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24
25 #ifndef SHARE_OOPS_ACCESSDECORATORS_HPP
26 #define SHARE_OOPS_ACCESSDECORATORS_HPP
27
28 #include "metaprogramming/integralConstant.hpp"
29 #include "utilities/globalDefinitions.hpp"
30
31 // A decorator is an attribute or property that affects the way a memory access is performed in some way.
32 // There are different groups of decorators. Some have to do with memory ordering, others to do with,
33 // e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
34 // Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
35 // at callsites such as whether an access is in the heap or not, and others are resolved at runtime
36 // such as GC-specific barriers and encoding/decoding compressed oops.
37 typedef uint64_t DecoratorSet;
38
39 // The HasDecorator trait can help at compile-time determining whether a decorator set
40 // has an intersection with a certain other decorator set
41 template <DecoratorSet decorators, DecoratorSet decorator>
42 struct HasDecorator: public IntegralConstant<bool, (decorators & decorator) != 0> {};
43
44 // == Internal Decorators - do not use ==
45 // * INTERNAL_EMPTY: This is the name for the empty decorator set (in absence of other decorators).
46 // * INTERNAL_CONVERT_COMPRESSED_OOPS: This is an oop access that will require converting an oop
47 // to a narrowOop or vice versa, if UseCompressedOops is known to be set.
48 // * INTERNAL_VALUE_IS_OOP: Remember that the involved access is on oop rather than primitive.
49 const DecoratorSet INTERNAL_EMPTY = UCONST64(0);
50 const DecoratorSet INTERNAL_CONVERT_COMPRESSED_OOP = UCONST64(1) << 1;
51 const DecoratorSet INTERNAL_VALUE_IS_OOP = UCONST64(1) << 2;
52
53 // == Internal build-time Decorators ==
54 // * INTERNAL_BT_BARRIER_ON_PRIMITIVES: This is set in the barrierSetConfig.hpp file.
55 // * INTERNAL_BT_TO_SPACE_INVARIANT: This is set in the barrierSetConfig.hpp file iff
56 // no GC is bundled in the build that is to-space invariant.
57 const DecoratorSet INTERNAL_BT_BARRIER_ON_PRIMITIVES = UCONST64(1) << 3;
58 const DecoratorSet INTERNAL_BT_TO_SPACE_INVARIANT = UCONST64(1) << 4;
59
60 // == Internal run-time Decorators ==
61 // * INTERNAL_RT_USE_COMPRESSED_OOPS: This decorator will be set in runtime resolved
62 // access backends iff UseCompressedOops is true.
63 const DecoratorSet INTERNAL_RT_USE_COMPRESSED_OOPS = UCONST64(1) << 5;
64
65 const DecoratorSet INTERNAL_DECORATOR_MASK = INTERNAL_CONVERT_COMPRESSED_OOP | INTERNAL_VALUE_IS_OOP |
66 INTERNAL_BT_BARRIER_ON_PRIMITIVES | INTERNAL_RT_USE_COMPRESSED_OOPS;
67
68 // == Memory Ordering Decorators ==
69 // The memory ordering decorators can be described in the following way:
70 // === Decorator Rules ===
71 // The different types of memory ordering guarantees have a strict order of strength.
72 // Explicitly specifying the stronger ordering implies that the guarantees of the weaker
73 // property holds too. The names come from the C++11 atomic operations, and typically
74 // have a JMM equivalent property.
75 // The equivalence may be viewed like this:
76 // MO_UNORDERED is equivalent to JMM plain.
77 // MO_VOLATILE has no equivalence in JMM, because it's a C++ thing.
78 // MO_RELAXED is equivalent to JMM opaque.
79 // MO_ACQUIRE is equivalent to JMM acquire.
80 // MO_RELEASE is equivalent to JMM release.
81 // MO_SEQ_CST is equivalent to JMM volatile.
82 //
83 // === Stores ===
84 // * MO_UNORDERED (Default): No guarantees.
85 // - The compiler and hardware are free to reorder aggressively. And they will.
86 // * MO_VOLATILE: Volatile stores (in the C++ sense).
87 // - The stores are not reordered by the compiler (but possibly the HW) w.r.t. other
88 // volatile accesses in program order (but possibly non-volatile accesses).
89 // * MO_RELAXED: Relaxed atomic stores.
90 // - The stores are atomic.
91 // - Guarantees from volatile stores hold.
92 // * MO_RELEASE: Releasing stores.
93 // - The releasing store will make its preceding memory accesses observable to memory accesses
94 // subsequent to an acquiring load observing this releasing store.
95 // - Guarantees from relaxed stores hold.
96 // * MO_SEQ_CST: Sequentially consistent stores.
97 // - The stores are observed in the same order by MO_SEQ_CST loads on other processors
98 // - Preceding loads and stores in program order are not reordered with subsequent loads and stores in program order.
99 // - Guarantees from releasing stores hold.
100 // === Loads ===
101 // * MO_UNORDERED (Default): No guarantees
102 // - The compiler and hardware are free to reorder aggressively. And they will.
103 // * MO_VOLATILE: Volatile loads (in the C++ sense).
104 // - The loads 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 loads.
107 // - The loads are atomic.
108 // - Guarantees from volatile loads hold.
109 // * MO_ACQUIRE: Acquiring loads.
110 // - An acquiring load will make subsequent memory accesses observe the memory accesses
111 // preceding the releasing store that the acquiring load observed.
112 // - Guarantees from relaxed loads hold.
113 // * MO_SEQ_CST: Sequentially consistent loads.
114 // - These loads observe MO_SEQ_CST stores in the same order 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 acquiring loads hold.
117 // === Atomic Cmpxchg ===
118 // * MO_RELAXED: Atomic but relaxed cmpxchg.
119 // - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold unconditionally.
120 // * MO_SEQ_CST: Sequentially consistent cmpxchg.
121 // - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold unconditionally.
122 // === Atomic Xchg ===
123 // * MO_RELAXED: Atomic but relaxed atomic xchg.
124 // - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold.
125 // * MO_SEQ_CST: Sequentially consistent xchg.
126 // - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold.
127 const DecoratorSet MO_UNORDERED = UCONST64(1) << 6;
128 const DecoratorSet MO_VOLATILE = UCONST64(1) << 7;
129 const DecoratorSet MO_RELAXED = UCONST64(1) << 8;
130 const DecoratorSet MO_ACQUIRE = UCONST64(1) << 9;
131 const DecoratorSet MO_RELEASE = UCONST64(1) << 10;
132 const DecoratorSet MO_SEQ_CST = UCONST64(1) << 11;
133 const DecoratorSet MO_DECORATOR_MASK = MO_UNORDERED | MO_VOLATILE | MO_RELAXED |
134 MO_ACQUIRE | MO_RELEASE | MO_SEQ_CST;
135
136 // === Barrier Strength Decorators ===
137 // * AS_RAW: The access will translate into a raw memory access, hence ignoring all semantic concerns
138 // except memory ordering and compressed oops. This will bypass runtime function pointer dispatching
139 // in the pipeline and hardwire to raw accesses without going trough the GC access barriers.
140 // - Accesses on oop* translate to raw memory accesses without runtime checks
141 // - Accesses on narrowOop* translate to encoded/decoded memory accesses without runtime checks
142 // - Accesses on HeapWord* translate to a runtime check choosing one of the above
143 // - Accesses on other types translate to raw memory accesses without runtime checks
144 // * AS_DEST_NOT_INITIALIZED: This property can be important to e.g. SATB barriers by
145 // marking that the previous value is uninitialized nonsense rather than a real value.
146 // * AS_NO_KEEPALIVE: The barrier is used only on oop references and will not keep any involved objects
147 // alive, regardless of the type of reference being accessed. It will however perform the memory access
148 // in a consistent way w.r.t. e.g. concurrent compaction, so that the right field is being accessed,
149 // or maintain, e.g. intergenerational or interregional pointers if applicable. This should be used with
150 // extreme caution in isolated scopes.
151 // * AS_NORMAL: The accesses will be resolved to an accessor on the BarrierSet class, giving the
152 // responsibility of performing the access and what barriers to be performed to the GC. This is the default.
153 // Note that primitive accesses will only be resolved on the barrier set if the appropriate build-time
154 // decorator for enabling primitive barriers is enabled for the build.
155 const DecoratorSet AS_RAW = UCONST64(1) << 12;
156 const DecoratorSet AS_DEST_NOT_INITIALIZED = UCONST64(1) << 13;
157 const DecoratorSet AS_NO_KEEPALIVE = UCONST64(1) << 14;
158 const DecoratorSet AS_NORMAL = UCONST64(1) << 15;
159 const DecoratorSet AS_DECORATOR_MASK = AS_RAW | AS_DEST_NOT_INITIALIZED |
160 AS_NO_KEEPALIVE | AS_NORMAL;
161
162 // === Reference Strength Decorators ===
163 // These decorators only apply to accesses on oop-like types (oop/narrowOop).
164 // * ON_STRONG_OOP_REF: Memory access is performed on a strongly reachable reference.
165 // * ON_WEAK_OOP_REF: The memory access is performed on a weakly reachable reference.
166 // * ON_PHANTOM_OOP_REF: The memory access is performed on a phantomly reachable reference.
167 // This is the same ring of strength as jweak and weak oops in the VM.
168 // * ON_UNKNOWN_OOP_REF: The memory access is performed on a reference of unknown strength.
169 // This could for example come from the unsafe API.
170 // * Default (no explicit reference strength specified): ON_STRONG_OOP_REF
171 const DecoratorSet ON_STRONG_OOP_REF = UCONST64(1) << 16;
172 const DecoratorSet ON_WEAK_OOP_REF = UCONST64(1) << 17;
173 const DecoratorSet ON_PHANTOM_OOP_REF = UCONST64(1) << 18;
174 const DecoratorSet ON_UNKNOWN_OOP_REF = UCONST64(1) << 19;
175 const DecoratorSet ON_DECORATOR_MASK = ON_STRONG_OOP_REF | ON_WEAK_OOP_REF |
176 ON_PHANTOM_OOP_REF | ON_UNKNOWN_OOP_REF;
177
178 // === Access Location ===
179 // Accesses can take place in, e.g. the heap, old or young generation and different native roots.
180 // The location is important to the GC as it may imply different actions. The following decorators are used:
181 // * IN_HEAP: The access is performed in the heap. Many barriers such as card marking will
182 // be omitted if this decorator is not set.
183 // * IN_HEAP_ARRAY: The access is performed on a heap allocated array. This is sometimes a special case
184 // for some GCs, and implies that it is an IN_HEAP.
185 // * IN_ROOT: The access is performed in an off-heap data structure pointing into the Java heap.
186 // * IN_CONCURRENT_ROOT: The access is performed in an off-heap data structure pointing into the Java heap,
187 // but is notably not scanned during safepoints. This is sometimes a special case for some GCs and
188 // implies that it is also an IN_ROOT.
189 const DecoratorSet IN_HEAP = UCONST64(1) << 20;
190 const DecoratorSet IN_HEAP_ARRAY = UCONST64(1) << 21;
191 const DecoratorSet IN_ROOT = UCONST64(1) << 22;
192 const DecoratorSet IN_CONCURRENT_ROOT = UCONST64(1) << 23;
193 const DecoratorSet IN_ARCHIVE_ROOT = UCONST64(1) << 24;
194 const DecoratorSet IN_DECORATOR_MASK = IN_HEAP | IN_HEAP_ARRAY |
195 IN_ROOT | IN_CONCURRENT_ROOT |
196 IN_ARCHIVE_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 #endif // SHARE_OOPS_ACCESSDECORATORS_HPP