circular_buffer.hpp

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/*
 * (c) Copyright 2016 Hewlett Packard Enterprise Development LP
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version. This program is
 * distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * for more details. You should have received a copy of the GNU Lesser
 * General Public License along with this program. If not, see
 * <http://www.gnu.org/licenses/>.
 */
 

#ifndef _LOG_ALLOC_H
#define _LOG_ALLOC_H

#include <atomic>

namespace Atlas {
    
template<class T>
struct CbLog
{
    explicit CbLog(uint32_t sz, uint32_t is_filled,
          uint32_t start_cb, uint32_t end_cb)
        : Size{sz},
        isFilled{is_filled},
        Start{start_cb},
        End{end_cb},
        LogArray{nullptr} {}
    CbLog() = delete;
    CbLog(const CbLog&) = delete;
    CbLog(CbLog&&) = delete;
    CbLog& operator=(const CbLog&) = delete;
    CbLog& operator=(CbLog&&) = delete;
    
    uint32_t Size;
    std::atomic<uint32_t> isFilled;
    std::atomic<uint32_t> Start;
    std::atomic<uint32_t> End;
    T *LogArray;

    bool isFull() {
        return (End.load(std::memory_order_acquire)+1) % Size ==
            Start.load(std::memory_order_acquire);
    }

    bool isEmpty() {
        return Start.load(std::memory_order_acquire) ==
            End.load(std::memory_order_acquire);
    }
};

template<class T>
struct CbListNode
{
    explicit CbListNode(CbLog<T> *cb, char *start_addr, char *end_addr)
        : Cb{cb},
        StartAddr{start_addr},
        EndAddr{end_addr},
        Next{nullptr},
        Tid{pthread_self()},
        isAvailable{false} {}
    CbListNode() = delete;
    CbListNode(const CbListNode&) = delete;
    CbListNode(CbListNode&&) = delete;
    CbListNode& operator=(const CbListNode&) = delete;
    CbListNode& operator=(CbListNode&&) = delete;
    
    CbLog<T> *Cb;
    char *StartAddr;
    char *EndAddr;
    CbListNode<T> *Next;
    pthread_t Tid;
    std::atomic<uint32_t> isAvailable;
};

// CbList is a data structure shared among threads. When a new slot is
// requested, if the current buffer is found full, the current thread
// creates a new buffer, adds it to the CbList and
// return the first slot from this new buffer. If a buffer ever becomes
// empty, it can be reused. A partially empty buffer cannot be reused.

// TODO eventual GC on cb_list

} // namespace Atlas

#endif