1 /*
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24
25 #ifndef SHARE_OOPS_ACCESSDECORATORS_HPP
26 #define SHARE_OOPS_ACCESSDECORATORS_HPP
27
28 #include "gc/shared/barrierSetConfig.hpp"
29 #include "memory/allocation.hpp"
30 #include "metaprogramming/integralConstant.hpp"
31 #include "utilities/globalDefinitions.hpp"
32
33 // A decorator is an attribute or property that affects the way a memory access is performed in some way.
34 // There are different groups of decorators. Some have to do with memory ordering, others to do with,
35 // e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
36 // Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
37 // at callsites such as whether an access is in the heap or not, and others are resolved at runtime
38 // such as GC-specific barriers and encoding/decoding compressed oops.
39 typedef uint64_t DecoratorSet;
40
41 // The HasDecorator trait can help at compile-time determining whether a decorator set
42 // has an intersection with a certain other decorator set
43 template <DecoratorSet decorators, DecoratorSet decorator>
44 struct HasDecorator: public IntegralConstant<bool, (decorators & decorator) != 0> {};
45
46 // == Internal Decorators - do not use ==
47 // * INTERNAL_EMPTY: This is the name for the empty decorator set (in absence of other decorators).
48 // * INTERNAL_CONVERT_COMPRESSED_OOPS: This is an oop access that will require converting an oop
49 // to a narrowOop or vice versa, if UseCompressedOops is known to be set.
50 // * INTERNAL_VALUE_IS_OOP: Remember that the involved access is on oop rather than primitive.
51 const DecoratorSet INTERNAL_EMPTY = UCONST64(0);
52 const DecoratorSet INTERNAL_CONVERT_COMPRESSED_OOP = UCONST64(1) << 1;
53 const DecoratorSet INTERNAL_VALUE_IS_OOP = UCONST64(1) << 2;
54
55 // == Internal build-time Decorators ==
56 // * INTERNAL_BT_BARRIER_ON_PRIMITIVES: This is set in the barrierSetConfig.hpp file.
57 // * INTERNAL_BT_TO_SPACE_INVARIANT: This is set in the barrierSetConfig.hpp file iff
58 // no GC is bundled in the build that is to-space invariant.
59 const DecoratorSet INTERNAL_BT_BARRIER_ON_PRIMITIVES = UCONST64(1) << 3;
60 const DecoratorSet INTERNAL_BT_TO_SPACE_INVARIANT = UCONST64(1) << 4;
61
62 // == Internal run-time Decorators ==
63 // * INTERNAL_RT_USE_COMPRESSED_OOPS: This decorator will be set in runtime resolved
64 // access backends iff UseCompressedOops is true.
65 const DecoratorSet INTERNAL_RT_USE_COMPRESSED_OOPS = UCONST64(1) << 5;
66
67 const DecoratorSet INTERNAL_DECORATOR_MASK = INTERNAL_CONVERT_COMPRESSED_OOP | INTERNAL_VALUE_IS_OOP |
68 INTERNAL_BT_BARRIER_ON_PRIMITIVES | INTERNAL_RT_USE_COMPRESSED_OOPS;
69
70 // == Memory Ordering Decorators ==
71 // The memory ordering decorators can be described in the following way:
72 // === Decorator Rules ===
73 // The different types of memory ordering guarantees have a strict order of strength.
74 // Explicitly specifying the stronger ordering implies that the guarantees of the weaker
75 // property holds too. The names come from the C++11 atomic operations, and typically
76 // have a JMM equivalent property.
77 // The equivalence may be viewed like this:
78 // MO_UNORDERED is equivalent to JMM plain.
79 // MO_VOLATILE has no equivalence in JMM, because it's a C++ thing.
80 // MO_RELAXED is equivalent to JMM opaque.
81 // MO_ACQUIRE is equivalent to JMM acquire.
82 // MO_RELEASE is equivalent to JMM release.
83 // MO_SEQ_CST is equivalent to JMM volatile.
84 //
85 // === Stores ===
86 // * MO_UNORDERED (Default): No guarantees.
87 // - The compiler and hardware are free to reorder aggressively. And they will.
88 // * MO_VOLATILE: Volatile stores (in the C++ sense).
89 // - The stores are not reordered by the compiler (but possibly the HW) w.r.t. other
90 // volatile accesses in program order (but possibly non-volatile accesses).
91 // * MO_RELAXED: Relaxed atomic stores.
92 // - The stores are atomic.
93 // - Guarantees from volatile stores hold.
94 // * MO_RELEASE: Releasing stores.
95 // - The releasing store will make its preceding memory accesses observable to memory accesses
96 // subsequent to an acquiring load observing this releasing store.
97 // - Guarantees from relaxed stores hold.
98 // * MO_SEQ_CST: Sequentially consistent stores.
99 // - The stores are observed in the same order by MO_SEQ_CST loads on other processors
100 // - Preceding loads and stores in program order are not reordered with subsequent loads and stores in program order.
101 // - Guarantees from releasing stores hold.
102 // === Loads ===
103 // * MO_UNORDERED (Default): No guarantees
104 // - The compiler and hardware are free to reorder aggressively. And they will.
105 // * MO_VOLATILE: Volatile loads (in the C++ sense).
106 // - The loads are not reordered by the compiler (but possibly the HW) w.r.t. other
107 // volatile accesses in program order (but possibly non-volatile accesses).
108 // * MO_RELAXED: Relaxed atomic loads.
109 // - The loads are atomic.
110 // - Guarantees from volatile loads hold.
111 // * MO_ACQUIRE: Acquiring loads.
112 // - An acquiring load will make subsequent memory accesses observe the memory accesses
113 // preceding the releasing store that the acquiring load observed.
114 // - Guarantees from relaxed loads hold.
115 // * MO_SEQ_CST: Sequentially consistent loads.
116 // - These loads observe MO_SEQ_CST stores in the same order on other processors
117 // - Preceding loads and stores in program order are not reordered with subsequent loads and stores in program order.
118 // - Guarantees from acquiring loads hold.
119 // === Atomic Cmpxchg ===
120 // * MO_RELAXED: Atomic but relaxed cmpxchg.
121 // - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold unconditionally.
122 // * MO_SEQ_CST: Sequentially consistent cmpxchg.
123 // - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold unconditionally.
124 // === Atomic Xchg ===
125 // * MO_RELAXED: Atomic but relaxed atomic xchg.
126 // - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold.
127 // * MO_SEQ_CST: Sequentially consistent xchg.
128 // - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold.
129 const DecoratorSet MO_UNORDERED = UCONST64(1) << 6;
130 const DecoratorSet MO_VOLATILE = UCONST64(1) << 7;
131 const DecoratorSet MO_RELAXED = UCONST64(1) << 8;
132 const DecoratorSet MO_ACQUIRE = UCONST64(1) << 9;
133 const DecoratorSet MO_RELEASE = UCONST64(1) << 10;
134 const DecoratorSet MO_SEQ_CST = UCONST64(1) << 11;
135 const DecoratorSet MO_DECORATOR_MASK = MO_UNORDERED | MO_VOLATILE | MO_RELAXED |
136 MO_ACQUIRE | MO_RELEASE | MO_SEQ_CST;
137
138 // === Barrier Strength Decorators ===
139 // * AS_RAW: The access will translate into a raw memory access, hence ignoring all semantic concerns
140 // except memory ordering and compressed oops. This will bypass runtime function pointer dispatching
141 // in the pipeline and hardwire to raw accesses without going trough the GC access barriers.
142 // - Accesses on oop* translate to raw memory accesses without runtime checks
143 // - Accesses on narrowOop* translate to encoded/decoded memory accesses without runtime checks
144 // - Accesses on HeapWord* translate to a runtime check choosing one of the above
145 // - Accesses on other types translate to raw memory accesses without runtime checks
146 // * AS_DEST_NOT_INITIALIZED: This property can be important to e.g. SATB barriers by
147 // marking that the previous value is uninitialized nonsense rather than a real value.
148 // * AS_NO_KEEPALIVE: The barrier is used only on oop references and will not keep any involved objects
149 // alive, regardless of the type of reference being accessed. It will however perform the memory access
150 // in a consistent way w.r.t. e.g. concurrent compaction, so that the right field is being accessed,
151 // or maintain, e.g. intergenerational or interregional pointers if applicable. This should be used with
152 // extreme caution in isolated scopes.
153 // * AS_NORMAL: The accesses will be resolved to an accessor on the BarrierSet class, giving the
154 // responsibility of performing the access and what barriers to be performed to the GC. This is the default.
155 // Note that primitive accesses will only be resolved on the barrier set if the appropriate build-time
156 // decorator for enabling primitive barriers is enabled for the build.
157 const DecoratorSet AS_RAW = UCONST64(1) << 12;
158 const DecoratorSet AS_DEST_NOT_INITIALIZED = UCONST64(1) << 13;
159 const DecoratorSet AS_NO_KEEPALIVE = UCONST64(1) << 14;
160 const DecoratorSet AS_NORMAL = UCONST64(1) << 15;
161 const DecoratorSet AS_DECORATOR_MASK = AS_RAW | AS_DEST_NOT_INITIALIZED |
162 AS_NO_KEEPALIVE | AS_NORMAL;
163
164 // === Reference Strength Decorators ===
165 // These decorators only apply to accesses on oop-like types (oop/narrowOop).
166 // * ON_STRONG_OOP_REF: Memory access is performed on a strongly reachable reference.
167 // * ON_WEAK_OOP_REF: The memory access is performed on a weakly reachable reference.
168 // * ON_PHANTOM_OOP_REF: The memory access is performed on a phantomly reachable reference.
169 // This is the same ring of strength as jweak and weak oops in the VM.
170 // * ON_UNKNOWN_OOP_REF: The memory access is performed on a reference of unknown strength.
171 // This could for example come from the unsafe API.
172 // * Default (no explicit reference strength specified): ON_STRONG_OOP_REF
173 const DecoratorSet ON_STRONG_OOP_REF = UCONST64(1) << 16;
174 const DecoratorSet ON_WEAK_OOP_REF = UCONST64(1) << 17;
175 const DecoratorSet ON_PHANTOM_OOP_REF = UCONST64(1) << 18;
176 const DecoratorSet ON_UNKNOWN_OOP_REF = UCONST64(1) << 19;
177 const DecoratorSet ON_DECORATOR_MASK = ON_STRONG_OOP_REF | ON_WEAK_OOP_REF |
178 ON_PHANTOM_OOP_REF | ON_UNKNOWN_OOP_REF;
179
180 // === Access Location ===
181 // Accesses can take place in, e.g. the heap, old or young generation and different native roots.
182 // The location is important to the GC as it may imply different actions. The following decorators are used:
183 // * IN_HEAP: The access is performed in the heap. Many barriers such as card marking will
184 // be omitted if this decorator is not set.
185 // * IN_HEAP_ARRAY: The access is performed on a heap allocated array. This is sometimes a special case
186 // for some GCs, and implies that it is an IN_HEAP.
187 // * IN_ROOT: The access is performed in an off-heap data structure pointing into the Java heap.
188 // * IN_CONCURRENT_ROOT: The access is performed in an off-heap data structure pointing into the Java heap,
189 // but is notably not scanned during safepoints. This is sometimes a special case for some GCs and
190 // implies that it is also an IN_ROOT.
191 const DecoratorSet IN_HEAP = UCONST64(1) << 20;
192 const DecoratorSet IN_HEAP_ARRAY = UCONST64(1) << 21;
193 const DecoratorSet IN_ROOT = UCONST64(1) << 22;
194 const DecoratorSet IN_CONCURRENT_ROOT = UCONST64(1) << 23;
195 const DecoratorSet IN_DECORATOR_MASK = IN_HEAP | IN_HEAP_ARRAY |
196 IN_ROOT | IN_CONCURRENT_ROOT;
197
198 // == Value Decorators ==
199 // * OOP_NOT_NULL: This property can make certain barriers faster such as compressing oops.
200 const DecoratorSet OOP_NOT_NULL = UCONST64(1) << 25;
201 const DecoratorSet OOP_DECORATOR_MASK = OOP_NOT_NULL;
202
203 // == Arraycopy Decorators ==
204 // * ARRAYCOPY_CHECKCAST: This property means that the class of the objects in source
205 // are not guaranteed to be subclasses of the class of the destination array. This requires
206 // a check-cast barrier during the copying operation. If this is not set, it is assumed
207 // that the array is covariant: (the source array type is-a destination array type)
208 // * ARRAYCOPY_DISJOINT: This property means that it is known that the two array ranges
209 // are disjoint.
210 // * ARRAYCOPY_ARRAYOF: The copy is in the arrayof form.
211 // * ARRAYCOPY_ATOMIC: The accesses have to be atomic over the size of its elements.
212 // * ARRAYCOPY_ALIGNED: The accesses have to be aligned on a HeapWord.
213 const DecoratorSet ARRAYCOPY_CHECKCAST = UCONST64(1) << 26;
214 const DecoratorSet ARRAYCOPY_DISJOINT = UCONST64(1) << 27;
215 const DecoratorSet ARRAYCOPY_ARRAYOF = UCONST64(1) << 28;
216 const DecoratorSet ARRAYCOPY_ATOMIC = UCONST64(1) << 29;
217 const DecoratorSet ARRAYCOPY_ALIGNED = UCONST64(1) << 30;
218 const DecoratorSet ARRAYCOPY_DECORATOR_MASK = ARRAYCOPY_CHECKCAST | ARRAYCOPY_DISJOINT |
219 ARRAYCOPY_DISJOINT | ARRAYCOPY_ARRAYOF |
220 ARRAYCOPY_ATOMIC | ARRAYCOPY_ALIGNED;
221
222 // Keep track of the last decorator.
223 const DecoratorSet DECORATOR_LAST = UCONST64(1) << 30;
224
225 namespace AccessInternal {
226 // This class adds implied decorators that follow according to decorator rules.
227 // For example adding default reference strength and default memory ordering
228 // semantics.
229 template <DecoratorSet input_decorators>
230 struct DecoratorFixup: AllStatic {
231 // If no reference strength has been picked, then strong will be picked
232 static const DecoratorSet ref_strength_default = input_decorators |
233 (((ON_DECORATOR_MASK & input_decorators) == 0 && (INTERNAL_VALUE_IS_OOP & input_decorators) != 0) ?
234 ON_STRONG_OOP_REF : INTERNAL_EMPTY);
235 // If no memory ordering has been picked, unordered will be picked
236 static const DecoratorSet memory_ordering_default = ref_strength_default |
237 ((MO_DECORATOR_MASK & ref_strength_default) == 0 ? MO_UNORDERED : INTERNAL_EMPTY);
238 // If no barrier strength has been picked, normal will be used
239 static const DecoratorSet barrier_strength_default = memory_ordering_default |
240 ((AS_DECORATOR_MASK & memory_ordering_default) == 0 ? AS_NORMAL : INTERNAL_EMPTY);
241 // Heap array accesses imply it is a heap access
242 static const DecoratorSet heap_array_is_in_heap = barrier_strength_default |
243 ((IN_HEAP_ARRAY & barrier_strength_default) != 0 ? IN_HEAP : INTERNAL_EMPTY);
244 static const DecoratorSet conc_root_is_root = heap_array_is_in_heap |
245 ((IN_CONCURRENT_ROOT & heap_array_is_in_heap) != 0 ? IN_ROOT : INTERNAL_EMPTY);
246 static const DecoratorSet value = conc_root_is_root | BT_BUILDTIME_DECORATORS;
247 };
248
249 // This function implements the above DecoratorFixup rules, but without meta
250 // programming for code generation that does not use templates.
251 inline DecoratorSet decorator_fixup(DecoratorSet input_decorators) {
252 // If no reference strength has been picked, then strong will be picked
253 DecoratorSet ref_strength_default = input_decorators |
254 (((ON_DECORATOR_MASK & input_decorators) == 0 && (INTERNAL_VALUE_IS_OOP & input_decorators) != 0) ?
255 ON_STRONG_OOP_REF : INTERNAL_EMPTY);
256 // If no memory ordering has been picked, unordered will be picked
257 DecoratorSet memory_ordering_default = ref_strength_default |
258 ((MO_DECORATOR_MASK & ref_strength_default) == 0 ? MO_UNORDERED : INTERNAL_EMPTY);
259 // If no barrier strength has been picked, normal will be used
260 DecoratorSet barrier_strength_default = memory_ordering_default |
261 ((AS_DECORATOR_MASK & memory_ordering_default) == 0 ? AS_NORMAL : INTERNAL_EMPTY);
262 // Heap array accesses imply it is a heap access
263 DecoratorSet heap_array_is_in_heap = barrier_strength_default |
264 ((IN_HEAP_ARRAY & barrier_strength_default) != 0 ? IN_HEAP : INTERNAL_EMPTY);
265 DecoratorSet conc_root_is_root = heap_array_is_in_heap |
266 ((IN_CONCURRENT_ROOT & heap_array_is_in_heap) != 0 ? IN_ROOT : INTERNAL_EMPTY);
267 DecoratorSet value = conc_root_is_root | BT_BUILDTIME_DECORATORS;
268 return value;
269 }
270 }
271
272 #endif // SHARE_OOPS_ACCESSDECORATORS_HPP