blockOffsetTable.hpp revision 337
/*
* Copyright 2000-2008 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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
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// 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.
//
// BlockOffsetTable (abstract)
// - BlockOffsetArray (abstract)
// - BlockOffsetArrayNonContigSpace
// - BlockOffsetArrayContigSpace
//
class ContiguousSpace;
class SerializeOopClosure;
//////////////////////////////////////////////////////////////////////////
// The BlockOffsetTable "interface"
//////////////////////////////////////////////////////////////////////////
class BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
friend class VMStructs;
protected:
// These members describe the region covered by the table.
// The space this table is covering.
public:
// Initialize the table to cover the given space.
// The contents of the initial table are undefined.
}
// Note that the committed size of the covered space may have changed,
// so the table size might also wish to change.
}
// Requires "addr" to be contained by a block, and returns the address of
// the start of that block.
// Returns the address of the start of the block containing "addr", or
// else "null" if it is covered by no block.
};
//////////////////////////////////////////////////////////////////////////
// One implementation of "BlockOffsetTable," the BlockOffsetArray,
// 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. (Consider,
// for example, the garbage-first generation.)
// Here is the shared array type.
//////////////////////////////////////////////////////////////////////////
// BlockOffsetSharedArray
//////////////////////////////////////////////////////////////////////////
class BlockOffsetSharedArray: public CHeapObj {
friend class BlockOffsetArray;
friend class BlockOffsetArrayNonContigSpace;
friend class BlockOffsetArrayContigSpace;
friend class VMStructs;
private:
enum SomePrivateConstants {
LogN = 9,
};
// The reserved region covered by the shared array.
// End of the current committed region.
// Array for keeping offsets for retrieving object start fast given an
// address.
protected:
// Bounds checking accessors:
// For performance these have to devolve to array accesses in product builds.
return _offset_array[index];
}
}
}
"right address out of range");
}
}
"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.
}
public:
// 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
// BlockOffsetTable(s) to initialize cards.
// 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.
// Updates all the BlockOffsetArray's sharing this shared array to
// reflect the current "top"'s of their spaces.
void update_offset_arrays(); // Not yet implemented!
// Return the appropriate index into "_offset_array" for "p".
// Return the address indicating the start of the region corresponding to
// "index" in "_offset_array".
// Return the address "p" incremented by the size of
// a region. This method does not align the address
// returned to the start of a region. It is a simple
// primitive.
// Shared space support
};
//////////////////////////////////////////////////////////////////////////
// The BlockOffsetArray whose subtypes use the BlockOffsetSharedArray.
//////////////////////////////////////////////////////////////////////////
class BlockOffsetArray: public BlockOffsetTable {
friend class VMStructs;
protected:
// The following enums are used by do_block_internal() below
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()).
};
enum SomePrivateConstants {
// entries "e" of at least N_words mean "go back by Base^(e-N_words)."
// All entries are less than "N_words + N_powers".
LogBase = 4,
N_powers = 14
};
return 1 << (LogBase * i);
}
return power_to_cards_back(i) * N_words;
}
}
}
// The shared array, which is shared with other BlockOffsetArray's
// corresponding to different spaces within a generation or span of
// memory.
// The space that owns this subregion.
// 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;
// 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.
// Same as above, except that the args here are a card _index_ interval
// that is closed: [start_index, end_index]
// A helper function for BOT adjustment/verification work
public:
// The space may not have its 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.
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.
// Resets the covered region to the given "mr".
}
// Note that the committed size of the covered space may have changed,
// so the table size might also wish to change.
// verify that the old and new boundaries are also card boundaries
"_end not a card boundary");
"new _end would not be a card boundary");
// set all the newly added cards
}
}
// 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.
}
// When the alloc_block() call returns, the block offset table should
// have enough information such that any subsequent block_start() call
// with an argument equal to an address that is within the range
// [blk_start, blk_end) would return the value blk_start, provided
// there have been no calls in between that reset this information
// (e.g. see BlockOffsetArrayNonContigSpace::single_block() call
// for an appropriate range covering the said interval).
// These methods expect to be called with [blk_start, blk_end)
// representing a block of memory in the heap.
}
// 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; }
// Debugging
// Return the index of the last entry in the "active" region.
virtual size_t last_active_index() const = 0;
// Verify the block offset table
void verify() const;
};
////////////////////////////////////////////////////////////////////////////
// A subtype of BlockOffsetArray that takes advantage of the fact
// that its underlying space is a NonContiguousSpace, so that some
// specialized interfaces can be made available for spaces that
// manipulate the table.
////////////////////////////////////////////////////////////////////////////
class BlockOffsetArrayNonContigSpace: public BlockOffsetArray {
friend class VMStructs;
private:
// The portion [_unallocated_block, _sp.end()) of the space that
// is a single block known not to contain any objects.
// NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
public:
// accessor
HeapWord* unallocated_block() const {
"_unallocated_block is not being maintained");
return _unallocated_block;
}
"_unallocated_block is not being maintained");
}
// These methods expect to be called with [blk_start, blk_end)
// representing a block of memory in the heap.
}
// The following methods are useful and optimized for a
// non-contiguous space.
// 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.
// 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.
}
// 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.
// Verify that the BOT shows [blk, blk + blk_size) to be one block.
}
}
}
}
// Requires "addr" to be the start of a card and returns the
// start of the block that contains the given address.
// 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.
// Verify that the given block is before _unallocated_block
const PRODUCT_RETURN;
const PRODUCT_RETURN;
// Debugging support
virtual size_t last_active_index() 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 BlockOffsetArrayContigSpace: public BlockOffsetArray {
friend class VMStructs;
private:
// allocation boundary at which offset array must be updated
// Work function when allocation start crosses threshold.
public:
_next_offset_index = 0;
}
// Initialize the threshold for an empty heap.
// 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.
// In general, these methods expect to be called with
// [blk_start, blk_end) representing a block of memory in the heap.
// blk_end are NULL because NULL is represented as 0, and thus
// never exceeds the "_next_offset_threshold".
if (blk_end > _next_offset_threshold) {
}
}
}
// Debugging support
virtual size_t last_active_index() const;
};