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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

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 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

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#ifndef SHARE_VM_RUNTIME_ATOMIC_HPP

#define SHARE_VM_RUNTIME_ATOMIC_HPP

#include "memory/allocation.hpp"

#include "metaprogramming/conditional.hpp"

#include "metaprogramming/enableIf.hpp"

#include "metaprogramming/isIntegral.hpp"

#include "metaprogramming/isPointer.hpp"

#include "metaprogramming/isSame.hpp"

#include "metaprogramming/primitiveConversions.hpp"

#include "metaprogramming/removeCV.hpp"

#include "metaprogramming/removePointer.hpp"

#include "utilities/align.hpp"

#include "utilities/macros.hpp"

enum atomic_memory_order {

  // The modes that align with C++11 are intended to

  // follow the same semantics.

  memory_order_relaxed = 0,

  memory_order_acquire = 2,

  memory_order_release = 3,

  memory_order_acq_rel = 4,

  // Strong two-way memory barrier.

  memory_order_conservative = 8

};

class Atomic : AllStatic {

public:

  // Atomic operations on int64 types are not available on all 32-bit

  // platforms. If atomic ops on int64 are defined here they must only

  // be used from code that verifies they are available at runtime and

  // can provide an alternative action if not - see supports_cx8() for

  // a means to test availability.

  // The memory operations that are mentioned with each of the atomic

  // function families come from src/share/vm/runtime/orderAccess.hpp,

  // e.g., <fence> is described in that file and is implemented by the

  // OrderAccess::fence() function. See that file for the gory details

  // on the Memory Access Ordering Model.

  // All of the atomic operations that imply a read-modify-write action

  // guarantee a two-way memory barrier across that operation. Historically

  // these semantics reflect the strength of atomic operations that are

  // provided on SPARC/X86. We assume that strength is necessary unless

  // we can prove that a weaker form is sufficiently safe.

  // Atomically store to a location

  // The type T must be either a pointer type convertible to or equal

  // to D, an integral/enum type equal to D, or a type equal to D that

  // is primitive convertible using PrimitiveConversions.

  template<typename T, typename D>

  inline static void store(T store_value, volatile D* dest);

  // Atomically load from a location

  // The type T must be either a pointer type, an integral/enum type,

  // or a type that is primitive convertible using PrimitiveConversions.

  template<typename T>

  inline static T load(const volatile T* dest);

  // Atomically add to a location. Returns updated value. add*() provide:

  // <fence> add-value-to-dest <membar StoreLoad|StoreStore>

  template<typename I, typename D>

  inline static D add(I add_value, D volatile* dest,

                      atomic_memory_order order = memory_order_conservative);

  template<typename I, typename D>

  inline static D sub(I sub_value, D volatile* dest,

                      atomic_memory_order order = memory_order_conservative);

  // Atomically increment location. inc() provide:

  // <fence> increment-dest <membar StoreLoad|StoreStore>

  // The type D may be either a pointer type, or an integral

  // type. If it is a pointer type, then the increment is

  // scaled to the size of the type pointed to by the pointer.

  template<typename D>

  inline static void inc(D volatile* dest,

                         atomic_memory_order order = memory_order_conservative);

  // Atomically decrement a location. dec() provide:

  // <fence> decrement-dest <membar StoreLoad|StoreStore>

  // The type D may be either a pointer type, or an integral

  // type. If it is a pointer type, then the decrement is

  // scaled to the size of the type pointed to by the pointer.

  template<typename D>

  inline static void dec(D volatile* dest,

                         atomic_memory_order order = memory_order_conservative);

  // Performs atomic exchange of *dest with exchange_value. Returns old

  // prior value of *dest. xchg*() provide:

  // <fence> exchange-value-with-dest <membar StoreLoad|StoreStore>

  // The type T must be either a pointer type convertible to or equal

  // to D, an integral/enum type equal to D, or a type equal to D that

  // is primitive convertible using PrimitiveConversions.

  template<typename T, typename D>

  inline static D xchg(T exchange_value, volatile D* dest,

                       atomic_memory_order order = memory_order_conservative);

  // Performs atomic compare of *dest and compare_value, and exchanges

  // *dest with exchange_value if the comparison succeeded. Returns prior

  // value of *dest. cmpxchg*() provide:

  // <fence> compare-and-exchange <membar StoreLoad|StoreStore>

  template<typename T, typename D, typename U>

  inline static D cmpxchg(T exchange_value,

                          D volatile* dest,

                          U compare_value,

                          atomic_memory_order order = memory_order_conservative);

  // Performs atomic compare of *dest and NULL, and replaces *dest

  // with exchange_value if the comparison succeeded.  Returns true if

  // the comparison succeeded and the exchange occurred.  This is

  // often used as part of lazy initialization, as a lock-free

  // alternative to the Double-Checked Locking Pattern.

  template<typename T, typename D>

  inline static bool replace_if_null(T* value, D* volatile* dest,

                                     atomic_memory_order order = memory_order_conservative);

private:

WINDOWS_ONLY(public:) // VS2017 warns (C2027) use of undefined type if IsPointerConvertible is declared private

  // Test whether From is implicitly convertible to To.

  // From and To must be pointer types.

  // Note: Provides the limited subset of C++11 std::is_convertible

  // that is needed here.

  template<typename From, typename To> struct IsPointerConvertible;

protected:

  // Dispatch handler for store.  Provides type-based validity

  // checking and limited conversions around calls to the platform-

  // specific implementation layer provided by PlatformOp.

  template<typename T, typename D, typename PlatformOp, typename Enable = void>

  struct StoreImpl;

  // Platform-specific implementation of store.  Support for sizes

  // of 1, 2, 4, and (if different) pointer size bytes are required.

  // The class is a function object that must be default constructable,

  // with these requirements:

  //

  // either:

  // - dest is of type D*, an integral, enum or pointer type.

  // - new_value are of type T, an integral, enum or pointer type D or

  //   pointer type convertible to D.

  // or:

  // - T and D are the same and are primitive convertible using PrimitiveConversions

  // and either way:

  // - platform_store is an object of type PlatformStore<sizeof(T)>.

  //

  // Then

  //   platform_store(new_value, dest)

  // must be a valid expression.

  //

  // The default implementation is a volatile store. If a platform

  // requires more for e.g. 64 bit stores, a specialization is required

  template<size_t byte_size> struct PlatformStore;

  // Dispatch handler for load.  Provides type-based validity

  // checking and limited conversions around calls to the platform-

  // specific implementation layer provided by PlatformOp.

  template<typename T, typename PlatformOp, typename Enable = void>

  struct LoadImpl;

  // Platform-specific implementation of load. Support for sizes of

  // 1, 2, 4 bytes and (if different) pointer size bytes are required.

  // The class is a function object that must be default

  // constructable, with these requirements:

  //

  // - dest is of type T*, an integral, enum or pointer type, or

  //   T is convertible to a primitive type using PrimitiveConversions

  // - platform_load is an object of type PlatformLoad<sizeof(T)>.

  //

  // Then

  //   platform_load(src)

  // must be a valid expression, returning a result convertible to T.

  //

  // The default implementation is a volatile load. If a platform

  // requires more for e.g. 64 bit loads, a specialization is required

  template<size_t byte_size> struct PlatformLoad;

private:

  // Dispatch handler for add.  Provides type-based validity checking

  // and limited conversions around calls to the platform-specific

  // implementation layer provided by PlatformAdd.

  template<typename I, typename D, typename Enable = void>

  struct AddImpl;

  // Platform-specific implementation of add.  Support for sizes of 4

  // bytes and (if different) pointer size bytes are required.  The

  // class is a function object that must be default constructable,

  // with these requirements:

  //

  // - dest is of type D*, an integral or pointer type.

  // - add_value is of type I, an integral type.

  // - sizeof(I) == sizeof(D).

  // - if D is an integral type, I == D.

  // - platform_add is an object of type PlatformAdd<sizeof(D)>.

  //

  // Then

  //   platform_add(add_value, dest)

  // must be a valid expression, returning a result convertible to D.

  //

  // No definition is provided; all platforms must explicitly define

  // this class and any needed specializations.

  template<size_t byte_size> struct PlatformAdd;

  // Helper base classes for defining PlatformAdd.  To use, define

  // PlatformAdd or a specialization that derives from one of these,

  // and include in the PlatformAdd definition the support function

  // (described below) required by the base class.

  //

  // These classes implement the required function object protocol for

  // PlatformAdd, using a support function template provided by the

  // derived class.  Let add_value (of type I) and dest (of type D) be

  // the arguments the object is called with.  If D is a pointer type

  // P*, then let addend (of type I) be add_value * sizeof(P);

  // otherwise, addend is add_value.

  //

  // FetchAndAdd requires the derived class to provide

  //   fetch_and_add(addend, dest)

  // atomically adding addend to the value of dest, and returning the

  // old value.

  //

  // AddAndFetch requires the derived class to provide

  //   add_and_fetch(addend, dest)

  // atomically adding addend to the value of dest, and returning the

  // new value.

  //

  // When D is a pointer type P*, both fetch_and_add and add_and_fetch

  // treat it as if it were a uintptr_t; they do not perform any

  // scaling of the addend, as that has already been done by the

  // caller.

public: // Temporary, can't be private: C++03 11.4/2. Fixed by C++11.

  template<typename Derived> struct FetchAndAdd;

  template<typename Derived> struct AddAndFetch;

private:

  // Support for platforms that implement some variants of add using a

  // (typically out of line) non-template helper function.  The

  // generic arguments passed to PlatformAdd need to be translated to

  // the appropriate type for the helper function, the helper function

  // invoked on the translated arguments, and the result translated

  // back.  Type is the parameter / return type of the helper

  // function.  No scaling of add_value is performed when D is a pointer

  // type, so this function can be used to implement the support function

  // required by AddAndFetch.

  template<typename Type, typename Fn, typename I, typename D>

  static D add_using_helper(Fn fn, I add_value, D volatile* dest);

  // Dispatch handler for cmpxchg.  Provides type-based validity

  // checking and limited conversions around calls to the

  // platform-specific implementation layer provided by

  // PlatformCmpxchg.

  template<typename T, typename D, typename U, typename Enable = void>

  struct CmpxchgImpl;

  // Platform-specific implementation of cmpxchg.  Support for sizes

  // of 1, 4, and 8 are required.  The class is a function object that

  // must be default constructable, with these requirements:

  //

  // - dest is of type T*.

  // - exchange_value and compare_value are of type T.

  // - order is of type atomic_memory_order.

  // - platform_cmpxchg is an object of type PlatformCmpxchg<sizeof(T)>.

  //

  // Then

  //   platform_cmpxchg(exchange_value, dest, compare_value, order)

  // must be a valid expression, returning a result convertible to T.

  //

  // A default definition is provided, which declares a function template

  //   T operator()(T, T volatile*, T, atomic_memory_order) const

  //

  // For each required size, a platform must either provide an

  // appropriate definition of that function, or must entirely

  // specialize the class template for that size.

  template<size_t byte_size> struct PlatformCmpxchg;

  // Support for platforms that implement some variants of cmpxchg

  // using a (typically out of line) non-template helper function.

  // The generic arguments passed to PlatformCmpxchg need to be

  // translated to the appropriate type for the helper function, the

  // helper invoked on the translated arguments, and the result

  // translated back.  Type is the parameter / return type of the

  // helper function.

  template<typename Type, typename Fn, typename T>

  static T cmpxchg_using_helper(Fn fn,

                                T exchange_value,

                                T volatile* dest,

                                T compare_value);

  // Support platforms that do not provide Read-Modify-Write

  // byte-level atomic access. To use, derive PlatformCmpxchg<1> from

  // this class.

public: // Temporary, can't be private: C++03 11.4/2. Fixed by C++11.

  struct CmpxchgByteUsingInt;

private:

  // Dispatch handler for xchg.  Provides type-based validity

  // checking and limited conversions around calls to the

  // platform-specific implementation layer provided by

  // PlatformXchg.

  template<typename T, typename D, typename Enable = void>

  struct XchgImpl;

  // Platform-specific implementation of xchg.  Support for sizes

  // of 4, and sizeof(intptr_t) are required.  The class is a function

  // object that must be default constructable, with these requirements:

  //

  // - dest is of type T*.

  // - exchange_value is of type T.

  // - platform_xchg is an object of type PlatformXchg<sizeof(T)>.

  //

  // Then

  //   platform_xchg(exchange_value, dest)

  // must be a valid expression, returning a result convertible to T.

  //

  // A default definition is provided, which declares a function template

  //   T operator()(T, T volatile*, T, atomic_memory_order) const

  //

  // For each required size, a platform must either provide an

  // appropriate definition of that function, or must entirely

  // specialize the class template for that size.

  template<size_t byte_size> struct PlatformXchg;

  // Support for platforms that implement some variants of xchg

  // using a (typically out of line) non-template helper function.

  // The generic arguments passed to PlatformXchg need to be

  // translated to the appropriate type for the helper function, the

  // helper invoked on the translated arguments, and the result

  // translated back.  Type is the parameter / return type of the

  // helper function.

  template<typename Type, typename Fn, typename T>

  static T xchg_using_helper(Fn fn,

                             T exchange_value,

                             T volatile* dest);

};

template<typename From, typename To>

struct Atomic::IsPointerConvertible<From*, To*> : AllStatic {

  // Determine whether From* is implicitly convertible to To*, using

  // the "sizeof trick".

  typedef char yes;

  typedef char (&no)[2];

  static yes test(To*);

  static no test(...);

  static From* test_value;

  static const bool value = (sizeof(yes) == sizeof(test(test_value)));

};

// Handle load for pointer, integral and enum types.

template<typename T, typename PlatformOp>

struct Atomic::LoadImpl<

  T,

  PlatformOp,

  typename EnableIf<IsIntegral<T>::value || IsRegisteredEnum<T>::value || IsPointer<T>::value>::type>

{

  T operator()(T const volatile* dest) const {

    // Forward to the platform handler for the size of T.

    return PlatformOp()(dest);

  }

};

// Handle load for types that have a translator.

//

// All the involved types must be identical.

//

// This translates the original call into a call on the decayed

// arguments, and returns the recovered result of that translated

// call.

template<typename T, typename PlatformOp>

struct Atomic::LoadImpl<

  T,

  PlatformOp,

  typename EnableIf<PrimitiveConversions::Translate<T>::value>::type>

{

  T operator()(T const volatile* dest) const {

    typedef PrimitiveConversions::Translate<T> Translator;

    typedef typename Translator::Decayed Decayed;

    STATIC_ASSERT(sizeof(T) == sizeof(Decayed));

    Decayed result = PlatformOp()(reinterpret_cast<Decayed const volatile*>(dest));

    return Translator::recover(result);

  }

};

// Default implementation of atomic load if a specific platform

// does not provide a specialization for a certain size class.

// For increased safety, the default implementation only allows

// load types that are pointer sized or smaller. If a platform still

// supports wide atomics, then it has to use specialization

// of Atomic::PlatformLoad for that wider size class.

template<size_t byte_size>

struct Atomic::PlatformLoad {

  template<typename T>

  T operator()(T const volatile* dest) const {

    STATIC_ASSERT(sizeof(T) <= sizeof(void*)); // wide atomics need specialization

    return *dest;

  }

};

// Handle store for integral and enum types.

//

// All the involved types must be identical.

template<typename T, typename PlatformOp>

struct Atomic::StoreImpl<

  T, T,

  PlatformOp,

  typename EnableIf<IsIntegral<T>::value || IsRegisteredEnum<T>::value>::type>

{

  void operator()(T new_value, T volatile* dest) const {

    // Forward to the platform handler for the size of T.

    PlatformOp()(new_value, dest);

  }

};

// Handle store for pointer types.

//

// The new_value must be implicitly convertible to the

// destination's type; it must be type-correct to store the

// new_value in the destination.

template<typename T, typename D, typename PlatformOp>

struct Atomic::StoreImpl<

  T*, D*,

  PlatformOp,

  typename EnableIf<Atomic::IsPointerConvertible<T*, D*>::value>::type>

{

  void operator()(T* new_value, D* volatile* dest) const {

    // Allow derived to base conversion, and adding cv-qualifiers.

    D* value = new_value;

    PlatformOp()(value, dest);

  }

};

// Handle store for types that have a translator.

//

// All the involved types must be identical.

//

// This translates the original call into a call on the decayed

// arguments.

template<typename T, typename PlatformOp>

struct Atomic::StoreImpl<

  T, T,

  PlatformOp,

  typename EnableIf<PrimitiveConversions::Translate<T>::value>::type>

{

  void operator()(T new_value, T volatile* dest) const {

    typedef PrimitiveConversions::Translate<T> Translator;

    typedef typename Translator::Decayed Decayed;

    STATIC_ASSERT(sizeof(T) == sizeof(Decayed));

    PlatformOp()(Translator::decay(new_value),

                 reinterpret_cast<Decayed volatile*>(dest));

  }

};

// Default implementation of atomic store if a specific platform

// does not provide a specialization for a certain size class.

// For increased safety, the default implementation only allows

// storing types that are pointer sized or smaller. If a platform still

// supports wide atomics, then it has to use specialization

// of Atomic::PlatformStore for that wider size class.

template<size_t byte_size>

struct Atomic::PlatformStore {

  template<typename T>

  void operator()(T new_value,

                  T volatile* dest) const {

    STATIC_ASSERT(sizeof(T) <= sizeof(void*)); // wide atomics need specialization

    (void)const_cast<T&>(*dest = new_value);

  }

};