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src/hotspot/share/oops/access.hpp
erik_version
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
! #ifndef SHARE_VM_RUNTIME_ACCESS_HPP
! #define SHARE_VM_RUNTIME_ACCESS_HPP
#include "memory/allocation.hpp"
! #include "metaprogramming/decay.hpp"
! #include "metaprogramming/integralConstant.hpp"
#include "oops/oopsHierarchy.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"
// = GENERAL =
// Access is an API for performing accesses with declarative semantics. Each access can have a number of "decorators".
// A decorator is an attribute or property that affects the way a memory access is performed in some way.
// There are different groups of decorators. Some have to do with memory ordering, others to do with,
// e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
// Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
// at callsites such as whether an access is in the heap or not, and others are resolved at runtime
! // such as GC-specific barriers and encoding/decoding compressed oops.
// By pipelining handling of these decorators, the design of the Access API allows separation of concern
// over the different orthogonal concerns of decorators, while providing a powerful way of
// expressing these orthogonal semantic properties in a unified way.
!
// == OPERATIONS ==
// * load: Load a value from an address.
// * load_at: Load a value from an internal pointer relative to a base object.
// * store: Store a value at an address.
// * store_at: Store a value in an internal pointer relative to a base object.
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
! #ifndef SHARE_OOPS_ACCESS_HPP
! #define SHARE_OOPS_ACCESS_HPP
#include "memory/allocation.hpp"
! #include "oops/accessBackend.hpp"
! #include "oops/accessDecorators.hpp"
#include "oops/oopsHierarchy.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"
+
// = GENERAL =
// Access is an API for performing accesses with declarative semantics. Each access can have a number of "decorators".
// A decorator is an attribute or property that affects the way a memory access is performed in some way.
// There are different groups of decorators. Some have to do with memory ordering, others to do with,
// e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
// Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
// at callsites such as whether an access is in the heap or not, and others are resolved at runtime
! // such as GC-specific barriers and encoding/decoding compressed oops. For more information about what
! // decorators are available, cf. oops/accessDecorators.hpp.
// By pipelining handling of these decorators, the design of the Access API allows separation of concern
// over the different orthogonal concerns of decorators, while providing a powerful way of
// expressing these orthogonal semantic properties in a unified way.
! //
// == OPERATIONS ==
// * load: Load a value from an address.
// * load_at: Load a value from an internal pointer relative to a base object.
// * store: Store a value at an address.
// * store_at: Store a value in an internal pointer relative to a base object.
***************
// * atomic_xchg_at: Atomically swap a new value at an internal pointer address if previous value matched the compared value.
// * arraycopy: Copy data from one heap array to another heap array.
// * clone: Clone the contents of an object to a newly allocated object.
// * resolve: Resolve a stable to-space invariant oop that is guaranteed not to relocate its payload until a subsequent thread transition.
// * equals: Object equality, e.g. when different copies of the same objects are in use (from-space vs. to-space)
- typedef uint64_t DecoratorSet;
-
- // == Internal Decorators - do not use ==
- // * INTERNAL_EMPTY: This is the name for the empty decorator set (in absence of other decorators).
- // * INTERNAL_CONVERT_COMPRESSED_OOPS: This is an oop access that will require converting an oop
- // to a narrowOop or vice versa, if UseCompressedOops is known to be set.
- // * INTERNAL_VALUE_IS_OOP: Remember that the involved access is on oop rather than primitive.
- const DecoratorSet INTERNAL_EMPTY = UCONST64(0);
- const DecoratorSet INTERNAL_CONVERT_COMPRESSED_OOP = UCONST64(1) << 1;
- const DecoratorSet INTERNAL_VALUE_IS_OOP = UCONST64(1) << 2;
-
- // == Internal build-time Decorators ==
- // * INTERNAL_BT_BARRIER_ON_PRIMITIVES: This is set in the barrierSetConfig.hpp file.
- // * INTERNAL_BT_TO_SPACE_INVARIANT: This is set in the barrierSetConfig.hpp file iff
- // no GC is bundled in the build that is to-space invariant.
- const DecoratorSet INTERNAL_BT_BARRIER_ON_PRIMITIVES = UCONST64(1) << 3;
- const DecoratorSet INTERNAL_BT_TO_SPACE_INVARIANT = UCONST64(1) << 4;
-
- // == Internal run-time Decorators ==
- // * INTERNAL_RT_USE_COMPRESSED_OOPS: This decorator will be set in runtime resolved
- // access backends iff UseCompressedOops is true.
- const DecoratorSet INTERNAL_RT_USE_COMPRESSED_OOPS = UCONST64(1) << 5;
-
- const DecoratorSet INTERNAL_DECORATOR_MASK = INTERNAL_CONVERT_COMPRESSED_OOP | INTERNAL_VALUE_IS_OOP |
- INTERNAL_BT_BARRIER_ON_PRIMITIVES | INTERNAL_RT_USE_COMPRESSED_OOPS;
-
- // == Memory Ordering Decorators ==
- // The memory ordering decorators can be described in the following way:
- // === Decorator Rules ===
- // The different types of memory ordering guarantees have a strict order of strength.
- // Explicitly specifying the stronger ordering implies that the guarantees of the weaker
- // property holds too. The names come from the C++11 atomic operations, and typically
- // have a JMM equivalent property.
- // The equivalence may be viewed like this:
- // MO_UNORDERED is equivalent to JMM plain.
- // MO_VOLATILE has no equivalence in JMM, because it's a C++ thing.
- // MO_RELAXED is equivalent to JMM opaque.
- // MO_ACQUIRE is equivalent to JMM acquire.
- // MO_RELEASE is equivalent to JMM release.
- // MO_SEQ_CST is equivalent to JMM volatile.
//
! // === Stores ===
! // * MO_UNORDERED (Default): No guarantees.
! // - The compiler and hardware are free to reorder aggressively. And they will.
! // * MO_VOLATILE: Volatile stores (in the C++ sense).
! // - The stores are not reordered by the compiler (but possibly the HW) w.r.t. other
! // volatile accesses in program order (but possibly non-volatile accesses).
! // * MO_RELAXED: Relaxed atomic stores.
! // - The stores are atomic.
! // - Guarantees from volatile stores hold.
! // * MO_RELEASE: Releasing stores.
! // - The releasing store will make its preceding memory accesses observable to memory accesses
! // subsequent to an acquiring load observing this releasing store.
! // - Guarantees from relaxed stores hold.
! // * MO_SEQ_CST: Sequentially consistent stores.
! // - The stores are observed in the same order by MO_SEQ_CST loads on other processors
! // - Preceding loads and stores in program order are not reordered with subsequent loads and stores in program order.
! // - Guarantees from releasing stores hold.
! // === Loads ===
! // * MO_UNORDERED (Default): No guarantees
! // - The compiler and hardware are free to reorder aggressively. And they will.
! // * MO_VOLATILE: Volatile loads (in the C++ sense).
! // - The loads are not reordered by the compiler (but possibly the HW) w.r.t. other
! // volatile accesses in program order (but possibly non-volatile accesses).
! // * MO_RELAXED: Relaxed atomic loads.
! // - The stores are atomic.
! // - Guarantees from volatile loads hold.
! // * MO_ACQUIRE: Acquiring loads.
! // - An acquiring load will make subsequent memory accesses observe the memory accesses
! // preceding the releasing store that the acquiring load observed.
! // - Guarantees from relaxed loads hold.
! // * MO_SEQ_CST: Sequentially consistent loads.
! // - These loads observe MO_SEQ_CST stores in the same order on other processors
! // - Preceding loads and stores in program order are not reordered with subsequent loads and stores in program order.
! // - Guarantees from acquiring loads hold.
! // === Atomic Cmpxchg ===
! // * MO_RELAXED: Atomic but relaxed cmpxchg.
! // - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold unconditionally.
! // * MO_SEQ_CST: Sequentially consistent cmpxchg.
! // - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold unconditionally.
! // === Atomic Xchg ===
! // * MO_RELAXED: Atomic but relaxed atomic xchg.
! // - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold.
! // * MO_SEQ_CST: Sequentially consistent xchg.
! // - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold.
! const DecoratorSet MO_UNORDERED = UCONST64(1) << 6;
! const DecoratorSet MO_VOLATILE = UCONST64(1) << 7;
! const DecoratorSet MO_RELAXED = UCONST64(1) << 8;
! const DecoratorSet MO_ACQUIRE = UCONST64(1) << 9;
! const DecoratorSet MO_RELEASE = UCONST64(1) << 10;
! const DecoratorSet MO_SEQ_CST = UCONST64(1) << 11;
! const DecoratorSet MO_DECORATOR_MASK = MO_UNORDERED | MO_VOLATILE | MO_RELAXED |
! MO_ACQUIRE | MO_RELEASE | MO_SEQ_CST;
!
! // === Barrier Strength Decorators ===
! // * AS_RAW: The access will translate into a raw memory access, hence ignoring all semantic concerns
! // except memory ordering and compressed oops. This will bypass runtime function pointer dispatching
! // in the pipeline and hardwire to raw accesses without going trough the GC access barriers.
! // - Accesses on oop* translate to raw memory accesses without runtime checks
! // - Accesses on narrowOop* translate to encoded/decoded memory accesses without runtime checks
! // - Accesses on HeapWord* translate to a runtime check choosing one of the above
! // - Accesses on other types translate to raw memory accesses without runtime checks
! // * AS_DEST_NOT_INITIALIZED: This property can be important to e.g. SATB barriers by
! // marking that the previous value is uninitialized nonsense rather than a real value.
! // * AS_NO_KEEPALIVE: The barrier is used only on oop references and will not keep any involved objects
! // alive, regardless of the type of reference being accessed. It will however perform the memory access
! // in a consistent way w.r.t. e.g. concurrent compaction, so that the right field is being accessed,
! // or maintain, e.g. intergenerational or interregional pointers if applicable. This should be used with
! // extreme caution in isolated scopes.
! // * AS_NORMAL: The accesses will be resolved to an accessor on the BarrierSet class, giving the
! // responsibility of performing the access and what barriers to be performed to the GC. This is the default.
! // Note that primitive accesses will only be resolved on the barrier set if the appropriate build-time
! // decorator for enabling primitive barriers is enabled for the build.
! const DecoratorSet AS_RAW = UCONST64(1) << 12;
! const DecoratorSet AS_DEST_NOT_INITIALIZED = UCONST64(1) << 13;
! const DecoratorSet AS_NO_KEEPALIVE = UCONST64(1) << 14;
! const DecoratorSet AS_NORMAL = UCONST64(1) << 15;
! const DecoratorSet AS_DECORATOR_MASK = AS_RAW | AS_DEST_NOT_INITIALIZED |
! AS_NO_KEEPALIVE | AS_NORMAL;
!
! // === Reference Strength Decorators ===
! // These decorators only apply to accesses on oop-like types (oop/narrowOop).
! // * ON_STRONG_OOP_REF: Memory access is performed on a strongly reachable reference.
! // * ON_WEAK_OOP_REF: The memory access is performed on a weakly reachable reference.
! // * ON_PHANTOM_OOP_REF: The memory access is performed on a phantomly reachable reference.
! // This is the same ring of strength as jweak and weak oops in the VM.
! // * ON_UNKNOWN_OOP_REF: The memory access is performed on a reference of unknown strength.
! // This could for example come from the unsafe API.
! // * Default (no explicit reference strength specified): ON_STRONG_OOP_REF
! const DecoratorSet ON_STRONG_OOP_REF = UCONST64(1) << 16;
! const DecoratorSet ON_WEAK_OOP_REF = UCONST64(1) << 17;
! const DecoratorSet ON_PHANTOM_OOP_REF = UCONST64(1) << 18;
! const DecoratorSet ON_UNKNOWN_OOP_REF = UCONST64(1) << 19;
! const DecoratorSet ON_DECORATOR_MASK = ON_STRONG_OOP_REF | ON_WEAK_OOP_REF |
! ON_PHANTOM_OOP_REF | ON_UNKNOWN_OOP_REF;
!
! // === Access Location ===
! // Accesses can take place in, e.g. the heap, old or young generation and different native roots.
! // The location is important to the GC as it may imply different actions. The following decorators are used:
! // * IN_HEAP: The access is performed in the heap. Many barriers such as card marking will
! // be omitted if this decorator is not set.
! // * IN_HEAP_ARRAY: The access is performed on a heap allocated array. This is sometimes a special case
! // for some GCs, and implies that it is an IN_HEAP.
! // * IN_ROOT: The access is performed in an off-heap data structure pointing into the Java heap.
! // * IN_CONCURRENT_ROOT: The access is performed in an off-heap data structure pointing into the Java heap,
! // but is notably not scanned during safepoints. This is sometimes a special case for some GCs and
! // implies that it is also an IN_ROOT.
! const DecoratorSet IN_HEAP = UCONST64(1) << 20;
! const DecoratorSet IN_HEAP_ARRAY = UCONST64(1) << 21;
! const DecoratorSet IN_ROOT = UCONST64(1) << 22;
! const DecoratorSet IN_CONCURRENT_ROOT = UCONST64(1) << 23;
! const DecoratorSet IN_ARCHIVE_ROOT = UCONST64(1) << 24;
! const DecoratorSet IN_DECORATOR_MASK = IN_HEAP | IN_HEAP_ARRAY |
! IN_ROOT | IN_CONCURRENT_ROOT |
! IN_ARCHIVE_ROOT;
!
! // == Value Decorators ==
! // * OOP_NOT_NULL: This property can make certain barriers faster such as compressing oops.
! const DecoratorSet OOP_NOT_NULL = UCONST64(1) << 25;
! const DecoratorSet OOP_DECORATOR_MASK = OOP_NOT_NULL;
!
! // == Arraycopy Decorators ==
! // * ARRAYCOPY_CHECKCAST: This property means that the class of the objects in source
! // are not guaranteed to be subclasses of the class of the destination array. This requires
! // a check-cast barrier during the copying operation. If this is not set, it is assumed
! // that the array is covariant: (the source array type is-a destination array type)
! // * ARRAYCOPY_DISJOINT: This property means that it is known that the two array ranges
! // are disjoint.
! // * ARRAYCOPY_ARRAYOF: The copy is in the arrayof form.
! // * ARRAYCOPY_ATOMIC: The accesses have to be atomic over the size of its elements.
! // * ARRAYCOPY_ALIGNED: The accesses have to be aligned on a HeapWord.
! const DecoratorSet ARRAYCOPY_CHECKCAST = UCONST64(1) << 26;
! const DecoratorSet ARRAYCOPY_DISJOINT = UCONST64(1) << 27;
! const DecoratorSet ARRAYCOPY_ARRAYOF = UCONST64(1) << 28;
! const DecoratorSet ARRAYCOPY_ATOMIC = UCONST64(1) << 29;
! const DecoratorSet ARRAYCOPY_ALIGNED = UCONST64(1) << 30;
! const DecoratorSet ARRAYCOPY_DECORATOR_MASK = ARRAYCOPY_CHECKCAST | ARRAYCOPY_DISJOINT |
! ARRAYCOPY_DISJOINT | ARRAYCOPY_ARRAYOF |
! ARRAYCOPY_ATOMIC | ARRAYCOPY_ALIGNED;
!
! // The HasDecorator trait can help at compile-time determining whether a decorator set
! // has an intersection with a certain other decorator set
! template <DecoratorSet decorators, DecoratorSet decorator>
! struct HasDecorator: public IntegralConstant<bool, (decorators & decorator) != 0> {};
namespace AccessInternal {
- template <typename T>
- struct OopOrNarrowOopInternal: AllStatic {
- typedef oop type;
- };
-
- template <>
- struct OopOrNarrowOopInternal<narrowOop>: AllStatic {
- typedef narrowOop type;
- };
-
- // This metafunction returns a canonicalized oop/narrowOop type for a passed
- // in oop-like types passed in from oop_* overloads where the user has sworn
- // that the passed in values should be oop-like (e.g. oop, oopDesc*, arrayOop,
- // narrowOoop, instanceOopDesc*, and random other things).
- // In the oop_* overloads, it must hold that if the passed in type T is not
- // narrowOop, then it by contract has to be one of many oop-like types implicitly
- // convertible to oop, and hence returns oop as the canonical oop type.
- // If it turns out it was not, then the implicit conversion to oop will fail
- // to compile, as desired.
- template <typename T>
- struct OopOrNarrowOop: AllStatic {
- typedef typename OopOrNarrowOopInternal<typename Decay<T>::type>::type type;
- };
-
- inline void* field_addr(oop base, ptrdiff_t byte_offset) {
- return reinterpret_cast<void*>(reinterpret_cast<intptr_t>((void*)base) + byte_offset);
- }
-
template <DecoratorSet decorators, typename T>
void store_at(oop base, ptrdiff_t offset, T value);
template <DecoratorSet decorators, typename T>
T load_at(oop base, ptrdiff_t offset);
// * atomic_xchg_at: Atomically swap a new value at an internal pointer address if previous value matched the compared value.
// * arraycopy: Copy data from one heap array to another heap array.
// * clone: Clone the contents of an object to a newly allocated object.
// * resolve: Resolve a stable to-space invariant oop that is guaranteed not to relocate its payload until a subsequent thread transition.
// * equals: Object equality, e.g. when different copies of the same objects are in use (from-space vs. to-space)
//
! // == IMPLEMENTATION ==
! // Each access goes through the following steps in a template pipeline.
! // There are essentially 5 steps for each access:
! // * Step 1: Set default decorators and decay types. This step gets rid of CV qualifiers
! // and sets default decorators to sensible values.
! // * Step 2: Reduce types. This step makes sure there is only a single T type and not
! // multiple types. The P type of the address and T type of the value must
! // match.
! // * Step 3: Pre-runtime dispatch. This step checks whether a runtime call can be
! // avoided, and in that case avoids it (calling raw accesses or
! // primitive accesses in a build that does not require primitive GC barriers)
! // * Step 4: Runtime-dispatch. This step performs a runtime dispatch to the corresponding
! // BarrierSet::AccessBarrier accessor that attaches GC-required barriers
! // to the access.
! // * Step 5.a: Barrier resolution. This step is invoked the first time a runtime-dispatch
! // happens for an access. The appropriate BarrierSet::AccessBarrier accessor
! // is resolved, then the function pointer is updated to that accessor for
! // future invocations.
! // * Step 5.b: Post-runtime dispatch. This step now casts previously unknown types such
! // as the address type of an oop on the heap (is it oop* or narrowOop*) to
! // the appropriate type. It also splits sufficiently orthogonal accesses into
! // different functions, such as whether the access involves oops or primitives
! // and whether the access is performed on the heap or outside. Then the
! // appropriate BarrierSet::AccessBarrier is called to perform the access.
! //
! // The implementation of step 1-4 resides in in accessBackend.hpp, to allow selected
! // accesses to be accessible from only access.hpp, as opposed to access.inline.hpp.
! // Steps 5.a and 5.b require knowledge about the GC backends, and therefore needs to
! // include the various GC backend .inline.hpp headers. Their implementation resides in
! // access.inline.hpp. The accesses that are allowed through the access.hpp file
! // must be instantiated in access.cpp using the INSTANTIATE_HPP_ACCESS macro.
namespace AccessInternal {
template <DecoratorSet decorators, typename T>
void store_at(oop base, ptrdiff_t offset, T value);
template <DecoratorSet decorators, typename T>
T load_at(oop base, ptrdiff_t offset);
***************
// Helper for performing normal accesses in roots. These accesses
// may resolve an accessor on a GC barrier set
template <DecoratorSet decorators = INTERNAL_EMPTY>
class RootAccess: public Access<IN_ROOT | decorators> {};
! #endif // SHARE_VM_RUNTIME_ACCESS_HPP
// Helper for performing normal accesses in roots. These accesses
// may resolve an accessor on a GC barrier set
template <DecoratorSet decorators = INTERNAL_EMPTY>
class RootAccess: public Access<IN_ROOT | decorators> {};
! template <DecoratorSet decorators>
! template <DecoratorSet expected_decorators>
! void Access<decorators>::verify_decorators() {
! STATIC_ASSERT((~expected_decorators & decorators) == 0); // unexpected decorator used
! const DecoratorSet barrier_strength_decorators = decorators & AS_DECORATOR_MASK;
! STATIC_ASSERT(barrier_strength_decorators == 0 || ( // make sure barrier strength decorators are disjoint if set
! (barrier_strength_decorators ^ AS_NO_KEEPALIVE) == 0 ||
! (barrier_strength_decorators ^ AS_DEST_NOT_INITIALIZED) == 0 ||
! (barrier_strength_decorators ^ AS_RAW) == 0 ||
! (barrier_strength_decorators ^ AS_NORMAL) == 0
! ));
! const DecoratorSet ref_strength_decorators = decorators & ON_DECORATOR_MASK;
! STATIC_ASSERT(ref_strength_decorators == 0 || ( // make sure ref strength decorators are disjoint if set
! (ref_strength_decorators ^ ON_STRONG_OOP_REF) == 0 ||
! (ref_strength_decorators ^ ON_WEAK_OOP_REF) == 0 ||
! (ref_strength_decorators ^ ON_PHANTOM_OOP_REF) == 0 ||
! (ref_strength_decorators ^ ON_UNKNOWN_OOP_REF) == 0
! ));
! const DecoratorSet memory_ordering_decorators = decorators & MO_DECORATOR_MASK;
! STATIC_ASSERT(memory_ordering_decorators == 0 || ( // make sure memory ordering decorators are disjoint if set
! (memory_ordering_decorators ^ MO_UNORDERED) == 0 ||
! (memory_ordering_decorators ^ MO_VOLATILE) == 0 ||
! (memory_ordering_decorators ^ MO_RELAXED) == 0 ||
! (memory_ordering_decorators ^ MO_ACQUIRE) == 0 ||
! (memory_ordering_decorators ^ MO_RELEASE) == 0 ||
! (memory_ordering_decorators ^ MO_SEQ_CST) == 0
! ));
! const DecoratorSet location_decorators = decorators & IN_DECORATOR_MASK;
! STATIC_ASSERT(location_decorators == 0 || ( // make sure location decorators are disjoint if set
! (location_decorators ^ IN_ROOT) == 0 ||
! (location_decorators ^ IN_HEAP) == 0 ||
! (location_decorators ^ (IN_HEAP | IN_HEAP_ARRAY)) == 0 ||
! (location_decorators ^ (IN_ROOT | IN_CONCURRENT_ROOT)) == 0 ||
! (location_decorators ^ (IN_ROOT | IN_ARCHIVE_ROOT)) == 0
! ));
! }
!
! #endif // SHARE_OOPS_ACCESS_HPP
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