Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1540 insertions, 0 deletions

diff --git a/widget/android/jni/Natives.h b/widget/android/jni/Natives.h
new file mode 100644
index 0000000000..45b351ba21
--- /dev/null
+++ b/widget/android/jni/Natives.h
@@ -0,0 +1,1540 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_jni_Natives_h__
+#define mozilla_jni_Natives_h__
+
+#include <jni.h>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+
+#include "mozilla/RefPtr.h"
+#include "mozilla/RWLock.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/WeakPtr.h"
+#include "mozilla/jni/Accessors.h"
+#include "mozilla/jni/Refs.h"
+#include "mozilla/jni/Types.h"
+#include "mozilla/jni/Utils.h"
+#include "nsThreadUtils.h"
+
+#if defined(_MSC_VER)  // MSVC
+#  define FUNCTION_SIGNATURE __FUNCSIG__
+#elif defined(__GNUC__)  // GCC, Clang
+#  define FUNCTION_SIGNATURE __PRETTY_FUNCTION__
+#endif
+
+struct NativeException {
+  const char* str;
+};
+
+template <class T>
+static NativeException NullHandle() {
+  return {FUNCTION_SIGNATURE};
+}
+
+template <class T>
+static NativeException NullWeakPtr() {
+  return {FUNCTION_SIGNATURE};
+}
+
+namespace mozilla {
+
+template <typename ResolveValueT, typename RejectValueT, bool IsExclusive>
+class MozPromise;
+
+namespace jni {
+
+/**
+ * C++ classes implementing instance (non-static) native methods can choose
+ * from one of two ownership models, when associating a C++ object with a Java
+ * instance.
+ *
+ * * If the C++ class inherits from mozilla::SupportsWeakPtr, weak pointers
+ *   will be used. The Java instance will store and own the pointer to a
+ *   WeakPtr object. The C++ class itself is otherwise not owned or directly
+ *   referenced. Note that mozilla::SupportsWeakPtr only supports being used on
+ *   a single thread. To attach a Java instance to a C++ instance, pass in a
+ *   mozilla::SupportsWeakPtr pointer to the C++ class (i.e. MyClass*).
+ *
+ *   class MyClass : public SupportsWeakPtr
+ *                 , public MyJavaClass::Natives<MyClass>
+ *   {
+ *       // ...
+ *
+ *   public:
+ *       using MyJavaClass::Natives<MyClass>::DisposeNative;
+ *
+ *       void AttachTo(const MyJavaClass::LocalRef& instance)
+ *       {
+ *           MyJavaClass::Natives<MyClass>::AttachNative(
+ *                   instance, static_cast<SupportsWeakPtr*>(this));
+ *
+ *           // "instance" does NOT own "this", so the C++ object
+ *           // lifetime is separate from the Java object lifetime.
+ *       }
+ *   };
+ *
+ * * If the C++ class contains public members AddRef() and Release(), the Java
+ *   instance will store and own the pointer to a RefPtr object, which holds a
+ *   strong reference on the C++ instance. Normal ref-counting considerations
+ *   apply in this case; for example, disposing may cause the C++ instance to
+ *   be deleted and the destructor to be run on the current thread, which may
+ *   not be desirable. To attach a Java instance to a C++ instance, pass in a
+ *   pointer to the C++ class (i.e. MyClass*).
+ *
+ *   class MyClass : public RefCounted<MyClass>
+ *                 , public MyJavaClass::Natives<MyClass>
+ *   {
+ *       // ...
+ *
+ *   public:
+ *       using MyJavaClass::Natives<MyClass>::DisposeNative;
+ *
+ *       void AttachTo(const MyJavaClass::LocalRef& instance)
+ *       {
+ *           MyJavaClass::Natives<MyClass>::AttachNative(instance, this);
+ *
+ *           // "instance" owns "this" through the RefPtr, so the C++ object
+ *           // may be destroyed as soon as instance.disposeNative() is called.
+ *       }
+ *   };
+ *
+ * * In other cases, the Java instance will store and own a pointer to the C++
+ *   object itself. This pointer must not be stored or deleted elsewhere. To
+ *   attach a Java instance to a C++ instance, pass in a reference to a
+ *   UniquePtr of the C++ class (i.e. UniquePtr<MyClass>).
+ *
+ *   class MyClass : public MyJavaClass::Natives<MyClass>
+ *   {
+ *       // ...
+ *
+ *   public:
+ *       using MyJavaClass::Natives<MyClass>::DisposeNative;
+ *
+ *       static void AttachTo(const MyJavaClass::LocalRef& instance)
+ *       {
+ *           MyJavaClass::Natives<MyClass>::AttachNative(
+ *                   instance, mozilla::MakeUnique<MyClass>());
+ *
+ *           // "instance" owns the newly created C++ object, so the C++
+ *           // object is destroyed as soon as instance.disposeNative() is
+ *           // called.
+ *       }
+ *   };
+ */
+
+namespace detail {
+
+/**
+ * Type trait that determines whether a given class has a member named
+ * T::OnWeakNonIntrusiveDetach.
+ *
+ * Example usage:
+ * class Foo {};
+ * class Bar {
+ *  public:
+ *   void OnWeakNonIntrusiveDetach(already_AddRefed<nsIRunnable> aRunnable);
+ * };
+ *
+ * constexpr bool foo = HasWeakNonIntrusiveDetach<Foo>::value; // Expect false
+ * constexpr bool bar = HasWeakNonIntrusiveDetach<Bar>::value; // Expect true
+ */
+template <typename, typename = std::void_t<>>
+struct HasWeakNonIntrusiveDetach : std::false_type {};
+
+template <typename T>
+struct HasWeakNonIntrusiveDetach<
+    T, std::void_t<decltype(std::declval<T>().OnWeakNonIntrusiveDetach(
+           std::declval<already_AddRefed<nsIRunnable>>()))>> : std::true_type {
+};
+
+/**
+ * Type trait that determines whether a given class is refcounted, ie. it has
+ * both T::AddRef and T::Release methods.
+ *
+ * Example usage:
+ * class Foo {};
+ * class Bar {
+ *  public:
+ *   void AddRef();
+ *   void Release();
+ * };
+ *
+ * constexpr bool foo = IsRefCounted<Foo>::value; // Expect false
+ * constexpr bool bar = IsRefCounted<Bar>::value; // Expect true
+ */
+template <typename, typename = std::void_t<>>
+struct IsRefCounted : std::false_type {};
+
+template <typename T>
+struct IsRefCounted<T, std::void_t<decltype(std::declval<T>().AddRef(),
+                                            std::declval<T>().Release())>>
+    : std::true_type {};
+
+/**
+ * This enum is used for classifying the type of pointer that is stored
+ * within a NativeWeakPtr. This classification is different from the one used
+ * for normal native pointers.
+ */
+enum class NativePtrInternalType : size_t {
+  OWNING = 1,
+  WEAK = 2,
+  REFPTR = 3,
+};
+
+/**
+ * NativePtrInternalPicker uses some C++ SFINAE template-fu to figure out
+ * what type of pointer the class specified by Impl needs to be.
+ *
+ * It does this by supplying multiple overloads of a method named Test.
+ * Various overloads are enabled or disabled depending on whether or not Impl
+ * can possibly support them.
+ *
+ * Each overload "returns" a reference to an array whose size corresponds to the
+ * value of each enum in NativePtrInternalType. That size is then converted back
+ * to the enum value, yielding the right type.
+ */
+template <class Impl>
+class NativePtrInternalPicker {
+  // Enable if Impl derives from SupportsWeakPtr, yielding type WEAK
+  template <class I>
+  static std::enable_if_t<
+      std::is_base_of<SupportsWeakPtr, I>::value,
+      char (&)[static_cast<size_t>(NativePtrInternalType::WEAK)]>
+  Test(char);
+
+  // Enable if Impl implements AddRef and Release, yielding type REFPTR
+  template <class I, typename = decltype(&I::AddRef, &I::Release)>
+  static char (&Test(int))[static_cast<size_t>(NativePtrInternalType::REFPTR)];
+
+  // This overload uses '...' as its param to make its arguments less specific;
+  // the compiler prefers more-specific overloads to less-specific ones.
+  // OWNING is the fallback type.
+  template <class>
+  static char (&Test(...))[static_cast<size_t>(NativePtrInternalType::OWNING)];
+
+ public:
+  // Given a hypothetical function call Test<Impl>, convert the size of its
+  // resulting array back into a NativePtrInternalType enum value.
+  static const NativePtrInternalType value = static_cast<NativePtrInternalType>(
+      sizeof(Test<Impl>('\0')) / sizeof(char));
+};
+
+/**
+ * This enum is used for classifying the type of pointer that is stored in a
+ * JNIObject's handle.
+ *
+ * We have two different weak pointer types:
+ *   * WEAK_INTRUSIVE is a pointer to a class that derives from
+ *     mozilla::SupportsWeakPtr.
+ *   * WEAK_NON_INTRUSIVE is a pointer to a class that does not have any
+ *     internal support for weak pointers, but does supply a
+ *     OnWeakNonIntrusiveDetach method.
+ */
+enum class NativePtrType : size_t {
+  OWNING = 1,
+  WEAK_INTRUSIVE = 2,
+  WEAK_NON_INTRUSIVE = 3,
+  REFPTR = 4,
+};
+
+/**
+ * NativePtrPicker uses some C++ SFINAE template-fu to figure out what type of
+ * pointer the class specified by Impl needs to be.
+ *
+ * It does this by supplying multiple overloads of a method named Test.
+ * Various overloads are enabled or disabled depending on whether or not Impl
+ * can possibly support them.
+ *
+ * Each overload "returns" a reference to an array whose size corresponds to the
+ * value of each enum in NativePtrInternalType. That size is then converted back
+ * to the enum value, yielding the right type.
+ */
+template <class Impl>
+class NativePtrPicker {
+  // Just shorthand for each overload's return type
+  template <NativePtrType PtrType>
+  using ResultTypeT = char (&)[static_cast<size_t>(PtrType)];
+
+  // Enable if Impl derives from SupportsWeakPtr, yielding type WEAK_INTRUSIVE
+  template <typename I>
+  static auto Test(void*)
+      -> std::enable_if_t<std::is_base_of<SupportsWeakPtr, I>::value,
+                          ResultTypeT<NativePtrType::WEAK_INTRUSIVE>>;
+
+  // Enable if Impl implements OnWeakNonIntrusiveDetach, yielding type
+  // WEAK_NON_INTRUSIVE
+  template <typename I>
+  static auto Test(void*)
+      -> std::enable_if_t<HasWeakNonIntrusiveDetach<I>::value,
+                          ResultTypeT<NativePtrType::WEAK_NON_INTRUSIVE>>;
+
+  // We want the WEAK_NON_INTRUSIVE overload to take precedence over this one,
+  // so we only enable this overload if Impl is refcounted AND it does not
+  // implement OnWeakNonIntrusiveDetach. Yields type REFPTR.
+  template <typename I>
+  static auto Test(void*) -> std::enable_if_t<
+      std::conjunction_v<IsRefCounted<I>,
+                         std::negation<HasWeakNonIntrusiveDetach<I>>>,
+      ResultTypeT<NativePtrType::REFPTR>>;
+
+  // This overload uses '...' as its param to make its arguments less specific;
+  // the compiler prefers more-specific overloads to less-specific ones.
+  // OWNING is the fallback type.
+  template <typename>
+  static char (&Test(...))[static_cast<size_t>(NativePtrType::OWNING)];
+
+ public:
+  // Given a hypothetical function call Test<Impl>, convert the size of its
+  // resulting array back into a NativePtrType enum value.
+  static const NativePtrType value =
+      static_cast<NativePtrType>(sizeof(Test<Impl>(nullptr)));
+};
+
+template <class Impl>
+inline uintptr_t CheckNativeHandle(JNIEnv* env, uintptr_t handle) {
+  if (!handle) {
+    if (!env->ExceptionCheck()) {
+      ThrowException(env, "java/lang/NullPointerException",
+                     NullHandle<Impl>().str);
+    }
+    return 0;
+  }
+  return handle;
+}
+
+/**
+ * This struct is used to describe various traits of a native pointer of type
+ * Impl that will be attached to a JNIObject.
+ *
+ * See the definition of the NativePtrType::OWNING specialization for comments
+ * describing the required fields.
+ */
+template <class Impl, NativePtrType Type = NativePtrPicker<Impl>::value>
+struct NativePtrTraits;
+
+template <class Impl>
+struct NativePtrTraits<Impl, /* Type = */ NativePtrType::OWNING> {
+  using AccessorType =
+      Impl*;  // Pointer-like type returned by Access() (an actual pointer in
+              // this case, but this is not strictly necessary)
+  using HandleType = Impl*;  // Type of the pointer stored in JNIObject.mHandle
+  using RefType = Impl*;     // Type of the pointer returned by Get()
+
+  /**
+   * Returns a RefType to the native implementation belonging to
+   * the given Java object.
+   */
+  static RefType Get(JNIEnv* env, jobject instance) {
+    static_assert(
+        std::is_same<HandleType, RefType>::value,
+        "HandleType and RefType must be identical for owning pointers");
+    return reinterpret_cast<HandleType>(
+        CheckNativeHandle<Impl>(env, GetNativeHandle(env, instance)));
+  }
+
+  /**
+   * Returns a RefType to the native implementation belonging to
+   * the given Java object.
+   */
+  template <class LocalRef>
+  static RefType Get(const LocalRef& instance) {
+    return Get(instance.Env(), instance.Get());
+  }
+
+  /**
+   * Given a RefType, returns the pointer-like AccessorType used for
+   * manipulating the native object.
+   */
+  static AccessorType Access(RefType aImpl, JNIEnv* aEnv = nullptr) {
+    static_assert(
+        std::is_same<AccessorType, RefType>::value,
+        "AccessorType and RefType must be identical for owning pointers");
+    return aImpl;
+  }
+
+  /**
+   * Set the JNIObject's handle to the provided pointer, clearing any previous
+   * handle if necessary.
+   */
+  template <class LocalRef>
+  static void Set(const LocalRef& instance, UniquePtr<Impl>&& ptr) {
+    Clear(instance);
+    SetNativeHandle(instance.Env(), instance.Get(),
+                    reinterpret_cast<uintptr_t>(ptr.release()));
+    MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+  }
+
+  /**
+   * Clear the JNIObject's handle.
+   */
+  template <class LocalRef>
+  static void Clear(const LocalRef& instance) {
+    UniquePtr<Impl> ptr(reinterpret_cast<RefType>(
+        GetNativeHandle(instance.Env(), instance.Get())));
+    MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+
+    if (ptr) {
+      SetNativeHandle(instance.Env(), instance.Get(), 0);
+      MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+    }
+  }
+};
+
+template <class Impl>
+struct NativePtrTraits<Impl, /* Type = */ NativePtrType::WEAK_INTRUSIVE> {
+  using AccessorType = Impl*;
+  using HandleType = WeakPtr<Impl>*;
+  using RefType = WeakPtr<Impl>;
+
+  static RefType Get(JNIEnv* env, jobject instance) {
+    const auto ptr = reinterpret_cast<HandleType>(
+        CheckNativeHandle<Impl>(env, GetNativeHandle(env, instance)));
+    return *ptr;
+  }
+
+  template <class LocalRef>
+  static RefType Get(const LocalRef& instance) {
+    return Get(instance.Env(), instance.Get());
+  }
+
+  static AccessorType Access(RefType aPtr, JNIEnv* aEnv = nullptr) {
+    AccessorType const impl = *aPtr;
+    if (!impl) {
+      JNIEnv* env = aEnv ? aEnv : mozilla::jni::GetEnvForThread();
+      ThrowException(env, "java/lang/NullPointerException",
+                     NullWeakPtr<Impl>().str);
+    }
+
+    return impl;
+  }
+
+  template <class LocalRef>
+  static void Set(const LocalRef& instance, Impl* ptr) {
+    // Create the new handle first before clearing any old handle, so the
+    // new handle is guaranteed to have different value than any old handle.
+    const uintptr_t handle =
+        reinterpret_cast<uintptr_t>(new WeakPtr<Impl>(ptr));
+    Clear(instance);
+    SetNativeHandle(instance.Env(), instance.Get(), handle);
+    MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+  }
+
+  template <class LocalRef>
+  static void Clear(const LocalRef& instance) {
+    const auto ptr = reinterpret_cast<HandleType>(
+        GetNativeHandle(instance.Env(), instance.Get()));
+    MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+
+    if (ptr) {
+      SetNativeHandle(instance.Env(), instance.Get(), 0);
+      MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+      delete ptr;
+    }
+  }
+};
+
+template <class Impl>
+struct NativePtrTraits<Impl, /* Type = */ NativePtrType::REFPTR> {
+  using AccessorType = Impl*;
+  using HandleType = RefPtr<Impl>*;
+  using RefType = Impl*;
+
+  static RefType Get(JNIEnv* env, jobject instance) {
+    const auto ptr = reinterpret_cast<HandleType>(
+        CheckNativeHandle<Impl>(env, GetNativeHandle(env, instance)));
+    if (!ptr) {
+      return nullptr;
+    }
+
+    MOZ_ASSERT(*ptr);
+    return *ptr;
+  }
+
+  template <class LocalRef>
+  static RefType Get(const LocalRef& instance) {
+    return Get(instance.Env(), instance.Get());
+  }
+
+  static AccessorType Access(RefType aImpl, JNIEnv* aEnv = nullptr) {
+    static_assert(std::is_same<AccessorType, RefType>::value,
+                  "AccessorType and RefType must be identical for refpointers");
+    return aImpl;
+  }
+
+  template <class LocalRef>
+  static void Set(const LocalRef& instance, RefType ptr) {
+    // Create the new handle first before clearing any old handle, so the
+    // new handle is guaranteed to have different value than any old handle.
+    const uintptr_t handle = reinterpret_cast<uintptr_t>(new RefPtr<Impl>(ptr));
+    Clear(instance);
+    SetNativeHandle(instance.Env(), instance.Get(), handle);
+    MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+  }
+
+  template <class LocalRef>
+  static void Clear(const LocalRef& instance) {
+    const auto ptr = reinterpret_cast<HandleType>(
+        GetNativeHandle(instance.Env(), instance.Get()));
+    MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+
+    if (ptr) {
+      SetNativeHandle(instance.Env(), instance.Get(), 0);
+      MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+      delete ptr;
+    }
+  }
+};
+
+}  // namespace detail
+
+// Forward declarations
+template <typename NativeImpl>
+class NativeWeakPtr;
+template <typename NativeImpl>
+class NativeWeakPtrHolder;
+
+namespace detail {
+
+/**
+ * Given the class of a native implementation, as well as its
+ * NativePtrInternalType, resolve traits for that type that will be used by
+ * the NativeWeakPtrControlBlock.
+ *
+ * Note that we only implement specializations for OWNING and REFPTR types,
+ * as a WEAK_INTRUSIVE type should not be using NativeWeakPtr anyway. The build
+ * will fail if such an attempt is made.
+ *
+ * Traits need to implement two things:
+ * 1. A |Type| field that resolves to a pointer type to be stored in the
+ *    JNIObject's handle. It is assumed that setting a |Type| object to nullptr
+ *    is sufficient to delete the underlying object.
+ * 2. A static |AsRaw| method that converts a pointer of |Type| into a raw
+ *    pointer.
+ */
+template <
+    typename NativeImpl,
+    NativePtrInternalType PtrType =
+        ::mozilla::jni::detail::NativePtrInternalPicker<NativeImpl>::value>
+struct NativeWeakPtrControlBlockStorageTraits;
+
+template <typename NativeImpl>
+struct NativeWeakPtrControlBlockStorageTraits<
+    NativeImpl, ::mozilla::jni::detail::NativePtrInternalType::OWNING> {
+  using Type = UniquePtr<NativeImpl>;
+
+  static NativeImpl* AsRaw(const Type& aStorage) { return aStorage.get(); }
+};
+
+template <typename NativeImpl>
+struct NativeWeakPtrControlBlockStorageTraits<
+    NativeImpl, ::mozilla::jni::detail::NativePtrInternalType::REFPTR> {
+  using Type = RefPtr<NativeImpl>;
+
+  static NativeImpl* AsRaw(const Type& aStorage) { return aStorage.get(); }
+};
+
+// Forward Declaration
+template <typename NativeImpl>
+class Accessor;
+
+/**
+ * This class contains the shared data that is referenced by all NativeWeakPtr
+ * objects that reference the same object.
+ *
+ * It retains a WeakRef to the Java object that owns this native object.
+ * It uses a RWLock to control access to the native pointer itself.
+ * Read locks are used when accessing the pointer (even when calling non-const
+ * methods on the native object).
+ * A write lock is only used when it is time to destroy the native object and
+ * we need to clear the value of mNativeImpl.
+ */
+template <typename NativeImpl>
+class MOZ_HEAP_CLASS NativeWeakPtrControlBlock final {
+ public:
+  using StorageTraits = NativeWeakPtrControlBlockStorageTraits<NativeImpl>;
+  using StorageType = typename StorageTraits::Type;
+
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(NativeWeakPtrControlBlock)
+
+  NativeWeakPtrControlBlock(const NativeWeakPtrControlBlock&) = delete;
+  NativeWeakPtrControlBlock(NativeWeakPtrControlBlock&&) = delete;
+  NativeWeakPtrControlBlock& operator=(const NativeWeakPtrControlBlock&) =
+      delete;
+  NativeWeakPtrControlBlock& operator=(NativeWeakPtrControlBlock&&) = delete;
+
+  // This is safe to call on any thread because mJavaOwner is immutable.
+  mozilla::jni::Object::WeakRef GetJavaOwner() const { return mJavaOwner; }
+
+ private:
+  NativeWeakPtrControlBlock(::mozilla::jni::Object::Param aJavaOwner,
+                            StorageType&& aNativeImpl)
+      : mJavaOwner(aJavaOwner),
+        mLock("mozilla::jni::detail::NativeWeakPtrControlBlock"),
+        mNativeImpl(std::move(aNativeImpl)) {}
+
+  ~NativeWeakPtrControlBlock() {
+    // Make sure that somebody, somewhere, has detached us before destroying.
+    MOZ_ASSERT(!(*this));
+  }
+
+  /**
+   * Clear the native pointer so that subsequent accesses to the native pointer
+   * via this control block are no longer available.
+   *
+   * We return the native pointer to the caller so that it may proceed with
+   * cleaning up its resources.
+   */
+  StorageType Clear() {
+    StorageType nativeImpl(nullptr);
+
+    {  // Scope for lock
+      AutoWriteLock lock(mLock);
+      std::swap(mNativeImpl, nativeImpl);
+    }
+
+    return nativeImpl;
+  }
+
+  MOZ_PUSH_IGNORE_THREAD_SAFETY
+  void Lock() const { mLock.ReadLock(); }
+
+  void Unlock() const { mLock.ReadUnlock(); }
+  MOZ_POP_THREAD_SAFETY
+
+#if defined(DEBUG)
+  // This is kind of expensive, so we only support it in debug builds.
+  explicit operator bool() const {
+    AutoReadLock lock(mLock);
+    return !!mNativeImpl;
+  }
+#endif  // defined(DEBUG)
+
+ private:
+  friend class Accessor<NativeImpl>;
+  friend class NativeWeakPtr<NativeImpl>;
+  friend class NativeWeakPtrHolder<NativeImpl>;
+
+ private:
+  const mozilla::jni::Object::WeakRef mJavaOwner;
+  mutable RWLock mLock MOZ_UNANNOTATED;  // Protects mNativeImpl
+  StorageType mNativeImpl;
+};
+
+/**
+ * If you want to temporarily access the object held by a NativeWeakPtr, you
+ * must obtain one of these Accessor objects from the pointer. Access must
+ * be done _exclusively_ using once of these objects!
+ */
+template <typename NativeImpl>
+class MOZ_STACK_CLASS Accessor final {
+ public:
+  ~Accessor() {
+    if (mCtlBlock) {
+      mCtlBlock->Unlock();
+    }
+  }
+
+  // Check whether the object is still valid before doing anything else
+  explicit operator bool() const { return mCtlBlock && mCtlBlock->mNativeImpl; }
+
+  // Normal member access
+  NativeImpl* operator->() const {
+    return NativeWeakPtrControlBlockStorageTraits<NativeImpl>::AsRaw(
+        mCtlBlock->mNativeImpl);
+  }
+
+  // This allows us to support calling a pointer to a member function
+  template <typename Member>
+  auto operator->*(Member aMember) const {
+    NativeImpl* impl =
+        NativeWeakPtrControlBlockStorageTraits<NativeImpl>::AsRaw(
+            mCtlBlock->mNativeImpl);
+    return [impl, member = aMember](auto&&... aArgs) {
+      return (impl->*member)(std::forward<decltype(aArgs)>(aArgs)...);
+    };
+  }
+
+  // Only available for NativeImpl types that actually use refcounting.
+  // The idea here is that it should be possible to obtain a strong ref from
+  // a NativeWeakPtr if and only if NativeImpl supports refcounting.
+  template <typename I = NativeImpl>
+  auto AsRefPtr() const -> std::enable_if_t<IsRefCounted<I>::value, RefPtr<I>> {
+    MOZ_ASSERT(I::HasThreadSafeRefCnt::value || NS_IsMainThread());
+    return mCtlBlock->mNativeImpl;
+  }
+
+  Accessor(const Accessor&) = delete;
+  Accessor(Accessor&&) = delete;
+  Accessor& operator=(const Accessor&) = delete;
+  Accessor& operator=(Accessor&&) = delete;
+
+ private:
+  explicit Accessor(
+      const RefPtr<detail::NativeWeakPtrControlBlock<NativeImpl>>& aCtlBlock)
+      : mCtlBlock(aCtlBlock) {
+    if (aCtlBlock) {
+      aCtlBlock->Lock();
+    }
+  }
+
+ private:
+  friend class NativeWeakPtr<NativeImpl>;
+  friend class NativeWeakPtrHolder<NativeImpl>;
+
+ private:
+  const RefPtr<NativeWeakPtrControlBlock<NativeImpl>> mCtlBlock;
+};
+
+}  // namespace detail
+
+using DetachPromise = mozilla::MozPromise<bool, nsresult, true>;
+
+/**
+ * This class implements support for thread-safe weak pointers to native objects
+ * that are owned by Java objects deriving from JNIObject.
+ *
+ * Any code that wants to access such a native object must have a copy of
+ * a NativeWeakPtr to that object.
+ */
+template <typename NativeImpl>
+class NativeWeakPtr {
+ public:
+  using Accessor = detail::Accessor<NativeImpl>;
+
+  /**
+   * Call this method to access the underlying object referenced by this
+   * NativeWeakPtr.
+   *
+   * Always check the returned Accessor object for availability before calling
+   * methods on it.
+   *
+   * For example, given:
+   *
+   * NativeWeakPtr<Foo> foo;
+   * auto accessor = foo.Access();
+   * if (accessor) {
+   *   // Okay, safe to work with
+   *   accessor->DoStuff();
+   * } else {
+   *   // The object's strong reference was cleared and is no longer available!
+   * }
+   */
+  Accessor Access() const { return Accessor(mCtlBlock); }
+
+  /**
+   * Detach the underlying object's strong reference from its owning Java object
+   * and clean it up.
+   */
+  RefPtr<DetachPromise> Detach();
+
+  /**
+   * This method does not indicate whether or not the weak pointer is still
+   * valid; it only indicates whether we're actually attached to one.
+   */
+  bool IsAttached() const { return !!mCtlBlock; }
+
+  /**
+   * Does this pointer reference the same object as the one referenced by the
+   * provided Accessor?
+   */
+  bool IsSame(const Accessor& aAccessor) const {
+    return mCtlBlock == aAccessor.mCtlBlock;
+  }
+
+  /**
+   * Does this pointer reference the same object as the one referenced by the
+   * provided Control Block?
+   */
+  bool IsSame(const RefPtr<detail::NativeWeakPtrControlBlock<NativeImpl>>&
+                  aOther) const {
+    return mCtlBlock == aOther;
+  }
+
+  NativeWeakPtr() = default;
+  MOZ_IMPLICIT NativeWeakPtr(decltype(nullptr)) {}
+  NativeWeakPtr(const NativeWeakPtr& aOther) = default;
+  NativeWeakPtr(NativeWeakPtr&& aOther) = default;
+  NativeWeakPtr& operator=(const NativeWeakPtr& aOther) = default;
+  NativeWeakPtr& operator=(NativeWeakPtr&& aOther) = default;
+
+  NativeWeakPtr& operator=(decltype(nullptr)) {
+    mCtlBlock = nullptr;
+    return *this;
+  }
+
+ protected:
+  // Construction of initial NativeWeakPtr for aCtlBlock
+  explicit NativeWeakPtr(
+      already_AddRefed<detail::NativeWeakPtrControlBlock<NativeImpl>> aCtlBlock)
+      : mCtlBlock(aCtlBlock) {}
+
+ private:
+  // Construction of subsequent NativeWeakPtrs for aCtlBlock
+  explicit NativeWeakPtr(
+      const RefPtr<detail::NativeWeakPtrControlBlock<NativeImpl>>& aCtlBlock)
+      : mCtlBlock(aCtlBlock) {}
+
+  friend class NativeWeakPtrHolder<NativeImpl>;
+
+ protected:
+  RefPtr<detail::NativeWeakPtrControlBlock<NativeImpl>> mCtlBlock;
+};
+
+/**
+ * A pointer to an instance of this class should be stored in a Java object's
+ * JNIObject handle. New instances of native objects wrapped by NativeWeakPtr
+ * are created using the static methods of this class.
+ *
+ * Why do we have distinct methods here instead of using AttachNative like other
+ * pointer types that may be stored in JNIObject?
+ *
+ * Essentially, we want the creation and use of NativeWeakPtr to be as
+ * deliberate as possible. Forcing a different creation mechanism is part of
+ * that emphasis.
+ *
+ * Example:
+ *
+ * class NativeFoo {
+ *  public:
+ *   NativeFoo();
+ *   void Bar();
+ *   // The following method is required to be used with NativeWeakPtr
+ *   void OnWeakNonIntrusiveDetach(already_AddRefed<Runnable> aDisposer);
+ * };
+ *
+ * java::Object::LocalRef javaObj(...);
+ *
+ * // Create a new Foo that is attached to javaObj
+ * auto weakFoo = NativeWeakPtrHolder<NativeFoo>::Attach(javaObj);
+ *
+ * // Now I can save weakFoo, access it, do whatever I want
+ * if (auto accWeakFoo = weakFoo.Access()) {
+ *   accWeakFoo->Bar();
+ * }
+ *
+ * // Detach from javaObj and clean up
+ * weakFoo.Detach();
+ */
+template <typename NativeImpl>
+class MOZ_HEAP_CLASS NativeWeakPtrHolder final
+    : public NativeWeakPtr<NativeImpl> {
+  using Base = NativeWeakPtr<NativeImpl>;
+
+ public:
+  using Accessor = typename Base::Accessor;
+  using StorageTraits =
+      typename detail::NativeWeakPtrControlBlock<NativeImpl>::StorageTraits;
+  using StorageType = typename StorageTraits::Type;
+
+  /**
+   * Create a new NativeImpl object, wrap it in a NativeWeakPtr, and store it
+   * in the Java object's JNIObject handle.
+   *
+   * @return A NativeWeakPtr object that references the newly-attached object.
+   */
+  template <typename Cls, typename JNIType, typename... Args>
+  static NativeWeakPtr<NativeImpl> Attach(const Ref<Cls, JNIType>& aJavaObject,
+                                          Args&&... aArgs) {
+    MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+    StorageType nativeImpl(new NativeImpl(std::forward<Args>(aArgs)...));
+    return AttachInternal(aJavaObject, std::move(nativeImpl));
+  }
+
+  /**
+   * Given a new NativeImpl object, wrap it in a NativeWeakPtr, and store it
+   * in the Java object's JNIObject handle.
+   *
+   * @return A NativeWeakPtr object that references the newly-attached object.
+   */
+  template <typename Cls, typename JNIType>
+  static NativeWeakPtr<NativeImpl> AttachExisting(
+      const Ref<Cls, JNIType>& aJavaObject,
+      already_AddRefed<NativeImpl> aNativeImpl) {
+    MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+    StorageType nativeImpl(aNativeImpl);
+    return AttachInternal(aJavaObject, std::move(nativeImpl));
+  }
+
+  ~NativeWeakPtrHolder() = default;
+
+  MOZ_IMPLICIT NativeWeakPtrHolder(decltype(nullptr)) = delete;
+  NativeWeakPtrHolder(const NativeWeakPtrHolder&) = delete;
+  NativeWeakPtrHolder(NativeWeakPtrHolder&&) = delete;
+  NativeWeakPtrHolder& operator=(const NativeWeakPtrHolder&) = delete;
+  NativeWeakPtrHolder& operator=(NativeWeakPtrHolder&&) = delete;
+  NativeWeakPtrHolder& operator=(decltype(nullptr)) = delete;
+
+ private:
+  template <typename Cls>
+  NativeWeakPtrHolder(const LocalRef<Cls>& aJavaObject,
+                      StorageType&& aNativeImpl)
+      : NativeWeakPtr<NativeImpl>(
+            do_AddRef(new NativeWeakPtrControlBlock<NativeImpl>(
+                aJavaObject, std::move(aNativeImpl)))) {}
+
+  /**
+   * Internal function that actually wraps the native pointer, binds it to the
+   * JNIObject, and then returns the NativeWeakPtr result.
+   */
+  template <typename Cls, typename JNIType>
+  static NativeWeakPtr<NativeImpl> AttachInternal(
+      const Ref<Cls, JNIType>& aJavaObject, StorageType&& aPtr) {
+    auto localJavaObject = ToLocalRef(aJavaObject);
+    NativeWeakPtrHolder<NativeImpl>* holder =
+        new NativeWeakPtrHolder<NativeImpl>(localJavaObject, std::move(aPtr));
+    static_assert(
+        NativePtrPicker<NativeImpl>::value == NativePtrType::WEAK_NON_INTRUSIVE,
+        "This type is not compatible with mozilla::jni::NativeWeakPtr");
+    NativePtrTraits<NativeImpl>::Set(localJavaObject, holder);
+    return NativeWeakPtr<NativeImpl>(holder->mCtlBlock);
+  }
+};
+
+namespace detail {
+
+/**
+ * NativePtrTraits for the WEAK_NON_INTRUSIVE pointer type.
+ */
+template <class Impl>
+struct NativePtrTraits<Impl, /* Type = */ NativePtrType::WEAK_NON_INTRUSIVE> {
+  using AccessorType = typename NativeWeakPtrHolder<Impl>::Accessor;
+  using HandleType = NativeWeakPtrHolder<Impl>*;
+  using RefType = NativeWeakPtrHolder<Impl>* const;
+
+  static RefType Get(JNIEnv* env, jobject instance) {
+    return GetHandle(env, instance);
+  }
+
+  template <typename Cls>
+  static RefType Get(const LocalRef<Cls>& instance) {
+    return GetHandle(instance.Env(), instance.Get());
+  }
+
+  static AccessorType Access(RefType aPtr) { return aPtr->Access(); }
+
+  template <typename Cls>
+  static void Set(const LocalRef<Cls>& instance, HandleType ptr) {
+    MOZ_RELEASE_ASSERT(NS_IsMainThread());
+    const uintptr_t handle = reinterpret_cast<uintptr_t>(ptr);
+    Clear(instance);
+    SetNativeHandle(instance.Env(), instance.Get(), handle);
+    MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+  }
+
+  template <typename Cls>
+  static void Clear(const LocalRef<Cls>& instance) {
+    auto ptr = reinterpret_cast<HandleType>(
+        GetNativeHandle(instance.Env(), instance.Get()));
+    MOZ_CATCH_JNI_EXCEPTION(instance.Env());
+
+    if (!ptr) {
+      return;
+    }
+
+    ptr->Detach();
+  }
+
+  // This call is not safe to do unless we know for sure that instance's
+  // native handle has not changed. It is up to NativeWeakPtrDetachRunnable
+  // to perform this check.
+  template <typename Cls>
+  static void ClearFinish(const LocalRef<Cls>& instance) {
+    MOZ_RELEASE_ASSERT(NS_IsMainThread());
+    JNIEnv* const env = instance.Env();
+    auto ptr =
+        reinterpret_cast<HandleType>(GetNativeHandle(env, instance.Get()));
+    MOZ_CATCH_JNI_EXCEPTION(env);
+    MOZ_RELEASE_ASSERT(!!ptr);
+
+    SetNativeHandle(env, instance.Get(), 0);
+    MOZ_CATCH_JNI_EXCEPTION(env);
+    // Deletion of ptr is done by the caller
+  }
+
+  // The call is stale if the native object has been destroyed on the
+  // Gecko side, but the Java object is still attached to it through
+  // a weak pointer. Stale calls should be discarded. Note that it's
+  // an error if holder is nullptr here; we return false but the
+  // native call will throw an error.
+  template <class LocalRef>
+  static bool IsStale(const LocalRef& instance) {
+    JNIEnv* const env = mozilla::jni::GetEnvForThread();
+
+    // We cannot use Get here because that method throws an exception when the
+    // object is null, which is a valid state for a stale call.
+    const auto holder =
+        reinterpret_cast<HandleType>(GetNativeHandle(env, instance.Get()));
+    MOZ_CATCH_JNI_EXCEPTION(env);
+
+    if (!holder || !holder->IsAttached()) {
+      return true;
+    }
+
+    auto acc(holder->Access());
+    return !acc;
+  }
+
+ private:
+  static HandleType GetHandle(JNIEnv* env, jobject instance) {
+    return reinterpret_cast<HandleType>(
+        CheckNativeHandle<Impl>(env, GetNativeHandle(env, instance)));
+  }
+
+  template <typename Cls>
+  static HandleType GetHandle(const LocalRef<Cls>& instance) {
+    return GetHandle(instance.Env(), instance.Get());
+  }
+
+  friend class NativeWeakPtrHolder<Impl>;
+};
+
+}  // namespace detail
+
+using namespace detail;
+
+/**
+ * For JNI native methods that are dispatched to a proxy, i.e. using
+ * @WrapForJNI(dispatchTo = "proxy"), the implementing C++ class must provide a
+ * OnNativeCall member. Subsequently, every native call is automatically
+ * wrapped in a functor object, and the object is passed to OnNativeCall. The
+ * OnNativeCall implementation can choose to invoke the call, save it, dispatch
+ * it to a different thread, etc. Each copy of functor may only be invoked
+ * once.
+ *
+ * class MyClass : public MyJavaClass::Natives<MyClass>
+ * {
+ *     // ...
+ *
+ *     template<class Functor>
+ *     class ProxyRunnable final : public Runnable
+ *     {
+ *         Functor mCall;
+ *     public:
+ *         ProxyRunnable(Functor&& call) : mCall(std::move(call)) {}
+ *         virtual void run() override { mCall(); }
+ *     };
+ *
+ * public:
+ *     template<class Functor>
+ *     static void OnNativeCall(Functor&& call)
+ *     {
+ *         RunOnAnotherThread(new ProxyRunnable(std::move(call)));
+ *     }
+ * };
+ */
+
+namespace detail {
+
+// ProxyArg is used to handle JNI ref arguments for proxies. Because a proxied
+// call may happen outside of the original JNI native call, we must save all
+// JNI ref arguments as global refs to avoid the arguments going out of scope.
+template <typename T>
+struct ProxyArg {
+  static_assert(std::is_trivial_v<T> && std::is_standard_layout_v<T>,
+                "T must be primitive type");
+
+  // Primitive types can be saved by value.
+  typedef T Type;
+  typedef typename TypeAdapter<T>::JNIType JNIType;
+
+  static void Clear(JNIEnv* env, Type&) {}
+
+  static Type From(JNIEnv* env, JNIType val) {
+    return TypeAdapter<T>::ToNative(env, val);
+  }
+};
+
+template <class C, typename T>
+struct ProxyArg<Ref<C, T>> {
+  // Ref types need to be saved by global ref.
+  typedef typename C::GlobalRef Type;
+  typedef typename TypeAdapter<Ref<C, T>>::JNIType JNIType;
+
+  static void Clear(JNIEnv* env, Type& ref) { ref.Clear(env); }
+
+  static Type From(JNIEnv* env, JNIType val) {
+    return Type(env, C::Ref::From(val));
+  }
+};
+
+template <typename C>
+struct ProxyArg<const C&> : ProxyArg<C> {};
+template <>
+struct ProxyArg<StringParam> : ProxyArg<String::Ref> {};
+template <class C>
+struct ProxyArg<LocalRef<C>> : ProxyArg<typename C::Ref> {};
+
+// ProxyNativeCall implements the functor object that is passed to OnNativeCall
+template <class Impl, class Owner, bool IsStatic,
+          bool HasThisArg /* has instance/class local ref in the call */,
+          typename... Args>
+class ProxyNativeCall {
+  // "this arg" refers to the Class::LocalRef (for static methods) or
+  // Owner::LocalRef (for instance methods) that we optionally (as indicated
+  // by HasThisArg) pass into the destination C++ function.
+  using ThisArgClass = std::conditional_t<IsStatic, Class, Owner>;
+  using ThisArgJNIType = std::conditional_t<IsStatic, jclass, jobject>;
+
+  // Type signature of the destination C++ function, which matches the
+  // Method template parameter in NativeStubImpl::Wrap.
+  using NativeCallType = std::conditional_t<
+      IsStatic,
+      std::conditional_t<HasThisArg, void (*)(const Class::LocalRef&, Args...),
+                         void (*)(Args...)>,
+      std::conditional_t<
+          HasThisArg, void (Impl::*)(const typename Owner::LocalRef&, Args...),
+          void (Impl::*)(Args...)>>;
+
+  // Destination C++ function.
+  NativeCallType mNativeCall;
+  // Saved this arg.
+  typename ThisArgClass::GlobalRef mThisArg;
+  // Saved arguments.
+  std::tuple<typename ProxyArg<Args>::Type...> mArgs;
+
+  // We cannot use IsStatic and HasThisArg directly (without going through
+  // extra hoops) because GCC complains about invalid overloads, so we use
+  // another pair of template parameters, Static and ThisArg.
+
+  template <bool Static, bool ThisArg, size_t... Indices>
+  std::enable_if_t<Static && ThisArg, void> Call(
+      const Class::LocalRef& cls, std::index_sequence<Indices...>) const {
+    (*mNativeCall)(cls, std::get<Indices>(mArgs)...);
+  }
+
+  template <bool Static, bool ThisArg, size_t... Indices>
+  std::enable_if_t<Static && !ThisArg, void> Call(
+      const Class::LocalRef& cls, std::index_sequence<Indices...>) const {
+    (*mNativeCall)(std::get<Indices>(mArgs)...);
+  }
+
+  template <bool Static, bool ThisArg, size_t... Indices>
+  std::enable_if_t<!Static && ThisArg, void> Call(
+      const typename Owner::LocalRef& inst,
+      std::index_sequence<Indices...>) const {
+    auto impl = NativePtrTraits<Impl>::Access(NativePtrTraits<Impl>::Get(inst));
+    MOZ_CATCH_JNI_EXCEPTION(inst.Env());
+    (impl->*mNativeCall)(inst, std::get<Indices>(mArgs)...);
+  }
+
+  template <bool Static, bool ThisArg, size_t... Indices>
+  std::enable_if_t<!Static && !ThisArg, void> Call(
+      const typename Owner::LocalRef& inst,
+      std::index_sequence<Indices...>) const {
+    auto impl = NativePtrTraits<Impl>::Access(NativePtrTraits<Impl>::Get(inst));
+    MOZ_CATCH_JNI_EXCEPTION(inst.Env());
+    (impl->*mNativeCall)(std::get<Indices>(mArgs)...);
+  }
+
+  template <size_t... Indices>
+  void Clear(JNIEnv* env, std::index_sequence<Indices...>) {
+    int dummy[] = {
+        (ProxyArg<Args>::Clear(env, std::get<Indices>(mArgs)), 0)...};
+    mozilla::Unused << dummy;
+  }
+
+  static decltype(auto) GetNativeObject(Class::Param thisArg) {
+    return nullptr;
+  }
+
+  static decltype(auto) GetNativeObject(typename Owner::Param thisArg) {
+    return NativePtrTraits<Impl>::Access(
+        NativePtrTraits<Impl>::Get(GetEnvForThread(), thisArg.Get()));
+  }
+
+ public:
+  // The class that implements the call target.
+  typedef Impl TargetClass;
+  typedef typename ThisArgClass::Param ThisArgType;
+
+  static const bool isStatic = IsStatic;
+
+  ProxyNativeCall(ThisArgJNIType thisArg, NativeCallType nativeCall,
+                  JNIEnv* env, typename ProxyArg<Args>::JNIType... args)
+      : mNativeCall(nativeCall),
+        mThisArg(env, ThisArgClass::Ref::From(thisArg)),
+        mArgs(ProxyArg<Args>::From(env, args)...) {}
+
+  ProxyNativeCall(ProxyNativeCall&&) = default;
+  ProxyNativeCall(const ProxyNativeCall&) = default;
+
+  // Get class ref for static calls or object ref for instance calls.
+  typename ThisArgClass::Param GetThisArg() const { return mThisArg; }
+
+  // Get the native object targeted by this call.
+  // Returns nullptr for static calls.
+  decltype(auto) GetNativeObject() const { return GetNativeObject(mThisArg); }
+
+  // Return if target is the given function pointer / pointer-to-member.
+  // Because we can only compare pointers of the same type, we use a
+  // templated overload that is chosen only if given a different type of
+  // pointer than our target pointer type.
+  bool IsTarget(NativeCallType call) const { return call == mNativeCall; }
+  template <typename T>
+  bool IsTarget(T&&) const {
+    return false;
+  }
+
+  // Redirect the call to another function / class member with the same
+  // signature as the original target. Crash if given a wrong signature.
+  void SetTarget(NativeCallType call) { mNativeCall = call; }
+  template <typename T>
+  void SetTarget(T&&) const {
+    MOZ_CRASH();
+  }
+
+  void operator()() {
+    JNIEnv* const env = GetEnvForThread();
+    typename ThisArgClass::LocalRef thisArg(env, mThisArg);
+    Call<IsStatic, HasThisArg>(thisArg, std::index_sequence_for<Args...>{});
+
+    // Clear all saved global refs. We do this after the call is invoked,
+    // and not inside the destructor because we already have a JNIEnv here,
+    // so it's more efficient to clear out the saved args here. The
+    // downside is that the call can only be invoked once.
+    Clear(env, std::index_sequence_for<Args...>{});
+    mThisArg.Clear(env);
+  }
+};
+
+template <class Impl, bool HasThisArg, typename... Args>
+struct Dispatcher {
+  template <class Traits, bool IsStatic = Traits::isStatic,
+            typename... ProxyArgs>
+  static std::enable_if_t<Traits::dispatchTarget == DispatchTarget::PROXY, void>
+  Run(ProxyArgs&&... args) {
+    Impl::OnNativeCall(
+        ProxyNativeCall<Impl, typename Traits::Owner, IsStatic, HasThisArg,
+                        Args...>(std::forward<ProxyArgs>(args)...));
+  }
+
+  template <class Traits, bool IsStatic = Traits::isStatic, typename ThisArg,
+            typename... ProxyArgs>
+  static std::enable_if_t<
+      Traits::dispatchTarget == DispatchTarget::GECKO_PRIORITY, void>
+  Run(ThisArg thisArg, ProxyArgs&&... args) {
+    // For a static method, do not forward the "this arg" (i.e. the class
+    // local ref) if the implementation does not request it. This saves us
+    // a pair of calls to add/delete global ref.
+    auto proxy =
+        ProxyNativeCall<Impl, typename Traits::Owner, IsStatic, HasThisArg,
+                        Args...>((HasThisArg || !IsStatic) ? thisArg : nullptr,
+                                 std::forward<ProxyArgs>(args)...);
+    DispatchToGeckoPriorityQueue(
+        NS_NewRunnableFunction("PriorityNativeCall", std::move(proxy)));
+  }
+
+  template <class Traits, bool IsStatic = Traits::isStatic, typename ThisArg,
+            typename... ProxyArgs>
+  static std::enable_if_t<Traits::dispatchTarget == DispatchTarget::GECKO, void>
+  Run(ThisArg thisArg, ProxyArgs&&... args) {
+    // For a static method, do not forward the "this arg" (i.e. the class
+    // local ref) if the implementation does not request it. This saves us
+    // a pair of calls to add/delete global ref.
+    auto proxy =
+        ProxyNativeCall<Impl, typename Traits::Owner, IsStatic, HasThisArg,
+                        Args...>((HasThisArg || !IsStatic) ? thisArg : nullptr,
+                                 std::forward<ProxyArgs>(args)...);
+    NS_DispatchToMainThread(
+        NS_NewRunnableFunction("GeckoNativeCall", std::move(proxy)));
+  }
+
+  template <class Traits, bool IsStatic = false, typename... ProxyArgs>
+  static std::enable_if_t<Traits::dispatchTarget == DispatchTarget::CURRENT,
+                          void>
+  Run(ProxyArgs&&... args) {
+    MOZ_CRASH("Unreachable code");
+  }
+};
+
+}  // namespace detail
+
+// Wrapper methods that convert arguments from the JNI types to the native
+// types, e.g. from jobject to jni::Object::Ref. For instance methods, the
+// wrapper methods also convert calls to calls on objects.
+//
+// We need specialization for static/non-static because the two have different
+// signatures (jobject vs jclass and Impl::*Method vs *Method).
+// We need specialization for return type, because void return type requires
+// us to not deal with the return value.
+
+// Bug 1207642 - Work around Dalvik bug by realigning stack on JNI entry
+#ifdef __i386__
+#  define MOZ_JNICALL JNICALL __attribute__((force_align_arg_pointer))
+#else
+#  define MOZ_JNICALL JNICALL
+#endif
+
+template <class Traits, class Impl, class Args = typename Traits::Args>
+class NativeStub;
+
+template <class Traits, class Impl, typename... Args>
+class NativeStub<Traits, Impl, jni::Args<Args...>> {
+  using Owner = typename Traits::Owner;
+  using ReturnType = typename Traits::ReturnType;
+
+  static constexpr bool isStatic = Traits::isStatic;
+  static constexpr bool isVoid = std::is_void_v<ReturnType>;
+
+  struct VoidType {
+    using JNIType = void;
+  };
+  using ReturnJNIType =
+      typename std::conditional_t<isVoid, VoidType,
+                                  TypeAdapter<ReturnType>>::JNIType;
+
+  using ReturnTypeForNonVoidInstance =
+      std::conditional_t<!isStatic && !isVoid, ReturnType, VoidType>;
+  using ReturnTypeForVoidInstance =
+      std::conditional_t<!isStatic && isVoid, ReturnType, VoidType&>;
+  using ReturnTypeForNonVoidStatic =
+      std::conditional_t<isStatic && !isVoid, ReturnType, VoidType>;
+  using ReturnTypeForVoidStatic =
+      std::conditional_t<isStatic && isVoid, ReturnType, VoidType&>;
+
+  static_assert(Traits::dispatchTarget == DispatchTarget::CURRENT || isVoid,
+                "Dispatched calls must have void return type");
+
+ public:
+  // Non-void instance method
+  template <ReturnTypeForNonVoidInstance (Impl::*Method)(Args...)>
+  static MOZ_JNICALL ReturnJNIType
+  Wrap(JNIEnv* env, jobject instance,
+       typename TypeAdapter<Args>::JNIType... args) {
+    MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+    auto impl = NativePtrTraits<Impl>::Access(
+        NativePtrTraits<Impl>::Get(env, instance));
+    if (!impl) {
+      // There is a pending JNI exception at this point.
+      return ReturnJNIType();
+    }
+    return TypeAdapter<ReturnType>::FromNative(
+        env, (impl->*Method)(TypeAdapter<Args>::ToNative(env, args)...));
+  }
+
+  // Non-void instance method with instance reference
+  template <ReturnTypeForNonVoidInstance (Impl::*Method)(
+      const typename Owner::LocalRef&, Args...)>
+  static MOZ_JNICALL ReturnJNIType
+  Wrap(JNIEnv* env, jobject instance,
+       typename TypeAdapter<Args>::JNIType... args) {
+    MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+    auto impl = NativePtrTraits<Impl>::Access(
+        NativePtrTraits<Impl>::Get(env, instance));
+    if (!impl) {
+      // There is a pending JNI exception at this point.
+      return ReturnJNIType();
+    }
+    auto self = Owner::LocalRef::Adopt(env, instance);
+    const auto res = TypeAdapter<ReturnType>::FromNative(
+        env, (impl->*Method)(self, TypeAdapter<Args>::ToNative(env, args)...));
+    self.Forget();
+    return res;
+  }
+
+  // Void instance method
+  template <ReturnTypeForVoidInstance (Impl::*Method)(Args...)>
+  static MOZ_JNICALL void Wrap(JNIEnv* env, jobject instance,
+                               typename TypeAdapter<Args>::JNIType... args) {
+    MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+    if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+      Dispatcher<Impl, /* HasThisArg */ false, Args...>::template Run<Traits>(
+          instance, Method, env, args...);
+      return;
+    }
+
+    auto impl = NativePtrTraits<Impl>::Access(
+        NativePtrTraits<Impl>::Get(env, instance));
+    if (!impl) {
+      // There is a pending JNI exception at this point.
+      return;
+    }
+    (impl->*Method)(TypeAdapter<Args>::ToNative(env, args)...);
+  }
+
+  // Void instance method with instance reference
+  template <ReturnTypeForVoidInstance (Impl::*Method)(
+      const typename Owner::LocalRef&, Args...)>
+  static MOZ_JNICALL void Wrap(JNIEnv* env, jobject instance,
+                               typename TypeAdapter<Args>::JNIType... args) {
+    MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+    if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+      Dispatcher<Impl, /* HasThisArg */ true, Args...>::template Run<Traits>(
+          instance, Method, env, args...);
+      return;
+    }
+
+    auto impl = NativePtrTraits<Impl>::Access(
+        NativePtrTraits<Impl>::Get(env, instance));
+    if (!impl) {
+      // There is a pending JNI exception at this point.
+      return;
+    }
+    auto self = Owner::LocalRef::Adopt(env, instance);
+    (impl->*Method)(self, TypeAdapter<Args>::ToNative(env, args)...);
+    self.Forget();
+  }
+
+  // Overload for DisposeNative
+  template <ReturnTypeForVoidInstance (*DisposeNative)(
+      const typename Owner::LocalRef&)>
+  static MOZ_JNICALL void Wrap(JNIEnv* env, jobject instance) {
+    MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+    if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+      using LocalRef = typename Owner::LocalRef;
+      Dispatcher<Impl, /* HasThisArg */ false, const LocalRef&>::template Run<
+          Traits, /* IsStatic */ true>(
+          /* ThisArg */ nullptr, DisposeNative, env, instance);
+      return;
+    }
+
+    auto self = Owner::LocalRef::Adopt(env, instance);
+    DisposeNative(self);
+    self.Forget();
+  }
+
+  // Non-void static method
+  template <ReturnTypeForNonVoidStatic (*Method)(Args...)>
+  static MOZ_JNICALL ReturnJNIType
+  Wrap(JNIEnv* env, jclass, typename TypeAdapter<Args>::JNIType... args) {
+    MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+    return TypeAdapter<ReturnType>::FromNative(
+        env, (*Method)(TypeAdapter<Args>::ToNative(env, args)...));
+  }
+
+  // Non-void static method with class reference
+  template <ReturnTypeForNonVoidStatic (*Method)(const Class::LocalRef&,
+                                                 Args...)>
+  static MOZ_JNICALL ReturnJNIType
+  Wrap(JNIEnv* env, jclass cls, typename TypeAdapter<Args>::JNIType... args) {
+    MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+    auto clazz = Class::LocalRef::Adopt(env, cls);
+    const auto res = TypeAdapter<ReturnType>::FromNative(
+        env, (*Method)(clazz, TypeAdapter<Args>::ToNative(env, args)...));
+    clazz.Forget();
+    return res;
+  }
+
+  // Void static method
+  template <ReturnTypeForVoidStatic (*Method)(Args...)>
+  static MOZ_JNICALL void Wrap(JNIEnv* env, jclass cls,
+                               typename TypeAdapter<Args>::JNIType... args) {
+    MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+    if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+      Dispatcher<Impl, /* HasThisArg */ false, Args...>::template Run<Traits>(
+          cls, Method, env, args...);
+      return;
+    }
+
+    (*Method)(TypeAdapter<Args>::ToNative(env, args)...);
+  }
+
+  // Void static method with class reference
+  template <ReturnTypeForVoidStatic (*Method)(const Class::LocalRef&, Args...)>
+  static MOZ_JNICALL void Wrap(JNIEnv* env, jclass cls,
+                               typename TypeAdapter<Args>::JNIType... args) {
+    MOZ_ASSERT_JNI_THREAD(Traits::callingThread);
+
+    if (Traits::dispatchTarget != DispatchTarget::CURRENT) {
+      Dispatcher<Impl, /* HasThisArg */ true, Args...>::template Run<Traits>(
+          cls, Method, env, args...);
+      return;
+    }
+
+    auto clazz = Class::LocalRef::Adopt(env, cls);
+    (*Method)(clazz, TypeAdapter<Args>::ToNative(env, args)...);
+    clazz.Forget();
+  }
+};
+
+// Generate a JNINativeMethod from a native
+// method's traits class and a wrapped stub.
+template <class Traits, typename Ret, typename... Args>
+constexpr JNINativeMethod MakeNativeMethod(MOZ_JNICALL Ret (*stub)(JNIEnv*,
+                                                                   Args...)) {
+  return {Traits::name, Traits::signature, reinterpret_cast<void*>(stub)};
+}
+
+// Class inherited by implementing class.
+template <class Cls, class Impl>
+class NativeImpl {
+  typedef typename Cls::template Natives<Impl> Natives;
+
+  static bool sInited;
+
+ public:
+  static void Init() {
+    if (sInited) {
+      return;
+    }
+    const auto& ctx = typename Cls::Context();
+    ctx.Env()->RegisterNatives(
+        ctx.ClassRef(), Natives::methods,
+        sizeof(Natives::methods) / sizeof(Natives::methods[0]));
+    MOZ_CATCH_JNI_EXCEPTION(ctx.Env());
+    sInited = true;
+  }
+
+ protected:
+  // Associate a C++ instance with a Java instance.
+  static void AttachNative(const typename Cls::LocalRef& instance,
+                           SupportsWeakPtr* ptr) {
+    static_assert(NativePtrPicker<Impl>::value == NativePtrType::WEAK_INTRUSIVE,
+                  "Use another AttachNative for non-WeakPtr usage");
+    return NativePtrTraits<Impl>::Set(instance, static_cast<Impl*>(ptr));
+  }
+
+  static void AttachNative(const typename Cls::LocalRef& instance,
+                           UniquePtr<Impl>&& ptr) {
+    static_assert(NativePtrPicker<Impl>::value == NativePtrType::OWNING,
+                  "Use another AttachNative for WeakPtr or RefPtr usage");
+    return NativePtrTraits<Impl>::Set(instance, std::move(ptr));
+  }
+
+  static void AttachNative(const typename Cls::LocalRef& instance, Impl* ptr) {
+    static_assert(NativePtrPicker<Impl>::value == NativePtrType::REFPTR,
+                  "Use another AttachNative for non-RefPtr usage");
+    return NativePtrTraits<Impl>::Set(instance, ptr);
+  }
+
+  // Get the C++ instance associated with a Java instance.
+  // There is always a pending exception if the return value is nullptr.
+  static decltype(auto) GetNative(const typename Cls::LocalRef& instance) {
+    return NativePtrTraits<Impl>::Get(instance);
+  }
+
+  static void DisposeNative(const typename Cls::LocalRef& instance) {
+    NativePtrTraits<Impl>::Clear(instance);
+  }
+
+  NativeImpl() {
+    // Initialize on creation if not already initialized.
+    Init();
+  }
+};
+
+// Define static member.
+template <class C, class I>
+bool NativeImpl<C, I>::sInited;
+
+}  // namespace jni
+}  // namespace mozilla
+
+#endif  // mozilla_jni_Natives_h__