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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* 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).
*
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* 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_OOPS_ARRAYOOP_HPP
#define SHARE_VM_OOPS_ARRAYOOP_HPP
#include "memory/universe.inline.hpp"
#include "oops/oop.hpp"
// arrayOopDesc is the abstract baseclass for all arrays. It doesn't
// declare pure virtual to enforce this because that would allocate a vtbl
// in each instance, which we don't want.
// The layout of array Oops is:
//
// markOop
// klassOop // 32 bits if compressed but declared 64 in LP64.
// length // shares klass memory or allocated after declared fields.
class arrayOopDesc : public oopDesc {
friend class VMStructs;
// Interpreter/Compiler offsets
// Header size computation.
// The header is considered the oop part of this type plus the length.
// Returns the aligned header_size_in_bytes. This is not equivalent to
// sizeof(arrayOopDesc) which should not appear in the code.
static int header_size_in_bytes() {
size_t hs = align_size_up(length_offset_in_bytes() + sizeof(int),
HeapWordSize);
#ifdef ASSERT
// make sure it isn't called before UseCompressedOops is initialized.
static size_t arrayoopdesc_hs = 0;
if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs;
assert(arrayoopdesc_hs == hs, "header size can't change");
#endif // ASSERT
return (int)hs;
}
public:
// The _length field is not declared in C++. It is allocated after the
// declared nonstatic fields in arrayOopDesc if not compressed, otherwise
// it occupies the second half of the _klass field in oopDesc.
static int length_offset_in_bytes() {
return UseCompressedOops ? klass_gap_offset_in_bytes() :
sizeof(arrayOopDesc);
}
// Returns the offset of the first element.
static int base_offset_in_bytes(BasicType type) {
return header_size(type) * HeapWordSize;
}
// Returns the address of the first element.
void* base(BasicType type) const {
return (void*) (((intptr_t) this) + base_offset_in_bytes(type));
}
// Tells whether index is within bounds.
bool is_within_bounds(int index) const { return 0 <= index && index < length(); }
// Accessors for instance variable which is not a C++ declared nonstatic
// field.
int length() const {
return *(int*)(((intptr_t)this) + length_offset_in_bytes());
}
void set_length(int length) {
*(int*)(((intptr_t)this) + length_offset_in_bytes()) = length;
}
// Should only be called with constants as argument
// (will not constant fold otherwise)
// Returns the header size in words aligned to the requirements of the
// array object type.
static int header_size(BasicType type) {
size_t typesize_in_bytes = header_size_in_bytes();
return (int)(Universe::element_type_should_be_aligned(type)
? align_object_offset(typesize_in_bytes/HeapWordSize)
: typesize_in_bytes/HeapWordSize);
}
// Return the maximum length of an array of BasicType. The length can passed
// to typeArrayOop::object_size(scale, length, header_size) without causing an
// overflow. We also need to make sure that this will not overflow a size_t on
// 32 bit platforms when we convert it to a byte size.
static int32_t max_array_length(BasicType type) {
assert(type >= 0 && type < T_CONFLICT, "wrong type");
assert(type2aelembytes(type) != 0, "wrong type");
const size_t max_element_words_per_size_t =
align_size_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment);
const size_t max_elements_per_size_t =
HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);
if ((size_t)max_jint < max_elements_per_size_t) {
// It should be ok to return max_jint here, but parts of the code
// (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
// passing around the size (in words) of an object. So, we need to avoid
// overflowing an int when we add the header. See CRs 4718400 and 7110613.
return align_size_down(max_jint - header_size(type), MinObjAlignment);
}
return (int32_t)max_elements_per_size_t;
}
// for unit testing
#ifndef PRODUCT
static bool check_max_length_overflow(BasicType type);
static int32_t old_max_array_length(BasicType type);
static void test_max_array_length();
#endif
};
#endif // SHARE_VM_OOPS_ARRAYOOP_HPP