annotate base/Scavenger.h @ 14:b101cc2ae1ab

* Introduce potentially-separate read and write ring buffers, so we can swap
  in a new set when something changes -- thus allowing us to respond quickly
  when something changes during playback, without losing the long buffers

* Some fixes for display & editing

/* -*- c-basic-offset: 4 -*-  vi:set ts=8 sts=4 sw=4: */

/*
    A waveform viewer and audio annotation editor.
    Chris Cannam, Queen Mary University of London, 2005-2006
    
    This is experimental software.  Not for distribution.
*/

/*
   This is a modified version of a source file from the 
   Rosegarden MIDI and audio sequencer and notation editor.
   This file copyright 2000-2005 Chris Cannam.
*/

#ifndef _SCAVENGER_H_
#define _SCAVENGER_H_

#include "System.h"

#include <vector>
#include <sys/time.h>

/**
 * A very simple class that facilitates running things like plugins
 * without locking, by collecting unwanted objects and deleting them
 * after a delay so as to be sure nobody's in the middle of using
 * them.  Requires scavenge() to be called regularly from a non-RT
 * thread.
 *
 * This is currently not at all suitable for large numbers of objects
 * -- it's just a quick hack for use with things like plugins.
 */

template <typename T>
class Scavenger
{
public:
    Scavenger(int sec = 2, int defaultObjectListSize = 200);

    /**
     * Call from an RT thread etc., to pass ownership of t to us.
     * Only one thread should be calling this on any given scavenger.
     */
    void claim(T *t);

    /**
     * Call from a non-RT thread.
     * Only one thread should be calling this on any given scavenger.
     */
    void scavenge(bool clearNow = false);

protected:
    typedef std::pair<T *, int> ObjectTimePair;
    typedef std::vector<ObjectTimePair> ObjectTimeList;
    ObjectTimeList m_objects;
    int m_sec;

    unsigned int m_claimed;
    unsigned int m_scavenged;
};

/**
 * A wrapper to permit arrays to be scavenged.
 */

template <typename T>
class ScavengerArrayWrapper
{
public:
    ScavengerArrayWrapper(T *array) : m_array(array) { }
    ~ScavengerArrayWrapper() { delete[] m_array; }

private:
    T *m_array;
};


template <typename T>
Scavenger<T>::Scavenger(int sec, int defaultObjectListSize) :
    m_objects(ObjectTimeList(defaultObjectListSize)),
    m_sec(sec),
    m_claimed(0),
    m_scavenged(0)
{
}

template <typename T>
void
Scavenger<T>::claim(T *t)
{
//    std::cerr << "Scavenger::claim(" << t << ")" << std::endl;

    struct timeval tv;
    (void)gettimeofday(&tv, 0);
    int sec = tv.tv_sec;

    for (size_t i = 0; i < m_objects.size(); ++i) {
	ObjectTimePair &pair = m_objects[i];
	if (pair.first == 0) {
	    pair.second = sec;
	    pair.first = t;
	    ++m_claimed;
	    return;
	}
    }

    // Oh no -- run out of slots!  Warn and discard something at
    // random (without deleting it -- it's probably safer to leak).

    for (size_t i = 0; i < m_objects.size(); ++i) {
	ObjectTimePair &pair = m_objects[i];
	if (pair.first != 0) {
	    pair.second = sec;
	    pair.first = t;
	    ++m_claimed;
	    ++m_scavenged;
	}
    }
}

template <typename T>
void
Scavenger<T>::scavenge(bool clearNow)
{
//    std::cerr << "Scavenger::scavenge: scavenged " << m_scavenged << ", claimed " << m_claimed << std::endl;

    if (m_scavenged >= m_claimed) return;
    
    struct timeval tv;
    (void)gettimeofday(&tv, 0);
    int sec = tv.tv_sec;

    for (size_t i = 0; i < m_objects.size(); ++i) {
	ObjectTimePair &pair = m_objects[i];
	if (clearNow ||
	    (pair.first != 0 && pair.second + m_sec < sec)) {
	    T *ot = pair.first;
	    pair.first = 0;
	    delete ot;
	    ++m_scavenged;
	}
    }
}

#endif