Java example source code file (space.hpp)
The space.hpp Java example source code
/*
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* 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.
*
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* 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.
*
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#ifndef SHARE_VM_MEMORY_SPACE_HPP
#define SHARE_VM_MEMORY_SPACE_HPP
#include "memory/allocation.hpp"
#include "memory/blockOffsetTable.hpp"
#include "memory/cardTableModRefBS.hpp"
#include "memory/iterator.hpp"
#include "memory/memRegion.hpp"
#include "memory/watermark.hpp"
#include "oops/markOop.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/prefetch.hpp"
#include "utilities/macros.hpp"
#include "utilities/workgroup.hpp"
#ifdef TARGET_OS_FAMILY_linux
# include "os_linux.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_solaris
# include "os_solaris.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_windows
# include "os_windows.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_bsd
# include "os_bsd.inline.hpp"
#endif
// A space is an abstraction for the "storage units" backing
// up the generation abstraction. It includes specific
// implementations for keeping track of free and used space,
// for iterating over objects and free blocks, etc.
// Here's the Space hierarchy:
//
// - Space -- an asbtract base class describing a heap area
// - CompactibleSpace -- a space supporting compaction
// - CompactibleFreeListSpace -- (used for CMS generation)
// - ContiguousSpace -- a compactible space in which all free space
// is contiguous
// - EdenSpace -- contiguous space used as nursery
// - ConcEdenSpace -- contiguous space with a 'soft end safe' allocation
// - OffsetTableContigSpace -- contiguous space with a block offset array
// that allows "fast" block_start calls
// - TenuredSpace -- (used for TenuredGeneration)
// Forward decls.
class Space;
class BlockOffsetArray;
class BlockOffsetArrayContigSpace;
class Generation;
class CompactibleSpace;
class BlockOffsetTable;
class GenRemSet;
class CardTableRS;
class DirtyCardToOopClosure;
// An oop closure that is circumscribed by a filtering memory region.
class SpaceMemRegionOopsIterClosure: public ExtendedOopClosure {
private:
ExtendedOopClosure* _cl;
MemRegion _mr;
protected:
template <class T> void do_oop_work(T* p) {
if (_mr.contains(p)) {
_cl->do_oop(p);
}
}
public:
SpaceMemRegionOopsIterClosure(ExtendedOopClosure* cl, MemRegion mr):
_cl(cl), _mr(mr) {}
virtual void do_oop(oop* p);
virtual void do_oop(narrowOop* p);
virtual bool do_metadata() {
// _cl is of type ExtendedOopClosure instead of OopClosure, so that we can check this.
assert(!_cl->do_metadata(), "I've checked all call paths, this shouldn't happen.");
return false;
}
virtual void do_klass(Klass* k) { ShouldNotReachHere(); }
virtual void do_class_loader_data(ClassLoaderData* cld) { ShouldNotReachHere(); }
};
// A Space describes a heap area. Class Space is an abstract
// base class.
//
// Space supports allocation, size computation and GC support is provided.
//
// Invariant: bottom() and end() are on page_size boundaries and
// bottom() <= top() <= end()
// top() is inclusive and end() is exclusive.
class Space: public CHeapObj<mtGC> {
friend class VMStructs;
protected:
HeapWord* _bottom;
HeapWord* _end;
// Used in support of save_marks()
HeapWord* _saved_mark_word;
MemRegionClosure* _preconsumptionDirtyCardClosure;
// A sequential tasks done structure. This supports
// parallel GC, where we have threads dynamically
// claiming sub-tasks from a larger parallel task.
SequentialSubTasksDone _par_seq_tasks;
Space():
_bottom(NULL), _end(NULL), _preconsumptionDirtyCardClosure(NULL) { }
public:
// Accessors
HeapWord* bottom() const { return _bottom; }
HeapWord* end() const { return _end; }
virtual void set_bottom(HeapWord* value) { _bottom = value; }
virtual void set_end(HeapWord* value) { _end = value; }
virtual HeapWord* saved_mark_word() const { return _saved_mark_word; }
void set_saved_mark_word(HeapWord* p) { _saved_mark_word = p; }
MemRegionClosure* preconsumptionDirtyCardClosure() const {
return _preconsumptionDirtyCardClosure;
}
void setPreconsumptionDirtyCardClosure(MemRegionClosure* cl) {
_preconsumptionDirtyCardClosure = cl;
}
// Returns a subregion of the space containing all the objects in
// the space.
virtual MemRegion used_region() const { return MemRegion(bottom(), end()); }
// Returns a region that is guaranteed to contain (at least) all objects
// allocated at the time of the last call to "save_marks". If the space
// initializes its DirtyCardToOopClosure's specifying the "contig" option
// (that is, if the space is contiguous), then this region must contain only
// such objects: the memregion will be from the bottom of the region to the
// saved mark. Otherwise, the "obj_allocated_since_save_marks" method of
// the space must distiguish between objects in the region allocated before
// and after the call to save marks.
virtual MemRegion used_region_at_save_marks() const {
return MemRegion(bottom(), saved_mark_word());
}
// Initialization.
// "initialize" should be called once on a space, before it is used for
// any purpose. The "mr" arguments gives the bounds of the space, and
// the "clear_space" argument should be true unless the memory in "mr" is
// known to be zeroed.
virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
// The "clear" method must be called on a region that may have
// had allocation performed in it, but is now to be considered empty.
virtual void clear(bool mangle_space);
// For detecting GC bugs. Should only be called at GC boundaries, since
// some unused space may be used as scratch space during GC's.
// Default implementation does nothing. We also call this when expanding
// a space to satisfy an allocation request. See bug #4668531
virtual void mangle_unused_area() {}
virtual void mangle_unused_area_complete() {}
virtual void mangle_region(MemRegion mr) {}
// Testers
bool is_empty() const { return used() == 0; }
bool not_empty() const { return used() > 0; }
// Returns true iff the given the space contains the
// given address as part of an allocated object. For
// ceratin kinds of spaces, this might be a potentially
// expensive operation. To prevent performance problems
// on account of its inadvertent use in product jvm's,
// we restrict its use to assertion checks only.
virtual bool is_in(const void* p) const = 0;
// Returns true iff the given reserved memory of the space contains the
// given address.
bool is_in_reserved(const void* p) const { return _bottom <= p && p < _end; }
// Returns true iff the given block is not allocated.
virtual bool is_free_block(const HeapWord* p) const = 0;
// Test whether p is double-aligned
static bool is_aligned(void* p) {
return ((intptr_t)p & (sizeof(double)-1)) == 0;
}
// Size computations. Sizes are in bytes.
size_t capacity() const { return byte_size(bottom(), end()); }
virtual size_t used() const = 0;
virtual size_t free() const = 0;
// Iterate over all the ref-containing fields of all objects in the
// space, calling "cl.do_oop" on each. Fields in objects allocated by
// applications of the closure are not included in the iteration.
virtual void oop_iterate(ExtendedOopClosure* cl);
// Same as above, restricted to the intersection of a memory region and
// the space. Fields in objects allocated by applications of the closure
// are not included in the iteration.
virtual void oop_iterate(MemRegion mr, ExtendedOopClosure* cl) = 0;
// Iterate over all objects in the space, calling "cl.do_object" on
// each. Objects allocated by applications of the closure are not
// included in the iteration.
virtual void object_iterate(ObjectClosure* blk) = 0;
// Similar to object_iterate() except only iterates over
// objects whose internal references point to objects in the space.
virtual void safe_object_iterate(ObjectClosure* blk) = 0;
// Iterate over all objects that intersect with mr, calling "cl->do_object"
// on each. There is an exception to this: if this closure has already
// been invoked on an object, it may skip such objects in some cases. This is
// Most likely to happen in an "upwards" (ascending address) iteration of
// MemRegions.
virtual void object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl);
// Iterate over as many initialized objects in the space as possible,
// calling "cl.do_object_careful" on each. Return NULL if all objects
// in the space (at the start of the iteration) were iterated over.
// Return an address indicating the extent of the iteration in the
// event that the iteration had to return because of finding an
// uninitialized object in the space, or if the closure "cl"
// signalled early termination.
virtual HeapWord* object_iterate_careful(ObjectClosureCareful* cl);
virtual HeapWord* object_iterate_careful_m(MemRegion mr,
ObjectClosureCareful* cl);
// Create and return a new dirty card to oop closure. Can be
// overriden to return the appropriate type of closure
// depending on the type of space in which the closure will
// operate. ResourceArea allocated.
virtual DirtyCardToOopClosure* new_dcto_cl(ExtendedOopClosure* cl,
CardTableModRefBS::PrecisionStyle precision,
HeapWord* boundary = NULL);
// If "p" is in the space, returns the address of the start of the
// "block" that contains "p". We say "block" instead of "object" since
// some heaps may not pack objects densely; a chunk may either be an
// object or a non-object. If "p" is not in the space, return NULL.
virtual HeapWord* block_start_const(const void* p) const = 0;
// The non-const version may have benevolent side effects on the data
// structure supporting these calls, possibly speeding up future calls.
// The default implementation, however, is simply to call the const
// version.
inline virtual HeapWord* block_start(const void* p);
// Requires "addr" to be the start of a chunk, and returns its size.
// "addr + size" is required to be the start of a new chunk, or the end
// of the active area of the heap.
virtual size_t block_size(const HeapWord* addr) const = 0;
// Requires "addr" to be the start of a block, and returns "TRUE" iff
// the block is an object.
virtual bool block_is_obj(const HeapWord* addr) const = 0;
// Requires "addr" to be the start of a block, and returns "TRUE" iff
// the block is an object and the object is alive.
virtual bool obj_is_alive(const HeapWord* addr) const;
// Allocation (return NULL if full). Assumes the caller has established
// mutually exclusive access to the space.
virtual HeapWord* allocate(size_t word_size) = 0;
// Allocation (return NULL if full). Enforces mutual exclusion internally.
virtual HeapWord* par_allocate(size_t word_size) = 0;
// Returns true if this object has been allocated since a
// generation's "save_marks" call.
virtual bool obj_allocated_since_save_marks(const oop obj) const = 0;
// Mark-sweep-compact support: all spaces can update pointers to objects
// moving as a part of compaction.
virtual void adjust_pointers();
// PrintHeapAtGC support
virtual void print() const;
virtual void print_on(outputStream* st) const;
virtual void print_short() const;
virtual void print_short_on(outputStream* st) const;
// Accessor for parallel sequential tasks.
SequentialSubTasksDone* par_seq_tasks() { return &_par_seq_tasks; }
// IF "this" is a ContiguousSpace, return it, else return NULL.
virtual ContiguousSpace* toContiguousSpace() {
return NULL;
}
// Debugging
virtual void verify() const = 0;
};
// A MemRegionClosure (ResourceObj) whose "do_MemRegion" function applies an
// OopClosure to (the addresses of) all the ref-containing fields that could
// be modified by virtue of the given MemRegion being dirty. (Note that
// because of the imprecise nature of the write barrier, this may iterate
// over oops beyond the region.)
// This base type for dirty card to oop closures handles memory regions
// in non-contiguous spaces with no boundaries, and should be sub-classed
// to support other space types. See ContiguousDCTOC for a sub-class
// that works with ContiguousSpaces.
class DirtyCardToOopClosure: public MemRegionClosureRO {
protected:
ExtendedOopClosure* _cl;
Space* _sp;
CardTableModRefBS::PrecisionStyle _precision;
HeapWord* _boundary; // If non-NULL, process only non-NULL oops
// pointing below boundary.
HeapWord* _min_done; // ObjHeadPreciseArray precision requires
// a downwards traversal; this is the
// lowest location already done (or,
// alternatively, the lowest address that
// shouldn't be done again. NULL means infinity.)
NOT_PRODUCT(HeapWord* _last_bottom;)
NOT_PRODUCT(HeapWord* _last_explicit_min_done;)
// Get the actual top of the area on which the closure will
// operate, given where the top is assumed to be (the end of the
// memory region passed to do_MemRegion) and where the object
// at the top is assumed to start. For example, an object may
// start at the top but actually extend past the assumed top,
// in which case the top becomes the end of the object.
virtual HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);
// Walk the given memory region from bottom to (actual) top
// looking for objects and applying the oop closure (_cl) to
// them. The base implementation of this treats the area as
// blocks, where a block may or may not be an object. Sub-
// classes should override this to provide more accurate
// or possibly more efficient walking.
virtual void walk_mem_region(MemRegion mr, HeapWord* bottom, HeapWord* top);
public:
DirtyCardToOopClosure(Space* sp, ExtendedOopClosure* cl,
CardTableModRefBS::PrecisionStyle precision,
HeapWord* boundary) :
_sp(sp), _cl(cl), _precision(precision), _boundary(boundary),
_min_done(NULL) {
NOT_PRODUCT(_last_bottom = NULL);
NOT_PRODUCT(_last_explicit_min_done = NULL);
}
void do_MemRegion(MemRegion mr);
void set_min_done(HeapWord* min_done) {
_min_done = min_done;
NOT_PRODUCT(_last_explicit_min_done = _min_done);
}
#ifndef PRODUCT
void set_last_bottom(HeapWord* last_bottom) {
_last_bottom = last_bottom;
}
#endif
};
// A structure to represent a point at which objects are being copied
// during compaction.
class CompactPoint : public StackObj {
public:
Generation* gen;
CompactibleSpace* space;
HeapWord* threshold;
CompactPoint(Generation* _gen, CompactibleSpace* _space,
HeapWord* _threshold) :
gen(_gen), space(_space), threshold(_threshold) {}
};
// A space that supports compaction operations. This is usually, but not
// necessarily, a space that is normally contiguous. But, for example, a
// free-list-based space whose normal collection is a mark-sweep without
// compaction could still support compaction in full GC's.
class CompactibleSpace: public Space {
friend class VMStructs;
friend class CompactibleFreeListSpace;
private:
HeapWord* _compaction_top;
CompactibleSpace* _next_compaction_space;
public:
CompactibleSpace() :
_compaction_top(NULL), _next_compaction_space(NULL) {}
virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
virtual void clear(bool mangle_space);
// Used temporarily during a compaction phase to hold the value
// top should have when compaction is complete.
HeapWord* compaction_top() const { return _compaction_top; }
void set_compaction_top(HeapWord* value) {
assert(value == NULL || (value >= bottom() && value <= end()),
"should point inside space");
_compaction_top = value;
}
// Perform operations on the space needed after a compaction
// has been performed.
virtual void reset_after_compaction() {}
// Returns the next space (in the current generation) to be compacted in
// the global compaction order. Also is used to select the next
// space into which to compact.
virtual CompactibleSpace* next_compaction_space() const {
return _next_compaction_space;
}
void set_next_compaction_space(CompactibleSpace* csp) {
_next_compaction_space = csp;
}
// MarkSweep support phase2
// Start the process of compaction of the current space: compute
// post-compaction addresses, and insert forwarding pointers. The fields
// "cp->gen" and "cp->compaction_space" are the generation and space into
// which we are currently compacting. This call updates "cp" as necessary,
// and leaves the "compaction_top" of the final value of
// "cp->compaction_space" up-to-date. Offset tables may be updated in
// this phase as if the final copy had occurred; if so, "cp->threshold"
// indicates when the next such action should be taken.
virtual void prepare_for_compaction(CompactPoint* cp);
// MarkSweep support phase3
virtual void adjust_pointers();
// MarkSweep support phase4
virtual void compact();
// The maximum percentage of objects that can be dead in the compacted
// live part of a compacted space ("deadwood" support.)
virtual size_t allowed_dead_ratio() const { return 0; };
// Some contiguous spaces may maintain some data structures that should
// be updated whenever an allocation crosses a boundary. This function
// returns the first such boundary.
// (The default implementation returns the end of the space, so the
// boundary is never crossed.)
virtual HeapWord* initialize_threshold() { return end(); }
// "q" is an object of the given "size" that should be forwarded;
// "cp" names the generation ("gen") and containing "this" (which must
// also equal "cp->space"). "compact_top" is where in "this" the
// next object should be forwarded to. If there is room in "this" for
// the object, insert an appropriate forwarding pointer in "q".
// If not, go to the next compaction space (there must
// be one, since compaction must succeed -- we go to the first space of
// the previous generation if necessary, updating "cp"), reset compact_top
// and then forward. In either case, returns the new value of "compact_top".
// If the forwarding crosses "cp->threshold", invokes the "cross_threhold"
// function of the then-current compaction space, and updates "cp->threshold
// accordingly".
virtual HeapWord* forward(oop q, size_t size, CompactPoint* cp,
HeapWord* compact_top);
// Return a size with adjusments as required of the space.
virtual size_t adjust_object_size_v(size_t size) const { return size; }
protected:
// Used during compaction.
HeapWord* _first_dead;
HeapWord* _end_of_live;
// Minimum size of a free block.
virtual size_t minimum_free_block_size() const = 0;
// This the function is invoked when an allocation of an object covering
// "start" to "end occurs crosses the threshold; returns the next
// threshold. (The default implementation does nothing.)
virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* the_end) {
return end();
}
// Requires "allowed_deadspace_words > 0", that "q" is the start of a
// free block of the given "word_len", and that "q", were it an object,
// would not move if forwared. If the size allows, fill the free
// block with an object, to prevent excessive compaction. Returns "true"
// iff the free region was made deadspace, and modifies
// "allowed_deadspace_words" to reflect the number of available deadspace
// words remaining after this operation.
bool insert_deadspace(size_t& allowed_deadspace_words, HeapWord* q,
size_t word_len);
};
#define SCAN_AND_FORWARD(cp,scan_limit,block_is_obj,block_size) { \
/* Compute the new addresses for the live objects and store it in the mark \
* Used by universe::mark_sweep_phase2() \
*/ \
HeapWord* compact_top; /* This is where we are currently compacting to. */ \
\
/* We're sure to be here before any objects are compacted into this \
* space, so this is a good time to initialize this: \
*/ \
set_compaction_top(bottom()); \
\
if (cp->space == NULL) { \
assert(cp->gen != NULL, "need a generation"); \
assert(cp->threshold == NULL, "just checking"); \
assert(cp->gen->first_compaction_space() == this, "just checking"); \
cp->space = cp->gen->first_compaction_space(); \
compact_top = cp->space->bottom(); \
cp->space->set_compaction_top(compact_top); \
cp->threshold = cp->space->initialize_threshold(); \
} else { \
compact_top = cp->space->compaction_top(); \
} \
\
/* We allow some amount of garbage towards the bottom of the space, so \
* we don't start compacting before there is a significant gain to be made.\
* Occasionally, we want to ensure a full compaction, which is determined \
* by the MarkSweepAlwaysCompactCount parameter. \
*/ \
uint invocations = MarkSweep::total_invocations(); \
bool skip_dead = ((invocations % MarkSweepAlwaysCompactCount) != 0); \
\
size_t allowed_deadspace = 0; \
if (skip_dead) { \
const size_t ratio = allowed_dead_ratio(); \
allowed_deadspace = (capacity() * ratio / 100) / HeapWordSize; \
} \
\
HeapWord* q = bottom(); \
HeapWord* t = scan_limit(); \
\
HeapWord* end_of_live= q; /* One byte beyond the last byte of the last \
live object. */ \
HeapWord* first_dead = end();/* The first dead object. */ \
LiveRange* liveRange = NULL; /* The current live range, recorded in the \
first header of preceding free area. */ \
_first_dead = first_dead; \
\
const intx interval = PrefetchScanIntervalInBytes; \
\
while (q < t) { \
assert(!block_is_obj(q) || \
oop(q)->mark()->is_marked() || oop(q)->mark()->is_unlocked() || \
oop(q)->mark()->has_bias_pattern(), \
"these are the only valid states during a mark sweep"); \
if (block_is_obj(q) && oop(q)->is_gc_marked()) { \
/* prefetch beyond q */ \
Prefetch::write(q, interval); \
size_t size = block_size(q); \
compact_top = cp->space->forward(oop(q), size, cp, compact_top); \
q += size; \
end_of_live = q; \
} else { \
/* run over all the contiguous dead objects */ \
HeapWord* end = q; \
do { \
/* prefetch beyond end */ \
Prefetch::write(end, interval); \
end += block_size(end); \
} while (end < t && (!block_is_obj(end) || !oop(end)->is_gc_marked()));\
\
/* see if we might want to pretend this object is alive so that \
* we don't have to compact quite as often. \
*/ \
if (allowed_deadspace > 0 && q == compact_top) { \
size_t sz = pointer_delta(end, q); \
if (insert_deadspace(allowed_deadspace, q, sz)) { \
compact_top = cp->space->forward(oop(q), sz, cp, compact_top); \
q = end; \
end_of_live = end; \
continue; \
} \
} \
\
/* otherwise, it really is a free region. */ \
\
/* for the previous LiveRange, record the end of the live objects. */ \
if (liveRange) { \
liveRange->set_end(q); \
} \
\
/* record the current LiveRange object. \
* liveRange->start() is overlaid on the mark word. \
*/ \
liveRange = (LiveRange*)q; \
liveRange->set_start(end); \
liveRange->set_end(end); \
\
/* see if this is the first dead region. */ \
if (q < first_dead) { \
first_dead = q; \
} \
\
/* move on to the next object */ \
q = end; \
} \
} \
\
assert(q == t, "just checking"); \
if (liveRange != NULL) { \
liveRange->set_end(q); \
} \
_end_of_live = end_of_live; \
if (end_of_live < first_dead) { \
first_dead = end_of_live; \
} \
_first_dead = first_dead; \
\
/* save the compaction_top of the compaction space. */ \
cp->space->set_compaction_top(compact_top); \
}
#define SCAN_AND_ADJUST_POINTERS(adjust_obj_size) { \
/* adjust all the interior pointers to point at the new locations of objects \
* Used by MarkSweep::mark_sweep_phase3() */ \
\
HeapWord* q = bottom(); \
HeapWord* t = _end_of_live; /* Established by "prepare_for_compaction". */ \
\
assert(_first_dead <= _end_of_live, "Stands to reason, no?"); \
\
if (q < t && _first_dead > q && \
!oop(q)->is_gc_marked()) { \
/* we have a chunk of the space which hasn't moved and we've \
* reinitialized the mark word during the previous pass, so we can't \
* use is_gc_marked for the traversal. */ \
HeapWord* end = _first_dead; \
\
while (q < end) { \
/* I originally tried to conjoin "block_start(q) == q" to the \
* assertion below, but that doesn't work, because you can't \
* accurately traverse previous objects to get to the current one \
* after their pointers have been \
* updated, until the actual compaction is done. dld, 4/00 */ \
assert(block_is_obj(q), \
"should be at block boundaries, and should be looking at objs"); \
\
/* point all the oops to the new location */ \
size_t size = oop(q)->adjust_pointers(); \
size = adjust_obj_size(size); \
\
q += size; \
} \
\
if (_first_dead == t) { \
q = t; \
} else { \
/* $$$ This is funky. Using this to read the previously written \
* LiveRange. See also use below. */ \
q = (HeapWord*)oop(_first_dead)->mark()->decode_pointer(); \
} \
} \
\
const intx interval = PrefetchScanIntervalInBytes; \
\
debug_only(HeapWord* prev_q = NULL); \
while (q < t) { \
/* prefetch beyond q */ \
Prefetch::write(q, interval); \
if (oop(q)->is_gc_marked()) { \
/* q is alive */ \
/* point all the oops to the new location */ \
size_t size = oop(q)->adjust_pointers(); \
size = adjust_obj_size(size); \
debug_only(prev_q = q); \
q += size; \
} else { \
/* q is not a live object, so its mark should point at the next \
* live object */ \
debug_only(prev_q = q); \
q = (HeapWord*) oop(q)->mark()->decode_pointer(); \
assert(q > prev_q, "we should be moving forward through memory"); \
} \
} \
\
assert(q == t, "just checking"); \
}
#define SCAN_AND_COMPACT(obj_size) { \
/* Copy all live objects to their new location \
* Used by MarkSweep::mark_sweep_phase4() */ \
\
HeapWord* q = bottom(); \
HeapWord* const t = _end_of_live; \
debug_only(HeapWord* prev_q = NULL); \
\
if (q < t && _first_dead > q && \
!oop(q)->is_gc_marked()) { \
debug_only( \
/* we have a chunk of the space which hasn't moved and we've reinitialized \
* the mark word during the previous pass, so we can't use is_gc_marked for \
* the traversal. */ \
HeapWord* const end = _first_dead; \
\
while (q < end) { \
size_t size = obj_size(q); \
assert(!oop(q)->is_gc_marked(), \
"should be unmarked (special dense prefix handling)"); \
debug_only(prev_q = q); \
q += size; \
} \
) /* debug_only */ \
\
if (_first_dead == t) { \
q = t; \
} else { \
/* $$$ Funky */ \
q = (HeapWord*) oop(_first_dead)->mark()->decode_pointer(); \
} \
} \
\
const intx scan_interval = PrefetchScanIntervalInBytes; \
const intx copy_interval = PrefetchCopyIntervalInBytes; \
while (q < t) { \
if (!oop(q)->is_gc_marked()) { \
/* mark is pointer to next marked oop */ \
debug_only(prev_q = q); \
q = (HeapWord*) oop(q)->mark()->decode_pointer(); \
assert(q > prev_q, "we should be moving forward through memory"); \
} else { \
/* prefetch beyond q */ \
Prefetch::read(q, scan_interval); \
\
/* size and destination */ \
size_t size = obj_size(q); \
HeapWord* compaction_top = (HeapWord*)oop(q)->forwardee(); \
\
/* prefetch beyond compaction_top */ \
Prefetch::write(compaction_top, copy_interval); \
\
/* copy object and reinit its mark */ \
assert(q != compaction_top, "everything in this pass should be moving"); \
Copy::aligned_conjoint_words(q, compaction_top, size); \
oop(compaction_top)->init_mark(); \
assert(oop(compaction_top)->klass() != NULL, "should have a class"); \
\
debug_only(prev_q = q); \
q += size; \
} \
} \
\
/* Let's remember if we were empty before we did the compaction. */ \
bool was_empty = used_region().is_empty(); \
/* Reset space after compaction is complete */ \
reset_after_compaction(); \
/* We do this clear, below, since it has overloaded meanings for some */ \
/* space subtypes. For example, OffsetTableContigSpace's that were */ \
/* compacted into will have had their offset table thresholds updated */ \
/* continuously, but those that weren't need to have their thresholds */ \
/* re-initialized. Also mangles unused area for debugging. */ \
if (used_region().is_empty()) { \
if (!was_empty) clear(SpaceDecorator::Mangle); \
} else { \
if (ZapUnusedHeapArea) mangle_unused_area(); \
} \
}
class GenSpaceMangler;
// A space in which the free area is contiguous. It therefore supports
// faster allocation, and compaction.
class ContiguousSpace: public CompactibleSpace {
friend class OneContigSpaceCardGeneration;
friend class VMStructs;
protected:
HeapWord* _top;
HeapWord* _concurrent_iteration_safe_limit;
// A helper for mangling the unused area of the space in debug builds.
GenSpaceMangler* _mangler;
GenSpaceMangler* mangler() { return _mangler; }
// Allocation helpers (return NULL if full).
inline HeapWord* allocate_impl(size_t word_size, HeapWord* end_value);
inline HeapWord* par_allocate_impl(size_t word_size, HeapWord* end_value);
public:
ContiguousSpace();
~ContiguousSpace();
virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
virtual void clear(bool mangle_space);
// Accessors
HeapWord* top() const { return _top; }
void set_top(HeapWord* value) { _top = value; }
virtual void set_saved_mark() { _saved_mark_word = top(); }
void reset_saved_mark() { _saved_mark_word = bottom(); }
WaterMark bottom_mark() { return WaterMark(this, bottom()); }
WaterMark top_mark() { return WaterMark(this, top()); }
WaterMark saved_mark() { return WaterMark(this, saved_mark_word()); }
bool saved_mark_at_top() const { return saved_mark_word() == top(); }
// In debug mode mangle (write it with a particular bit
// pattern) the unused part of a space.
// Used to save the an address in a space for later use during mangling.
void set_top_for_allocations(HeapWord* v) PRODUCT_RETURN;
// Used to save the space's current top for later use during mangling.
void set_top_for_allocations() PRODUCT_RETURN;
// Mangle regions in the space from the current top up to the
// previously mangled part of the space.
void mangle_unused_area() PRODUCT_RETURN;
// Mangle [top, end)
void mangle_unused_area_complete() PRODUCT_RETURN;
// Mangle the given MemRegion.
void mangle_region(MemRegion mr) PRODUCT_RETURN;
// Do some sparse checking on the area that should have been mangled.
void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;
// Check the complete area that should have been mangled.
// This code may be NULL depending on the macro DEBUG_MANGLING.
void check_mangled_unused_area_complete() PRODUCT_RETURN;
// Size computations: sizes in bytes.
size_t capacity() const { return byte_size(bottom(), end()); }
size_t used() const { return byte_size(bottom(), top()); }
size_t free() const { return byte_size(top(), end()); }
// Override from space.
bool is_in(const void* p) const;
virtual bool is_free_block(const HeapWord* p) const;
// In a contiguous space we have a more obvious bound on what parts
// contain objects.
MemRegion used_region() const { return MemRegion(bottom(), top()); }
MemRegion used_region_at_save_marks() const {
return MemRegion(bottom(), saved_mark_word());
}
// Allocation (return NULL if full)
virtual HeapWord* allocate(size_t word_size);
virtual HeapWord* par_allocate(size_t word_size);
virtual bool obj_allocated_since_save_marks(const oop obj) const {
return (HeapWord*)obj >= saved_mark_word();
}
// Iteration
void oop_iterate(ExtendedOopClosure* cl);
void oop_iterate(MemRegion mr, ExtendedOopClosure* cl);
void object_iterate(ObjectClosure* blk);
// For contiguous spaces this method will iterate safely over objects
// in the space (i.e., between bottom and top) when at a safepoint.
void safe_object_iterate(ObjectClosure* blk);
void object_iterate_mem(MemRegion mr, UpwardsObjectClosure* cl);
// iterates on objects up to the safe limit
HeapWord* object_iterate_careful(ObjectClosureCareful* cl);
HeapWord* concurrent_iteration_safe_limit() {
assert(_concurrent_iteration_safe_limit <= top(),
"_concurrent_iteration_safe_limit update missed");
return _concurrent_iteration_safe_limit;
}
// changes the safe limit, all objects from bottom() to the new
// limit should be properly initialized
void set_concurrent_iteration_safe_limit(HeapWord* new_limit) {
assert(new_limit <= top(), "uninitialized objects in the safe range");
_concurrent_iteration_safe_limit = new_limit;
}
#if INCLUDE_ALL_GCS
// In support of parallel oop_iterate.
#define ContigSpace_PAR_OOP_ITERATE_DECL(OopClosureType, nv_suffix) \
void par_oop_iterate(MemRegion mr, OopClosureType* blk);
ALL_PAR_OOP_ITERATE_CLOSURES(ContigSpace_PAR_OOP_ITERATE_DECL)
#undef ContigSpace_PAR_OOP_ITERATE_DECL
#endif // INCLUDE_ALL_GCS
// Compaction support
virtual void reset_after_compaction() {
assert(compaction_top() >= bottom() && compaction_top() <= end(), "should point inside space");
set_top(compaction_top());
// set new iteration safe limit
set_concurrent_iteration_safe_limit(compaction_top());
}
virtual size_t minimum_free_block_size() const { return 0; }
// Override.
DirtyCardToOopClosure* new_dcto_cl(ExtendedOopClosure* cl,
CardTableModRefBS::PrecisionStyle precision,
HeapWord* boundary = NULL);
// Apply "blk->do_oop" to the addresses of all reference fields in objects
// starting with the _saved_mark_word, which was noted during a generation's
// save_marks and is required to denote the head of an object.
// Fields in objects allocated by applications of the closure
// *are* included in the iteration.
// Updates _saved_mark_word to point to just after the last object
// iterated over.
#define ContigSpace_OOP_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
void oop_since_save_marks_iterate##nv_suffix(OopClosureType* blk);
ALL_SINCE_SAVE_MARKS_CLOSURES(ContigSpace_OOP_SINCE_SAVE_MARKS_DECL)
#undef ContigSpace_OOP_SINCE_SAVE_MARKS_DECL
// Same as object_iterate, but starting from "mark", which is required
// to denote the start of an object. Objects allocated by
// applications of the closure *are* included in the iteration.
virtual void object_iterate_from(WaterMark mark, ObjectClosure* blk);
// Very inefficient implementation.
virtual HeapWord* block_start_const(const void* p) const;
size_t block_size(const HeapWord* p) const;
// If a block is in the allocated area, it is an object.
bool block_is_obj(const HeapWord* p) const { return p < top(); }
// Addresses for inlined allocation
HeapWord** top_addr() { return &_top; }
HeapWord** end_addr() { return &_end; }
// Overrides for more efficient compaction support.
void prepare_for_compaction(CompactPoint* cp);
// PrintHeapAtGC support.
virtual void print_on(outputStream* st) const;
// Checked dynamic downcasts.
virtual ContiguousSpace* toContiguousSpace() {
return this;
}
// Debugging
virtual void verify() const;
// Used to increase collection frequency. "factor" of 0 means entire
// space.
void allocate_temporary_filler(int factor);
};
// A dirty card to oop closure that does filtering.
// It knows how to filter out objects that are outside of the _boundary.
class Filtering_DCTOC : public DirtyCardToOopClosure {
protected:
// Override.
void walk_mem_region(MemRegion mr,
HeapWord* bottom, HeapWord* top);
// Walk the given memory region, from bottom to top, applying
// the given oop closure to (possibly) all objects found. The
// given oop closure may or may not be the same as the oop
// closure with which this closure was created, as it may
// be a filtering closure which makes use of the _boundary.
// We offer two signatures, so the FilteringClosure static type is
// apparent.
virtual void walk_mem_region_with_cl(MemRegion mr,
HeapWord* bottom, HeapWord* top,
ExtendedOopClosure* cl) = 0;
virtual void walk_mem_region_with_cl(MemRegion mr,
HeapWord* bottom, HeapWord* top,
FilteringClosure* cl) = 0;
public:
Filtering_DCTOC(Space* sp, ExtendedOopClosure* cl,
CardTableModRefBS::PrecisionStyle precision,
HeapWord* boundary) :
DirtyCardToOopClosure(sp, cl, precision, boundary) {}
};
// A dirty card to oop closure for contiguous spaces
// (ContiguousSpace and sub-classes).
// It is a FilteringClosure, as defined above, and it knows:
//
// 1. That the actual top of any area in a memory region
// contained by the space is bounded by the end of the contiguous
// region of the space.
// 2. That the space is really made up of objects and not just
// blocks.
class ContiguousSpaceDCTOC : public Filtering_DCTOC {
protected:
// Overrides.
HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);
virtual void walk_mem_region_with_cl(MemRegion mr,
HeapWord* bottom, HeapWord* top,
ExtendedOopClosure* cl);
virtual void walk_mem_region_with_cl(MemRegion mr,
HeapWord* bottom, HeapWord* top,
FilteringClosure* cl);
public:
ContiguousSpaceDCTOC(ContiguousSpace* sp, ExtendedOopClosure* cl,
CardTableModRefBS::PrecisionStyle precision,
HeapWord* boundary) :
Filtering_DCTOC(sp, cl, precision, boundary)
{}
};
// Class EdenSpace describes eden-space in new generation.
class DefNewGeneration;
class EdenSpace : public ContiguousSpace {
friend class VMStructs;
private:
DefNewGeneration* _gen;
// _soft_end is used as a soft limit on allocation. As soft limits are
// reached, the slow-path allocation code can invoke other actions and then
// adjust _soft_end up to a new soft limit or to end().
HeapWord* _soft_end;
public:
EdenSpace(DefNewGeneration* gen) :
_gen(gen), _soft_end(NULL) {}
// Get/set just the 'soft' limit.
HeapWord* soft_end() { return _soft_end; }
HeapWord** soft_end_addr() { return &_soft_end; }
void set_soft_end(HeapWord* value) { _soft_end = value; }
// Override.
void clear(bool mangle_space);
// Set both the 'hard' and 'soft' limits (_end and _soft_end).
void set_end(HeapWord* value) {
set_soft_end(value);
ContiguousSpace::set_end(value);
}
// Allocation (return NULL if full)
HeapWord* allocate(size_t word_size);
HeapWord* par_allocate(size_t word_size);
};
// Class ConcEdenSpace extends EdenSpace for the sake of safe
// allocation while soft-end is being modified concurrently
class ConcEdenSpace : public EdenSpace {
public:
ConcEdenSpace(DefNewGeneration* gen) : EdenSpace(gen) { }
// Allocation (return NULL if full)
HeapWord* par_allocate(size_t word_size);
};
// A ContigSpace that Supports an efficient "block_start" operation via
// a BlockOffsetArray (whose BlockOffsetSharedArray may be shared with
// other spaces.) This is the abstract base class for old generation
// (tenured) spaces.
class OffsetTableContigSpace: public ContiguousSpace {
friend class VMStructs;
protected:
BlockOffsetArrayContigSpace _offsets;
Mutex _par_alloc_lock;
public:
// Constructor
OffsetTableContigSpace(BlockOffsetSharedArray* sharedOffsetArray,
MemRegion mr);
void set_bottom(HeapWord* value);
void set_end(HeapWord* value);
void clear(bool mangle_space);
inline HeapWord* block_start_const(const void* p) const;
// Add offset table update.
virtual inline HeapWord* allocate(size_t word_size);
inline HeapWord* par_allocate(size_t word_size);
// MarkSweep support phase3
virtual HeapWord* initialize_threshold();
virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* end);
virtual void print_on(outputStream* st) const;
// Debugging
void verify() const;
};
// Class TenuredSpace is used by TenuredGeneration
class TenuredSpace: public OffsetTableContigSpace {
friend class VMStructs;
protected:
// Mark sweep support
size_t allowed_dead_ratio() const;
public:
// Constructor
TenuredSpace(BlockOffsetSharedArray* sharedOffsetArray,
MemRegion mr) :
OffsetTableContigSpace(sharedOffsetArray, mr) {}
};
#endif // SHARE_VM_MEMORY_SPACE_HPP
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