1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/gc_implementation/parNew/parCardTableModRefBS.cpp Wed Apr 27 01:25:04 2016 +0800
1.3 @@ -0,0 +1,483 @@
1.4 +/*
1.5 + * Copyright (c) 2007, 2014, Oracle and/or its affiliates. All rights reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation.
1.11 + *
1.12 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.13 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.14 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.15 + * version 2 for more details (a copy is included in the LICENSE file that
1.16 + * accompanied this code).
1.17 + *
1.18 + * You should have received a copy of the GNU General Public License version
1.19 + * 2 along with this work; if not, write to the Free Software Foundation,
1.20 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.21 + *
1.22 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.23 + * or visit www.oracle.com if you need additional information or have any
1.24 + * questions.
1.25 + *
1.26 + */
1.27 +
1.28 +#include "precompiled.hpp"
1.29 +#include "memory/allocation.inline.hpp"
1.30 +#include "memory/cardTableModRefBS.hpp"
1.31 +#include "memory/cardTableRS.hpp"
1.32 +#include "memory/sharedHeap.hpp"
1.33 +#include "memory/space.inline.hpp"
1.34 +#include "memory/universe.hpp"
1.35 +#include "oops/oop.inline.hpp"
1.36 +#include "runtime/java.hpp"
1.37 +#include "runtime/mutexLocker.hpp"
1.38 +#include "runtime/virtualspace.hpp"
1.39 +#include "runtime/vmThread.hpp"
1.40 +
1.41 +PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
1.42 +
1.43 +void CardTableModRefBS::non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,
1.44 + OopsInGenClosure* cl,
1.45 + CardTableRS* ct,
1.46 + int n_threads) {
1.47 + assert(n_threads > 0, "Error: expected n_threads > 0");
1.48 + assert((n_threads == 1 && ParallelGCThreads == 0) ||
1.49 + n_threads <= (int)ParallelGCThreads,
1.50 + "# worker threads != # requested!");
1.51 + assert(!Thread::current()->is_VM_thread() || (n_threads == 1), "There is only 1 VM thread");
1.52 + assert(UseDynamicNumberOfGCThreads ||
1.53 + !FLAG_IS_DEFAULT(ParallelGCThreads) ||
1.54 + n_threads == (int)ParallelGCThreads,
1.55 + "# worker threads != # requested!");
1.56 + // Make sure the LNC array is valid for the space.
1.57 + jbyte** lowest_non_clean;
1.58 + uintptr_t lowest_non_clean_base_chunk_index;
1.59 + size_t lowest_non_clean_chunk_size;
1.60 + get_LNC_array_for_space(sp, lowest_non_clean,
1.61 + lowest_non_clean_base_chunk_index,
1.62 + lowest_non_clean_chunk_size);
1.63 +
1.64 + uint n_strides = n_threads * ParGCStridesPerThread;
1.65 + SequentialSubTasksDone* pst = sp->par_seq_tasks();
1.66 + // Sets the condition for completion of the subtask (how many threads
1.67 + // need to finish in order to be done).
1.68 + pst->set_n_threads(n_threads);
1.69 + pst->set_n_tasks(n_strides);
1.70 +
1.71 + uint stride = 0;
1.72 + while (!pst->is_task_claimed(/* reference */ stride)) {
1.73 + process_stride(sp, mr, stride, n_strides, cl, ct,
1.74 + lowest_non_clean,
1.75 + lowest_non_clean_base_chunk_index,
1.76 + lowest_non_clean_chunk_size);
1.77 + }
1.78 + if (pst->all_tasks_completed()) {
1.79 + // Clear lowest_non_clean array for next time.
1.80 + intptr_t first_chunk_index = addr_to_chunk_index(mr.start());
1.81 + uintptr_t last_chunk_index = addr_to_chunk_index(mr.last());
1.82 + for (uintptr_t ch = first_chunk_index; ch <= last_chunk_index; ch++) {
1.83 + intptr_t ind = ch - lowest_non_clean_base_chunk_index;
1.84 + assert(0 <= ind && ind < (intptr_t)lowest_non_clean_chunk_size,
1.85 + "Bounds error");
1.86 + lowest_non_clean[ind] = NULL;
1.87 + }
1.88 + }
1.89 +}
1.90 +
1.91 +void
1.92 +CardTableModRefBS::
1.93 +process_stride(Space* sp,
1.94 + MemRegion used,
1.95 + jint stride, int n_strides,
1.96 + OopsInGenClosure* cl,
1.97 + CardTableRS* ct,
1.98 + jbyte** lowest_non_clean,
1.99 + uintptr_t lowest_non_clean_base_chunk_index,
1.100 + size_t lowest_non_clean_chunk_size) {
1.101 + // We go from higher to lower addresses here; it wouldn't help that much
1.102 + // because of the strided parallelism pattern used here.
1.103 +
1.104 + // Find the first card address of the first chunk in the stride that is
1.105 + // at least "bottom" of the used region.
1.106 + jbyte* start_card = byte_for(used.start());
1.107 + jbyte* end_card = byte_after(used.last());
1.108 + uintptr_t start_chunk = addr_to_chunk_index(used.start());
1.109 + uintptr_t start_chunk_stride_num = start_chunk % n_strides;
1.110 + jbyte* chunk_card_start;
1.111 +
1.112 + if ((uintptr_t)stride >= start_chunk_stride_num) {
1.113 + chunk_card_start = (jbyte*)(start_card +
1.114 + (stride - start_chunk_stride_num) *
1.115 + ParGCCardsPerStrideChunk);
1.116 + } else {
1.117 + // Go ahead to the next chunk group boundary, then to the requested stride.
1.118 + chunk_card_start = (jbyte*)(start_card +
1.119 + (n_strides - start_chunk_stride_num + stride) *
1.120 + ParGCCardsPerStrideChunk);
1.121 + }
1.122 +
1.123 + while (chunk_card_start < end_card) {
1.124 + // Even though we go from lower to higher addresses below, the
1.125 + // strided parallelism can interleave the actual processing of the
1.126 + // dirty pages in various ways. For a specific chunk within this
1.127 + // stride, we take care to avoid double scanning or missing a card
1.128 + // by suitably initializing the "min_done" field in process_chunk_boundaries()
1.129 + // below, together with the dirty region extension accomplished in
1.130 + // DirtyCardToOopClosure::do_MemRegion().
1.131 + jbyte* chunk_card_end = chunk_card_start + ParGCCardsPerStrideChunk;
1.132 + // Invariant: chunk_mr should be fully contained within the "used" region.
1.133 + MemRegion chunk_mr = MemRegion(addr_for(chunk_card_start),
1.134 + chunk_card_end >= end_card ?
1.135 + used.end() : addr_for(chunk_card_end));
1.136 + assert(chunk_mr.word_size() > 0, "[chunk_card_start > used_end)");
1.137 + assert(used.contains(chunk_mr), "chunk_mr should be subset of used");
1.138 +
1.139 + DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(),
1.140 + cl->gen_boundary());
1.141 + ClearNoncleanCardWrapper clear_cl(dcto_cl, ct);
1.142 +
1.143 +
1.144 + // Process the chunk.
1.145 + process_chunk_boundaries(sp,
1.146 + dcto_cl,
1.147 + chunk_mr,
1.148 + used,
1.149 + lowest_non_clean,
1.150 + lowest_non_clean_base_chunk_index,
1.151 + lowest_non_clean_chunk_size);
1.152 +
1.153 + // We want the LNC array updates above in process_chunk_boundaries
1.154 + // to be visible before any of the card table value changes as a
1.155 + // result of the dirty card iteration below.
1.156 + OrderAccess::storestore();
1.157 +
1.158 + // We do not call the non_clean_card_iterate_serial() version because
1.159 + // we want to clear the cards: clear_cl here does the work of finding
1.160 + // contiguous dirty ranges of cards to process and clear.
1.161 + clear_cl.do_MemRegion(chunk_mr);
1.162 +
1.163 + // Find the next chunk of the stride.
1.164 + chunk_card_start += ParGCCardsPerStrideChunk * n_strides;
1.165 + }
1.166 +}
1.167 +
1.168 +
1.169 +// If you want a talkative process_chunk_boundaries,
1.170 +// then #define NOISY(x) x
1.171 +#ifdef NOISY
1.172 +#error "Encountered a global preprocessor flag, NOISY, which might clash with local definition to follow"
1.173 +#else
1.174 +#define NOISY(x)
1.175 +#endif
1.176 +
1.177 +void
1.178 +CardTableModRefBS::
1.179 +process_chunk_boundaries(Space* sp,
1.180 + DirtyCardToOopClosure* dcto_cl,
1.181 + MemRegion chunk_mr,
1.182 + MemRegion used,
1.183 + jbyte** lowest_non_clean,
1.184 + uintptr_t lowest_non_clean_base_chunk_index,
1.185 + size_t lowest_non_clean_chunk_size)
1.186 +{
1.187 + // We must worry about non-array objects that cross chunk boundaries,
1.188 + // because such objects are both precisely and imprecisely marked:
1.189 + // .. if the head of such an object is dirty, the entire object
1.190 + // needs to be scanned, under the interpretation that this
1.191 + // was an imprecise mark
1.192 + // .. if the head of such an object is not dirty, we can assume
1.193 + // precise marking and it's efficient to scan just the dirty
1.194 + // cards.
1.195 + // In either case, each scanned reference must be scanned precisely
1.196 + // once so as to avoid cloning of a young referent. For efficiency,
1.197 + // our closures depend on this property and do not protect against
1.198 + // double scans.
1.199 +
1.200 + uintptr_t cur_chunk_index = addr_to_chunk_index(chunk_mr.start());
1.201 + cur_chunk_index = cur_chunk_index - lowest_non_clean_base_chunk_index;
1.202 +
1.203 + NOISY(tty->print_cr("===========================================================================");)
1.204 + NOISY(tty->print_cr(" process_chunk_boundary: Called with [" PTR_FORMAT "," PTR_FORMAT ")",
1.205 + chunk_mr.start(), chunk_mr.end());)
1.206 +
1.207 + // First, set "our" lowest_non_clean entry, which would be
1.208 + // used by the thread scanning an adjoining left chunk with
1.209 + // a non-array object straddling the mutual boundary.
1.210 + // Find the object that spans our boundary, if one exists.
1.211 + // first_block is the block possibly straddling our left boundary.
1.212 + HeapWord* first_block = sp->block_start(chunk_mr.start());
1.213 + assert((chunk_mr.start() != used.start()) || (first_block == chunk_mr.start()),
1.214 + "First chunk should always have a co-initial block");
1.215 + // Does the block straddle the chunk's left boundary, and is it
1.216 + // a non-array object?
1.217 + if (first_block < chunk_mr.start() // first block straddles left bdry
1.218 + && sp->block_is_obj(first_block) // first block is an object
1.219 + && !(oop(first_block)->is_objArray() // first block is not an array (arrays are precisely dirtied)
1.220 + || oop(first_block)->is_typeArray())) {
1.221 + // Find our least non-clean card, so that a left neighbour
1.222 + // does not scan an object straddling the mutual boundary
1.223 + // too far to the right, and attempt to scan a portion of
1.224 + // that object twice.
1.225 + jbyte* first_dirty_card = NULL;
1.226 + jbyte* last_card_of_first_obj =
1.227 + byte_for(first_block + sp->block_size(first_block) - 1);
1.228 + jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
1.229 + jbyte* last_card_of_cur_chunk = byte_for(chunk_mr.last());
1.230 + jbyte* last_card_to_check =
1.231 + (jbyte*) MIN2((intptr_t) last_card_of_cur_chunk,
1.232 + (intptr_t) last_card_of_first_obj);
1.233 + // Note that this does not need to go beyond our last card
1.234 + // if our first object completely straddles this chunk.
1.235 + for (jbyte* cur = first_card_of_cur_chunk;
1.236 + cur <= last_card_to_check; cur++) {
1.237 + jbyte val = *cur;
1.238 + if (card_will_be_scanned(val)) {
1.239 + first_dirty_card = cur; break;
1.240 + } else {
1.241 + assert(!card_may_have_been_dirty(val), "Error");
1.242 + }
1.243 + }
1.244 + if (first_dirty_card != NULL) {
1.245 + NOISY(tty->print_cr(" LNC: Found a dirty card at " PTR_FORMAT " in current chunk",
1.246 + first_dirty_card);)
1.247 + assert(0 <= cur_chunk_index && cur_chunk_index < lowest_non_clean_chunk_size,
1.248 + "Bounds error.");
1.249 + assert(lowest_non_clean[cur_chunk_index] == NULL,
1.250 + "Write exactly once : value should be stable hereafter for this round");
1.251 + lowest_non_clean[cur_chunk_index] = first_dirty_card;
1.252 + } NOISY(else {
1.253 + tty->print_cr(" LNC: Found no dirty card in current chunk; leaving LNC entry NULL");
1.254 + // In the future, we could have this thread look for a non-NULL value to copy from its
1.255 + // right neighbour (up to the end of the first object).
1.256 + if (last_card_of_cur_chunk < last_card_of_first_obj) {
1.257 + tty->print_cr(" LNC: BEWARE!!! first obj straddles past right end of chunk:\n"
1.258 + " might be efficient to get value from right neighbour?");
1.259 + }
1.260 + })
1.261 + } else {
1.262 + // In this case we can help our neighbour by just asking them
1.263 + // to stop at our first card (even though it may not be dirty).
1.264 + NOISY(tty->print_cr(" LNC: first block is not a non-array object; setting LNC to first card of current chunk");)
1.265 + assert(lowest_non_clean[cur_chunk_index] == NULL, "Write once : value should be stable hereafter");
1.266 + jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
1.267 + lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk;
1.268 + }
1.269 + NOISY(tty->print_cr(" process_chunk_boundary: lowest_non_clean[" INTPTR_FORMAT "] = " PTR_FORMAT
1.270 + " which corresponds to the heap address " PTR_FORMAT,
1.271 + cur_chunk_index, lowest_non_clean[cur_chunk_index],
1.272 + (lowest_non_clean[cur_chunk_index] != NULL)
1.273 + ? addr_for(lowest_non_clean[cur_chunk_index])
1.274 + : NULL);)
1.275 + NOISY(tty->print_cr("---------------------------------------------------------------------------");)
1.276 +
1.277 + // Next, set our own max_to_do, which will strictly/exclusively bound
1.278 + // the highest address that we will scan past the right end of our chunk.
1.279 + HeapWord* max_to_do = NULL;
1.280 + if (chunk_mr.end() < used.end()) {
1.281 + // This is not the last chunk in the used region.
1.282 + // What is our last block? We check the first block of
1.283 + // the next (right) chunk rather than strictly check our last block
1.284 + // because it's potentially more efficient to do so.
1.285 + HeapWord* const last_block = sp->block_start(chunk_mr.end());
1.286 + assert(last_block <= chunk_mr.end(), "In case this property changes.");
1.287 + if ((last_block == chunk_mr.end()) // our last block does not straddle boundary
1.288 + || !sp->block_is_obj(last_block) // last_block isn't an object
1.289 + || oop(last_block)->is_objArray() // last_block is an array (precisely marked)
1.290 + || oop(last_block)->is_typeArray()) {
1.291 + max_to_do = chunk_mr.end();
1.292 + NOISY(tty->print_cr(" process_chunk_boundary: Last block on this card is not a non-array object;\n"
1.293 + " max_to_do left at " PTR_FORMAT, max_to_do);)
1.294 + } else {
1.295 + assert(last_block < chunk_mr.end(), "Tautology");
1.296 + // It is a non-array object that straddles the right boundary of this chunk.
1.297 + // last_obj_card is the card corresponding to the start of the last object
1.298 + // in the chunk. Note that the last object may not start in
1.299 + // the chunk.
1.300 + jbyte* const last_obj_card = byte_for(last_block);
1.301 + const jbyte val = *last_obj_card;
1.302 + if (!card_will_be_scanned(val)) {
1.303 + assert(!card_may_have_been_dirty(val), "Error");
1.304 + // The card containing the head is not dirty. Any marks on
1.305 + // subsequent cards still in this chunk must have been made
1.306 + // precisely; we can cap processing at the end of our chunk.
1.307 + max_to_do = chunk_mr.end();
1.308 + NOISY(tty->print_cr(" process_chunk_boundary: Head of last object on this card is not dirty;\n"
1.309 + " max_to_do left at " PTR_FORMAT,
1.310 + max_to_do);)
1.311 + } else {
1.312 + // The last object must be considered dirty, and extends onto the
1.313 + // following chunk. Look for a dirty card in that chunk that will
1.314 + // bound our processing.
1.315 + jbyte* limit_card = NULL;
1.316 + const size_t last_block_size = sp->block_size(last_block);
1.317 + jbyte* const last_card_of_last_obj =
1.318 + byte_for(last_block + last_block_size - 1);
1.319 + jbyte* const first_card_of_next_chunk = byte_for(chunk_mr.end());
1.320 + // This search potentially goes a long distance looking
1.321 + // for the next card that will be scanned, terminating
1.322 + // at the end of the last_block, if no earlier dirty card
1.323 + // is found.
1.324 + assert(byte_for(chunk_mr.end()) - byte_for(chunk_mr.start()) == ParGCCardsPerStrideChunk,
1.325 + "last card of next chunk may be wrong");
1.326 + for (jbyte* cur = first_card_of_next_chunk;
1.327 + cur <= last_card_of_last_obj; cur++) {
1.328 + const jbyte val = *cur;
1.329 + if (card_will_be_scanned(val)) {
1.330 + NOISY(tty->print_cr(" Found a non-clean card " PTR_FORMAT " with value 0x%x",
1.331 + cur, (int)val);)
1.332 + limit_card = cur; break;
1.333 + } else {
1.334 + assert(!card_may_have_been_dirty(val), "Error: card can't be skipped");
1.335 + }
1.336 + }
1.337 + if (limit_card != NULL) {
1.338 + max_to_do = addr_for(limit_card);
1.339 + assert(limit_card != NULL && max_to_do != NULL, "Error");
1.340 + NOISY(tty->print_cr(" process_chunk_boundary: Found a dirty card at " PTR_FORMAT
1.341 + " max_to_do set at " PTR_FORMAT " which is before end of last block in chunk: "
1.342 + PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,
1.343 + limit_card, max_to_do, last_block, last_block_size, (last_block+last_block_size));)
1.344 + } else {
1.345 + // The following is a pessimistic value, because it's possible
1.346 + // that a dirty card on a subsequent chunk has been cleared by
1.347 + // the time we get to look at it; we'll correct for that further below,
1.348 + // using the LNC array which records the least non-clean card
1.349 + // before cards were cleared in a particular chunk.
1.350 + limit_card = last_card_of_last_obj;
1.351 + max_to_do = last_block + last_block_size;
1.352 + assert(limit_card != NULL && max_to_do != NULL, "Error");
1.353 + NOISY(tty->print_cr(" process_chunk_boundary: Found no dirty card before end of last block in chunk\n"
1.354 + " Setting limit_card to " PTR_FORMAT
1.355 + " and max_to_do " PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,
1.356 + limit_card, last_block, last_block_size, max_to_do);)
1.357 + }
1.358 + assert(0 < cur_chunk_index+1 && cur_chunk_index+1 < lowest_non_clean_chunk_size,
1.359 + "Bounds error.");
1.360 + // It is possible that a dirty card for the last object may have been
1.361 + // cleared before we had a chance to examine it. In that case, the value
1.362 + // will have been logged in the LNC for that chunk.
1.363 + // We need to examine as many chunks to the right as this object
1.364 + // covers. However, we need to bound this checking to the largest
1.365 + // entry in the LNC array: this is because the heap may expand
1.366 + // after the LNC array has been created but before we reach this point,
1.367 + // and the last block in our chunk may have been expanded to include
1.368 + // the expansion delta (and possibly subsequently allocated from, so
1.369 + // it wouldn't be sufficient to check whether that last block was
1.370 + // or was not an object at this point).
1.371 + uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1)
1.372 + - lowest_non_clean_base_chunk_index;
1.373 + const uintptr_t last_chunk_index = addr_to_chunk_index(used.last())
1.374 + - lowest_non_clean_base_chunk_index;
1.375 + if (last_chunk_index_to_check > last_chunk_index) {
1.376 + assert(last_block + last_block_size > used.end(),
1.377 + err_msg("Inconsistency detected: last_block [" PTR_FORMAT "," PTR_FORMAT "]"
1.378 + " does not exceed used.end() = " PTR_FORMAT ","
1.379 + " yet last_chunk_index_to_check " INTPTR_FORMAT
1.380 + " exceeds last_chunk_index " INTPTR_FORMAT,
1.381 + last_block, last_block + last_block_size,
1.382 + used.end(),
1.383 + last_chunk_index_to_check, last_chunk_index));
1.384 + assert(sp->used_region().end() > used.end(),
1.385 + err_msg("Expansion did not happen: "
1.386 + "[" PTR_FORMAT "," PTR_FORMAT ") -> [" PTR_FORMAT "," PTR_FORMAT ")",
1.387 + sp->used_region().start(), sp->used_region().end(), used.start(), used.end()));
1.388 + NOISY(tty->print_cr(" process_chunk_boundary: heap expanded; explicitly bounding last_chunk");)
1.389 + last_chunk_index_to_check = last_chunk_index;
1.390 + }
1.391 + for (uintptr_t lnc_index = cur_chunk_index + 1;
1.392 + lnc_index <= last_chunk_index_to_check;
1.393 + lnc_index++) {
1.394 + jbyte* lnc_card = lowest_non_clean[lnc_index];
1.395 + if (lnc_card != NULL) {
1.396 + // we can stop at the first non-NULL entry we find
1.397 + if (lnc_card <= limit_card) {
1.398 + NOISY(tty->print_cr(" process_chunk_boundary: LNC card " PTR_FORMAT " is lower than limit_card " PTR_FORMAT,
1.399 + " max_to_do will be lowered to " PTR_FORMAT " from " PTR_FORMAT,
1.400 + lnc_card, limit_card, addr_for(lnc_card), max_to_do);)
1.401 + limit_card = lnc_card;
1.402 + max_to_do = addr_for(limit_card);
1.403 + assert(limit_card != NULL && max_to_do != NULL, "Error");
1.404 + }
1.405 + // In any case, we break now
1.406 + break;
1.407 + } // else continue to look for a non-NULL entry if any
1.408 + }
1.409 + assert(limit_card != NULL && max_to_do != NULL, "Error");
1.410 + }
1.411 + assert(max_to_do != NULL, "OOPS 1 !");
1.412 + }
1.413 + assert(max_to_do != NULL, "OOPS 2!");
1.414 + } else {
1.415 + max_to_do = used.end();
1.416 + NOISY(tty->print_cr(" process_chunk_boundary: Last chunk of this space;\n"
1.417 + " max_to_do left at " PTR_FORMAT,
1.418 + max_to_do);)
1.419 + }
1.420 + assert(max_to_do != NULL, "OOPS 3!");
1.421 + // Now we can set the closure we're using so it doesn't to beyond
1.422 + // max_to_do.
1.423 + dcto_cl->set_min_done(max_to_do);
1.424 +#ifndef PRODUCT
1.425 + dcto_cl->set_last_bottom(max_to_do);
1.426 +#endif
1.427 + NOISY(tty->print_cr("===========================================================================\n");)
1.428 +}
1.429 +
1.430 +#undef NOISY
1.431 +
1.432 +void
1.433 +CardTableModRefBS::
1.434 +get_LNC_array_for_space(Space* sp,
1.435 + jbyte**& lowest_non_clean,
1.436 + uintptr_t& lowest_non_clean_base_chunk_index,
1.437 + size_t& lowest_non_clean_chunk_size) {
1.438 +
1.439 + int i = find_covering_region_containing(sp->bottom());
1.440 + MemRegion covered = _covered[i];
1.441 + size_t n_chunks = chunks_to_cover(covered);
1.442 +
1.443 + // Only the first thread to obtain the lock will resize the
1.444 + // LNC array for the covered region. Any later expansion can't affect
1.445 + // the used_at_save_marks region.
1.446 + // (I observed a bug in which the first thread to execute this would
1.447 + // resize, and then it would cause "expand_and_allocate" that would
1.448 + // increase the number of chunks in the covered region. Then a second
1.449 + // thread would come and execute this, see that the size didn't match,
1.450 + // and free and allocate again. So the first thread would be using a
1.451 + // freed "_lowest_non_clean" array.)
1.452 +
1.453 + // Do a dirty read here. If we pass the conditional then take the rare
1.454 + // event lock and do the read again in case some other thread had already
1.455 + // succeeded and done the resize.
1.456 + int cur_collection = Universe::heap()->total_collections();
1.457 + if (_last_LNC_resizing_collection[i] != cur_collection) {
1.458 + MutexLocker x(ParGCRareEvent_lock);
1.459 + if (_last_LNC_resizing_collection[i] != cur_collection) {
1.460 + if (_lowest_non_clean[i] == NULL ||
1.461 + n_chunks != _lowest_non_clean_chunk_size[i]) {
1.462 +
1.463 + // Should we delete the old?
1.464 + if (_lowest_non_clean[i] != NULL) {
1.465 + assert(n_chunks != _lowest_non_clean_chunk_size[i],
1.466 + "logical consequence");
1.467 + FREE_C_HEAP_ARRAY(CardPtr, _lowest_non_clean[i], mtGC);
1.468 + _lowest_non_clean[i] = NULL;
1.469 + }
1.470 + // Now allocate a new one if necessary.
1.471 + if (_lowest_non_clean[i] == NULL) {
1.472 + _lowest_non_clean[i] = NEW_C_HEAP_ARRAY(CardPtr, n_chunks, mtGC);
1.473 + _lowest_non_clean_chunk_size[i] = n_chunks;
1.474 + _lowest_non_clean_base_chunk_index[i] = addr_to_chunk_index(covered.start());
1.475 + for (int j = 0; j < (int)n_chunks; j++)
1.476 + _lowest_non_clean[i][j] = NULL;
1.477 + }
1.478 + }
1.479 + _last_LNC_resizing_collection[i] = cur_collection;
1.480 + }
1.481 + }
1.482 + // In any case, now do the initialization.
1.483 + lowest_non_clean = _lowest_non_clean[i];
1.484 + lowest_non_clean_base_chunk_index = _lowest_non_clean_base_chunk_index[i];
1.485 + lowest_non_clean_chunk_size = _lowest_non_clean_chunk_size[i];
1.486 +}
