/*
* Copyright (c) 2000, 2017, 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/shared/blockOffsetTable.inline.hpp"
#include "gc/shared/collectedHeap.inline.hpp"
#include "gc/shared/space.inline.hpp"
#include "memory/iterator.hpp"
#include "memory/universe.hpp"
#include "logging/log.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/java.hpp"
#include "services/memTracker.hpp"
//////////////////////////////////////////////////////////////////////
// BlockOffsetSharedArray
//////////////////////////////////////////////////////////////////////
BlockOffsetSharedArray::BlockOffsetSharedArray(MemRegion reserved,
size_t init_word_size):
_reserved(reserved), _end(NULL)
{
size_t size = compute_size(reserved.word_size());
ReservedSpace rs(size);
if (!rs.is_reserved()) {
vm_exit_during_initialization("Could not reserve enough space for heap offset array");
}
MemTracker::record_virtual_memory_type((address)rs.base(), mtGC);
if (!_vs.initialize(rs, 0)) {
vm_exit_during_initialization("Could not reserve enough space for heap offset array");
}
_offset_array = (u_char*)_vs.low_boundary();
resize(init_word_size);
log_trace(gc, bot)("BlockOffsetSharedArray::BlockOffsetSharedArray: ");
log_trace(gc, bot)(" rs.base(): " INTPTR_FORMAT " rs.size(): " INTPTR_FORMAT " rs end(): " INTPTR_FORMAT,
p2i(rs.base()), rs.size(), p2i(rs.base() + rs.size()));
log_trace(gc, bot)(" _vs.low_boundary(): " INTPTR_FORMAT " _vs.high_boundary(): " INTPTR_FORMAT,
p2i(_vs.low_boundary()), p2i(_vs.high_boundary()));
}
void BlockOffsetSharedArray::resize(size_t new_word_size) {
assert(new_word_size <= _reserved.word_size(), "Resize larger than reserved");
size_t new_size = compute_size(new_word_size);
size_t old_size = _vs.committed_size();
size_t delta;
char* high = _vs.high();
_end = _reserved.start() + new_word_size;
if (new_size > old_size) {
delta = ReservedSpace::page_align_size_up(new_size - old_size);
assert(delta > 0, "just checking");
if (!_vs.expand_by(delta)) {
// Do better than this for Merlin
vm_exit_out_of_memory(delta, OOM_MMAP_ERROR, "offset table expansion");
}
assert(_vs.high() == high + delta, "invalid expansion");
} else {
delta = ReservedSpace::page_align_size_down(old_size - new_size);
if (delta == 0) return;
_vs.shrink_by(delta);
assert(_vs.high() == high - delta, "invalid expansion");
}
}
bool BlockOffsetSharedArray::is_card_boundary(HeapWord* p) const {
assert(p >= _reserved.start(), "just checking");
size_t delta = pointer_delta(p, _reserved.start());
return (delta & right_n_bits((int)BOTConstants::LogN_words)) == (size_t)NoBits;
}
//////////////////////////////////////////////////////////////////////
// BlockOffsetArray
//////////////////////////////////////////////////////////////////////
BlockOffsetArray::BlockOffsetArray(BlockOffsetSharedArray* array,
MemRegion mr, bool init_to_zero_) :
BlockOffsetTable(mr.start(), mr.end()),
_array(array)
{
assert(_bottom <= _end, "arguments out of order");
set_init_to_zero(init_to_zero_);
if (!init_to_zero_) {
// initialize cards to point back to mr.start()
set_remainder_to_point_to_start(mr.start() + BOTConstants::N_words, mr.end());
_array->set_offset_array(0, 0); // set first card to 0
}
}
// The arguments follow the normal convention of denoting
// a right-open interval: [start, end)
void
BlockOffsetArray::
set_remainder_to_point_to_start(HeapWord* start, HeapWord* end, bool reducing) {
check_reducing_assertion(reducing);
if (start >= end) {
// The start address is equal to the end address (or to
// the right of the end address) so there are not cards
// that need to be updated..
return;
}
// Write the backskip value for each region.
//
// offset
// card 2nd 3rd
// | +- 1st | |
// v v v v
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-
// |x|0|0|0|0|0|0|0|1|1|1|1|1|1| ... |1|1|1|1|2|2|2|2|2|2| ...
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-
// 11 19 75
// 12
//
// offset card is the card that points to the start of an object
// x - offset value of offset card
// 1st - start of first logarithmic region
// 0 corresponds to logarithmic value N_words + 0 and 2**(3 * 0) = 1
// 2nd - start of second logarithmic region
// 1 corresponds to logarithmic value N_words + 1 and 2**(3 * 1) = 8
// 3rd - start of third logarithmic region
// 2 corresponds to logarithmic value N_words + 2 and 2**(3 * 2) = 64
//
// integer below the block offset entry is an example of
// the index of the entry
//
// Given an address,
// Find the index for the address
// Find the block offset table entry
// Convert the entry to a back slide
// (e.g., with today's, offset = 0x81 =>
// back slip = 2**(3*(0x81 - N_words)) = 2**3) = 8
// Move back N (e.g., 8) entries and repeat with the
// value of the new entry
//
size_t start_card = _array->index_for(start);
size_t end_card = _array->index_for(end-1);
assert(start ==_array->address_for_index(start_card), "Precondition");
assert(end ==_array->address_for_index(end_card)+BOTConstants::N_words, "Precondition");
set_remainder_to_point_to_start_incl(start_card, end_card, reducing); // closed interval
}
// Unlike the normal convention in this code, the argument here denotes
// a closed, inclusive interval: [start_card, end_card], cf set_remainder_to_point_to_start()
// above.
void
BlockOffsetArray::set_remainder_to_point_to_start_incl(size_t start_card, size_t end_card, bool reducing) {
check_reducing_assertion(reducing);
if (start_card > end_card) {
return;
}
assert(start_card > _array->index_for(_bottom), "Cannot be first card");
assert(_array->offset_array(start_card-1) <= BOTConstants::N_words,
"Offset card has an unexpected value");
size_t start_card_for_region = start_card;
u_char offset = max_jubyte;
for (uint i = 0; i < BOTConstants::N_powers; i++) {
// -1 so that the the card with the actual offset is counted. Another -1
// so that the reach ends in this region and not at the start
// of the next.
size_t reach = start_card - 1 + (BOTConstants::power_to_cards_back(i+1) - 1);
offset = BOTConstants::N_words + i;
if (reach >= end_card) {
_array->set_offset_array(start_card_for_region, end_card, offset, reducing);
start_card_for_region = reach + 1;
break;
}
_array->set_offset_array(start_card_for_region, reach, offset, reducing);
start_card_for_region = reach + 1;
}
assert(start_card_for_region > end_card, "Sanity check");
DEBUG_ONLY(check_all_cards(start_card, end_card);)
}
// The card-interval [start_card, end_card] is a closed interval; this
// is an expensive check -- use with care and only under protection of
// suitable flag.
void BlockOffsetArray::check_all_cards(size_t start_card, size_t end_card) const {
if (end_card < start_card) {
return;
}
guarantee(_array->offset_array(start_card) == BOTConstants::N_words, "Wrong value in second card");
u_char last_entry = BOTConstants::N_words;
for (size_t c = start_card + 1; c <= end_card; c++ /* yeah! */) {
u_char entry = _array->offset_array(c);
guarantee(entry >= last_entry, "Monotonicity");
if (c - start_card > BOTConstants::power_to_cards_back(1)) {
guarantee(entry > BOTConstants::N_words, "Should be in logarithmic region");
}
size_t backskip = BOTConstants::entry_to_cards_back(entry);
size_t landing_card = c - backskip;
guarantee(landing_card >= (start_card - 1), "Inv");
if (landing_card >= start_card) {
guarantee(_array->offset_array(landing_card) <= entry, "Monotonicity");
} else {
guarantee(landing_card == (start_card - 1), "Tautology");
// Note that N_words is the maximum offset value
guarantee(_array->offset_array(landing_card) <= BOTConstants::N_words, "Offset value");
}
last_entry = entry; // remember for monotonicity test
}
}
void
BlockOffsetArray::alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
assert(blk_start != NULL && blk_end > blk_start,
"phantom block");
single_block(blk_start, blk_end);
}
// Action_mark - update the BOT for the block [blk_start, blk_end).
// Current typical use is for splitting a block.
// Action_single - udpate the BOT for an allocation.
// Action_verify - BOT verification.
void
BlockOffsetArray::do_block_internal(HeapWord* blk_start,
HeapWord* blk_end,
Action action, bool reducing) {
assert(Universe::heap()->is_in_reserved(blk_start),
"reference must be into the heap");
assert(Universe::heap()->is_in_reserved(blk_end-1),
"limit must be within the heap");
// This is optimized to make the test fast, assuming we only rarely
// cross boundaries.
uintptr_t end_ui = (uintptr_t)(blk_end - 1);
uintptr_t start_ui = (uintptr_t)blk_start;
// Calculate the last card boundary preceding end of blk
intptr_t boundary_before_end = (intptr_t)end_ui;
clear_bits(boundary_before_end, right_n_bits((int)BOTConstants::LogN));
if (start_ui <= (uintptr_t)boundary_before_end) {
// blk starts at or crosses a boundary
// Calculate index of card on which blk begins
size_t start_index = _array->index_for(blk_start);
// Index of card on which blk ends
size_t end_index = _array->index_for(blk_end - 1);
// Start address of card on which blk begins
HeapWord* boundary = _array->address_for_index(start_index);
assert(boundary <= blk_start, "blk should start at or after boundary");
if (blk_start != boundary) {
// blk starts strictly after boundary
// adjust card boundary and start_index forward to next card
boundary += BOTConstants::N_words;
start_index++;
}
assert(start_index <= end_index, "monotonicity of index_for()");
assert(boundary <= (HeapWord*)boundary_before_end, "tautology");
switch (action) {
case Action_mark: {
if (init_to_zero()) {
_array->set_offset_array(start_index, boundary, blk_start, reducing);
break;
} // Else fall through to the next case
}
case Action_single: {
_array->set_offset_array(start_index, boundary, blk_start, reducing);
// We have finished marking the "offset card". We need to now
// mark the subsequent cards that this blk spans.
if (start_index < end_index) {
HeapWord* rem_st = _array->address_for_index(start_index) + BOTConstants::N_words;
HeapWord* rem_end = _array->address_for_index(end_index) + BOTConstants::N_words;
set_remainder_to_point_to_start(rem_st, rem_end, reducing);
}
break;
}
case Action_check: {
_array->check_offset_array(start_index, boundary, blk_start);
// We have finished checking the "offset card". We need to now
// check the subsequent cards that this blk spans.
check_all_cards(start_index + 1, end_index);
break;
}
default:
ShouldNotReachHere();
}
}
}
// The range [blk_start, blk_end) represents a single contiguous block
// of storage; modify the block offset table to represent this
// information; Right-open interval: [blk_start, blk_end)
// NOTE: this method does _not_ adjust _unallocated_block.
void
BlockOffsetArray::single_block(HeapWord* blk_start,
HeapWord* blk_end) {
do_block_internal(blk_start, blk_end, Action_single);
}
void BlockOffsetArray::verify() const {
// For each entry in the block offset table, verify that
// the entry correctly finds the start of an object at the
// first address covered by the block or to the left of that
// first address.
size_t next_index = 1;
size_t last_index = last_active_index();
// Use for debugging. Initialize to NULL to distinguish the
// first iteration through the while loop.
HeapWord* last_p = NULL;
HeapWord* last_start = NULL;
oop last_o = NULL;
while (next_index <= last_index) {
// Use an address past the start of the address for
// the entry.
HeapWord* p = _array->address_for_index(next_index) + 1;
if (p >= _end) {
// That's all of the allocated block table.
return;
}
// block_start() asserts that start <= p.
HeapWord* start = block_start(p);
// First check if the start is an allocated block and only
// then if it is a valid object.
oop o = oop(start);
assert(!Universe::is_fully_initialized() ||
_sp->is_free_block(start) ||
oopDesc::is_oop_or_null(o), "Bad object was found");
next_index++;
last_p = p;
last_start = start;
last_o = o;
}
}
//////////////////////////////////////////////////////////////////////
// BlockOffsetArrayNonContigSpace
//////////////////////////////////////////////////////////////////////
// The block [blk_start, blk_end) has been allocated;
// adjust the block offset table to represent this information;
// NOTE: Clients of BlockOffsetArrayNonContigSpace: consider using
// the somewhat more lightweight split_block() or
// (when init_to_zero()) mark_block() wherever possible.
// right-open interval: [blk_start, blk_end)
void
BlockOffsetArrayNonContigSpace::alloc_block(HeapWord* blk_start,
HeapWord* blk_end) {
assert(blk_start != NULL && blk_end > blk_start,
"phantom block");
single_block(blk_start, blk_end);
allocated(blk_start, blk_end);
}
// Adjust BOT to show that a previously whole block has been split
// into two. We verify the BOT for the first part (prefix) and
// update the BOT for the second part (suffix).
// blk is the start of the block
// blk_size is the size of the original block
// left_blk_size is the size of the first part of the split
void BlockOffsetArrayNonContigSpace::split_block(HeapWord* blk,
size_t blk_size,
size_t left_blk_size) {
// Verify that the BOT shows [blk, blk + blk_size) to be one block.
verify_single_block(blk, blk_size);
// Update the BOT to indicate that [blk + left_blk_size, blk + blk_size)
// is one single block.
assert(blk_size > 0, "Should be positive");
assert(left_blk_size > 0, "Should be positive");
assert(left_blk_size < blk_size, "Not a split");
// Start addresses of prefix block and suffix block.
HeapWord* pref_addr = blk;
HeapWord* suff_addr = blk + left_blk_size;
HeapWord* end_addr = blk + blk_size;
// Indices for starts of prefix block and suffix block.
size_t pref_index = _array->index_for(pref_addr);
if (_array->address_for_index(pref_index) != pref_addr) {
// pref_addr does not begin pref_index
pref_index++;
}
size_t suff_index = _array->index_for(suff_addr);
if (_array->address_for_index(suff_index) != suff_addr) {
// suff_addr does not begin suff_index
suff_index++;
}
// Definition: A block B, denoted [B_start, B_end) __starts__
// a card C, denoted [C_start, C_end), where C_start and C_end
// are the heap addresses that card C covers, iff
// B_start <= C_start < B_end.
//
// We say that a card C "is started by" a block B, iff
// B "starts" C.
//
// Note that the cardinality of the set of cards {C}
// started by a block B can be 0, 1, or more.
//
// Below, pref_index and suff_index are, respectively, the
// first (least) card indices that the prefix and suffix of
// the split start; end_index is one more than the index of
// the last (greatest) card that blk starts.
size_t end_index = _array->index_for(end_addr - 1) + 1;
// Calculate the # cards that the prefix and suffix affect.
size_t num_pref_cards = suff_index - pref_index;
size_t num_suff_cards = end_index - suff_index;
// Change the cards that need changing
if (num_suff_cards > 0) {
HeapWord* boundary = _array->address_for_index(suff_index);
// Set the offset card for suffix block
_array->set_offset_array(suff_index, boundary, suff_addr, true /* reducing */);
// Change any further cards that need changing in the suffix
if (num_pref_cards > 0) {
if (num_pref_cards >= num_suff_cards) {
// Unilaterally fix all of the suffix cards: closed card
// index interval in args below.
set_remainder_to_point_to_start_incl(suff_index + 1, end_index - 1, true /* reducing */);
} else {
// Unilaterally fix the first (num_pref_cards - 1) following
// the "offset card" in the suffix block.
const size_t right_most_fixed_index = suff_index + num_pref_cards - 1;
set_remainder_to_point_to_start_incl(suff_index + 1,
right_most_fixed_index, true /* reducing */);
// Fix the appropriate cards in the remainder of the
// suffix block -- these are the last num_pref_cards
// cards in each power block of the "new" range plumbed
// from suff_addr.
bool more = true;
uint i = 1;
// Fix the first power block with back_by > num_pref_cards.
while (more && (i < BOTConstants::N_powers)) {
size_t back_by = BOTConstants::power_to_cards_back(i);
size_t right_index = suff_index + back_by - 1;
size_t left_index = right_index - num_pref_cards + 1;
if (right_index >= end_index - 1) { // last iteration
right_index = end_index - 1;
more = false;
}
if (left_index <= right_most_fixed_index) {
left_index = right_most_fixed_index + 1;
}
if (back_by > num_pref_cards) {
// Fill in the remainder of this "power block", if it
// is non-null.
if (left_index <= right_index) {
_array->set_offset_array(left_index, right_index,
BOTConstants::N_words + i - 1, true /* reducing */);
} else {
more = false; // we are done
assert((end_index - 1) == right_index, "Must be at the end.");
}
i++;
break;
}
i++;
}
// Fix the rest of the power blocks.
while (more && (i < BOTConstants::N_powers)) {
size_t back_by = BOTConstants::power_to_cards_back(i);
size_t right_index = suff_index + back_by - 1;
size_t left_index = right_index - num_pref_cards + 1;
if (right_index >= end_index - 1) { // last iteration
right_index = end_index - 1;
if (left_index > right_index) {
break;
}
more = false;
}
assert(left_index <= right_index, "Error");
_array->set_offset_array(left_index, right_index, BOTConstants::N_words + i - 1, true /* reducing */);
i++;
}
}
} // else no more cards to fix in suffix
} // else nothing needs to be done
// Verify that we did the right thing
verify_single_block(pref_addr, left_blk_size);
verify_single_block(suff_addr, blk_size - left_blk_size);
}
// Mark the BOT such that if [blk_start, blk_end) straddles a card
// boundary, the card following the first such boundary is marked
// with the appropriate offset.
// NOTE: this method does _not_ adjust _unallocated_block or
// any cards subsequent to the first one.
void
BlockOffsetArrayNonContigSpace::mark_block(HeapWord* blk_start,
HeapWord* blk_end, bool reducing) {
do_block_internal(blk_start, blk_end, Action_mark, reducing);
}
HeapWord* BlockOffsetArrayNonContigSpace::block_start_unsafe(
const void* addr) const {
assert(_array->offset_array(0) == 0, "objects can't cross covered areas");
assert(_bottom <= addr && addr < _end,
"addr must be covered by this Array");
// Must read this exactly once because it can be modified by parallel
// allocation.
HeapWord* ub = _unallocated_block;
if (BlockOffsetArrayUseUnallocatedBlock && addr >= ub) {
assert(ub < _end, "tautology (see above)");
return ub;
}
// Otherwise, find the block start using the table.
size_t index = _array->index_for(addr);
HeapWord* q = _array->address_for_index(index);
uint offset = _array->offset_array(index); // Extend u_char to uint.
while (offset >= BOTConstants::N_words) {
// The excess of the offset from N_words indicates a power of Base
// to go back by.
size_t n_cards_back = BOTConstants::entry_to_cards_back(offset);
q -= (BOTConstants::N_words * n_cards_back);
assert(q >= _sp->bottom(),
"q = " PTR_FORMAT " crossed below bottom = " PTR_FORMAT,
p2i(q), p2i(_sp->bottom()));
assert(q < _sp->end(),
"q = " PTR_FORMAT " crossed above end = " PTR_FORMAT,
p2i(q), p2i(_sp->end()));
index -= n_cards_back;
offset = _array->offset_array(index);
}
assert(offset < BOTConstants::N_words, "offset too large");
index--;
q -= offset;
assert(q >= _sp->bottom(),
"q = " PTR_FORMAT " crossed below bottom = " PTR_FORMAT,
p2i(q), p2i(_sp->bottom()));
assert(q < _sp->end(),
"q = " PTR_FORMAT " crossed above end = " PTR_FORMAT,
p2i(q), p2i(_sp->end()));
HeapWord* n = q;
while (n <= addr) {
debug_only(HeapWord* last = q); // for debugging
q = n;
n += _sp->block_size(n);
assert(n > q,
"Looping at n = " PTR_FORMAT " with last = " PTR_FORMAT ","
" while querying blk_start(" PTR_FORMAT ")"
" on _sp = [" PTR_FORMAT "," PTR_FORMAT ")",
p2i(n), p2i(last), p2i(addr), p2i(_sp->bottom()), p2i(_sp->end()));
}
assert(q <= addr,
"wrong order for current (" INTPTR_FORMAT ")" " <= arg (" INTPTR_FORMAT ")",
p2i(q), p2i(addr));
assert(addr <= n,
"wrong order for arg (" INTPTR_FORMAT ") <= next (" INTPTR_FORMAT ")",
p2i(addr), p2i(n));
return q;
}
HeapWord* BlockOffsetArrayNonContigSpace::block_start_careful(
const void* addr) const {
assert(_array->offset_array(0) == 0, "objects can't cross covered areas");
assert(_bottom <= addr && addr < _end,
"addr must be covered by this Array");
// Must read this exactly once because it can be modified by parallel
// allocation.
HeapWord* ub = _unallocated_block;
if (BlockOffsetArrayUseUnallocatedBlock && addr >= ub) {
assert(ub < _end, "tautology (see above)");
return ub;
}
// Otherwise, find the block start using the table, but taking
// care (cf block_start_unsafe() above) not to parse any objects/blocks
// on the cards themselves.
size_t index = _array->index_for(addr);
assert(_array->address_for_index(index) == addr,
"arg should be start of card");
HeapWord* q = (HeapWord*)addr;
uint offset;
do {
offset = _array->offset_array(index);
if (offset < BOTConstants::N_words) {
q -= offset;
} else {
size_t n_cards_back = BOTConstants::entry_to_cards_back(offset);
q -= (n_cards_back * BOTConstants::N_words);
index -= n_cards_back;
}
} while (offset >= BOTConstants::N_words);
assert(q <= addr, "block start should be to left of arg");
return q;
}
#ifndef PRODUCT
// Verification & debugging - ensure that the offset table reflects the fact
// that the block [blk_start, blk_end) or [blk, blk + size) is a
// single block of storage. NOTE: can't const this because of
// call to non-const do_block_internal() below.
void BlockOffsetArrayNonContigSpace::verify_single_block(
HeapWord* blk_start, HeapWord* blk_end) {
if (VerifyBlockOffsetArray) {
do_block_internal(blk_start, blk_end, Action_check);
}
}
void BlockOffsetArrayNonContigSpace::verify_single_block(
HeapWord* blk, size_t size) {
verify_single_block(blk, blk + size);
}
// Verify that the given block is before _unallocated_block
void BlockOffsetArrayNonContigSpace::verify_not_unallocated(
HeapWord* blk_start, HeapWord* blk_end) const {
if (BlockOffsetArrayUseUnallocatedBlock) {
assert(blk_start < blk_end, "Block inconsistency?");
assert(blk_end <= _unallocated_block, "_unallocated_block problem");
}
}
void BlockOffsetArrayNonContigSpace::verify_not_unallocated(
HeapWord* blk, size_t size) const {
verify_not_unallocated(blk, blk + size);
}
#endif // PRODUCT
size_t BlockOffsetArrayNonContigSpace::last_active_index() const {
if (_unallocated_block == _bottom) {
return 0;
} else {
return _array->index_for(_unallocated_block - 1);
}
}
//////////////////////////////////////////////////////////////////////
// BlockOffsetArrayContigSpace
//////////////////////////////////////////////////////////////////////
HeapWord* BlockOffsetArrayContigSpace::block_start_unsafe(const void* addr) const {
assert(_array->offset_array(0) == 0, "objects can't cross covered areas");
// Otherwise, find the block start using the table.
assert(_bottom <= addr && addr < _end,
"addr must be covered by this Array");
size_t index = _array->index_for(addr);
// We must make sure that the offset table entry we use is valid. If
// "addr" is past the end, start at the last known one and go forward.
index = MIN2(index, _next_offset_index-1);
HeapWord* q = _array->address_for_index(index);
uint offset = _array->offset_array(index); // Extend u_char to uint.
while (offset > BOTConstants::N_words) {
// The excess of the offset from N_words indicates a power of Base
// to go back by.
size_t n_cards_back = BOTConstants::entry_to_cards_back(offset);
q -= (BOTConstants::N_words * n_cards_back);
assert(q >= _sp->bottom(), "Went below bottom!");
index -= n_cards_back;
offset = _array->offset_array(index);
}
while (offset == BOTConstants::N_words) {
assert(q >= _sp->bottom(), "Went below bottom!");
q -= BOTConstants::N_words;
index--;
offset = _array->offset_array(index);
}
assert(offset < BOTConstants::N_words, "offset too large");
q -= offset;
HeapWord* n = q;
while (n <= addr) {
debug_only(HeapWord* last = q); // for debugging
q = n;
n += _sp->block_size(n);
}
assert(q <= addr, "wrong order for current and arg");
assert(addr <= n, "wrong order for arg and next");
return q;
}
//
// _next_offset_threshold
// | _next_offset_index
// v v
// +-------+-------+-------+-------+-------+
// | i-1 | i | i+1 | i+2 | i+3 |
// +-------+-------+-------+-------+-------+
// ( ^ ]
// block-start
//
void BlockOffsetArrayContigSpace::alloc_block_work(HeapWord* blk_start,
HeapWord* blk_end) {
assert(blk_start != NULL && blk_end > blk_start,
"phantom block");
assert(blk_end > _next_offset_threshold,
"should be past threshold");
assert(blk_start <= _next_offset_threshold,
"blk_start should be at or before threshold");
assert(pointer_delta(_next_offset_threshold, blk_start) <= BOTConstants::N_words,
"offset should be <= BlockOffsetSharedArray::N");
assert(Universe::heap()->is_in_reserved(blk_start),
"reference must be into the heap");
assert(Universe::heap()->is_in_reserved(blk_end-1),
"limit must be within the heap");
assert(_next_offset_threshold ==
_array->_reserved.start() + _next_offset_index*BOTConstants::N_words,
"index must agree with threshold");
debug_only(size_t orig_next_offset_index = _next_offset_index;)
// Mark the card that holds the offset into the block. Note
// that _next_offset_index and _next_offset_threshold are not
// updated until the end of this method.
_array->set_offset_array(_next_offset_index,
_next_offset_threshold,
blk_start);
// We need to now mark the subsequent cards that this blk spans.
// Index of card on which blk ends.
size_t end_index = _array->index_for(blk_end - 1);
// Are there more cards left to be updated?
if (_next_offset_index + 1 <= end_index) {
HeapWord* rem_st = _array->address_for_index(_next_offset_index + 1);
// Calculate rem_end this way because end_index
// may be the last valid index in the covered region.
HeapWord* rem_end = _array->address_for_index(end_index) + BOTConstants::N_words;
set_remainder_to_point_to_start(rem_st, rem_end);
}
// _next_offset_index and _next_offset_threshold updated here.
_next_offset_index = end_index + 1;
// Calculate _next_offset_threshold this way because end_index
// may be the last valid index in the covered region.
_next_offset_threshold = _array->address_for_index(end_index) + BOTConstants::N_words;
assert(_next_offset_threshold >= blk_end, "Incorrect offset threshold");
#ifdef ASSERT
// The offset can be 0 if the block starts on a boundary. That
// is checked by an assertion above.
size_t start_index = _array->index_for(blk_start);
HeapWord* boundary = _array->address_for_index(start_index);
assert((_array->offset_array(orig_next_offset_index) == 0 &&
blk_start == boundary) ||
(_array->offset_array(orig_next_offset_index) > 0 &&
_array->offset_array(orig_next_offset_index) <= BOTConstants::N_words),
"offset array should have been set");
for (size_t j = orig_next_offset_index + 1; j <= end_index; j++) {
assert(_array->offset_array(j) > 0 &&
_array->offset_array(j) <= (u_char) (BOTConstants::N_words+BOTConstants::N_powers-1),
"offset array should have been set");
}
#endif
}
HeapWord* BlockOffsetArrayContigSpace::initialize_threshold() {
assert(!Universe::heap()->is_in_reserved(_array->_offset_array),
"just checking");
_next_offset_index = _array->index_for(_bottom);
_next_offset_index++;
_next_offset_threshold =
_array->address_for_index(_next_offset_index);
return _next_offset_threshold;
}
void BlockOffsetArrayContigSpace::zero_bottom_entry() {
assert(!Universe::heap()->is_in_reserved(_array->_offset_array),
"just checking");
size_t bottom_index = _array->index_for(_bottom);
_array->set_offset_array(bottom_index, 0);
}
size_t BlockOffsetArrayContigSpace::last_active_index() const {
return _next_offset_index == 0 ? 0 : _next_offset_index - 1;
}