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 /*

  * Copyright (c) 2007, 2011, 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 "memory/allocation.inline.hpp"

 #include "memory/cardTableModRefBS.hpp"

 #include "memory/cardTableRS.hpp"

 #include "memory/sharedHeap.hpp"

 #include "memory/space.inline.hpp"

 #include "memory/universe.hpp"

 #include "oops/oop.inline.hpp"

 #include "runtime/java.hpp"

 #include "runtime/mutexLocker.hpp"

 #include "runtime/virtualspace.hpp"

 #include "runtime/vmThread.hpp"

 void CardTableModRefBS::non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,

                                                              OopsInGenClosure* cl,

                                                              CardTableRS* ct,

                                                              int n_threads) {

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

   assert((n_threads == 1 && ParallelGCThreads == 0) ||

          n_threads <= (int)ParallelGCThreads,

          "# worker threads != # requested!");

   assert(!Thread::current()->is_VM_thread() || (n_threads == 1), "There is only 1 VM thread");

   assert(UseDynamicNumberOfGCThreads ||

          !FLAG_IS_DEFAULT(ParallelGCThreads) ||

          n_threads == (int)ParallelGCThreads,

          "# worker threads != # requested!");

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

   jbyte**   lowest_non_clean;

   uintptr_t lowest_non_clean_base_chunk_index;

   size_t    lowest_non_clean_chunk_size;

   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->is_task_claimed(/* 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

 CardTableModRefBS::

 process_stride(Space* sp,

                MemRegion used,

                jint stride, int n_strides,

                OopsInGenClosure* cl,

                CardTableRS* ct,

                jbyte** lowest_non_clean,

                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.

   jbyte*    start_card  = byte_for(used.start());

   jbyte*    end_card    = byte_after(used.last());

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

   uintptr_t start_chunk_stride_num = start_chunk % n_strides;

   jbyte* chunk_card_start;

   if ((uintptr_t)stride >= start_chunk_stride_num) {

     chunk_card_start = (jbyte*)(start_card +

                                 (stride - start_chunk_stride_num) *

                                 ParGCCardsPerStrideChunk);

   } else {

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

     chunk_card_start = (jbyte*)(start_card +

                                 (n_strides - start_chunk_stride_num + stride) *

                                 ParGCCardsPerStrideChunk);

   }

   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().

     jbyte*    chunk_card_end = chunk_card_start + ParGCCardsPerStrideChunk;

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

     MemRegion chunk_mr       = MemRegion(addr_for(chunk_card_start),

                                          chunk_card_end >= end_card ?

                                            used.end() : addr_for(chunk_card_end));

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

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

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

                                                      cl->gen_boundary());

     ClearNoncleanCardWrapper clear_cl(dcto_cl, ct);

     // 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 do not call the non_clean_card_iterate_serial() version because

     // 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;

   }

 }

 // If you want a talkative process_chunk_boundaries,

 // then #define NOISY(x) x

 #ifdef NOISY

 #error "Encountered a global preprocessor flag, NOISY, which might clash with local definition to follow"

 #else

 #define NOISY(x)

 #endif

 void

 CardTableModRefBS::

 process_chunk_boundaries(Space* sp,

                          DirtyCardToOopClosure* dcto_cl,

                          MemRegion chunk_mr,

                          MemRegion used,

                          jbyte** lowest_non_clean,

                          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 cur_chunk_index = addr_to_chunk_index(chunk_mr.start());

   cur_chunk_index           = cur_chunk_index - lowest_non_clean_base_chunk_index;

   NOISY(tty->print_cr("===========================================================================");)

   NOISY(tty->print_cr(" process_chunk_boundary: Called with [" PTR_FORMAT "," PTR_FORMAT ")",

                       chunk_mr.start(), chunk_mr.end());)

   // 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 neighbour

     // does not scan an object straddling the mutual boundary

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

     // that object twice.

     jbyte* first_dirty_card = NULL;

     jbyte* last_card_of_first_obj =

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

     jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());

     jbyte* last_card_of_cur_chunk = byte_for(chunk_mr.last());

     jbyte* last_card_to_check =

       (jbyte*) MIN2((intptr_t) last_card_of_cur_chunk,

                     (intptr_t) last_card_of_first_obj);

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

     // if our first object completely straddles this chunk.

     for (jbyte* cur = first_card_of_cur_chunk;

          cur <= last_card_to_check; cur++) {

       jbyte val = *cur;

       if (card_will_be_scanned(val)) {

         first_dirty_card = cur; break;

       } else {

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

       }

     }

     if (first_dirty_card != NULL) {

       NOISY(tty->print_cr(" LNC: Found a dirty card at " PTR_FORMAT " in current chunk",

                     first_dirty_card);)

       assert(0 <= cur_chunk_index && 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;

     } NOISY(else {

       tty->print_cr(" LNC: Found no dirty card in current chunk; leaving LNC entry NULL");

       // In the future, we could have this thread look for a non-NULL value to copy from its

       // right neighbour (up to the end of the first object).

       if (last_card_of_cur_chunk < last_card_of_first_obj) {

         tty->print_cr(" LNC: BEWARE!!! first obj straddles past right end of chunk:\n"

                       "   might be efficient to get value from right neighbour?");

       }

     })

   } else {

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

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

     NOISY(tty->print_cr(" LNC: first block is not a non-array object; setting LNC to first card of current chunk");)

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

     jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());

     lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk;

   }

   NOISY(tty->print_cr(" process_chunk_boundary: lowest_non_clean[" INTPTR_FORMAT "] = " PTR_FORMAT

                 "   which corresponds to the heap address " PTR_FORMAT,

                 cur_chunk_index, lowest_non_clean[cur_chunk_index],

                 (lowest_non_clean[cur_chunk_index] != NULL)

                 ? addr_for(lowest_non_clean[cur_chunk_index])

                 : NULL);)

   NOISY(tty->print_cr("---------------------------------------------------------------------------");)

   // 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();

       NOISY(tty->print_cr(" process_chunk_boundary: Last block on this card is not a non-array object;\n"

                          "   max_to_do left at " PTR_FORMAT, max_to_do);)

     } 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.

       jbyte* const last_obj_card = byte_for(last_block);

       const jbyte val = *last_obj_card;

       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();

         NOISY(tty->print_cr(" process_chunk_boundary: Head of last object on this card is not dirty;\n"

                             "   max_to_do left at " PTR_FORMAT,

                             max_to_do);)

       } 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.

         jbyte* limit_card = NULL;

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

         jbyte* const last_card_of_last_obj =

           byte_for(last_block + last_block_size - 1);

         jbyte* const first_card_of_next_chunk = byte_for(chunk_mr.end());

         // 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");

         for (jbyte* cur = first_card_of_next_chunk;

              cur <= last_card_of_last_obj; cur++) {

           const jbyte val = *cur;

           if (card_will_be_scanned(val)) {

             NOISY(tty->print_cr(" Found a non-clean card " PTR_FORMAT " with value 0x%x",

                                 cur, (int)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");

           NOISY(tty->print_cr(" process_chunk_boundary: Found a dirty card at " PTR_FORMAT

                         "   max_to_do set at " PTR_FORMAT " which is before end of last block in chunk: "

                         PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,

                         limit_card, max_to_do, last_block, last_block_size, (last_block+last_block_size));)

         } 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");

           NOISY(tty->print_cr(" process_chunk_boundary: Found no dirty card before end of last block in chunk\n"

                               "   Setting limit_card to " PTR_FORMAT

                               " and max_to_do " PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,

                               limit_card, last_block, last_block_size, max_to_do);)

         }

         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(),

                  err_msg("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,

                          last_chunk_index_to_check, last_chunk_index));

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

                  err_msg("Expansion did not happen: "

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

                          sp->used_region().start(), sp->used_region().end(), used.start(), used.end()));

           NOISY(tty->print_cr(" process_chunk_boundary: heap expanded; explicitly bounding last_chunk");)

           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++) {

           jbyte* lnc_card = lowest_non_clean[lnc_index];

           if (lnc_card != NULL) {

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

             if (lnc_card <= limit_card) {

               NOISY(tty->print_cr(" process_chunk_boundary: LNC card " PTR_FORMAT " is lower than limit_card " PTR_FORMAT,

                                   "   max_to_do will be lowered to " PTR_FORMAT " from " PTR_FORMAT,

                                   lnc_card, limit_card, addr_for(lnc_card), max_to_do);)

               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();

     NOISY(tty->print_cr(" process_chunk_boundary: Last chunk of this space;\n"

                   "   max_to_do left at " PTR_FORMAT,

                   max_to_do);)

   }

   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

   NOISY(tty->print_cr("===========================================================================\n");)

 }

 #undef NOISY

 void

 CardTableModRefBS::

 get_LNC_array_for_space(Space* sp,

                         jbyte**& lowest_non_clean,

                         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 = Universe::heap()->total_collections();

   if (_last_LNC_resizing_collection[i] != cur_collection) {

     MutexLocker x(ParGCRareEvent_lock);

     if (_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);

           _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;

         }

       }

       _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];

 }