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// Copyright 2017 The Dawn Authors
//
// 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 SRC_DAWN_COMMON_REFCOUNTED_H_
#define SRC_DAWN_COMMON_REFCOUNTED_H_
#include <atomic>
#include <cstdint>
#include <type_traits>
namespace dawn {
namespace detail {
class WeakRefData;
} // namespace detail
class RefCount {
public:
// Create a refcount with a payload. The refcount starts initially at one.
explicit RefCount(uint64_t payload = 0);
uint64_t GetValueForTesting() const;
uint64_t GetPayload() const;
// Add a reference.
void Increment();
// Tries to add a reference. Returns false if the ref count is already at 0. This is used when
// operating on a raw pointer to a RefCounted instead of a valid Ref that may be soon deleted.
bool TryIncrement();
// Remove a reference. Returns true if this was the last reference.
bool Decrement();
private:
std::atomic<uint64_t> mRefCount;
};
// Forward declaration for Ref needed until TryGetRef can be removed with WeakRefs.
// TODO(dawn:1769) Remove once WeakRef implementation is complete with cache.
template <typename T>
class Ref;
// TODO(dawn:1769) Move to Ref.h once TryGetRef can be removed.
template <typename T>
Ref<T> AcquireRef(T* pointee) {
Ref<T> ref;
ref.Acquire(pointee);
return ref;
}
class RefCounted {
public:
explicit RefCounted(uint64_t payload = 0);
uint64_t GetRefCountForTesting() const;
uint64_t GetRefCountPayload() const;
void Reference();
// Release() is called by internal code, so it's assumed that there is already a thread
// synchronization in place for destruction.
void Release();
// Tries to return a valid Ref to `object` if it's internal refcount is not already 0. If the
// internal refcount has already reached 0, returns nullptr instead.
// TODO(dawn:1769) Remove this once ContentLessObjectCache is converted to use WeakRefs.
template <typename T, typename = typename std::is_convertible<T, RefCounted>>
friend Ref<T> TryGetRef(T* object) {
// Since this is called on the RefCounted class directly, and can race with destruction, we
// verify that we can safely increment the refcount first, create the Ref, then decrement
// the refcount in that order to ensure that the resultant Ref is a valid Ref.
if (!object->mRefCount.TryIncrement()) {
return nullptr;
}
return AcquireRef(object);
}
void APIReference() { Reference(); }
// APIRelease() can be called without any synchronization guarantees so we need to use a Release
// method that will call LockAndDeleteThis() on destruction.
void APIRelease() { ReleaseAndLockBeforeDestroy(); }
protected:
// Friend class is needed to access the RefCount to TryIncrement.
friend class detail::WeakRefData;
virtual ~RefCounted();
void ReleaseAndLockBeforeDestroy();
// A Derived class may override these if they require a custom deleter.
virtual void DeleteThis();
// This calls DeleteThis() by default.
virtual void LockAndDeleteThis();
RefCount mRefCount;
};
} // namespace dawn
#endif // SRC_DAWN_COMMON_REFCOUNTED_H_