lockedpool.h

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// Copyright (c) 2016-2018 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_SUPPORT_LOCKEDPOOL_H
#define BITCOIN_SUPPORT_LOCKEDPOOL_H

#include <stdint.h>
#include <list>
#include <map>
#include <mutex>
#include <memory>
#include <unordered_map>

class LockedPageAllocator
{
public:
    virtual ~LockedPageAllocator() {}
    virtual void* AllocateLocked(size_t len, bool *lockingSuccess) = 0;

    virtual void FreeLocked(void* addr, size_t len) = 0;

    virtual size_t GetLimit() = 0;
};

/* An arena manages a contiguous region of memory by dividing it into
 * chunks.
 */
class Arena
{
public:
    Arena(void *base, size_t size, size_t alignment);
    virtual ~Arena();

    Arena(const Arena& other) = delete; // non construction-copyable
    Arena& operator=(const Arena&) = delete; // non copyable

    struct Stats
    {
        size_t used;
        size_t free;
        size_t total;
        size_t chunks_used;
        size_t chunks_free;
    };

    void* alloc(size_t size);

    void free(void *ptr);

    Stats stats() const;

#ifdef ARENA_DEBUG
    void walk() const;
#endif

    bool addressInArena(void *ptr) const { return ptr >= base && ptr < end; }
private:
    typedef std::multimap<size_t, char*> SizeToChunkSortedMap;
    SizeToChunkSortedMap size_to_free_chunk;

    typedef std::unordered_map<char*, SizeToChunkSortedMap::const_iterator> ChunkToSizeMap;
    ChunkToSizeMap chunks_free;
    ChunkToSizeMap chunks_free_end;

    std::unordered_map<char*, size_t> chunks_used;

    char* base;
    char* end;
    size_t alignment;
};

class LockedPool
{
public:
    static const size_t ARENA_SIZE = 256*1024;
    static const size_t ARENA_ALIGN = 16;

    typedef bool (*LockingFailed_Callback)();

    struct Stats
    {
        size_t used;
        size_t free;
        size_t total;
        size_t locked;
        size_t chunks_used;
        size_t chunks_free;
    };

    explicit LockedPool(std::unique_ptr<LockedPageAllocator> allocator, LockingFailed_Callback lf_cb_in = nullptr);
    ~LockedPool();

    LockedPool(const LockedPool& other) = delete; // non construction-copyable
    LockedPool& operator=(const LockedPool&) = delete; // non copyable

    void* alloc(size_t size);

    void free(void *ptr);

    Stats stats() const;
private:
    std::unique_ptr<LockedPageAllocator> allocator;

    class LockedPageArena: public Arena
    {
    public:
        LockedPageArena(LockedPageAllocator *alloc_in, void *base_in, size_t size, size_t align);
        ~LockedPageArena();
    private:
        void *base;
        size_t size;
        LockedPageAllocator *allocator;
    };

    bool new_arena(size_t size, size_t align);

    std::list<LockedPageArena> arenas;
    LockingFailed_Callback lf_cb;
    size_t cumulative_bytes_locked;
    mutable std::mutex mutex;
};

class LockedPoolManager : public LockedPool
{
public:
    static LockedPoolManager& Instance()
    {
        std::call_once(LockedPoolManager::init_flag, LockedPoolManager::CreateInstance);
        return *LockedPoolManager::_instance;
    }

private:
    explicit LockedPoolManager(std::unique_ptr<LockedPageAllocator> allocator);

    static void CreateInstance();
    static bool LockingFailed();

    static LockedPoolManager* _instance;
    static std::once_flag init_flag;
};

#endif // BITCOIN_SUPPORT_LOCKEDPOOL_H