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/*
Copyright (c) 2007-2014 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/>.
*/
#ifndef __ZMQ_DBUFFER_HPP_INCLUDED__
#define __ZMQ_DBUFFER_HPP_INCLUDED__
#include <stdlib.h>
#include <stddef.h>
#include <algorithm>
#include "mutex.hpp"
#include "msg.hpp"
namespace zmq
{
// dbuffer is a single-producer single-consumer double-buffer
// implementation.
//
// The producer writes to a back buffer and then tries to swap
// pointers between the back and front buffers. If it fails,
// due to the consumer reading from the front buffer, it just
// gives up, which is ok since writes are many and redundant.
//
// The reader simply reads from the front buffer.
//
// has_msg keeps track of whether there has been a not yet read
// value written, it is used by ypipe_conflate to mimic ypipe
// functionality regarding a reader being asleep
template <typename T> class dbuffer_t;
template <> class dbuffer_t<msg_t>
{
public:
inline dbuffer_t ()
: back (&storage[0])
, front (&storage[1])
, has_msg (false)
{
back->init ();
front->init ();
}
inline ~dbuffer_t()
{
back->close ();
front->close ();
}
inline void write (const msg_t &value_)
{
msg_t& xvalue = const_cast<msg_t&>(value_);
zmq_assert (xvalue.check ());
back->move (xvalue); // cannot just overwrite, might leak
zmq_assert (back->check ());
if (sync.try_lock ())
{
std::swap (back, front);
has_msg = true;
sync.unlock ();
}
}
inline bool read (msg_t *value_)
{
if (!value_)
return false;
{
scoped_lock_t lock (sync);
if (!has_msg)
return false;
zmq_assert (front->check ());
*value_ = *front;
front->init (); // avoid double free
has_msg = false;
return true;
}
}
inline bool check_read ()
{
scoped_lock_t lock (sync);
return has_msg;
}
inline bool probe (bool (*fn)(const msg_t &))
{
scoped_lock_t lock (sync);
return (*fn) (*front);
}
private:
msg_t storage[2];
msg_t *back, *front;
mutex_t sync;
bool has_msg;
// Disable copying of dbuffer.
dbuffer_t (const dbuffer_t&);
const dbuffer_t &operator = (const dbuffer_t&);
};
}
#endif