Convert the ast_channel data structure over to the astobj2 framework.

There is a lot that could be said about this, but the patch is a big 
improvement for performance, stability, code maintainability, 
and ease of future code development.

The channel list is no longer an unsorted linked list.  The main container 
for channels is an astobj2 hash table.  All of the code related to searching 
for channels or iterating active channels has been rewritten.  Let n be 
the number of active channels.  Iterating the channel list has gone from 
O(n^2) to O(n).  Searching for a channel by name went from O(n) to O(1).  
Searching for a channel by extension is still O(n), but uses a new method 
for doing so, which is more efficient.

The ast_channel object is now a reference counted object.  The benefits 
here are plentiful.  Some benefits directly related to issues in the 
previous code include:

1) When threads other than the channel thread owning a channel wanted 
   access to a channel, it had to hold the lock on it to ensure that it didn't 
   go away.  This is no longer a requirement.  Holding a reference is 
   sufficient.

2) There are places that now require less dealing with channel locks.

3) There are places where channel locks are held for much shorter periods 
   of time.

4) There are places where dealing with more than one channel at a time becomes 
   _MUCH_ easier.  ChanSpy is a great example of this.  Writing code in the 
   future that deals with multiple channels will be much easier.

Some additional information regarding channel locking and reference count 
handling can be found in channel.h, where a new section has been added that 
discusses some of the rules associated with it.

Mark Michelson also assisted with the development of this patch.  He did the 
conversion of ChanSpy and introduced a new API, ast_autochan, which makes it 
much easier to deal with holding on to a channel pointer for an extended period 
of time and having it get automatically updated if the channel gets masqueraded.
Mark was also a huge help in the code review process.

Thanks to David Vossel for his assistance with this branch, as well.  David 
did the conversion of the DAHDIScan application by making it become a wrapper 
for ChanSpy internally.

The changes come from the svn/asterisk/team/russell/ast_channel_ao2 branch.

Review: http://reviewboard.digium.com/r/203/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@190423 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 112 insertions, 0 deletions

diff --git a/include/asterisk/autochan.h b/include/asterisk/autochan.h
new file mode 100644
index 000000000..2ace4f2c2
--- /dev/null
+++ b/include/asterisk/autochan.h
@@ -0,0 +1,112 @@
+/*
+ * 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;
+};
+
+/*! 
+ * \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.
+ */
+
+/*!
+ * \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 from ast_do_masquerade 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 */