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/*
* Copyright (C) 2018 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 SRC_PROFILING_MEMORY_INTERNER_H_
#define SRC_PROFILING_MEMORY_INTERNER_H_
#include <stddef.h>
#include <stdint.h>
#include <functional>
#include <unordered_set>
#include "perfetto/base/logging.h"
namespace perfetto {
namespace profiling {
using InternID = uint32_t;
template <typename T>
class Interner {
private:
struct Entry {
template <typename... U>
Entry(Interner<T>* in, InternID i, U... args)
: data(std::forward<U...>(args...)), id(i), interner(in) {}
bool operator<(const Entry& other) const { return data < other.data; }
bool operator==(const Entry& other) const { return data == other.data; }
struct Hash {
size_t operator()(const Entry& e) const noexcept {
return std::hash<T>{}(e.data);
}
};
const T data;
InternID id;
size_t ref_count = 0;
Interner<T>* interner;
};
public:
class Interned {
public:
friend class Interner<T>;
Interned(Entry* entry) : entry_(entry) {}
Interned(const Interned& other) : entry_(other.entry_) {
if (entry_ != nullptr)
entry_->ref_count++;
}
Interned(Interned&& other) noexcept : entry_(other.entry_) {
other.entry_ = nullptr;
}
Interned& operator=(Interned other) noexcept {
using std::swap;
swap(*this, other);
return *this;
}
const T& data() const { return entry_->data; }
InternID id() const { return entry_->id; }
~Interned() {
if (entry_ != nullptr)
entry_->interner->Return(entry_);
}
bool operator<(const Interned& other) const {
return entry_ < other.entry_;
}
bool operator==(const Interned& other) const {
return entry_ == other.entry_;
}
const T* operator->() const { return &entry_->data; }
private:
Interner::Entry* entry_;
};
template <typename... U>
Interned Intern(U... args) {
Entry item(this, next_id, std::forward<U...>(args...));
auto it = entries_.find(item);
if (it == entries_.cend()) {
// This does not invalidate pointers to entries we hold in Interned. See
// https://timsong-cpp.github.io/cppwp/n3337/unord.req#8
auto it_and_inserted = entries_.emplace(std::move(item));
next_id++;
it = it_and_inserted.first;
PERFETTO_DCHECK(it_and_inserted.second);
}
Entry& entry = const_cast<Entry&>(*it);
entry.ref_count++;
return Interned(&entry);
}
~Interner() { PERFETTO_DCHECK(entries_.empty()); }
size_t entry_count_for_testing() { return entries_.size(); }
private:
void Return(Entry* entry) {
if (--entry->ref_count == 0)
entries_.erase(*entry);
}
InternID next_id = 1;
std::unordered_set<Entry, typename Entry::Hash> entries_;
static_assert(sizeof(Interned) == sizeof(void*),
"interned things should be small");
};
template <typename T>
void swap(typename Interner<T>::Interned a, typename Interner<T>::Interned b) {
std::swap(a.entry_, b.entry_);
}
template <typename T>
using Interned = typename Interner<T>::Interned;
} // namespace profiling
} // namespace perfetto
#endif // SRC_PROFILING_MEMORY_INTERNER_H_