annotate base/Scavenger.h @ 492:23945cdd7161

* Update RDF query stuff again so as to set up a temporary datastore
  each time we want to query over an rdf file, instead of using rasqal
  against the file.  Seems the only way to avoid threading and storage
  management issues when trying to load from a single-source file and
  perform queries against our main datastore at the same time.  Maybe.

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Sonic Visualiser
    An audio file viewer and annotation editor.
    Centre for Digital Music, Queen Mary, University of London.
    This file copyright 2006 Chris Cannam.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

/*
   This is a modified version of a source file from the 
   Rosegarden MIDI and audio sequencer and notation editor.
   This file copyright 2000-2006 Chris Cannam.
*/

#ifndef _SCAVENGER_H_
#define _SCAVENGER_H_

#include "system/System.h"

#include <vector>
#include <list>
#include <sys/time.h>
#include <QMutex>
#include <iostream>

/**
 * 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);
    ~Scavenger();

    /**
     * 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;

    typedef std::list<T *> ObjectList;
    ObjectList m_excess;
    int m_lastExcess;
    QMutex m_excessMutex;
    void pushExcess(T *);
    void clearExcess(int);

    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_lastExcess(0),
    m_claimed(0),
    m_scavenged(0)
{
}

template <typename T>
Scavenger<T>::~Scavenger()
{
    if (m_scavenged < m_claimed) {
	for (size_t i = 0; i < m_objects.size(); ++i) {
	    ObjectTimePair &pair = m_objects[i];
	    if (pair.first != 0) {
		T *ot = pair.first;
		pair.first = 0;
		delete ot;
		++m_scavenged;
	    }
	}
    }

    clearExcess(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;
	}
    }

    std::cerr << "WARNING: Scavenger::claim(" << t << "): run out of slots, "
	      << "using non-RT-safe method" << std::endl;
    pushExcess(t);
}

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;
	}
    }

    if (sec > m_lastExcess + m_sec) {
        clearExcess(sec);
    }
}

template <typename T>
void
Scavenger<T>::pushExcess(T *t)
{
    m_excessMutex.lock();
    m_excess.push_back(t);
    struct timeval tv;
    (void)gettimeofday(&tv, 0);
    m_lastExcess = tv.tv_sec;
    m_excessMutex.unlock();
}

template <typename T>
void
Scavenger<T>::clearExcess(int sec)
{
    m_excessMutex.lock();
    for (typename ObjectList::iterator i = m_excess.begin();
	 i != m_excess.end(); ++i) {
	delete *i;
    }
    m_excess.clear();
    m_lastExcess = sec;
    m_excessMutex.unlock();
}

#endif