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/*
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* Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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* CA 95054 USA or visit www.sun.com if you need additional information or
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* have any questions.
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*
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*/
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// The CollectedHeap type requires subtypes to implement a method
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// "block_start". For some subtypes, notably generational
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// systems using card-table-based write barriers, the efficiency of this
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// operation may be important. Implementations of the "BlockOffsetArray"
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// class may be useful in providing such efficient implementations.
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//
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// While generally mirroring the structure of the BOT for GenCollectedHeap,
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// the following types are tailored more towards G1's uses; these should,
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// however, be merged back into a common BOT to avoid code duplication
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// and reduce maintenance overhead.
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//
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// G1BlockOffsetTable (abstract)
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// -- G1BlockOffsetArray (uses G1BlockOffsetSharedArray)
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// -- G1BlockOffsetArrayContigSpace
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//
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// A main impediment to the consolidation of this code might be the
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// effect of making some of the block_start*() calls non-const as
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// below. Whether that might adversely affect performance optimizations
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// that compilers might normally perform in the case of non-G1
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// collectors needs to be carefully investigated prior to any such
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// consolidation.
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// Forward declarations
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class ContiguousSpace;
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class G1BlockOffsetSharedArray;
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class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
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friend class VMStructs;
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protected:
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// These members describe the region covered by the table.
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// The space this table is covering.
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HeapWord* _bottom; // == reserved.start
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HeapWord* _end; // End of currently allocated region.
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public:
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// Initialize the table to cover the given space.
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// The contents of the initial table are undefined.
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G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) :
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_bottom(bottom), _end(end)
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{
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assert(_bottom <= _end, "arguments out of order");
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}
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// Note that the committed size of the covered space may have changed,
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// so the table size might also wish to change.
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virtual void resize(size_t new_word_size) = 0;
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virtual void set_bottom(HeapWord* new_bottom) {
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assert(new_bottom <= _end, "new_bottom > _end");
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_bottom = new_bottom;
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resize(pointer_delta(_end, _bottom));
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}
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// Requires "addr" to be contained by a block, and returns the address of
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// the start of that block. (May have side effects, namely updating of
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// shared array entries that "point" too far backwards. This can occur,
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// for example, when LAB allocation is used in a space covered by the
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// table.)
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virtual HeapWord* block_start_unsafe(const void* addr) = 0;
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// Same as above, but does not have any of the possible side effects
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// discussed above.
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virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0;
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// Returns the address of the start of the block containing "addr", or
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// else "null" if it is covered by no block. (May have side effects,
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// namely updating of shared array entries that "point" too far
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// backwards. This can occur, for example, when lab allocation is used
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// in a space covered by the table.)
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inline HeapWord* block_start(const void* addr);
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// Same as above, but does not have any of the possible side effects
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// discussed above.
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inline HeapWord* block_start_const(const void* addr) const;
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};
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// This implementation of "G1BlockOffsetTable" divides the covered region
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// into "N"-word subregions (where "N" = 2^"LogN". An array with an entry
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// for each such subregion indicates how far back one must go to find the
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// start of the chunk that includes the first word of the subregion.
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//
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// Each BlockOffsetArray is owned by a Space. However, the actual array
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// may be shared by several BlockOffsetArrays; this is useful
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// when a single resizable area (such as a generation) is divided up into
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// several spaces in which contiguous allocation takes place,
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// such as, for example, in G1 or in the train generation.)
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// Here is the shared array type.
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class G1BlockOffsetSharedArray: public CHeapObj {
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friend class G1BlockOffsetArray;
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friend class G1BlockOffsetArrayContigSpace;
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friend class VMStructs;
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private:
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// The reserved region covered by the shared array.
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MemRegion _reserved;
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// End of the current committed region.
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HeapWord* _end;
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// Array for keeping offsets for retrieving object start fast given an
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// address.
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VirtualSpace _vs;
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u_char* _offset_array; // byte array keeping backwards offsets
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// Bounds checking accessors:
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// For performance these have to devolve to array accesses in product builds.
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u_char offset_array(size_t index) const {
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assert(index < _vs.committed_size(), "index out of range");
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return _offset_array[index];
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}
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void set_offset_array(size_t index, u_char offset) {
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assert(index < _vs.committed_size(), "index out of range");
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assert(offset <= N_words, "offset too large");
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_offset_array[index] = offset;
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}
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void set_offset_array(size_t index, HeapWord* high, HeapWord* low) {
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assert(index < _vs.committed_size(), "index out of range");
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assert(high >= low, "addresses out of order");
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assert(pointer_delta(high, low) <= N_words, "offset too large");
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_offset_array[index] = (u_char) pointer_delta(high, low);
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}
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void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) {
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assert(index_for(right - 1) < _vs.committed_size(),
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"right address out of range");
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assert(left < right, "Heap addresses out of order");
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size_t num_cards = pointer_delta(right, left) >> LogN_words;
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memset(&_offset_array[index_for(left)], offset, num_cards);
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}
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void set_offset_array(size_t left, size_t right, u_char offset) {
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assert(right < _vs.committed_size(), "right address out of range");
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assert(left <= right, "indexes out of order");
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size_t num_cards = right - left + 1;
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memset(&_offset_array[left], offset, num_cards);
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}
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void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
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assert(index < _vs.committed_size(), "index out of range");
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assert(high >= low, "addresses out of order");
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assert(pointer_delta(high, low) <= N_words, "offset too large");
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assert(_offset_array[index] == pointer_delta(high, low),
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"Wrong offset");
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}
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bool is_card_boundary(HeapWord* p) const;
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// Return the number of slots needed for an offset array
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// that covers mem_region_words words.
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// We always add an extra slot because if an object
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// ends on a card boundary we put a 0 in the next
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// offset array slot, so we want that slot always
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// to be reserved.
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size_t compute_size(size_t mem_region_words) {
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size_t number_of_slots = (mem_region_words / N_words) + 1;
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return ReservedSpace::page_align_size_up(number_of_slots);
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}
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public:
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enum SomePublicConstants {
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LogN = 9,
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LogN_words = LogN - LogHeapWordSize,
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N_bytes = 1 << LogN,
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N_words = 1 << LogN_words
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};
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// Initialize the table to cover from "base" to (at least)
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// "base + init_word_size". In the future, the table may be expanded
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// (see "resize" below) up to the size of "_reserved" (which must be at
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// least "init_word_size".) The contents of the initial table are
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// undefined; it is the responsibility of the constituent
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// G1BlockOffsetTable(s) to initialize cards.
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G1BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
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// Notes a change in the committed size of the region covered by the
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// table. The "new_word_size" may not be larger than the size of the
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// reserved region this table covers.
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void resize(size_t new_word_size);
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void set_bottom(HeapWord* new_bottom);
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// Updates all the BlockOffsetArray's sharing this shared array to
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// reflect the current "top"'s of their spaces.
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void update_offset_arrays();
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// Return the appropriate index into "_offset_array" for "p".
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inline size_t index_for(const void* p) const;
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// Return the address indicating the start of the region corresponding to
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// "index" in "_offset_array".
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inline HeapWord* address_for_index(size_t index) const;
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};
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// And here is the G1BlockOffsetTable subtype that uses the array.
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class G1BlockOffsetArray: public G1BlockOffsetTable {
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friend class G1BlockOffsetSharedArray;
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friend class G1BlockOffsetArrayContigSpace;
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friend class VMStructs;
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private:
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enum SomePrivateConstants {
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N_words = G1BlockOffsetSharedArray::N_words,
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LogN = G1BlockOffsetSharedArray::LogN
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};
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// The following enums are used by do_block_helper
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enum Action {
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Action_single, // BOT records a single block (see single_block())
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Action_mark, // BOT marks the start of a block (see mark_block())
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Action_check // Check that BOT records block correctly
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// (see verify_single_block()).
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};
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// This is the array, which can be shared by several BlockOffsetArray's
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// servicing different
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G1BlockOffsetSharedArray* _array;
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// The space that owns this subregion.
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Space* _sp;
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// If "_sp" is a contiguous space, the field below is the view of "_sp"
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// as a contiguous space, else NULL.
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ContiguousSpace* _csp;
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// If true, array entries are initialized to 0; otherwise, they are
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// initialized to point backwards to the beginning of the covered region.
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bool _init_to_zero;
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// The portion [_unallocated_block, _sp.end()) of the space that
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// is a single block known not to contain any objects.
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// NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
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HeapWord* _unallocated_block;
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// Sets the entries
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// corresponding to the cards starting at "start" and ending at "end"
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// to point back to the card before "start": the interval [start, end)
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// is right-open.
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void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
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// Same as above, except that the args here are a card _index_ interval
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// that is closed: [start_index, end_index]
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void set_remainder_to_point_to_start_incl(size_t start, size_t end);
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// A helper function for BOT adjustment/verification work
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void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
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protected:
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ContiguousSpace* csp() const { return _csp; }
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// Returns the address of a block whose start is at most "addr".
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// If "has_max_index" is true, "assumes "max_index" is the last valid one
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// in the array.
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inline HeapWord* block_at_or_preceding(const void* addr,
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bool has_max_index,
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size_t max_index) const;
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// "q" is a block boundary that is <= "addr"; "n" is the address of the
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// next block (or the end of the space.) Return the address of the
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// beginning of the block that contains "addr". Does so without side
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// effects (see, e.g., spec of block_start.)
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inline HeapWord*
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forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
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const void* addr) const;
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// "q" is a block boundary that is <= "addr"; return the address of the
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// beginning of the block that contains "addr". May have side effects
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// on "this", by updating imprecise entries.
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inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
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const void* addr);
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// "q" is a block boundary that is <= "addr"; "n" is the address of the
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// next block (or the end of the space.) Return the address of the
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// beginning of the block that contains "addr". May have side effects
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// on "this", by updating imprecise entries.
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HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
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HeapWord* n,
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const void* addr);
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// Requires that "*threshold_" be the first array entry boundary at or
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// above "blk_start", and that "*index_" be the corresponding array
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// index. If the block starts at or crosses "*threshold_", records
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// "blk_start" as the appropriate block start for the array index
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// starting at "*threshold_", and for any other indices crossed by the
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// block. Updates "*threshold_" and "*index_" to correspond to the first
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// index after the block end.
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void alloc_block_work2(HeapWord** threshold_, size_t* index_,
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HeapWord* blk_start, HeapWord* blk_end);
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public:
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// The space may not have it's bottom and top set yet, which is why the
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// region is passed as a parameter. If "init_to_zero" is true, the
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// elements of the array are initialized to zero. Otherwise, they are
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// initialized to point backwards to the beginning.
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G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr,
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bool init_to_zero);
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// Note: this ought to be part of the constructor, but that would require
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// "this" to be passed as a parameter to a member constructor for
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// the containing concrete subtype of Space.
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// This would be legal C++, but MS VC++ doesn't allow it.
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void set_space(Space* sp);
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// Resets the covered region to the given "mr".
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void set_region(MemRegion mr);
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// Resets the covered region to one with the same _bottom as before but
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// the "new_word_size".
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void resize(size_t new_word_size);
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// These must be guaranteed to work properly (i.e., do nothing)
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// when "blk_start" ("blk" for second version) is "NULL".
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virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
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virtual void alloc_block(HeapWord* blk, size_t size) {
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alloc_block(blk, blk + size);
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}
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// The following methods are useful and optimized for a
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// general, non-contiguous space.
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// The given arguments are required to be the starts of adjacent ("blk1"
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// before "blk2") well-formed blocks covered by "this". After this call,
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// they should be considered to form one block.
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virtual void join_blocks(HeapWord* blk1, HeapWord* blk2);
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// Given a block [blk_start, blk_start + full_blk_size), and
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// a left_blk_size < full_blk_size, adjust the BOT to show two
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// blocks [blk_start, blk_start + left_blk_size) and
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// [blk_start + left_blk_size, blk_start + full_blk_size).
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// It is assumed (and verified in the non-product VM) that the
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// BOT was correct for the original block.
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void split_block(HeapWord* blk_start, size_t full_blk_size,
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size_t left_blk_size);
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// Adjust the BOT to show that it has a single block in the
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// range [blk_start, blk_start + size). All necessary BOT
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// cards are adjusted, but _unallocated_block isn't.
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void single_block(HeapWord* blk_start, HeapWord* blk_end);
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void single_block(HeapWord* blk, size_t size) {
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single_block(blk, blk + size);
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}
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// Adjust BOT to show that it has a block in the range
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371 |
// [blk_start, blk_start + size). Only the first card
|
|
372 |
// of BOT is touched. It is assumed (and verified in the
|
|
373 |
// non-product VM) that the remaining cards of the block
|
|
374 |
// are correct.
|
|
375 |
void mark_block(HeapWord* blk_start, HeapWord* blk_end);
|
|
376 |
void mark_block(HeapWord* blk, size_t size) {
|
|
377 |
mark_block(blk, blk + size);
|
|
378 |
}
|
|
379 |
|
|
380 |
// Adjust _unallocated_block to indicate that a particular
|
|
381 |
// block has been newly allocated or freed. It is assumed (and
|
|
382 |
// verified in the non-product VM) that the BOT is correct for
|
|
383 |
// the given block.
|
|
384 |
inline void allocated(HeapWord* blk_start, HeapWord* blk_end) {
|
|
385 |
// Verify that the BOT shows [blk, blk + blk_size) to be one block.
|
|
386 |
verify_single_block(blk_start, blk_end);
|
|
387 |
if (BlockOffsetArrayUseUnallocatedBlock) {
|
|
388 |
_unallocated_block = MAX2(_unallocated_block, blk_end);
|
|
389 |
}
|
|
390 |
}
|
|
391 |
|
|
392 |
inline void allocated(HeapWord* blk, size_t size) {
|
|
393 |
allocated(blk, blk + size);
|
|
394 |
}
|
|
395 |
|
|
396 |
inline void freed(HeapWord* blk_start, HeapWord* blk_end);
|
|
397 |
|
|
398 |
inline void freed(HeapWord* blk, size_t size);
|
|
399 |
|
|
400 |
virtual HeapWord* block_start_unsafe(const void* addr);
|
|
401 |
virtual HeapWord* block_start_unsafe_const(const void* addr) const;
|
|
402 |
|
|
403 |
// Requires "addr" to be the start of a card and returns the
|
|
404 |
// start of the block that contains the given address.
|
|
405 |
HeapWord* block_start_careful(const void* addr) const;
|
|
406 |
|
|
407 |
// If true, initialize array slots with no allocated blocks to zero.
|
|
408 |
// Otherwise, make them point back to the front.
|
|
409 |
bool init_to_zero() { return _init_to_zero; }
|
|
410 |
|
|
411 |
// Verification & debugging - ensure that the offset table reflects the fact
|
|
412 |
// that the block [blk_start, blk_end) or [blk, blk + size) is a
|
|
413 |
// single block of storage. NOTE: can;t const this because of
|
|
414 |
// call to non-const do_block_internal() below.
|
|
415 |
inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) {
|
|
416 |
if (VerifyBlockOffsetArray) {
|
|
417 |
do_block_internal(blk_start, blk_end, Action_check);
|
|
418 |
}
|
|
419 |
}
|
|
420 |
|
|
421 |
inline void verify_single_block(HeapWord* blk, size_t size) {
|
|
422 |
verify_single_block(blk, blk + size);
|
|
423 |
}
|
|
424 |
|
|
425 |
// Verify that the given block is before _unallocated_block
|
|
426 |
inline void verify_not_unallocated(HeapWord* blk_start,
|
|
427 |
HeapWord* blk_end) const {
|
|
428 |
if (BlockOffsetArrayUseUnallocatedBlock) {
|
|
429 |
assert(blk_start < blk_end, "Block inconsistency?");
|
|
430 |
assert(blk_end <= _unallocated_block, "_unallocated_block problem");
|
|
431 |
}
|
|
432 |
}
|
|
433 |
|
|
434 |
inline void verify_not_unallocated(HeapWord* blk, size_t size) const {
|
|
435 |
verify_not_unallocated(blk, blk + size);
|
|
436 |
}
|
|
437 |
|
|
438 |
void check_all_cards(size_t left_card, size_t right_card) const;
|
|
439 |
};
|
|
440 |
|
|
441 |
// A subtype of BlockOffsetArray that takes advantage of the fact
|
|
442 |
// that its underlying space is a ContiguousSpace, so that its "active"
|
|
443 |
// region can be more efficiently tracked (than for a non-contiguous space).
|
|
444 |
class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
|
|
445 |
friend class VMStructs;
|
|
446 |
|
|
447 |
// allocation boundary at which offset array must be updated
|
|
448 |
HeapWord* _next_offset_threshold;
|
|
449 |
size_t _next_offset_index; // index corresponding to that boundary
|
|
450 |
|
|
451 |
// Work function to be called when allocation start crosses the next
|
|
452 |
// threshold in the contig space.
|
|
453 |
void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
|
|
454 |
alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
|
|
455 |
blk_start, blk_end);
|
|
456 |
}
|
|
457 |
|
|
458 |
|
|
459 |
public:
|
|
460 |
G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
|
|
461 |
|
|
462 |
// Initialize the threshold to reflect the first boundary after the
|
|
463 |
// bottom of the covered region.
|
|
464 |
HeapWord* initialize_threshold();
|
|
465 |
|
|
466 |
// Zero out the entry for _bottom (offset will be zero).
|
|
467 |
void zero_bottom_entry();
|
|
468 |
|
|
469 |
// Return the next threshold, the point at which the table should be
|
|
470 |
// updated.
|
|
471 |
HeapWord* threshold() const { return _next_offset_threshold; }
|
|
472 |
|
|
473 |
// These must be guaranteed to work properly (i.e., do nothing)
|
|
474 |
// when "blk_start" ("blk" for second version) is "NULL". In this
|
|
475 |
// implementation, that's true because NULL is represented as 0, and thus
|
|
476 |
// never exceeds the "_next_offset_threshold".
|
|
477 |
void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
|
|
478 |
if (blk_end > _next_offset_threshold)
|
|
479 |
alloc_block_work1(blk_start, blk_end);
|
|
480 |
}
|
|
481 |
void alloc_block(HeapWord* blk, size_t size) {
|
|
482 |
alloc_block(blk, blk+size);
|
|
483 |
}
|
|
484 |
|
|
485 |
HeapWord* block_start_unsafe(const void* addr);
|
|
486 |
HeapWord* block_start_unsafe_const(const void* addr) const;
|
|
487 |
};
|