4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #ifndef SHARE_VM_RUNTIME_ACCESS_HPP
25 #define SHARE_VM_RUNTIME_ACCESS_HPP
26
27 #include "memory/allocation.hpp"
28 #include "metaprogramming/decay.hpp"
29 #include "metaprogramming/integralConstant.hpp"
30 #include "oops/oopsHierarchy.hpp"
31 #include "utilities/debug.hpp"
32 #include "utilities/globalDefinitions.hpp"
33
34 // = GENERAL =
35 // Access is an API for performing accesses with declarative semantics. Each access can have a number of "decorators".
36 // A decorator is an attribute or property that affects the way a memory access is performed in some way.
37 // There are different groups of decorators. Some have to do with memory ordering, others to do with,
38 // e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
39 // Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
40 // at callsites such as whether an access is in the heap or not, and others are resolved at runtime
41 // such as GC-specific barriers and encoding/decoding compressed oops.
42 // By pipelining handling of these decorators, the design of the Access API allows separation of concern
43 // over the different orthogonal concerns of decorators, while providing a powerful way of
44 // expressing these orthogonal semantic properties in a unified way.
45
46 // == OPERATIONS ==
47 // * load: Load a value from an address.
48 // * load_at: Load a value from an internal pointer relative to a base object.
49 // * store: Store a value at an address.
50 // * store_at: Store a value in an internal pointer relative to a base object.
51 // * atomic_cmpxchg: Atomically compare-and-swap a new value at an address if previous value matched the compared value.
52 // * atomic_cmpxchg_at: Atomically compare-and-swap a new value at an internal pointer address if previous value matched the compared
53 // * atomic_xchg: Atomically swap a new value at an address if previous value matched the compared value.
54 // * atomic_xchg_at: Atomically swap a new value at an internal pointer address if previous value matched the compared value.
55 // * arraycopy: Copy data from one heap array to another heap array.
56 // * clone: Clone the contents of an object to a newly allocated object.
57 // * resolve: Resolve a stable to-space invariant oop that is guaranteed not to relocate its payload until a subsequent thread transi
58
59 typedef uint64_t DecoratorSet;
60
61 // == Internal Decorators - do not use ==
62 // * INTERNAL_EMPTY: This is the name for the empty decorator set (in absence of other decorators).
63 // * INTERNAL_CONVERT_COMPRESSED_OOPS: This is an oop access that will require converting an oop
64 // to a narrowOop or vice versa, if UseCompressedOops is known to be set.
65 // * INTERNAL_VALUE_IS_OOP: Remember that the involved access is on oop rather than primitive.
66 const DecoratorSet INTERNAL_EMPTY = UCONST64(0);
67 const DecoratorSet INTERNAL_CONVERT_COMPRESSED_OOP = UCONST64(1) << 1;
68 const DecoratorSet INTERNAL_VALUE_IS_OOP = UCONST64(1) << 2;
69
70 // == Internal build-time Decorators ==
71 // * INTERNAL_BT_BARRIER_ON_PRIMITIVES: This is set in the barrierSetConfig.hpp file.
72 // * INTERNAL_BT_TO_SPACE_INVARIANT: This is set in the barrierSetConfig.hpp file iff
73 // no GC is bundled in the build that is to-space invariant.
74 const DecoratorSet INTERNAL_BT_BARRIER_ON_PRIMITIVES = UCONST64(1) << 3;
75 const DecoratorSet INTERNAL_BT_TO_SPACE_INVARIANT = UCONST64(1) << 4;
76
77 // == Internal run-time Decorators ==
78 // * INTERNAL_RT_USE_COMPRESSED_OOPS: This decorator will be set in runtime resolved
79 // access backends iff UseCompressedOops is true.
80 const DecoratorSet INTERNAL_RT_USE_COMPRESSED_OOPS = UCONST64(1) << 5;
81
82 const DecoratorSet INTERNAL_DECORATOR_MASK = INTERNAL_CONVERT_COMPRESSED_OOP | INTERNAL_VALUE_IS_OOP |
83 INTERNAL_BT_BARRIER_ON_PRIMITIVES | INTERNAL_RT_USE_COMPRESSED_OOPS;
84
85 // == Memory Ordering Decorators ==
86 // The memory ordering decorators can be described in the following way:
87 // === Decorator Rules ===
88 // The different types of memory ordering guarantees have a strict order of strength.
89 // Explicitly specifying the stronger ordering implies that the guarantees of the weaker
90 // property holds too. The names come from the C++11 atomic operations, and typically
91 // have a JMM equivalent property.
92 // The equivalence may be viewed like this:
93 // MO_UNORDERED is equivalent to JMM plain.
94 // MO_VOLATILE has no equivalence in JMM, because it's a C++ thing.
95 // MO_RELAXED is equivalent to JMM opaque.
96 // MO_ACQUIRE is equivalent to JMM acquire.
97 // MO_RELEASE is equivalent to JMM release.
98 // MO_SEQ_CST is equivalent to JMM volatile.
99 //
100 // === Stores ===
101 // * MO_UNORDERED (Default): No guarantees.
102 // - The compiler and hardware are free to reorder aggressively. And they will.
103 // * MO_VOLATILE: Volatile stores (in the C++ sense).
104 // - The stores are not reordered by the compiler (but possibly the HW) w.r.t. other
105 // volatile accesses in program order (but possibly non-volatile accesses).
106 // * MO_RELAXED: Relaxed atomic stores.
107 // - The stores are atomic.
108 // - Guarantees from volatile stores hold.
109 // * MO_RELEASE: Releasing stores.
110 // - The releasing store will make its preceding memory accesses observable to memory accesses
111 // subsequent to an acquiring load observing this releasing store.
112 // - Guarantees from relaxed stores hold.
113 // * MO_SEQ_CST: Sequentially consistent stores.
114 // - The stores are observed in the same order by MO_SEQ_CST loads on other processors
115 // - Preceding loads and stores in program order are not reordered with subsequent loads and stores in program order.
116 // - Guarantees from releasing stores hold.
117 // === Loads ===
118 // * MO_UNORDERED (Default): No guarantees
119 // - The compiler and hardware are free to reorder aggressively. And they will.
120 // * MO_VOLATILE: Volatile loads (in the C++ sense).
121 // - The loads are not reordered by the compiler (but possibly the HW) w.r.t. other
122 // volatile accesses in program order (but possibly non-volatile accesses).
123 // * MO_RELAXED: Relaxed atomic loads.
124 // - The stores are atomic.
125 // - Guarantees from volatile loads hold.
126 // * MO_ACQUIRE: Acquiring loads.
127 // - An acquiring load will make subsequent memory accesses observe the memory accesses
128 // preceding the releasing store that the acquiring load observed.
129 // - Guarantees from relaxed loads hold.
130 // * MO_SEQ_CST: Sequentially consistent loads.
131 // - These loads observe MO_SEQ_CST stores in the same order on other processors
132 // - Preceding loads and stores in program order are not reordered with subsequent loads and stores in program order.
133 // - Guarantees from acquiring loads hold.
134 // === Atomic Cmpxchg ===
135 // * MO_RELAXED: Atomic but relaxed cmpxchg.
136 // - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold unconditionally.
137 // * MO_SEQ_CST: Sequentially consistent cmpxchg.
138 // - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold unconditionally.
139 // === Atomic Xchg ===
140 // * MO_RELAXED: Atomic but relaxed atomic xchg.
141 // - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold.
142 // * MO_SEQ_CST: Sequentially consistent xchg.
143 // - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold.
144 const DecoratorSet MO_UNORDERED = UCONST64(1) << 6;
145 const DecoratorSet MO_VOLATILE = UCONST64(1) << 7;
146 const DecoratorSet MO_RELAXED = UCONST64(1) << 8;
147 const DecoratorSet MO_ACQUIRE = UCONST64(1) << 9;
148 const DecoratorSet MO_RELEASE = UCONST64(1) << 10;
149 const DecoratorSet MO_SEQ_CST = UCONST64(1) << 11;
150 const DecoratorSet MO_DECORATOR_MASK = MO_UNORDERED | MO_VOLATILE | MO_RELAXED |
151 MO_ACQUIRE | MO_RELEASE | MO_SEQ_CST;
152
153 // === Barrier Strength Decorators ===
154 // * AS_RAW: The access will translate into a raw memory access, hence ignoring all semantic concerns
155 // except memory ordering and compressed oops. This will bypass runtime function pointer dispatching
156 // in the pipeline and hardwire to raw accesses without going trough the GC access barriers.
157 // - Accesses on oop* translate to raw memory accesses without runtime checks
158 // - Accesses on narrowOop* translate to encoded/decoded memory accesses without runtime checks
159 // - Accesses on HeapWord* translate to a runtime check choosing one of the above
160 // - Accesses on other types translate to raw memory accesses without runtime checks
161 // * AS_DEST_NOT_INITIALIZED: This property can be important to e.g. SATB barriers by
162 // marking that the previous value is uninitialized nonsense rather than a real value.
163 // * AS_NO_KEEPALIVE: The barrier is used only on oop references and will not keep any involved objects
164 // alive, regardless of the type of reference being accessed. It will however perform the memory access
165 // in a consistent way w.r.t. e.g. concurrent compaction, so that the right field is being accessed,
166 // or maintain, e.g. intergenerational or interregional pointers if applicable. This should be used with
167 // extreme caution in isolated scopes.
168 // * AS_NORMAL: The accesses will be resolved to an accessor on the BarrierSet class, giving the
169 // responsibility of performing the access and what barriers to be performed to the GC. This is the default.
170 // Note that primitive accesses will only be resolved on the barrier set if the appropriate build-time
171 // decorator for enabling primitive barriers is enabled for the build.
172 const DecoratorSet AS_RAW = UCONST64(1) << 12;
173 const DecoratorSet AS_DEST_NOT_INITIALIZED = UCONST64(1) << 13;
174 const DecoratorSet AS_NO_KEEPALIVE = UCONST64(1) << 14;
175 const DecoratorSet AS_NORMAL = UCONST64(1) << 15;
176 const DecoratorSet AS_DECORATOR_MASK = AS_RAW | AS_DEST_NOT_INITIALIZED |
177 AS_NO_KEEPALIVE | AS_NORMAL;
178
179 // === Reference Strength Decorators ===
180 // These decorators only apply to accesses on oop-like types (oop/narrowOop).
181 // * ON_STRONG_OOP_REF: Memory access is performed on a strongly reachable reference.
182 // * ON_WEAK_OOP_REF: The memory access is performed on a weakly reachable reference.
183 // * ON_PHANTOM_OOP_REF: The memory access is performed on a phantomly reachable reference.
184 // This is the same ring of strength as jweak and weak oops in the VM.
185 // * ON_UNKNOWN_OOP_REF: The memory access is performed on a reference of unknown strength.
186 // This could for example come from the unsafe API.
187 // * Default (no explicit reference strength specified): ON_STRONG_OOP_REF
188 const DecoratorSet ON_STRONG_OOP_REF = UCONST64(1) << 16;
189 const DecoratorSet ON_WEAK_OOP_REF = UCONST64(1) << 17;
190 const DecoratorSet ON_PHANTOM_OOP_REF = UCONST64(1) << 18;
191 const DecoratorSet ON_UNKNOWN_OOP_REF = UCONST64(1) << 19;
192 const DecoratorSet ON_DECORATOR_MASK = ON_STRONG_OOP_REF | ON_WEAK_OOP_REF |
193 ON_PHANTOM_OOP_REF | ON_UNKNOWN_OOP_REF;
194
195 // === Access Location ===
196 // Accesses can take place in, e.g. the heap, old or young generation and different native roots.
197 // The location is important to the GC as it may imply different actions. The following decorators are used:
198 // * IN_HEAP: The access is performed in the heap. Many barriers such as card marking will
199 // be omitted if this decorator is not set.
200 // * IN_HEAP_ARRAY: The access is performed on a heap allocated array. This is sometimes a special case
201 // for some GCs, and implies that it is an IN_HEAP.
202 // * IN_ROOT: The access is performed in an off-heap data structure pointing into the Java heap.
203 // * IN_CONCURRENT_ROOT: The access is performed in an off-heap data structure pointing into the Java heap,
204 // but is notably not scanned during safepoints. This is sometimes a special case for some GCs and
205 // implies that it is also an IN_ROOT.
206 const DecoratorSet IN_HEAP = UCONST64(1) << 20;
207 const DecoratorSet IN_HEAP_ARRAY = UCONST64(1) << 21;
208 const DecoratorSet IN_ROOT = UCONST64(1) << 22;
209 const DecoratorSet IN_CONCURRENT_ROOT = UCONST64(1) << 23;
210 const DecoratorSet IN_ARCHIVE_ROOT = UCONST64(1) << 24;
211 const DecoratorSet IN_DECORATOR_MASK = IN_HEAP | IN_HEAP_ARRAY |
212 IN_ROOT | IN_CONCURRENT_ROOT |
213 IN_ARCHIVE_ROOT;
214
215 // == Value Decorators ==
216 // * OOP_NOT_NULL: This property can make certain barriers faster such as compressing oops.
217 const DecoratorSet OOP_NOT_NULL = UCONST64(1) << 25;
218 const DecoratorSet OOP_DECORATOR_MASK = OOP_NOT_NULL;
219
220 // == Arraycopy Decorators ==
221 // * ARRAYCOPY_CHECKCAST: This property means that the class of the objects in source
222 // are not guaranteed to be subclasses of the class of the destination array. This requires
223 // a check-cast barrier during the copying operation. If this is not set, it is assumed
224 // that the array is covariant: (the source array type is-a destination array type)
225 // * ARRAYCOPY_DISJOINT: This property means that it is known that the two array ranges
226 // are disjoint.
227 // * ARRAYCOPY_ARRAYOF: The copy is in the arrayof form.
228 // * ARRAYCOPY_ATOMIC: The accesses have to be atomic over the size of its elements.
229 // * ARRAYCOPY_ALIGNED: The accesses have to be aligned on a HeapWord.
230 const DecoratorSet ARRAYCOPY_CHECKCAST = UCONST64(1) << 26;
231 const DecoratorSet ARRAYCOPY_DISJOINT = UCONST64(1) << 27;
232 const DecoratorSet ARRAYCOPY_ARRAYOF = UCONST64(1) << 28;
233 const DecoratorSet ARRAYCOPY_ATOMIC = UCONST64(1) << 29;
234 const DecoratorSet ARRAYCOPY_ALIGNED = UCONST64(1) << 30;
235 const DecoratorSet ARRAYCOPY_DECORATOR_MASK = ARRAYCOPY_CHECKCAST | ARRAYCOPY_DISJOINT |
236 ARRAYCOPY_DISJOINT | ARRAYCOPY_ARRAYOF |
237 ARRAYCOPY_ATOMIC | ARRAYCOPY_ALIGNED;
238
239 // The HasDecorator trait can help at compile-time determining whether a decorator set
240 // has an intersection with a certain other decorator set
241 template <DecoratorSet decorators, DecoratorSet decorator>
242 struct HasDecorator: public IntegralConstant<bool, (decorators & decorator) != 0> {};
243
244 namespace AccessInternal {
245 template <typename T>
246 struct OopOrNarrowOopInternal: AllStatic {
247 typedef oop type;
248 };
249
250 template <>
251 struct OopOrNarrowOopInternal<narrowOop>: AllStatic {
252 typedef narrowOop type;
253 };
254
255 // This metafunction returns a canonicalized oop/narrowOop type for a passed
256 // in oop-like types passed in from oop_* overloads where the user has sworn
257 // that the passed in values should be oop-like (e.g. oop, oopDesc*, arrayOop,
258 // narrowOoop, instanceOopDesc*, and random other things).
259 // In the oop_* overloads, it must hold that if the passed in type T is not
260 // narrowOop, then it by contract has to be one of many oop-like types implicitly
261 // convertible to oop, and hence returns oop as the canonical oop type.
262 // If it turns out it was not, then the implicit conversion to oop will fail
263 // to compile, as desired.
264 template <typename T>
265 struct OopOrNarrowOop: AllStatic {
266 typedef typename OopOrNarrowOopInternal<typename Decay<T>::type>::type type;
267 };
268
269 inline void* field_addr(oop base, ptrdiff_t byte_offset) {
270 return reinterpret_cast<void*>(reinterpret_cast<intptr_t>((void*)base) + byte_offset);
271 }
272
273 template <DecoratorSet decorators, typename T>
274 void store_at(oop base, ptrdiff_t offset, T value);
275
276 template <DecoratorSet decorators, typename T>
277 T load_at(oop base, ptrdiff_t offset);
278
279 template <DecoratorSet decorators, typename T>
280 T atomic_cmpxchg_at(T new_value, oop base, ptrdiff_t offset, T compare_value);
281
282 template <DecoratorSet decorators, typename T>
283 T atomic_xchg_at(T new_value, oop base, ptrdiff_t offset);
284
285 template <DecoratorSet decorators, typename P, typename T>
286 void store(P* addr, T value);
287
288 template <DecoratorSet decorators, typename P, typename T>
289 T load(P* addr);
290
291 template <DecoratorSet decorators, typename P, typename T>
292 T atomic_cmpxchg(T new_value, P* addr, T compare_value);
293
294 template <DecoratorSet decorators, typename P, typename T>
295 T atomic_xchg(T new_value, P* addr);
296
297 template <DecoratorSet decorators, typename T>
298 bool arraycopy(arrayOop src_obj, arrayOop dst_obj, T *src, T *dst, size_t length);
299
300 template <DecoratorSet decorators>
301 void clone(oop src, oop dst, size_t size);
302
303 template <DecoratorSet decorators>
304 oop resolve(oop src);
305
306 // Infer the type that should be returned from a load.
307 template <typename P, DecoratorSet decorators>
308 class OopLoadProxy: public StackObj {
309 private:
310 P *const _addr;
311 public:
312 OopLoadProxy(P* addr) : _addr(addr) {}
313
314 inline operator oop() {
315 return load<decorators | INTERNAL_VALUE_IS_OOP, P, oop>(_addr);
316 }
317
318 inline operator narrowOop() {
319 return load<decorators | INTERNAL_VALUE_IS_OOP, P, narrowOop>(_addr);
320 }
321
322 template <typename T>
323 inline bool operator ==(const T& other) const {
324 return load<decorators | INTERNAL_VALUE_IS_OOP, P, T>(_addr) == other;
325 }
326
327 template <typename T>
328 inline bool operator !=(const T& other) const {
329 return load<decorators | INTERNAL_VALUE_IS_OOP, P, T>(_addr) != other;
330 }
331 };
332
333 // Infer the type that should be returned from a load_at.
334 template <DecoratorSet decorators>
335 class LoadAtProxy: public StackObj {
336 private:
337 const oop _base;
338 const ptrdiff_t _offset;
339 public:
340 LoadAtProxy(oop base, ptrdiff_t offset) : _base(base), _offset(offset) {}
341
342 template <typename T>
343 inline operator T() const {
344 return load_at<decorators, T>(_base, _offset);
345 }
346
347 template <typename T>
348 inline bool operator ==(const T& other) const { return load_at<decorators, T>(_base, _offset) == other; }
349
350 template <typename T>
351 inline bool operator !=(const T& other) const { return load_at<decorators, T>(_base, _offset) != other; }
352 };
353
354 template <DecoratorSet decorators>
355 class OopLoadAtProxy: public StackObj {
356 private:
357 const oop _base;
358 const ptrdiff_t _offset;
359 public:
360 OopLoadAtProxy(oop base, ptrdiff_t offset) : _base(base), _offset(offset) {}
361
362 inline operator oop() const {
363 return load_at<decorators | INTERNAL_VALUE_IS_OOP, oop>(_base, _offset);
364 }
365
366 inline operator narrowOop() const {
367 return load_at<decorators | INTERNAL_VALUE_IS_OOP, narrowOop>(_base, _offset);
368 }
369
370 template <typename T>
371 inline bool operator ==(const T& other) const {
372 return load_at<decorators | INTERNAL_VALUE_IS_OOP, T>(_base, _offset) == other;
373 }
374
375 template <typename T>
376 inline bool operator !=(const T& other) const {
377 return load_at<decorators | INTERNAL_VALUE_IS_OOP, T>(_base, _offset) != other;
378 }
379 };
380 }
381
382 template <DecoratorSet decorators = INTERNAL_EMPTY>
383 class Access: public AllStatic {
384 // This function asserts that if an access gets passed in a decorator outside
385 // of the expected_decorators, then something is wrong. It additionally checks
386 // the consistency of the decorators so that supposedly disjoint decorators are indeed
387 // disjoint. For example, an access can not be both in heap and on root at the
388 // same time.
389 template <DecoratorSet expected_decorators>
390 static void verify_decorators();
391
392 template <DecoratorSet expected_mo_decorators>
393 static void verify_primitive_decorators() {
394 const DecoratorSet primitive_decorators = (AS_DECORATOR_MASK ^ AS_NO_KEEPALIVE ^ AS_DEST_NOT_INITIALIZED) |
395 IN_HEAP | IN_HEAP_ARRAY;
396 verify_decorators<expected_mo_decorators | primitive_decorators>();
397 }
398
399 template <DecoratorSet expected_mo_decorators>
|
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #ifndef SHARE_OOPS_ACCESS_HPP
25 #define SHARE_OOPS_ACCESS_HPP
26
27 #include "memory/allocation.hpp"
28 #include "oops/accessBackend.hpp"
29 #include "oops/accessDecorators.hpp"
30 #include "oops/oopsHierarchy.hpp"
31 #include "utilities/debug.hpp"
32 #include "utilities/globalDefinitions.hpp"
33
34
35 // = GENERAL =
36 // Access is an API for performing accesses with declarative semantics. Each access can have a number of "decorators".
37 // A decorator is an attribute or property that affects the way a memory access is performed in some way.
38 // There are different groups of decorators. Some have to do with memory ordering, others to do with,
39 // e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
40 // Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
41 // at callsites such as whether an access is in the heap or not, and others are resolved at runtime
42 // such as GC-specific barriers and encoding/decoding compressed oops. For more information about what
43 // decorators are available, cf. oops/accessDecorators.hpp.
44 // By pipelining handling of these decorators, the design of the Access API allows separation of concern
45 // over the different orthogonal concerns of decorators, while providing a powerful way of
46 // expressing these orthogonal semantic properties in a unified way.
47 //
48 // == OPERATIONS ==
49 // * load: Load a value from an address.
50 // * load_at: Load a value from an internal pointer relative to a base object.
51 // * store: Store a value at an address.
52 // * store_at: Store a value in an internal pointer relative to a base object.
53 // * atomic_cmpxchg: Atomically compare-and-swap a new value at an address if previous value matched the compared value.
54 // * atomic_cmpxchg_at: Atomically compare-and-swap a new value at an internal pointer address if previous value matched the compared
55 // * atomic_xchg: Atomically swap a new value at an address if previous value matched the compared value.
56 // * atomic_xchg_at: Atomically swap a new value at an internal pointer address if previous value matched the compared value.
57 // * arraycopy: Copy data from one heap array to another heap array.
58 // * clone: Clone the contents of an object to a newly allocated object.
59 // * resolve: Resolve a stable to-space invariant oop that is guaranteed not to relocate its payload until a subsequent thread transi
60 // * equals: Object equality, e.g. when different copies of the same objects are in use (from-space vs. to-space)
61 //
62 // == IMPLEMENTATION ==
63 // Each access goes through the following steps in a template pipeline.
64 // There are essentially 5 steps for each access:
65 // * Step 1: Set default decorators and decay types. This step gets rid of CV qualifiers
66 // and sets default decorators to sensible values.
67 // * Step 2: Reduce types. This step makes sure there is only a single T type and not
68 // multiple types. The P type of the address and T type of the value must
69 // match.
70 // * Step 3: Pre-runtime dispatch. This step checks whether a runtime call can be
71 // avoided, and in that case avoids it (calling raw accesses or
72 // primitive accesses in a build that does not require primitive GC barriers)
73 // * Step 4: Runtime-dispatch. This step performs a runtime dispatch to the corresponding
74 // BarrierSet::AccessBarrier accessor that attaches GC-required barriers
75 // to the access.
76 // * Step 5.a: Barrier resolution. This step is invoked the first time a runtime-dispatch
77 // happens for an access. The appropriate BarrierSet::AccessBarrier accessor
78 // is resolved, then the function pointer is updated to that accessor for
79 // future invocations.
80 // * Step 5.b: Post-runtime dispatch. This step now casts previously unknown types such
81 // as the address type of an oop on the heap (is it oop* or narrowOop*) to
82 // the appropriate type. It also splits sufficiently orthogonal accesses into
83 // different functions, such as whether the access involves oops or primitives
84 // and whether the access is performed on the heap or outside. Then the
85 // appropriate BarrierSet::AccessBarrier is called to perform the access.
86 //
87 // The implementation of step 1-4 resides in in accessBackend.hpp, to allow selected
88 // accesses to be accessible from only access.hpp, as opposed to access.inline.hpp.
89 // Steps 5.a and 5.b require knowledge about the GC backends, and therefore needs to
90 // include the various GC backend .inline.hpp headers. Their implementation resides in
91 // access.inline.hpp. The accesses that are allowed through the access.hpp file
92 // must be instantiated in access.cpp using the INSTANTIATE_HPP_ACCESS macro.
93
94 template <DecoratorSet decorators = INTERNAL_EMPTY>
95 class Access: public AllStatic {
96 // This function asserts that if an access gets passed in a decorator outside
97 // of the expected_decorators, then something is wrong. It additionally checks
98 // the consistency of the decorators so that supposedly disjoint decorators are indeed
99 // disjoint. For example, an access can not be both in heap and on root at the
100 // same time.
101 template <DecoratorSet expected_decorators>
102 static void verify_decorators();
103
104 template <DecoratorSet expected_mo_decorators>
105 static void verify_primitive_decorators() {
106 const DecoratorSet primitive_decorators = (AS_DECORATOR_MASK ^ AS_NO_KEEPALIVE ^ AS_DEST_NOT_INITIALIZED) |
107 IN_HEAP | IN_HEAP_ARRAY;
108 verify_decorators<expected_mo_decorators | primitive_decorators>();
109 }
110
111 template <DecoratorSet expected_mo_decorators>
|