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