diff -r 0b27f3512f9e -r 37f87013dfd8 src/share/vm/gc_implementation/g1/g1BlockOffsetTable.hpp --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/share/vm/gc_implementation/g1/g1BlockOffsetTable.hpp Thu Jun 05 15:57:56 2008 -0700 @@ -0,0 +1,487 @@ +/* + * Copyright 2001-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, + * CA 95054 USA or visit www.sun.com if you need additional information or + * have any questions. + * + */ + +// The CollectedHeap type requires subtypes to implement a method +// "block_start". For some subtypes, notably generational +// systems using card-table-based write barriers, the efficiency of this +// operation may be important. Implementations of the "BlockOffsetArray" +// class may be useful in providing such efficient implementations. +// +// While generally mirroring the structure of the BOT for GenCollectedHeap, +// the following types are tailored more towards G1's uses; these should, +// however, be merged back into a common BOT to avoid code duplication +// and reduce maintenance overhead. +// +// G1BlockOffsetTable (abstract) +// -- G1BlockOffsetArray (uses G1BlockOffsetSharedArray) +// -- G1BlockOffsetArrayContigSpace +// +// A main impediment to the consolidation of this code might be the +// effect of making some of the block_start*() calls non-const as +// below. Whether that might adversely affect performance optimizations +// that compilers might normally perform in the case of non-G1 +// collectors needs to be carefully investigated prior to any such +// consolidation. + +// Forward declarations +class ContiguousSpace; +class G1BlockOffsetSharedArray; + +class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC { + friend class VMStructs; +protected: + // These members describe the region covered by the table. + + // The space this table is covering. + HeapWord* _bottom; // == reserved.start + HeapWord* _end; // End of currently allocated region. + +public: + // Initialize the table to cover the given space. + // The contents of the initial table are undefined. + G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) : + _bottom(bottom), _end(end) + { + assert(_bottom <= _end, "arguments out of order"); + } + + // Note that the committed size of the covered space may have changed, + // so the table size might also wish to change. + virtual void resize(size_t new_word_size) = 0; + + virtual void set_bottom(HeapWord* new_bottom) { + assert(new_bottom <= _end, "new_bottom > _end"); + _bottom = new_bottom; + resize(pointer_delta(_end, _bottom)); + } + + // Requires "addr" to be contained by a block, and returns the address of + // the start of that block. (May have side effects, namely updating of + // shared array entries that "point" too far backwards. This can occur, + // for example, when LAB allocation is used in a space covered by the + // table.) + virtual HeapWord* block_start_unsafe(const void* addr) = 0; + // Same as above, but does not have any of the possible side effects + // discussed above. + virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0; + + // Returns the address of the start of the block containing "addr", or + // else "null" if it is covered by no block. (May have side effects, + // namely updating of shared array entries that "point" too far + // backwards. This can occur, for example, when lab allocation is used + // in a space covered by the table.) + inline HeapWord* block_start(const void* addr); + // Same as above, but does not have any of the possible side effects + // discussed above. + inline HeapWord* block_start_const(const void* addr) const; +}; + +// This implementation of "G1BlockOffsetTable" divides the covered region +// into "N"-word subregions (where "N" = 2^"LogN". An array with an entry +// for each such subregion indicates how far back one must go to find the +// start of the chunk that includes the first word of the subregion. +// +// Each BlockOffsetArray is owned by a Space. However, the actual array +// may be shared by several BlockOffsetArrays; this is useful +// when a single resizable area (such as a generation) is divided up into +// several spaces in which contiguous allocation takes place, +// such as, for example, in G1 or in the train generation.) + +// Here is the shared array type. + +class G1BlockOffsetSharedArray: public CHeapObj { + friend class G1BlockOffsetArray; + friend class G1BlockOffsetArrayContigSpace; + friend class VMStructs; + +private: + // The reserved region covered by the shared array. + MemRegion _reserved; + + // End of the current committed region. + HeapWord* _end; + + // Array for keeping offsets for retrieving object start fast given an + // address. + VirtualSpace _vs; + u_char* _offset_array; // byte array keeping backwards offsets + + // Bounds checking accessors: + // For performance these have to devolve to array accesses in product builds. + u_char offset_array(size_t index) const { + assert(index < _vs.committed_size(), "index out of range"); + return _offset_array[index]; + } + + void set_offset_array(size_t index, u_char offset) { + assert(index < _vs.committed_size(), "index out of range"); + assert(offset <= N_words, "offset too large"); + _offset_array[index] = offset; + } + + void set_offset_array(size_t index, HeapWord* high, HeapWord* low) { + assert(index < _vs.committed_size(), "index out of range"); + assert(high >= low, "addresses out of order"); + assert(pointer_delta(high, low) <= N_words, "offset too large"); + _offset_array[index] = (u_char) pointer_delta(high, low); + } + + void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) { + assert(index_for(right - 1) < _vs.committed_size(), + "right address out of range"); + assert(left < right, "Heap addresses out of order"); + size_t num_cards = pointer_delta(right, left) >> LogN_words; + memset(&_offset_array[index_for(left)], offset, num_cards); + } + + void set_offset_array(size_t left, size_t right, u_char offset) { + assert(right < _vs.committed_size(), "right address out of range"); + assert(left <= right, "indexes out of order"); + size_t num_cards = right - left + 1; + memset(&_offset_array[left], offset, num_cards); + } + + void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const { + assert(index < _vs.committed_size(), "index out of range"); + assert(high >= low, "addresses out of order"); + assert(pointer_delta(high, low) <= N_words, "offset too large"); + assert(_offset_array[index] == pointer_delta(high, low), + "Wrong offset"); + } + + bool is_card_boundary(HeapWord* p) const; + + // Return the number of slots needed for an offset array + // that covers mem_region_words words. + // We always add an extra slot because if an object + // ends on a card boundary we put a 0 in the next + // offset array slot, so we want that slot always + // to be reserved. + + size_t compute_size(size_t mem_region_words) { + size_t number_of_slots = (mem_region_words / N_words) + 1; + return ReservedSpace::page_align_size_up(number_of_slots); + } + +public: + enum SomePublicConstants { + LogN = 9, + LogN_words = LogN - LogHeapWordSize, + N_bytes = 1 << LogN, + N_words = 1 << LogN_words + }; + + // Initialize the table to cover from "base" to (at least) + // "base + init_word_size". In the future, the table may be expanded + // (see "resize" below) up to the size of "_reserved" (which must be at + // least "init_word_size".) The contents of the initial table are + // undefined; it is the responsibility of the constituent + // G1BlockOffsetTable(s) to initialize cards. + G1BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size); + + // Notes a change in the committed size of the region covered by the + // table. The "new_word_size" may not be larger than the size of the + // reserved region this table covers. + void resize(size_t new_word_size); + + void set_bottom(HeapWord* new_bottom); + + // Updates all the BlockOffsetArray's sharing this shared array to + // reflect the current "top"'s of their spaces. + void update_offset_arrays(); + + // Return the appropriate index into "_offset_array" for "p". + inline size_t index_for(const void* p) const; + + // Return the address indicating the start of the region corresponding to + // "index" in "_offset_array". + inline HeapWord* address_for_index(size_t index) const; +}; + +// And here is the G1BlockOffsetTable subtype that uses the array. + +class G1BlockOffsetArray: public G1BlockOffsetTable { + friend class G1BlockOffsetSharedArray; + friend class G1BlockOffsetArrayContigSpace; + friend class VMStructs; +private: + enum SomePrivateConstants { + N_words = G1BlockOffsetSharedArray::N_words, + LogN = G1BlockOffsetSharedArray::LogN + }; + + // The following enums are used by do_block_helper + enum Action { + Action_single, // BOT records a single block (see single_block()) + Action_mark, // BOT marks the start of a block (see mark_block()) + Action_check // Check that BOT records block correctly + // (see verify_single_block()). + }; + + // This is the array, which can be shared by several BlockOffsetArray's + // servicing different + G1BlockOffsetSharedArray* _array; + + // The space that owns this subregion. + Space* _sp; + + // If "_sp" is a contiguous space, the field below is the view of "_sp" + // as a contiguous space, else NULL. + ContiguousSpace* _csp; + + // If true, array entries are initialized to 0; otherwise, they are + // initialized to point backwards to the beginning of the covered region. + bool _init_to_zero; + + // The portion [_unallocated_block, _sp.end()) of the space that + // is a single block known not to contain any objects. + // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag. + HeapWord* _unallocated_block; + + // Sets the entries + // corresponding to the cards starting at "start" and ending at "end" + // to point back to the card before "start": the interval [start, end) + // is right-open. + void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end); + // Same as above, except that the args here are a card _index_ interval + // that is closed: [start_index, end_index] + void set_remainder_to_point_to_start_incl(size_t start, size_t end); + + // A helper function for BOT adjustment/verification work + void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action); + +protected: + + ContiguousSpace* csp() const { return _csp; } + + // Returns the address of a block whose start is at most "addr". + // If "has_max_index" is true, "assumes "max_index" is the last valid one + // in the array. + inline HeapWord* block_at_or_preceding(const void* addr, + bool has_max_index, + size_t max_index) const; + + // "q" is a block boundary that is <= "addr"; "n" is the address of the + // next block (or the end of the space.) Return the address of the + // beginning of the block that contains "addr". Does so without side + // effects (see, e.g., spec of block_start.) + inline HeapWord* + forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n, + const void* addr) const; + + // "q" is a block boundary that is <= "addr"; return the address of the + // beginning of the block that contains "addr". May have side effects + // on "this", by updating imprecise entries. + inline HeapWord* forward_to_block_containing_addr(HeapWord* q, + const void* addr); + + // "q" is a block boundary that is <= "addr"; "n" is the address of the + // next block (or the end of the space.) Return the address of the + // beginning of the block that contains "addr". May have side effects + // on "this", by updating imprecise entries. + HeapWord* forward_to_block_containing_addr_slow(HeapWord* q, + HeapWord* n, + const void* addr); + + // Requires that "*threshold_" be the first array entry boundary at or + // above "blk_start", and that "*index_" be the corresponding array + // index. If the block starts at or crosses "*threshold_", records + // "blk_start" as the appropriate block start for the array index + // starting at "*threshold_", and for any other indices crossed by the + // block. Updates "*threshold_" and "*index_" to correspond to the first + // index after the block end. + void alloc_block_work2(HeapWord** threshold_, size_t* index_, + HeapWord* blk_start, HeapWord* blk_end); + +public: + // The space may not have it's bottom and top set yet, which is why the + // region is passed as a parameter. If "init_to_zero" is true, the + // elements of the array are initialized to zero. Otherwise, they are + // initialized to point backwards to the beginning. + G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr, + bool init_to_zero); + + // Note: this ought to be part of the constructor, but that would require + // "this" to be passed as a parameter to a member constructor for + // the containing concrete subtype of Space. + // This would be legal C++, but MS VC++ doesn't allow it. + void set_space(Space* sp); + + // Resets the covered region to the given "mr". + void set_region(MemRegion mr); + + // Resets the covered region to one with the same _bottom as before but + // the "new_word_size". + void resize(size_t new_word_size); + + // These must be guaranteed to work properly (i.e., do nothing) + // when "blk_start" ("blk" for second version) is "NULL". + virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end); + virtual void alloc_block(HeapWord* blk, size_t size) { + alloc_block(blk, blk + size); + } + + // The following methods are useful and optimized for a + // general, non-contiguous space. + + // The given arguments are required to be the starts of adjacent ("blk1" + // before "blk2") well-formed blocks covered by "this". After this call, + // they should be considered to form one block. + virtual void join_blocks(HeapWord* blk1, HeapWord* blk2); + + // Given a block [blk_start, blk_start + full_blk_size), and + // a left_blk_size < full_blk_size, adjust the BOT to show two + // blocks [blk_start, blk_start + left_blk_size) and + // [blk_start + left_blk_size, blk_start + full_blk_size). + // It is assumed (and verified in the non-product VM) that the + // BOT was correct for the original block. + void split_block(HeapWord* blk_start, size_t full_blk_size, + size_t left_blk_size); + + // Adjust the BOT to show that it has a single block in the + // range [blk_start, blk_start + size). All necessary BOT + // cards are adjusted, but _unallocated_block isn't. + void single_block(HeapWord* blk_start, HeapWord* blk_end); + void single_block(HeapWord* blk, size_t size) { + single_block(blk, blk + size); + } + + // Adjust BOT to show that it has a block in the range + // [blk_start, blk_start + size). Only the first card + // of BOT is touched. It is assumed (and verified in the + // non-product VM) that the remaining cards of the block + // are correct. + void mark_block(HeapWord* blk_start, HeapWord* blk_end); + void mark_block(HeapWord* blk, size_t size) { + mark_block(blk, blk + size); + } + + // Adjust _unallocated_block to indicate that a particular + // block has been newly allocated or freed. It is assumed (and + // verified in the non-product VM) that the BOT is correct for + // the given block. + inline void allocated(HeapWord* blk_start, HeapWord* blk_end) { + // Verify that the BOT shows [blk, blk + blk_size) to be one block. + verify_single_block(blk_start, blk_end); + if (BlockOffsetArrayUseUnallocatedBlock) { + _unallocated_block = MAX2(_unallocated_block, blk_end); + } + } + + inline void allocated(HeapWord* blk, size_t size) { + allocated(blk, blk + size); + } + + inline void freed(HeapWord* blk_start, HeapWord* blk_end); + + inline void freed(HeapWord* blk, size_t size); + + virtual HeapWord* block_start_unsafe(const void* addr); + virtual HeapWord* block_start_unsafe_const(const void* addr) const; + + // Requires "addr" to be the start of a card and returns the + // start of the block that contains the given address. + HeapWord* block_start_careful(const void* addr) const; + + // If true, initialize array slots with no allocated blocks to zero. + // Otherwise, make them point back to the front. + bool init_to_zero() { return _init_to_zero; } + + // 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. + inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) { + if (VerifyBlockOffsetArray) { + do_block_internal(blk_start, blk_end, Action_check); + } + } + + inline void verify_single_block(HeapWord* blk, size_t size) { + verify_single_block(blk, blk + size); + } + + // Verify that the given block is before _unallocated_block + inline void 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"); + } + } + + inline void verify_not_unallocated(HeapWord* blk, size_t size) const { + verify_not_unallocated(blk, blk + size); + } + + void check_all_cards(size_t left_card, size_t right_card) const; +}; + +// A subtype of BlockOffsetArray that takes advantage of the fact +// that its underlying space is a ContiguousSpace, so that its "active" +// region can be more efficiently tracked (than for a non-contiguous space). +class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray { + friend class VMStructs; + + // allocation boundary at which offset array must be updated + HeapWord* _next_offset_threshold; + size_t _next_offset_index; // index corresponding to that boundary + + // Work function to be called when allocation start crosses the next + // threshold in the contig space. + void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) { + alloc_block_work2(&_next_offset_threshold, &_next_offset_index, + blk_start, blk_end); + } + + + public: + G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr); + + // Initialize the threshold to reflect the first boundary after the + // bottom of the covered region. + HeapWord* initialize_threshold(); + + // Zero out the entry for _bottom (offset will be zero). + void zero_bottom_entry(); + + // Return the next threshold, the point at which the table should be + // updated. + HeapWord* threshold() const { return _next_offset_threshold; } + + // These must be guaranteed to work properly (i.e., do nothing) + // when "blk_start" ("blk" for second version) is "NULL". In this + // implementation, that's true because NULL is represented as 0, and thus + // never exceeds the "_next_offset_threshold". + void alloc_block(HeapWord* blk_start, HeapWord* blk_end) { + if (blk_end > _next_offset_threshold) + alloc_block_work1(blk_start, blk_end); + } + void alloc_block(HeapWord* blk, size_t size) { + alloc_block(blk, blk+size); + } + + HeapWord* block_start_unsafe(const void* addr); + HeapWord* block_start_unsafe_const(const void* addr) const; +};