base/Pool.h

// Copyright 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.
#pragma once

#include "android/base/Allocator.h"

#include <unordered_set>

#include <inttypes.h>
#include <stddef.h>
#include <string.h>

namespace android {
namespace base {

// Class to make it easier to set up memory regions where it is fast
// to allocate/deallocate buffers that have size within
// the specified range.
class Pool : public Allocator {
public:
    // minSize/maxSize: the target range of sizes for which we want to
    // make allocations fast. the greater the range, the more space
    // traded off.
    // chunksPerSize: the target maximum number of live objects of
    // each size that are expected. the higher it is, the more space
    // traded off.
    //
    // Rough space cost formula:
    // O(chunksPerSize * log2(maxSize / minSize) * maxSize)
    Pool(size_t minSize = 4,
         size_t maxSize = 4096,
         size_t chunksPerSize = 1024);

    // All memory allocated by this pool
    // is automatically deleted when the pool
    // is deconstructed.
    ~Pool();

    void* alloc(size_t wantedSize) override;
    void free(void* ptr);

    // Convenience function to free everything currently allocated.
    void freeAll();

private:
    class Impl;
    Impl* mImpl = nullptr;

    std::unordered_set<void*> mFallbackPtrs;
};

} // namespace base
} // namespace android