slsDetectorPackage/slsReceiverSoftware/include/CircularFifo.h

#pragma once
/* CircularFifo.h
 * Code & platform dependent issues with it was originally
 * published at http://www.kjellkod.cc/threadsafecircularqueue
 * 2009-11-02
 * @author Kjell Hedstr<74>m, hedstrom@kjellkod.cc
 * modified by the sls detector group
 * */

#include <iostream>
#include <semaphore.h>
#include <vector>

/** Circular Fifo (a.k.a. Circular Buffer)
 * Thread safe for one reader, and one writer */
template <typename Element> class CircularFifo {
  private:
    size_t tail{0};
    size_t head{0};
    size_t capacity;
    std::vector<Element *> data;
    mutable sem_t data_mutex;
    mutable sem_t free_mutex;
    size_t increment(size_t i) const;

  public:
    explicit CircularFifo(size_t size) : capacity(size + 1), data(capacity) {
        sem_init(&data_mutex, 0, 0);
        sem_init(&free_mutex, 0, size);
    }

    CircularFifo(const CircularFifo &) = delete;
    CircularFifo(CircularFifo &&) = delete;

    virtual ~CircularFifo() {
        sem_destroy(&data_mutex);
        sem_destroy(&free_mutex);
    }

    bool push(Element *&item, bool no_block = false);
    bool pop(Element *&item, bool no_block = false);

    bool isEmpty() const;
    bool isFull() const;

    int getDataValue() const;
    int getFreeValue() const;
};

template <typename Element> int CircularFifo<Element>::getDataValue() const {
    int value;
    sem_getvalue(&data_mutex, &value);
    return value;
}

template <typename Element> int CircularFifo<Element>::getFreeValue() const {
    int value;
    sem_getvalue(&free_mutex, &value);
    return value;
}

/** Producer only: Adds item to the circular queue.
 * If queue is full at 'push' operation no update/overwrite
 * will happen, it is up to the caller to handle this case
 *
 * \param item copy by reference the input item
 * \param no_block if true, return immediately if fifo is full
 * \return whether operation was successful or not */
template <typename Element>
bool CircularFifo<Element>::push(Element *&item, bool no_block) {
    // check for fifo full
    if (no_block && isFull())
        return false;

    sem_wait(&free_mutex);
    data[tail] = item;
    tail = increment(tail);
    sem_post(&data_mutex);
    return true;
}

/** Consumer only: Removes and returns item from the queue
 * If queue is empty at 'pop' operation no retrieve will happen
 * It is up to the caller to handle this case
 *
 * \param item return by reference the wanted item
 * \param no_block if true, return immediately if fifo is full
 * \return whether operation was successful or not */
template <typename Element>
bool CircularFifo<Element>::pop(Element *&item, bool no_block) {
    // check for fifo empty
    if (no_block && isEmpty())
        return false;

    sem_wait(&data_mutex);
    item = data[head];
    head = increment(head);
    sem_post(&free_mutex);
    return true;
}

/** Useful for testing and Consumer check of status
 * Remember that the 'empty' status can change quickly
 * as the Producer adds more items.
 *
 * \return true if circular buffer is empty */
template <typename Element> bool CircularFifo<Element>::isEmpty() const {
    return (getDataValue() == 0);
}

/** Useful for testing and Producer check of status
 * Remember that the 'full' status can change quickly
 * as the Consumer catches up.
 *
 * \return true if circular buffer is full.  */
template <typename Element> bool CircularFifo<Element>::isFull() const {
    return (getFreeValue() == 0);
}

/** Increment helper function for index of the circular queue
 * index is incremented or wrapped
 *
 *  \param i the index to the incremented/wrapped
 *  \return new value for the index */
template <typename Element>
size_t CircularFifo<Element>::increment(size_t i) const {
    i = (i + 1) % capacity;
    return i;
}