diff --git a/src/hotspot/share/oops/access.hpp b/src/hotspot/share/oops/access.hpp index 0337d2a..7c9c38a 100644 --- a/src/hotspot/share/oops/access.hpp +++ b/src/hotspot/share/oops/access.hpp @@ -22,16 +22,17 @@ * */ -#ifndef SHARE_VM_RUNTIME_ACCESS_HPP -#define SHARE_VM_RUNTIME_ACCESS_HPP +#ifndef SHARE_OOPS_ACCESS_HPP +#define SHARE_OOPS_ACCESS_HPP #include "memory/allocation.hpp" -#include "metaprogramming/decay.hpp" -#include "metaprogramming/integralConstant.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. @@ -39,11 +40,12 @@ // 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. +// 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. @@ -56,221 +58,41 @@ // * 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. - -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. +// * 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. // -// === 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 -struct HasDecorator: public IntegralConstant {}; +// 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 - struct OopOrNarrowOopInternal: AllStatic { - typedef oop type; - }; - - template <> - struct OopOrNarrowOopInternal: 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 - struct OopOrNarrowOop: AllStatic { - typedef typename OopOrNarrowOopInternal::type>::type type; - }; - - inline void* field_addr(oop base, ptrdiff_t byte_offset) { - return reinterpret_cast(reinterpret_cast((void*)base) + byte_offset); - } - template void store_at(oop base, ptrdiff_t offset, T value); @@ -304,6 +126,9 @@ namespace AccessInternal { template oop resolve(oop src); + template + bool equals(oop o1, oop o2); + // Infer the type that should be returned from a load. template class OopLoadProxy: public StackObj { @@ -554,6 +379,11 @@ public: verify_decorators(); return AccessInternal::resolve(obj); } + + static bool equals(oop o1, oop o2) { + verify_decorators(); + return AccessInternal::equals(o1, o2); + } }; // Helper for performing raw accesses (knows only of memory ordering @@ -571,4 +401,41 @@ class HeapAccess: public Access {}; template class RootAccess: public Access {}; -#endif // SHARE_VM_RUNTIME_ACCESS_HPP +template +template +void Access::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