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/*
* Asterisk -- An open source telephony toolkit.
*
* Copyright (C) 2009, Digium, Inc.
*
* Mark Michelson <mmichelson@digium.com>
*
* See http://www.asterisk.org for more information about
* the Asterisk project. Please do not directly contact
* any of the maintainers of this project for assistance;
* the project provides a web site, mailing lists and IRC
* channels for your use.
*
* This program is free software, distributed under the terms of
* the GNU General Public License Version 2. See the LICENSE file
* at the top of the source tree.
*/
/*!
* \file
* \brief "smart" channels that update automatically if a channel is masqueraded
*
* \author Mark Michelson <mmichelson@digium.com>
*/
#include "asterisk.h"
#include "asterisk/linkedlists.h"
#ifndef _ASTERISK_AUTOCHAN_H
#define _ASTERISK_AUTOCHAN_H
struct ast_autochan {
struct ast_channel *chan;
AST_LIST_ENTRY(ast_autochan) list;
ast_mutex_t lock;
};
/*!
* \par Just what the $!@# is an autochan?
*
* An ast_autochan is a structure which contains an ast_channel. The pointer
* inside an autochan has the ability to update itself if the channel it points
* to is masqueraded into a different channel.
*
* This has a great benefit for any application or service which creates a thread
* outside of the channel's main operating thread which keeps a pointer to said
* channel. when a masquerade occurs on the channel, the autochan's chan pointer
* will automatically update to point to the new channel.
*
* Some rules for autochans
*
* 1. If you are going to use an autochan, then be sure to always refer to the
* channel using the chan pointer inside the autochan if possible, since this is
* the pointer that will be updated during a masquerade.
*
* 2. If you are going to save off a pointer to the autochan's chan, then be sure
* to save off the pointer using ast_channel_ref and to unref the channel when you
* are finished with the pointer. If you do not do this and a masquerade occurs on
* the channel, then it is possible that your saved pointer will become invalid.
*
* 3. If you want to lock the autochan->chan channel, be sure to use
* ast_autochan_channel_lock and ast_autochan_channel_unlock. An attempt to lock
* the autochan->chan directly may result in it being changed after you've
* retrieved the value of chan, but before you've had a chance to lock it.
* While chan is locked, the autochan structure is guaranteed to keep the
* same channel.
*/
/*!
* \brief Lock the autochan's channel lock.
*
* \note We must do deadlock avoidance because the channel lock is
* superior to the autochan lock in locking order.
*/
#define ast_autochan_channel_lock(autochan) \
do { \
ast_mutex_lock(&(autochan)->lock); \
while (ast_channel_trylock((autochan)->chan)) { \
DEADLOCK_AVOIDANCE(&(autochan)->lock); \
} \
ast_mutex_unlock(&(autochan)->lock); \
} while (0)
#define ast_autochan_channel_unlock(autochan) \
ast_channel_unlock(autochan->chan)
/*!
* \brief set up a new ast_autochan structure
*
* \details
* Allocates and initializes an ast_autochan, sets the
* autochan's chan pointer to point to the chan parameter, and
* adds the autochan to the global list of autochans. The newly-
* created autochan is returned to the caller. This function will
* cause the refcount of chan to increase by 1.
*
* \param chan The channel our new autochan will point to
*
* \note autochans must be freed using ast_autochan_destroy
*
* \retval NULL Failure
* \retval non-NULL success
*/
struct ast_autochan *ast_autochan_setup(struct ast_channel *chan);
/*!
* \brief destroy an ast_autochan structure
*
* \details
* Removes the passed-in autochan from the list of autochans and
* unrefs the channel that is pointed to. Also frees the autochan
* struct itself. This function will unref the channel reference
* which was made in ast_autochan_setup
*
* \param autochan The autochan that you wish to destroy
*
* \retval void
*/
void ast_autochan_destroy(struct ast_autochan *autochan);
/*!
* \brief Switch what channel autochans point to
*
* \details
* Traverses the list of autochans. All autochans which point to
* old_chan will be updated to point to new_chan instead. Currently
* this is only called during an ast_channel_move() operation in
* channel.c.
*
* \pre Both channels must be locked before calling this function.
*
* \param old_chan The channel that autochans may currently point to
* \param new_chan The channel that we want to point those autochans to now
*
* \retval void
*/
void ast_autochan_new_channel(struct ast_channel *old_chan, struct ast_channel *new_chan);
#endif /* _ASTERISK_AUTOCHAN_H */
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