lb.cpp

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/*
    Copyright (c) 2010-2011 250bpm s.r.o.
    Copyright (c) 2007-2009 iMatix Corporation
    Copyright (c) 2011 VMware, Inc.
    Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file

    This file is part of 0MQ.

    0MQ 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.

    0MQ 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 Lesser 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/>.
*/

#include "lb.hpp"
#include "pipe.hpp"
#include "err.hpp"
#include "msg.hpp"

zmq::lb_t::lb_t () :
    active (0),
    current (0),
    more (false),
    dropping (false)
{
}

zmq::lb_t::~lb_t ()
{
    zmq_assert (pipes.empty ());
}

void zmq::lb_t::attach (pipe_t *pipe_)
{
    pipes.push_back (pipe_);
    pipes.swap (active, pipes.size () - 1);
    active++;
}

void zmq::lb_t::terminated (pipe_t *pipe_)
{
    pipes_t::size_type index = pipes.index (pipe_);

    //  If we are in the middle of multipart message and current pipe
    //  have disconnected, we have to drop the remainder of the message.
    if (index == current && more)
        dropping = true;

    //  Remove the pipe from the list; adjust number of active pipes
    //  accordingly.
    if (index < active) {
        active--;
        if (current == active)
            current = 0;
    }
    pipes.erase (pipe_);
}

void zmq::lb_t::activated (pipe_t *pipe_)
{
    //  Move the pipe to the list of active pipes.
    pipes.swap (pipes.index (pipe_), active);
    active++;
}

int zmq::lb_t::send (msg_t *msg_, int flags_)
{
    //  Drop the message if required. If we are at the end of the message
    //  switch back to non-dropping mode.
    if (dropping) {

        more = msg_->flags () & msg_t::more ? true : false;
        if (!more)
            dropping = false;

        int rc = msg_->close ();
        errno_assert (rc == 0);
        rc = msg_->init ();
        zmq_assert (rc == 0);
        return 0;
    }

    while (active > 0) {
        if (pipes [current]->write (msg_)) {
            more = msg_->flags () & msg_t::more ? true : false;
            break;
        }

        zmq_assert (!more);
        active--;
        if (current < active)
            pipes.swap (current, active);
        else
            current = 0;
    }

    //  If there are no pipes we cannot send the message.
    if (active == 0) {
        errno = EAGAIN;
        return -1;
    }

    //  If it's final part of the message we can fluch it downstream and
    //  continue round-robinning (load balance).
    if (!more) {
        pipes [current]->flush ();
        current = (current + 1) % active;
    }

    //  Detach the message from the data buffer.
    int rc = msg_->init ();
    errno_assert (rc == 0);

    return 0;
}

bool zmq::lb_t::has_out ()
{
    //  If one part of the message was already written we can definitely
    //  write the rest of the message.
    if (more)
        return true;

    while (active > 0) {

        //  Check whether zero-sized message can be written to the pipe.
        msg_t msg;
        int rc = msg.init ();
        errno_assert (rc == 0);
        if (pipes [current]->check_write (&msg)) {
            rc = msg.close ();
            errno_assert (rc == 0);
            return true;
        }
        rc = msg.close ();
        errno_assert (rc == 0);

        //  Deactivate the pipe.
        active--;
        pipes.swap (current, active);
        if (current == active)
            current = 0;
    }

    return false;
}