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/*
* Copyright (C) 2014 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_RUNTIME_HANDLE_SCOPE_H_
#define ART_RUNTIME_HANDLE_SCOPE_H_
#include <stack>
#include "base/logging.h"
#include "base/macros.h"
#include "handle.h"
#include "stack.h"
#include "verify_object.h"
namespace art {
namespace mirror {
class Object;
}
class Thread;
// HandleScopes are scoped objects containing a number of Handles. They are used to allocate
// handles, for these handles (and the objects contained within them) to be visible/roots for the
// GC. It is most common to stack allocate HandleScopes using StackHandleScope.
class PACKED(4) HandleScope {
public:
~HandleScope() {}
// Number of references contained within this handle scope.
uint32_t NumberOfReferences() const {
return number_of_references_;
}
// We have versions with and without explicit pointer size of the following. The first two are
// used at runtime, so OFFSETOF_MEMBER computes the right offsets automatically. The last one
// takes the pointer size explicitly so that at compile time we can cross-compile correctly.
// Returns the size of a HandleScope containing num_references handles.
static size_t SizeOf(uint32_t num_references);
// Returns the size of a HandleScope containing num_references handles.
static size_t SizeOf(size_t pointer_size, uint32_t num_references);
// Link to previous HandleScope or null.
HandleScope* GetLink() const {
return link_;
}
ALWAYS_INLINE mirror::Object* GetReference(size_t i) const
SHARED_REQUIRES(Locks::mutator_lock_);
ALWAYS_INLINE Handle<mirror::Object> GetHandle(size_t i)
SHARED_REQUIRES(Locks::mutator_lock_);
ALWAYS_INLINE MutableHandle<mirror::Object> GetMutableHandle(size_t i)
SHARED_REQUIRES(Locks::mutator_lock_);
ALWAYS_INLINE void SetReference(size_t i, mirror::Object* object)
SHARED_REQUIRES(Locks::mutator_lock_);
ALWAYS_INLINE bool Contains(StackReference<mirror::Object>* handle_scope_entry) const;
// Offset of link within HandleScope, used by generated code.
static size_t LinkOffset(size_t pointer_size ATTRIBUTE_UNUSED) {
return 0;
}
// Offset of length within handle scope, used by generated code.
static size_t NumberOfReferencesOffset(size_t pointer_size) {
return pointer_size;
}
// Offset of link within handle scope, used by generated code.
static size_t ReferencesOffset(size_t pointer_size) {
return pointer_size + sizeof(number_of_references_);
}
// Placement new creation.
static HandleScope* Create(void* storage, HandleScope* link, uint32_t num_references)
WARN_UNUSED {
return new (storage) HandleScope(link, num_references);
}
protected:
// Return backing storage used for references.
ALWAYS_INLINE StackReference<mirror::Object>* GetReferences() const {
uintptr_t address = reinterpret_cast<uintptr_t>(this) + ReferencesOffset(sizeof(void*));
return reinterpret_cast<StackReference<mirror::Object>*>(address);
}
explicit HandleScope(size_t number_of_references) :
link_(nullptr), number_of_references_(number_of_references) {
}
// Semi-hidden constructor. Construction expected by generated code and StackHandleScope.
explicit HandleScope(HandleScope* link, uint32_t num_references) :
link_(link), number_of_references_(num_references) {
}
// Link-list of handle scopes. The root is held by a Thread.
HandleScope* const link_;
// Number of handlerized references.
const uint32_t number_of_references_;
// Storage for references.
// StackReference<mirror::Object> references_[number_of_references_]
private:
DISALLOW_COPY_AND_ASSIGN(HandleScope);
};
// A wrapper which wraps around Object** and restores the pointer in the destructor.
// TODO: Add more functionality.
template<class T>
class HandleWrapper : public MutableHandle<T> {
public:
HandleWrapper(T** obj, const MutableHandle<T>& handle)
: MutableHandle<T>(handle), obj_(obj) {
}
HandleWrapper(const HandleWrapper&) = default;
~HandleWrapper() {
*obj_ = MutableHandle<T>::Get();
}
private:
T** const obj_;
};
// Scoped handle storage of a fixed size that is usually stack allocated.
template<size_t kNumReferences>
class PACKED(4) StackHandleScope FINAL : public HandleScope {
public:
explicit ALWAYS_INLINE StackHandleScope(Thread* self, mirror::Object* fill_value = nullptr);
ALWAYS_INLINE ~StackHandleScope();
template<class T>
ALWAYS_INLINE MutableHandle<T> NewHandle(T* object) SHARED_REQUIRES(Locks::mutator_lock_);
template<class T>
ALWAYS_INLINE HandleWrapper<T> NewHandleWrapper(T** object)
SHARED_REQUIRES(Locks::mutator_lock_);
ALWAYS_INLINE void SetReference(size_t i, mirror::Object* object)
SHARED_REQUIRES(Locks::mutator_lock_);
Thread* Self() const {
return self_;
}
private:
template<class T>
ALWAYS_INLINE MutableHandle<T> GetHandle(size_t i) SHARED_REQUIRES(Locks::mutator_lock_) {
DCHECK_LT(i, kNumReferences);
return MutableHandle<T>(&GetReferences()[i]);
}
// Reference storage needs to be first as expected by the HandleScope layout.
StackReference<mirror::Object> storage_[kNumReferences];
// The thread that the stack handle scope is a linked list upon. The stack handle scope will
// push and pop itself from this thread.
Thread* const self_;
// Position new handles will be created.
size_t pos_;
template<size_t kNumRefs> friend class StackHandleScope;
};
// Utility class to manage a collection (stack) of StackHandleScope. All the managed
// scope handle have the same fixed sized.
// Calls to NewHandle will create a new handle inside the top StackHandleScope.
// When the handle scope becomes full a new one is created and push on top of the
// previous.
//
// NB:
// - it is not safe to use the *same* StackHandleScopeCollection intermix with
// other StackHandleScopes.
// - this is a an easy way around implementing a full ZoneHandleScope to manage an
// arbitrary number of handles.
class StackHandleScopeCollection {
public:
explicit StackHandleScopeCollection(Thread* const self) :
self_(self),
current_scope_num_refs_(0) {
}
~StackHandleScopeCollection() {
while (!scopes_.empty()) {
delete scopes_.top();
scopes_.pop();
}
}
template<class T>
MutableHandle<T> NewHandle(T* object) SHARED_REQUIRES(Locks::mutator_lock_) {
if (scopes_.empty() || current_scope_num_refs_ >= kNumReferencesPerScope) {
StackHandleScope<kNumReferencesPerScope>* scope =
new StackHandleScope<kNumReferencesPerScope>(self_);
scopes_.push(scope);
current_scope_num_refs_ = 0;
}
current_scope_num_refs_++;
return scopes_.top()->NewHandle(object);
}
private:
static constexpr size_t kNumReferencesPerScope = 4;
Thread* const self_;
std::stack<StackHandleScope<kNumReferencesPerScope>*> scopes_;
size_t current_scope_num_refs_;
DISALLOW_COPY_AND_ASSIGN(StackHandleScopeCollection);
};
} // namespace art
#endif // ART_RUNTIME_HANDLE_SCOPE_H_