dataqueue.cc

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///
/// \file       dataqueue.cc
///             FIFO queue of Data objects
///

/*
    Copyright (C) 2008-2012, Net Direct Inc. (http://www.netdirect.ca/)

    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.

    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 in the COPYING file at the
    root directory of this project for more details.
*/

#include "dataqueue.h"
#include "scoped_lock.h"
#include "data.h"
#include "time.h"
#include <iostream>

using namespace std;

namespace Barry {

//////////////////////////////////////////////////////////////////////////////
// DataQueue class

DataQueue::DataQueue()
{
        pthread_mutex_init(&m_waitMutex, NULL);
        pthread_cond_init(&m_waitCond, NULL);

        pthread_mutex_init(&m_accessMutex, NULL);
}

DataQueue::~DataQueue()
{
        scoped_lock lock(m_accessMutex);        // FIXME - is this sane?

        while( m_queue.size() ) {
                delete raw_pop();
        }
}

// a push without locking - adds to the back
void DataQueue::raw_push(Data *data)
{
        try {
                m_queue.push_back(data);
        }
        catch(...) {
                delete data;
                throw;
        }
}

// a pop without locking - removes from the front, and returns it
Data* DataQueue::raw_pop()
{
        if( m_queue.size() == 0 )
                return 0;

        Data *ret = m_queue.front();
        m_queue.pop_front();
        return ret;
}

//
// push
//
/// Pushes data into the end of the queue.
///
/// The queue owns this pointer as soon as the function is
/// called.  In the case of an exception, it will be freed.
/// Performs a thread broadcast once new data has been added.
///
void DataQueue::push(Data *data)
{
        {
                scoped_lock lock(m_accessMutex);
                raw_push(data);
        }

        // on success, signal
        scoped_lock wait(m_waitMutex);
        pthread_cond_broadcast(&m_waitCond);
}

//
// pop
//
/// Pops the next element off the front of the queue.
///
/// Returns 0 if empty.
/// The queue no longer owns this pointer upon return.
///
Data* DataQueue::pop()
{
        scoped_lock lock(m_accessMutex);
        return raw_pop();
}

//
// wait_pop
//
/// Pops the next element off the front of the queue, and
/// waits until one exists if empty.  If still no data
/// on timeout, returns null.
/// (unlock the access mutex while waiting!)
///
/// Timeout specified in milliseconds.  Default is wait forever.
///
Data* DataQueue::wait_pop(int timeout)
{
        // check if something's there already
        {
                scoped_lock access(m_accessMutex);
                if( m_queue.size() ) {
                        return raw_pop();
                }
        }

        // nothing there, so wait...

        if( timeout == -1 ) {
                // no timeout
                int size = 0;
                do {
                        {
                                scoped_lock wait(m_waitMutex);
                                pthread_cond_wait(&m_waitCond, &m_waitMutex);
                        }

                        // anything there?
                        scoped_lock access(m_accessMutex);
                        size = m_queue.size();
                        if( size != 0 ) {
                                // already have the lock, return now
                                return raw_pop();
                        }

                } while( size == 0 );
        }
        else {
                // timeout in conditional wait
                struct timespec to;
                scoped_lock wait(m_waitMutex);
                pthread_cond_timedwait(&m_waitCond, &m_waitMutex,
                        ThreadTimeout(timeout, &to));
        }

        scoped_lock access(m_accessMutex);
        return raw_pop();
}

//
// append_from
//
/// Pops all data from other and appends it to this.
///
/// After calling this function, other will be empty, and
/// this will contain all its data.
///
/// In the case of an exception, any uncopied data will
/// remain in other.
///
/// This is a locking optimization, so all copying can happen
/// inside one lock, instead of locking for each copy.
///
void DataQueue::append_from(DataQueue &other)
{
        scoped_lock us(m_accessMutex);
        scoped_lock them(other.m_accessMutex);

        while( other.m_queue.size() ) {
                raw_push( other.m_queue.front() );

                // only pop after the copy, since in the
                // case of an exception we want to leave other intact
                other.raw_pop();
        }
}

//
// empty
//
/// Returns true if the queue is empty.
///
bool DataQueue::empty() const
{
        scoped_lock access(m_accessMutex);
        return m_queue.size() == 0;
}

//
// size
//
/// Returns number of items in the queue.
///
size_t DataQueue::size() const
{
        scoped_lock access(m_accessMutex);
        return m_queue.size();
}

void DataQueue::DumpAll(std::ostream &os) const
{
        // queue is pushed to the back, and popped from the front
        // (see raw_() functions) so this iterator direction will
        // print the packets in the order they arrived
        scoped_lock access(m_accessMutex);
        queue_type::const_iterator b = m_queue.begin(), e = m_queue.end();
        for( ; b != e; ++b ) {
                os << **b << endl;
        }
}

} // namespace Barry


#ifdef __DQ_TEST_MODE__

#include <iostream>

using namespace std;
using namespace Barry;

void *WriteThread(void *userdata)
{
        DataQueue *dq = (DataQueue*) userdata;

        dq->push( new Data );
        dq->push( new Data );
        sleep(5);
        dq->push( new Data );

        return 0;
}

void *ReadThread(void *userdata)
{
        DataQueue *dq = (DataQueue*) userdata;

        sleep(1);
        if( Data *d = dq->pop() ) {
                cout << "Received via pop: " << d << endl;
                delete d;
        }
        else {
                cout << "No data in the queue yet." << endl;
        }

        while( Data *d = dq->wait_pop(5010) ) {
                cout << "Received: " << d << endl;
                delete d;
        }
        return 0;
}

int main()
{
        DataQueue from;
        from.push( new Data );

        DataQueue dq;
        dq.append_from(from);

        pthread_t t1, t2;
        pthread_create(&t1, NULL, &ReadThread, &dq);
        pthread_create(&t2, NULL, &WriteThread, &dq);

        pthread_join(t2, NULL);
        pthread_join(t1, NULL);
}

#endif