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  24 
  25 #ifndef SHARE_OOPS_ACCESS_HPP
  26 #define SHARE_OOPS_ACCESS_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "oops/accessBackend.hpp"
  30 #include "oops/accessDecorators.hpp"
  31 #include "oops/oopsHierarchy.hpp"
  32 #include "utilities/debug.hpp"
  33 #include "utilities/globalDefinitions.hpp"
  34 
  35 
  36 // = GENERAL =
  37 // Access is an API for performing accesses with declarative semantics. Each access can have a number of "decorators".
  38 // A decorator is an attribute or property that affects the way a memory access is performed in some way.
  39 // There are different groups of decorators. Some have to do with memory ordering, others to do with,
  40 // e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
  41 // Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
  42 // at callsites such as whether an access is in the heap or not, and others are resolved at runtime
  43 // such as GC-specific barriers and encoding/decoding compressed oops. For more information about what
  44 // decorators are available, cf. oops/accessDecorators.hpp.
  45 // By pipelining handling of these decorators, the design of the Access API allows separation of concern
  46 // over the different orthogonal concerns of decorators, while providing a powerful way of
  47 // expressing these orthogonal semantic properties in a unified way.
  48 //
  49 // == OPERATIONS ==
  50 // * load: Load a value from an address.
  51 // * load_at: Load a value from an internal pointer relative to a base object.
  52 // * store: Store a value at an address.
  53 // * store_at: Store a value in an internal pointer relative to a base object.
  54 // * atomic_cmpxchg: Atomically compare-and-swap a new value at an address if previous value matched the compared value.
  55 // * atomic_cmpxchg_at: Atomically compare-and-swap a new value at an internal pointer address if previous value matched the compared value.
  56 // * atomic_xchg: Atomically swap a new value at an address if previous value matched the compared value.
  57 // * atomic_xchg_at: Atomically swap a new value at an internal pointer address if previous value matched the compared value.
  58 // * arraycopy: Copy data from one heap array to another heap array. The ArrayAccess class has convenience functions for this.
  59 // * clone: Clone the contents of an object to a newly allocated object.
  60 // * resolve: Resolve a stable to-space invariant oop that is guaranteed not to relocate its payload until a subsequent thread transition.
  61 // * equals: Object equality, e.g. when different copies of the same objects are in use (from-space vs. to-space)
  62 //
  63 // == IMPLEMENTATION ==
  64 // Each access goes through the following steps in a template pipeline.
  65 // There are essentially 5 steps for each access:
  66 // * Step 1:   Set default decorators and decay types. This step gets rid of CV qualifiers
  67 //             and sets default decorators to sensible values.
  68 // * Step 2:   Reduce types. This step makes sure there is only a single T type and not
  69 //             multiple types. The P type of the address and T type of the value must
  70 //             match.
  71 // * Step 3:   Pre-runtime dispatch. This step checks whether a runtime call can be
  72 //             avoided, and in that case avoids it (calling raw accesses or
  73 //             primitive accesses in a build that does not require primitive GC barriers)
  74 // * Step 4:   Runtime-dispatch. This step performs a runtime dispatch to the corresponding
  75 //             BarrierSet::AccessBarrier accessor that attaches GC-required barriers
  76 //             to the access.
  77 // * Step 5.a: Barrier resolution. This step is invoked the first time a runtime-dispatch
  78 //             happens for an access. The appropriate BarrierSet::AccessBarrier accessor
  79 //             is resolved, then the function pointer is updated to that accessor for
  80 //             future invocations.
  81 // * Step 5.b: Post-runtime dispatch. This step now casts previously unknown types such
  82 //             as the address type of an oop on the heap (is it oop* or narrowOop*) to
  83 //             the appropriate type. It also splits sufficiently orthogonal accesses into
  84 //             different functions, such as whether the access involves oops or primitives
  85 //             and whether the access is performed on the heap or outside. Then the
  86 //             appropriate BarrierSet::AccessBarrier is called to perform the access.
  87 //
  88 // The implementation of step 1-4 resides in in accessBackend.hpp, to allow selected
  89 // accesses to be accessible from only access.hpp, as opposed to access.inline.hpp.
  90 // Steps 5.a and 5.b require knowledge about the GC backends, and therefore needs to
  91 // include the various GC backend .inline.hpp headers. Their implementation resides in
  92 // access.inline.hpp. The accesses that are allowed through the access.hpp file
  93 // must be instantiated in access.cpp using the INSTANTIATE_HPP_ACCESS macro.
  94 
  95 template <DecoratorSet decorators = DECORATORS_NONE>
  96 class Access: public AllStatic {
  97   // This function asserts that if an access gets passed in a decorator outside
  98   // of the expected_decorators, then something is wrong. It additionally checks
  99   // the consistency of the decorators so that supposedly disjoint decorators are indeed
 100   // disjoint. For example, an access can not be both in heap and on root at the
 101   // same time.
 102   template <DecoratorSet expected_decorators>
 103   static void verify_decorators();
 104 
 105   template <DecoratorSet expected_mo_decorators>
 106   static void verify_primitive_decorators() {
 107     const DecoratorSet primitive_decorators = (AS_DECORATOR_MASK ^ AS_NO_KEEPALIVE) |
 108                                               IN_HEAP | IS_ARRAY;
 109     verify_decorators<expected_mo_decorators | primitive_decorators>();
 110   }
 111 
 112   template <DecoratorSet expected_mo_decorators>
 113   static void verify_oop_decorators() {
 114     const DecoratorSet oop_decorators = AS_DECORATOR_MASK | IN_DECORATOR_MASK |
 115                                         (ON_DECORATOR_MASK ^ ON_UNKNOWN_OOP_REF) | // no unknown oop refs outside of the heap
 116                                         IS_ARRAY | IS_NOT_NULL | IS_DEST_UNINITIALIZED;
 117     verify_decorators<expected_mo_decorators | oop_decorators>();
 118   }
 119 
 120   template <DecoratorSet expected_mo_decorators>
 121   static void verify_heap_oop_decorators() {
 122     const DecoratorSet heap_oop_decorators = AS_DECORATOR_MASK | ON_DECORATOR_MASK |
 123                                              IN_HEAP | IS_ARRAY | IS_NOT_NULL | IS_DEST_UNINITIALIZED;
 124     verify_decorators<expected_mo_decorators | heap_oop_decorators>();
 125   }
 126 
 127   static const DecoratorSet load_mo_decorators = MO_UNORDERED | MO_VOLATILE | MO_RELAXED | MO_ACQUIRE | MO_SEQ_CST;
 128   static const DecoratorSet store_mo_decorators = MO_UNORDERED | MO_VOLATILE | MO_RELAXED | MO_RELEASE | MO_SEQ_CST;
 129   static const DecoratorSet atomic_xchg_mo_decorators = MO_SEQ_CST;
 130   static const DecoratorSet atomic_cmpxchg_mo_decorators = MO_RELAXED | MO_SEQ_CST;
 131 
 132 protected:
 133   template <typename T>
 134   static inline bool oop_arraycopy(arrayOop src_obj, size_t src_offset_in_bytes, const T* src_raw,
 135                                    arrayOop dst_obj, size_t dst_offset_in_bytes, T* dst_raw,
 136                                    size_t length) {
 137     verify_decorators<ARRAYCOPY_DECORATOR_MASK | IN_HEAP |
 138                       AS_DECORATOR_MASK | IS_ARRAY | IS_DEST_UNINITIALIZED>();
 139     return AccessInternal::arraycopy<decorators | INTERNAL_VALUE_IS_OOP>(src_obj, src_offset_in_bytes, src_raw,
 140                                                                          dst_obj, dst_offset_in_bytes, dst_raw,
 141                                                                          length);
 142   }
 143 
 144   template <typename T>
 145   static inline void arraycopy(arrayOop src_obj, size_t src_offset_in_bytes, const T* src_raw,
 146                                arrayOop dst_obj, size_t dst_offset_in_bytes, T* dst_raw,
 147                                size_t length) {
 148     verify_decorators<ARRAYCOPY_DECORATOR_MASK | IN_HEAP |
 149                       AS_DECORATOR_MASK | IS_ARRAY>();
 150     AccessInternal::arraycopy<decorators>(src_obj, src_offset_in_bytes, src_raw,
 151                                           dst_obj, dst_offset_in_bytes, dst_raw,
 152                                           length);
 153   }
 154 
 155 public:
 156   // Primitive heap accesses
 157   static inline AccessInternal::LoadAtProxy<decorators> load_at(oop base, ptrdiff_t offset) {
 158     verify_primitive_decorators<load_mo_decorators>();
 159     return AccessInternal::LoadAtProxy<decorators>(base, offset);
 160   }
 161 
 162   template <typename T>
 163   static inline void store_at(oop base, ptrdiff_t offset, T value) {
 164     verify_primitive_decorators<store_mo_decorators>();
 165     AccessInternal::store_at<decorators>(base, offset, value);
 166   }
 167 
 168   template <typename T>
 169   static inline T atomic_cmpxchg_at(T new_value, oop base, ptrdiff_t offset, T compare_value) {
 170     verify_primitive_decorators<atomic_cmpxchg_mo_decorators>();
 171     return AccessInternal::atomic_cmpxchg_at<decorators>(new_value, base, offset, compare_value);
 172   }
 173 
 174   template <typename T>
 175   static inline T atomic_xchg_at(T new_value, oop base, ptrdiff_t offset) {
 176     verify_primitive_decorators<atomic_xchg_mo_decorators>();
 177     return AccessInternal::atomic_xchg_at<decorators>(new_value, base, offset);
 178   }
 179 
 180   // Oop heap accesses
 181   static inline AccessInternal::OopLoadAtProxy<decorators> oop_load_at(oop base, ptrdiff_t offset) {
 182     verify_heap_oop_decorators<load_mo_decorators>();
 183     return AccessInternal::OopLoadAtProxy<decorators>(base, offset);
 184   }
 185 
 186   template <typename T>
 187   static inline void oop_store_at(oop base, ptrdiff_t offset, T value) {
 188     verify_heap_oop_decorators<store_mo_decorators>();
 189     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
 190     OopType oop_value = value;
 191     AccessInternal::store_at<decorators | INTERNAL_VALUE_IS_OOP>(base, offset, oop_value);
 192   }
 193 
 194   template <typename T>
 195   static inline T oop_atomic_cmpxchg_at(T new_value, oop base, ptrdiff_t offset, T compare_value) {
 196     verify_heap_oop_decorators<atomic_cmpxchg_mo_decorators>();
 197     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
 198     OopType new_oop_value = new_value;
 199     OopType compare_oop_value = compare_value;
 200     return AccessInternal::atomic_cmpxchg_at<decorators | INTERNAL_VALUE_IS_OOP>(new_oop_value, base, offset, compare_oop_value);
 201   }
 202 
 203   template <typename T>
 204   static inline T oop_atomic_xchg_at(T new_value, oop base, ptrdiff_t offset) {
 205     verify_heap_oop_decorators<atomic_xchg_mo_decorators>();
 206     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
 207     OopType new_oop_value = new_value;
 208     return AccessInternal::atomic_xchg_at<decorators | INTERNAL_VALUE_IS_OOP>(new_oop_value, base, offset);
 209   }
 210 
 211   // Clone an object from src to dst
 212   static inline void clone(oop src, oop dst, size_t size) {
 213     verify_decorators<IN_HEAP>();
 214     AccessInternal::clone<decorators>(src, dst, size);
 215   }
 216 
 217   // Primitive accesses
 218   template <typename P>
 219   static inline P load(P* addr) {
 220     verify_primitive_decorators<load_mo_decorators>();
 221     return AccessInternal::load<decorators, P, P>(addr);
 222   }
 223 
 224   template <typename P, typename T>
 225   static inline void store(P* addr, T value) {
 226     verify_primitive_decorators<store_mo_decorators>();
 227     AccessInternal::store<decorators>(addr, value);
 228   }
 229 
 230   template <typename P, typename T>
 231   static inline T atomic_cmpxchg(T new_value, P* addr, T compare_value) {
 232     verify_primitive_decorators<atomic_cmpxchg_mo_decorators>();
 233     return AccessInternal::atomic_cmpxchg<decorators>(new_value, addr, compare_value);
 234   }
 235 
 236   template <typename P, typename T>
 237   static inline T atomic_xchg(T new_value, P* addr) {
 238     verify_primitive_decorators<atomic_xchg_mo_decorators>();
 239     return AccessInternal::atomic_xchg<decorators>(new_value, addr);
 240   }
 241 
 242   // Oop accesses
 243   template <typename P>
 244   static inline AccessInternal::OopLoadProxy<P, decorators> oop_load(P* addr) {
 245     verify_oop_decorators<load_mo_decorators>();
 246     return AccessInternal::OopLoadProxy<P, decorators>(addr);
 247   }
 248 
 249   template <typename P, typename T>
 250   static inline void oop_store(P* addr, T value) {
 251     verify_oop_decorators<store_mo_decorators>();
 252     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
 253     OopType oop_value = value;
 254     AccessInternal::store<decorators | INTERNAL_VALUE_IS_OOP>(addr, oop_value);
 255   }
 256 
 257   template <typename P, typename T>
 258   static inline T oop_atomic_cmpxchg(T new_value, P* addr, T compare_value) {
 259     verify_oop_decorators<atomic_cmpxchg_mo_decorators>();
 260     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
 261     OopType new_oop_value = new_value;
 262     OopType compare_oop_value = compare_value;
 263     return AccessInternal::atomic_cmpxchg<decorators | INTERNAL_VALUE_IS_OOP>(new_oop_value, addr, compare_oop_value);
 264   }
 265 
 266   template <typename P, typename T>
 267   static inline T oop_atomic_xchg(T new_value, P* addr) {
 268     verify_oop_decorators<atomic_xchg_mo_decorators>();
 269     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
 270     OopType new_oop_value = new_value;
 271     return AccessInternal::atomic_xchg<decorators | INTERNAL_VALUE_IS_OOP>(new_oop_value, addr);
 272   }
 273 
 274   static oop resolve(oop obj) {
 275     verify_decorators<DECORATORS_NONE>();
 276     return AccessInternal::resolve<decorators>(obj);
 277   }
 278 
 279   static bool equals(oop o1, oop o2) {
 280     verify_decorators<AS_RAW>();
 281     return AccessInternal::equals<decorators>(o1, o2);
 282   }
 283 };
 284 
 285 // Helper for performing raw accesses (knows only of memory ordering
 286 // atomicity decorators as well as compressed oops)
 287 template <DecoratorSet decorators = DECORATORS_NONE>
 288 class RawAccess: public Access<AS_RAW | decorators> {};
 289 
 290 // Helper for performing normal accesses on the heap. These accesses
 291 // may resolve an accessor on a GC barrier set
 292 template <DecoratorSet decorators = DECORATORS_NONE>
 293 class HeapAccess: public Access<IN_HEAP | decorators> {};
 294 
 295 // Helper for performing normal accesses in roots. These accesses
 296 // may resolve an accessor on a GC barrier set
 297 template <DecoratorSet decorators = DECORATORS_NONE>
 298 class NativeAccess: public Access<IN_NATIVE | decorators> {};
 299 
 300 // Helper for array access.
 301 template <DecoratorSet decorators = DECORATORS_NONE>
 302 class ArrayAccess: public HeapAccess<IS_ARRAY | decorators> {
 303   typedef HeapAccess<IS_ARRAY | decorators> AccessT;
 304 public:
 305   template <typename T>
 306   static inline void arraycopy(arrayOop src_obj, size_t src_offset_in_bytes,
 307                                arrayOop dst_obj, size_t dst_offset_in_bytes,
 308                                size_t length) {
 309     AccessT::arraycopy(src_obj, src_offset_in_bytes, reinterpret_cast<const T*>(NULL),
 310                        dst_obj, dst_offset_in_bytes, reinterpret_cast<T*>(NULL),
 311                        length);
 312   }
 313 
 314   template <typename T>
 315   static inline void arraycopy_to_native(arrayOop src_obj, size_t src_offset_in_bytes,
 316                                          T* dst,
 317                                          size_t length) {
 318     AccessT::arraycopy(src_obj, src_offset_in_bytes, reinterpret_cast<const T*>(NULL),
 319                        NULL, 0, dst,
 320                        length);
 321   }
 322 
 323   template <typename T>
 324   static inline void arraycopy_from_native(const T* src,
 325                                            arrayOop dst_obj, size_t dst_offset_in_bytes,
 326                                            size_t length) {
 327     AccessT::arraycopy(NULL, 0, src,
 328                        dst_obj, dst_offset_in_bytes, reinterpret_cast<T*>(NULL),
 329                        length);
 330   }
 331 
 332   static inline bool oop_arraycopy(arrayOop src_obj, size_t src_offset_in_bytes,
 333                                    arrayOop dst_obj, size_t dst_offset_in_bytes,
 334                                    size_t length) {
 335     return AccessT::oop_arraycopy(src_obj, src_offset_in_bytes, reinterpret_cast<const HeapWord*>(NULL),
 336                                   dst_obj, dst_offset_in_bytes, reinterpret_cast<HeapWord*>(NULL),
 337                                   length);
 338   }
 339 
 340   template <typename T>
 341   static inline bool oop_arraycopy_raw(T* src, T* dst, size_t length) {
 342     return AccessT::oop_arraycopy(NULL, 0, src,
 343                                   NULL, 0, dst,
 344                                   length);
 345   }
 346 
 347 };
 348 
 349 template <DecoratorSet decorators>
 350 template <DecoratorSet expected_decorators>
 351 void Access<decorators>::verify_decorators() {
 352   STATIC_ASSERT((~expected_decorators & decorators) == 0); // unexpected decorator used
 353   const DecoratorSet barrier_strength_decorators = decorators & AS_DECORATOR_MASK;
 354   STATIC_ASSERT(barrier_strength_decorators == 0 || ( // make sure barrier strength decorators are disjoint if set
 355     (barrier_strength_decorators ^ AS_NO_KEEPALIVE) == 0 ||
 356     (barrier_strength_decorators ^ AS_RAW) == 0 ||
 357     (barrier_strength_decorators ^ AS_NORMAL) == 0
 358   ));
 359   const DecoratorSet ref_strength_decorators = decorators & ON_DECORATOR_MASK;
 360   STATIC_ASSERT(ref_strength_decorators == 0 || ( // make sure ref strength decorators are disjoint if set
 361     (ref_strength_decorators ^ ON_STRONG_OOP_REF) == 0 ||
 362     (ref_strength_decorators ^ ON_WEAK_OOP_REF) == 0 ||
 363     (ref_strength_decorators ^ ON_PHANTOM_OOP_REF) == 0 ||
 364     (ref_strength_decorators ^ ON_UNKNOWN_OOP_REF) == 0
 365   ));
 366   const DecoratorSet memory_ordering_decorators = decorators & MO_DECORATOR_MASK;
 367   STATIC_ASSERT(memory_ordering_decorators == 0 || ( // make sure memory ordering decorators are disjoint if set
 368     (memory_ordering_decorators ^ MO_UNORDERED) == 0 ||
 369     (memory_ordering_decorators ^ MO_VOLATILE) == 0 ||
 370     (memory_ordering_decorators ^ MO_RELAXED) == 0 ||
 371     (memory_ordering_decorators ^ MO_ACQUIRE) == 0 ||
 372     (memory_ordering_decorators ^ MO_RELEASE) == 0 ||
 373     (memory_ordering_decorators ^ MO_SEQ_CST) == 0
 374   ));
 375   const DecoratorSet location_decorators = decorators & IN_DECORATOR_MASK;
 376   STATIC_ASSERT(location_decorators == 0 || ( // make sure location decorators are disjoint if set
 377     (location_decorators ^ IN_NATIVE) == 0 ||
 378     (location_decorators ^ IN_HEAP) == 0
 379   ));
 380 }
 381 
 382 #endif // SHARE_OOPS_ACCESS_HPP