunk_index_to_check > last_chunk_index) {

          assert(last_block + last_block_size > used.end(),

                 "Inconsistency detected: last_block [" PTR_FORMAT "," PTR_FORMAT "]"

                 " does not exceed used.end() = " PTR_FORMAT ","

                 " yet last_chunk_index_to_check " INTPTR_FORMAT

                 " exceeds last_chunk_index " INTPTR_FORMAT,

                 p2i(last_block), p2i(last_block + last_block_size),

                 p2i(used.end()),

                 last_chunk_index_to_check, last_chunk_index);

          assert(sp->used_region().end() > used.end(),

                 "Expansion did not happen: "

                 "[" PTR_FORMAT "," PTR_FORMAT ") -> [" PTR_FORMAT "," PTR_FORMAT ")",

                 p2i(sp->used_region().start()), p2i(sp->used_region().end()),

                 p2i(used.start()), p2i(used.end()));

          last_chunk_index_to_check = last_chunk_index;

        }

        for (uintptr_t lnc_index = cur_chunk_index + 1;

             lnc_index <= last_chunk_index_to_check;

             lnc_index++) {

          if (lnc_card != NULL) {

            // we can stop at the first non-NULL entry we find

            if (lnc_card <= limit_card) {

              limit_card = lnc_card;

              max_to_do = addr_for(limit_card);

              assert(limit_card != NULL && max_to_do != NULL, "Error");

            }

            // In any case, we break now

            break;

          }  // else continue to look for a non-NULL entry if any

        }

        assert(limit_card != NULL && max_to_do != NULL, "Error");

      }

      assert(max_to_do != NULL, "OOPS 1 !");

    }

    assert(max_to_do != NULL, "OOPS 2!");

  } else {

    max_to_do = used.end();

  }

  assert(max_to_do != NULL, "OOPS 3!");

  // Now we can set the closure we're using so it doesn't to beyond

  // max_to_do.

  dcto_cl->set_min_done(max_to_do);

#ifndef PRODUCT

  dcto_cl->set_last_bottom(max_to_do);

#endif

}

void

CMSCardTable::

get_LNC_array_for_space(Space* sp,

                        uintptr_t& lowest_non_clean_base_chunk_index,

                        size_t& lowest_non_clean_chunk_size) {

  int       i        = find_covering_region_containing(sp->bottom());

  MemRegion covered  = _covered[i];

  size_t    n_chunks = chunks_to_cover(covered);

  // Only the first thread to obtain the lock will resize the

  // LNC array for the covered region.  Any later expansion can't affect

  // the used_at_save_marks region.

  // (I observed a bug in which the first thread to execute this would

  // resize, and then it would cause "expand_and_allocate" that would

  // increase the number of chunks in the covered region.  Then a second

  // thread would come and execute this, see that the size didn't match,

  // and free and allocate again.  So the first thread would be using a

  // freed "_lowest_non_clean" array.)

  // Do a dirty read here. If we pass the conditional then take the rare

  // event lock and do the read again in case some other thread had already

  // succeeded and done the resize.

  int cur_collection = CMSHeap::heap()->total_collections();

  // Updated _last_LNC_resizing_collection[i] must not be visible before

  // _lowest_non_clean and friends are visible. Therefore use acquire/release

  // to guarantee this on non TSO architecures.

  if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) {

    MutexLocker x(ParGCRareEvent_lock);

    // This load_acquire is here for clarity only. The MutexLocker already fences.

    if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) {

      if (_lowest_non_clean[i] == NULL ||

          n_chunks != _lowest_non_clean_chunk_size[i]) {

        // Should we delete the old?

        if (_lowest_non_clean[i] != NULL) {

          assert(n_chunks != _lowest_non_clean_chunk_size[i],

                 "logical consequence");

          FREE_C_HEAP_ARRAY(CardPtr, _lowest_non_clean[i]);

          _lowest_non_clean[i] = NULL;

        }

        // Now allocate a new one if necessary.

        if (_lowest_non_clean[i] == NULL) {

          _lowest_non_clean[i]                  = NEW_C_HEAP_ARRAY(CardPtr, n_chunks, mtGC);

          _lowest_non_clean_chunk_size[i]       = n_chunks;

          _lowest_non_clean_base_chunk_index[i] = addr_to_chunk_index(covered.start());

          for (int j = 0; j < (int)n_chunks; j++)

            _lowest_non_clean[i][j] = NULL;

        }

      }

      // Make sure this gets visible only after _lowest_non_clean* was initialized

      OrderAccess::release_store(&_last_LNC_resizing_collection[i], cur_collection);

    }

  }

  // In any case, now do the initialization.

  lowest_non_clean                  = _lowest_non_clean[i];

  lowest_non_clean_base_chunk_index = _lowest_non_clean_base_chunk_index[i];

  lowest_non_clean_chunk_size       = _lowest_non_clean_chunk_size[i];

}

#ifdef ASSERT

void CMSCardTable::verify_used_region_at_save_marks(Space* sp) const {

  MemRegion ur    = sp->used_region();

  MemRegion urasm = sp->used_region_at_save_marks();

  if (!ur.contains(urasm)) {

    log_warning(gc)("CMS+ParNew: Did you forget to call save_marks()? "

                    "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in "

                    "[" PTR_FORMAT ", " PTR_FORMAT ")",

                    p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end()));

    MemRegion ur2 = sp->used_region();

    MemRegion urasm2 = sp->used_region_at_save_marks();

    if (!ur.equals(ur2)) {

      log_warning(gc)("CMS+ParNew: Flickering used_region()!!");

    }

    if (!urasm.equals(urasm2)) {

      log_warning(gc)("CMS+ParNew: Flickering used_region_at_save_marks()!!");

    }

    ShouldNotReachHere();

  }

}

#endif // ASSERT