mirror of
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142 lines
3.7 KiB
C++
142 lines
3.7 KiB
C++
/*
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Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
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This file is part of libzmq, the ZeroMQ core engine in C++.
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libzmq is free software; you can redistribute it and/or modify it under
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the terms of the GNU Lesser General Public License (LGPL) as published
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by the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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As a special exception, the Contributors give you permission to link
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this library with independent modules to produce an executable,
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regardless of the license terms of these independent modules, and to
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copy and distribute the resulting executable under terms of your choice,
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provided that you also meet, for each linked independent module, the
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terms and conditions of the license of that module. An independent
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module is a module which is not derived from or based on this library.
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If you modify this library, you must extend this exception to your
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version of the library.
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libzmq is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef __ZMQ_DBUFFER_HPP_INCLUDED__
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#define __ZMQ_DBUFFER_HPP_INCLUDED__
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#include <stdlib.h>
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#include <stddef.h>
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#include <algorithm>
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#include "mutex.hpp"
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#include "msg.hpp"
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namespace zmq
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{
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// dbuffer is a single-producer single-consumer double-buffer
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// implementation.
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//
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// The producer writes to a back buffer and then tries to swap
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// pointers between the back and front buffers. If it fails,
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// due to the consumer reading from the front buffer, it just
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// gives up, which is ok since writes are many and redundant.
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//
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// The reader simply reads from the front buffer.
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//
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// has_msg keeps track of whether there has been a not yet read
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// value written, it is used by ypipe_conflate to mimic ypipe
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// functionality regarding a reader being asleep
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template <typename T> class dbuffer_t;
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template <> class dbuffer_t<msg_t>
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{
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public:
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inline dbuffer_t () :
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_back (&_storage[0]),
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_front (&_storage[1]),
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_has_msg (false)
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{
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_back->init ();
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_front->init ();
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}
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inline ~dbuffer_t ()
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{
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_back->close ();
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_front->close ();
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}
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inline void write (const msg_t &value_)
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{
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msg_t &xvalue = const_cast<msg_t &> (value_);
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zmq_assert (xvalue.check ());
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_back->move (xvalue); // cannot just overwrite, might leak
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zmq_assert (_back->check ());
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if (_sync.try_lock ()) {
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std::swap (_back, _front);
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_has_msg = true;
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_sync.unlock ();
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}
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}
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inline bool read (msg_t *value_)
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{
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if (!value_)
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return false;
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{
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scoped_lock_t lock (_sync);
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if (!_has_msg)
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return false;
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zmq_assert (_front->check ());
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*value_ = *_front;
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_front->init (); // avoid double free
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_has_msg = false;
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return true;
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}
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}
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inline bool check_read ()
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{
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scoped_lock_t lock (_sync);
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return _has_msg;
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}
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inline bool probe (bool (*fn_) (const msg_t &))
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{
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scoped_lock_t lock (_sync);
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return (*fn_) (*_front);
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}
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private:
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msg_t _storage[2];
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msg_t *_back, *_front;
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mutex_t _sync;
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bool _has_msg;
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// Disable copying of dbuffer.
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dbuffer_t (const dbuffer_t &);
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const dbuffer_t &operator= (const dbuffer_t &);
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};
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}
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#endif
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