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src/hotspot/share/oops/arrayOop.hpp

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  27 
  28 #include "oops/oop.hpp"
  29 #include "utilities/align.hpp"
  30 
  31 // arrayOopDesc is the abstract baseclass for all arrays.  It doesn't
  32 // declare pure virtual to enforce this because that would allocate a vtbl
  33 // in each instance, which we don't want.
  34 
  35 // The layout of array Oops is:
  36 //
  37 //  markOop
  38 //  Klass*    // 32 bits if compressed but declared 64 in LP64.
  39 //  length    // shares klass memory or allocated after declared fields.
  40 
  41 
  42 class arrayOopDesc : public oopDesc {
  43   friend class VMStructs;
  44   friend class arrayOopDescTest;
  45 
  46   // Interpreter/Compiler offsets
  47 
  48   // Header size computation.
  49   // The header is considered the oop part of this type plus the length.
  50   // Returns the aligned header_size_in_bytes.  This is not equivalent to
  51   // sizeof(arrayOopDesc) which should not appear in the code.
  52   static int header_size_in_bytes() {
  53     size_t hs = align_up(length_offset_in_bytes() + sizeof(int),
  54                               HeapWordSize);
  55 #ifdef ASSERT
  56     // make sure it isn't called before UseCompressedOops is initialized.
  57     static size_t arrayoopdesc_hs = 0;
  58     if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs;
  59     assert(arrayoopdesc_hs == hs, "header size can't change");
  60 #endif // ASSERT
  61     return (int)hs;
  62   }
  63 
  64   // Check whether an element of a typeArrayOop with the given type must be
  65   // aligned 0 mod 8.  The typeArrayOop itself must be aligned at least this
  66   // strongly.
  67   static bool element_type_should_be_aligned(BasicType type) {
  68     return type == T_DOUBLE || type == T_LONG;
  69   }
  70 
  71  public:
  72   // The _length field is not declared in C++.  It is allocated after the
  73   // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
  74   // it occupies the second half of the _klass field in oopDesc.
  75   static int length_offset_in_bytes() {
  76     return UseCompressedClassPointers ? klass_gap_offset_in_bytes() :
  77                                sizeof(arrayOopDesc);
  78   }
  79 
  80   // Returns the offset of the first element.
  81   static int base_offset_in_bytes(BasicType type) {
  82     return header_size(type) * HeapWordSize;
  83   }
  84 
  85   // Returns the address of the first element. The elements in the array will not
  86   // relocate from this address until a subsequent thread transition.
  87   inline void* base(BasicType type) const;
  88   inline void* base_raw(BasicType type) const; // GC barrier invariant


 106   // field.
 107   int length() const {
 108     return *(int*)(((intptr_t)this) + length_offset_in_bytes());
 109   }
 110   void set_length(int length) {
 111     set_length((HeapWord*)this, length);
 112   }
 113   static void set_length(HeapWord* mem, int length) {
 114     *(int*)(((char*)mem) + length_offset_in_bytes()) = length;
 115   }
 116 
 117   // Should only be called with constants as argument
 118   // (will not constant fold otherwise)
 119   // Returns the header size in words aligned to the requirements of the
 120   // array object type.
 121   static int header_size(BasicType type) {
 122     size_t typesize_in_bytes = header_size_in_bytes();
 123     return (int)(element_type_should_be_aligned(type)
 124       ? align_object_offset(typesize_in_bytes/HeapWordSize)
 125       : typesize_in_bytes/HeapWordSize);















 126   }
 127 
 128   // Return the maximum length of an array of BasicType.  The length can passed
 129   // to typeArrayOop::object_size(scale, length, header_size) without causing an
 130   // overflow. We also need to make sure that this will not overflow a size_t on
 131   // 32 bit platforms when we convert it to a byte size.
 132   static int32_t max_array_length(BasicType type) {
 133     assert(type >= 0 && type < T_CONFLICT, "wrong type");
 134     assert(type2aelembytes(type) != 0, "wrong type");
 135 
 136     const size_t max_element_words_per_size_t =
 137       align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment);
 138     const size_t max_elements_per_size_t =
 139       HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);
 140     if ((size_t)max_jint < max_elements_per_size_t) {
 141       // It should be ok to return max_jint here, but parts of the code
 142       // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
 143       // passing around the size (in words) of an object. So, we need to avoid
 144       // overflowing an int when we add the header. See CRs 4718400 and 7110613.
 145       return align_down(max_jint - header_size(type), MinObjAlignment);


  27 
  28 #include "oops/oop.hpp"
  29 #include "utilities/align.hpp"
  30 
  31 // arrayOopDesc is the abstract baseclass for all arrays.  It doesn't
  32 // declare pure virtual to enforce this because that would allocate a vtbl
  33 // in each instance, which we don't want.
  34 
  35 // The layout of array Oops is:
  36 //
  37 //  markOop
  38 //  Klass*    // 32 bits if compressed but declared 64 in LP64.
  39 //  length    // shares klass memory or allocated after declared fields.
  40 
  41 
  42 class arrayOopDesc : public oopDesc {
  43   friend class VMStructs;
  44   friend class arrayOopDescTest;
  45 
  46   // Interpreter/Compiler offsets
  47 protected:
  48   // Header size computation.
  49   // The header is considered the oop part of this type plus the length.
  50   // Returns the aligned header_size_in_bytes.  This is not equivalent to
  51   // sizeof(arrayOopDesc) which should not appear in the code.
  52   static int header_size_in_bytes() {
  53     size_t hs = align_up(length_offset_in_bytes() + sizeof(int),
  54                               HeapWordSize);
  55 #ifdef ASSERT
  56     // make sure it isn't called before UseCompressedOops is initialized.
  57     static size_t arrayoopdesc_hs = 0;
  58     if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs;
  59     assert(arrayoopdesc_hs == hs, "header size can't change");
  60 #endif // ASSERT
  61     return (int)hs;
  62   }
  63 
  64   // Check whether an element of a typeArrayOop with the given type must be
  65   // aligned 0 mod 8.  The typeArrayOop itself must be aligned at least this
  66   // strongly.
  67   static bool element_type_should_be_aligned(BasicType type) {
  68     return type == T_DOUBLE || type == T_LONG || type == T_VALUETYPE;
  69   }
  70 
  71  public:
  72   // The _length field is not declared in C++.  It is allocated after the
  73   // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
  74   // it occupies the second half of the _klass field in oopDesc.
  75   static int length_offset_in_bytes() {
  76     return UseCompressedClassPointers ? klass_gap_offset_in_bytes() :
  77                                sizeof(arrayOopDesc);
  78   }
  79 
  80   // Returns the offset of the first element.
  81   static int base_offset_in_bytes(BasicType type) {
  82     return header_size(type) * HeapWordSize;
  83   }
  84 
  85   // Returns the address of the first element. The elements in the array will not
  86   // relocate from this address until a subsequent thread transition.
  87   inline void* base(BasicType type) const;
  88   inline void* base_raw(BasicType type) const; // GC barrier invariant


 106   // field.
 107   int length() const {
 108     return *(int*)(((intptr_t)this) + length_offset_in_bytes());
 109   }
 110   void set_length(int length) {
 111     set_length((HeapWord*)this, length);
 112   }
 113   static void set_length(HeapWord* mem, int length) {
 114     *(int*)(((char*)mem) + length_offset_in_bytes()) = length;
 115   }
 116 
 117   // Should only be called with constants as argument
 118   // (will not constant fold otherwise)
 119   // Returns the header size in words aligned to the requirements of the
 120   // array object type.
 121   static int header_size(BasicType type) {
 122     size_t typesize_in_bytes = header_size_in_bytes();
 123     return (int)(element_type_should_be_aligned(type)
 124       ? align_object_offset(typesize_in_bytes/HeapWordSize)
 125       : typesize_in_bytes/HeapWordSize);
 126   }
 127 
 128   static int32_t max_array_length(int header_size, int elembytes) {
 129     const size_t max_element_words_per_size_t =
 130         align_down((SIZE_MAX/HeapWordSize - header_size), MinObjAlignment);
 131     const size_t max_elements_per_size_t =
 132         HeapWordSize * max_element_words_per_size_t / elembytes;
 133     if ((size_t)max_jint < max_elements_per_size_t) {
 134       // It should be ok to return max_jint here, but parts of the code
 135       // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
 136       // passing around the size (in words) of an object. So, we need to avoid
 137       // overflowing an int when we add the header. See CRs 4718400 and 7110613.
 138       return align_down(max_jint - header_size, MinObjAlignment);
 139     }
 140     return (int32_t)max_elements_per_size_t;
 141   }
 142 
 143   // Return the maximum length of an array of BasicType.  The length can passed
 144   // to typeArrayOop::object_size(scale, length, header_size) without causing an
 145   // overflow. We also need to make sure that this will not overflow a size_t on
 146   // 32 bit platforms when we convert it to a byte size.
 147   static int32_t max_array_length(BasicType type) {
 148     assert(type >= 0 && type < T_CONFLICT, "wrong type");
 149     assert(type2aelembytes(type) != 0, "wrong type");
 150 
 151     const size_t max_element_words_per_size_t =
 152       align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment);
 153     const size_t max_elements_per_size_t =
 154       HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);
 155     if ((size_t)max_jint < max_elements_per_size_t) {
 156       // It should be ok to return max_jint here, but parts of the code
 157       // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
 158       // passing around the size (in words) of an object. So, we need to avoid
 159       // overflowing an int when we add the header. See CRs 4718400 and 7110613.
 160       return align_down(max_jint - header_size(type), MinObjAlignment);
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